The document summarizes the cosmic distance ladder method used in astronomy to indirectly measure large distances in the universe. It describes how early astronomers were able to measure the size of Earth and distance to the Moon through simple geometric methods and observations, even without advanced technology. Aristarchus calculated the distance to the Moon by relating the duration of lunar eclipses to the Earth-Moon-Sun geometry. Eratosthenes calculated Earth's circumference by comparing solar observations in two cities, establishing the first rung of the cosmic distance ladder.
Venus is Earth's closest planetary neighbor and similar in size, but has extreme environmental conditions. It has a toxic atmosphere of thick clouds and strong winds, with surface temperatures reaching over 900°F due to its slow rotation. While once thought an Earth-like planet, it is now known to have volcanoes and landscapes unlike our own, rotating backwards with days lasting four months.
Comets are small cosmic bodies composed of rock, dust, ice and frozen gases that orbit the sun in elongated orbits. They develop tails and comas as solar radiation causes particles to dissipate from the comet as they approach the sun. Asteroids are small rocky bodies that orbit the sun and are remnants of larger planetesimals. Meteoroids are smaller particles that orbit the sun and create visible meteors when entering Earth's atmosphere due to pressure.
A presentation on the planet Venus. Designed for 5th grade students. Contains basic facts, including the space probes that helped us learn about Venus. Includes quiz questions at the end.
This document provides an overview of astronomy and the solar system. It defines astronomy as the study of anything seen in the sky and beyond. It describes how astronomy uses observation and integration with other sciences due to the difficulty of conducting experiments. It then reviews the key components of the solar system, including the sun, terrestrial planets like Earth and Mars, gas giants like Jupiter and Saturn, and smaller objects. Finally, it discusses units for measuring astronomical distances and provides examples to demonstrate the immense sizes within the universe.
Venus is the second planet from the sun. It has no rings and its atmosphere is dense and cloudy, making the surface impossible to see from space. Venus has about 85% of Earth's gravity and would weigh a 100 lb person about 90 lbs. The document provides fictional descriptions of life, real estate, transportation, and shopping on Venus to entertain readers.
The document summarizes key information about our solar system, including the 8 planets and 3 dwarf planets. It describes the differences between inner and outer planets, and provides details about the composition and features of each planet and dwarf planet. Mercury has a thin atmosphere due to its proximity to the sun. Venus rotates clockwise and has a dense carbon dioxide atmosphere. Earth has one moon and its atmosphere protects the surface. Mars may have once supported life and has the largest volcano in the solar system. Jupiter spins rapidly and has a Great Red Spot storm. Saturn's rings are composed of ice particles. Uranus rotates on its side and has methane in its atmosphere. Neptune has the strongest winds of all planets. Pluto, Cer
The inner planets Mercury, Venus, Earth, and Mars are similar to each other. They are the closest planets to the sun and are called terrestrial planets because they are rocky or earth-like. Mercury is the smallest planet and closest to the sun, with extreme temperature variations between its day and night sides. Venus is about the same size as Earth but has a dense carbon dioxide atmosphere that causes a runaway greenhouse effect and surface temperatures over 800 degrees Fahrenheit. Mars is about half the size of Earth, has a reddish appearance, seasonal polar ice caps, evidence of past water, and the lowest average temperature of the four inner planets.
Venus is Earth's closest planetary neighbor and similar in size, but has extreme environmental conditions. It has a toxic atmosphere of thick clouds and strong winds, with surface temperatures reaching over 900°F due to its slow rotation. While once thought an Earth-like planet, it is now known to have volcanoes and landscapes unlike our own, rotating backwards with days lasting four months.
Comets are small cosmic bodies composed of rock, dust, ice and frozen gases that orbit the sun in elongated orbits. They develop tails and comas as solar radiation causes particles to dissipate from the comet as they approach the sun. Asteroids are small rocky bodies that orbit the sun and are remnants of larger planetesimals. Meteoroids are smaller particles that orbit the sun and create visible meteors when entering Earth's atmosphere due to pressure.
A presentation on the planet Venus. Designed for 5th grade students. Contains basic facts, including the space probes that helped us learn about Venus. Includes quiz questions at the end.
This document provides an overview of astronomy and the solar system. It defines astronomy as the study of anything seen in the sky and beyond. It describes how astronomy uses observation and integration with other sciences due to the difficulty of conducting experiments. It then reviews the key components of the solar system, including the sun, terrestrial planets like Earth and Mars, gas giants like Jupiter and Saturn, and smaller objects. Finally, it discusses units for measuring astronomical distances and provides examples to demonstrate the immense sizes within the universe.
Venus is the second planet from the sun. It has no rings and its atmosphere is dense and cloudy, making the surface impossible to see from space. Venus has about 85% of Earth's gravity and would weigh a 100 lb person about 90 lbs. The document provides fictional descriptions of life, real estate, transportation, and shopping on Venus to entertain readers.
The document summarizes key information about our solar system, including the 8 planets and 3 dwarf planets. It describes the differences between inner and outer planets, and provides details about the composition and features of each planet and dwarf planet. Mercury has a thin atmosphere due to its proximity to the sun. Venus rotates clockwise and has a dense carbon dioxide atmosphere. Earth has one moon and its atmosphere protects the surface. Mars may have once supported life and has the largest volcano in the solar system. Jupiter spins rapidly and has a Great Red Spot storm. Saturn's rings are composed of ice particles. Uranus rotates on its side and has methane in its atmosphere. Neptune has the strongest winds of all planets. Pluto, Cer
The inner planets Mercury, Venus, Earth, and Mars are similar to each other. They are the closest planets to the sun and are called terrestrial planets because they are rocky or earth-like. Mercury is the smallest planet and closest to the sun, with extreme temperature variations between its day and night sides. Venus is about the same size as Earth but has a dense carbon dioxide atmosphere that causes a runaway greenhouse effect and surface temperatures over 800 degrees Fahrenheit. Mars is about half the size of Earth, has a reddish appearance, seasonal polar ice caps, evidence of past water, and the lowest average temperature of the four inner planets.
This document provides an overview of the characteristics, classifications, motions, and significance of stars. It discusses their sizes, colors, temperatures, compositions, and magnitudes. Stars are classified based on their spectral types, which relate to their surface temperatures. The Hertzsprung-Russell diagram plots stars' luminosities and temperatures. Stars exhibit both apparent and actual motions, including proper motion across the sky. Studying stars helps us understand how elements are formed, how our solar system evolved, and the dynamics influencing galaxies.
Uranus is about four times the diameter of Earth and is the third largest planet. It orbits the Sun at a distance of approximately 1.8 billion miles. Uranus has 27 known moons, including its five largest - Miranda, Ariel, Umbriel, Titania, and Oberon. Uranus has a system of rings composed of ice particles. Although larger than Earth, Uranus' surface gravity is less due to its gaseous composition, which also gives it a blue appearance when viewed from Earth. Voyager 2 took almost nine and a half years to reach Uranus during its journey through the solar system.
This document provides an overview of stars, galaxies, and the universe. It begins with definitions of key terms like stars, galaxies, and the universe. It then covers the composition of stars and how they are classified. The next sections discuss the life cycles of stars and the different types of galaxies. The document concludes with an explanation of the big bang theory of the universe and how scientists estimate the age of the universe.
Mercury is the closest planet to the sun and has thousands of huge craters from meteoroid and comet impacts. It rotates very slowly, resulting in a unusual sense of time. While astronomers previously believed Mercury's poles contained water ice, the MESSENGER spacecraft confirmed in 2011 there was no ice after sending back many pictures from its flybys of the planet.
SOLAR SYSTEM
The solar system is made up of the sun and everything that orbits around it, including planets, moons, asteroids, comets and meteoroids.
COMPOSITION OF SOLAR SYSTEM
Sun: 99.85%
Planets: 0.135%
Comets: 0.01%
Satellites: 0.00005%
Minor Planets: 0.0000002%
Meteoroids: 0.0000001%
Interplanetary Medium: 0.0000001%
Asteroids are small rocky or metallic bodies that orbit the sun and range in size from meters to over 500 km wide. They are found predominantly in the main asteroid belt between Mars and Jupiter. Ceres is the largest asteroid at 940 km in diameter. Asteroids are classified according to their composition, with C-type asteroids being the most common at 75% and consisting of carbon and dust. It is believed that an asteroid impact was responsible for the extinction of dinosaurs 65 million years ago.
India launched its first mission to Mars, called MOM or Mars Orbiter Mission, on November 5, 2013. The mission objectives were to develop technologies for designing, planning and operating interplanetary missions, and to study the Martian surface, atmosphere and climate. The Mars Orbiter spacecraft was launched using the Polar Satellite Launch Vehicle. It weighed 1.35 tons and cost $73 million. After traveling 300 days, it successfully entered orbit around Mars, making India the fifth space agency to do so. The orbiter carried scientific instruments to study Mars' morphology, topography, mineralogy and atmosphere. While some saw the mission as putting India among the leading space-faring nations, others criticized the large cost when India faces
Comets are made of dust, rock and frozen gases that vaporize as they near the Sun, forming a coma and tail. Comets eventually break apart after passing by the Sun multiple times. Small pieces of comets are called meteoroids, which appear as meteors or "shooting stars" when burning up in Earth's atmosphere, or meteorites if they reach the ground. Asteroids are rocky bodies like planets that mainly orbit in a belt between Mars and Jupiter.
The outer planets are Jupiter, Saturn, Uranus, and Neptune. They are the largest planets in our solar system and are mainly composed of gases like hydrogen and helium, giving them low density. Most have a similar structure with an atmosphere of gases, a liquid hydrogen mantle, and a small molten rock core. Jupiter is the largest and has a prominent Great Red Spot storm and over 60 moons. Saturn is notable for its extensive ring system. Uranus and Neptune are both blue-green due to methane in their atmospheres.
This document discusses dwarf planets in the solar system. It defines dwarf planets as celestial bodies that orbit the sun, are massive enough to be rounded by their own gravity, but have not cleared their orbit of other objects. It provides details on the five officially recognized dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake. It describes their sizes, compositions, orbits, and discoveries.
Mercury is the planet closest to the Sun and the least explored. It is very difficult to study from Earth due to its proximity to the Sun, which means it never gets more than 28 degrees from the Sun's glare. Mercury is the smallest planet and fastest planet in its orbit, taking 88 days to revolve around the Sun. The Mariner 10 spacecraft was the first to visit Mercury in 1974 and photographed nearly half of its surface, finding a landscape scarred by impacts and wrinkled with great ridges.
The document is a presentation on the equation of time. It begins by defining key terms like apparent sun, mean sun, apparent solar time, and mean solar time. It then defines the equation of time as the difference between apparent and mean solar time, which can range from -14 to +16 minutes. The chief causes of this difference are the unequal speed of the earth in its orbit and the fact that the apparent sun is on the ecliptic while the mean sun is on the equator. Graphs and tables are shown to represent the equation of time. Finally, some applications are discussed, such as correcting sundial times and accounting for the equation of time in solar energy systems.
1. Mercury is the closest planet to the Sun and has extreme surface temperatures, ranging from 450 degrees C during the day to -170 degrees C at night.
2. Mercury's thin atmosphere contains hydrogen, helium, and oxygen as the three most abundant gases.
3. Mercury's surface temperature reaches a blistering 740 degrees kelvin during the day.
Astronomy is known as the science of the entire universe beyond the Earth. It includes the Earth’s gross physical properties: its mass and rotation, as they interact with other bodies of the solar system.
The document summarizes the terrestrial and Jovian planets of our solar system, as well as interplanetary debris. It describes the four terrestrial planets - Mercury, Venus, Earth, and Mars - as being made of rock and metal with solid surfaces. It then outlines the gas giants Jupiter and Saturn and ice giants Uranus and Neptune. The document concludes by defining asteroids, comets, and meteoroids as the three main types of interplanetary debris leftover from planetary formation.
The moon goes through eight phases in a cycle that repeats every 27 days and 8 hours. The phases are caused by the changing orientation of the moon in relation to the Earth and sun, and the amount of sunlight that reflects off the moon's surface and is visible from Earth. The moon does not produce its own light but shines due to reflected sunlight. The document discusses the moon's phases and cycle, how its appearance changes nightly, and how the moon rotates to always keep the same face toward Earth.
introduction to galaxies in space.
chapter 9 earth and space class.
about the scientist edwin hubble.
and his theories. The study of asstronomy. space study of planets and galaxies.
This document provides information about Uranus in 3 paragraphs and a conclusion. It notes that Uranus was named after the god of the sky due to its color, and was the first planet spotted through a telescope. The document describes Uranus' surface as made of gases like hydrogen, methane and helium with winds up to 200 mph. It states Uranus has over 25 moons with Ariel being the best known and Mab the smallest. The concluding paragraph compares Uranus and Earth, noting Uranus is colder, has rings, different composition and no solid surface.
Saturn is the sixth planet from the sun and named after the Roman god of agriculture. It is a gas giant with 18 known moons, the largest being Titan which is bigger than Mercury. Saturn's iconic rings are made of ice particles and span over 270,000 km wide, though they are only about 30 meters thick. The rings are composed of three main sections divided by darker gaps. Saturn orbits the sun every 29.5 years and spins rapidly on its axis, completing a day every 10 hours.
Eratosthenes, the director of the Library of Alexandria in the 3rd century BC, conducted an experiment to calculate the circumference of the Earth. He measured the shadow of a vertical stick in Alexandria at noon on the summer solstice and found it made an angle of 7 degrees with the zenith. He knew the sun was directly overhead in Syene at the same time, so the 7 degree angle represented 1/50th of the circumference. Knowing the distance between Alexandria and Syene was 5000 stadia, he calculated the circumference of the Earth to be 250,000 stadia, which is remarkably close to the actual circumference of 40,075 km.
Eratosthenes's experiment measuring the EarthHupenyu Mutoro
Eratosthenes, a Greek scholar living in the 3rd century BC, conducted an experiment to measure the circumference of the Earth. He noticed that on the summer solstice in Syene, now Aswan, an obelisk cast no shadow at noon, meaning the sun's rays were directly overhead. Meanwhile at the same time in Alexandria, 800 km north, the sun's rays formed a 7.2 degree angle with the surface. Using simple geometry and knowing the distance between the cities, Eratosthenes calculated the circumference of the Earth to be approximately 40,000 km, remarkably close to the modern measurement. His innovative experiment demonstrated the spherical shape of the Earth over 200 years before the time of
This document provides an overview of the characteristics, classifications, motions, and significance of stars. It discusses their sizes, colors, temperatures, compositions, and magnitudes. Stars are classified based on their spectral types, which relate to their surface temperatures. The Hertzsprung-Russell diagram plots stars' luminosities and temperatures. Stars exhibit both apparent and actual motions, including proper motion across the sky. Studying stars helps us understand how elements are formed, how our solar system evolved, and the dynamics influencing galaxies.
Uranus is about four times the diameter of Earth and is the third largest planet. It orbits the Sun at a distance of approximately 1.8 billion miles. Uranus has 27 known moons, including its five largest - Miranda, Ariel, Umbriel, Titania, and Oberon. Uranus has a system of rings composed of ice particles. Although larger than Earth, Uranus' surface gravity is less due to its gaseous composition, which also gives it a blue appearance when viewed from Earth. Voyager 2 took almost nine and a half years to reach Uranus during its journey through the solar system.
This document provides an overview of stars, galaxies, and the universe. It begins with definitions of key terms like stars, galaxies, and the universe. It then covers the composition of stars and how they are classified. The next sections discuss the life cycles of stars and the different types of galaxies. The document concludes with an explanation of the big bang theory of the universe and how scientists estimate the age of the universe.
Mercury is the closest planet to the sun and has thousands of huge craters from meteoroid and comet impacts. It rotates very slowly, resulting in a unusual sense of time. While astronomers previously believed Mercury's poles contained water ice, the MESSENGER spacecraft confirmed in 2011 there was no ice after sending back many pictures from its flybys of the planet.
SOLAR SYSTEM
The solar system is made up of the sun and everything that orbits around it, including planets, moons, asteroids, comets and meteoroids.
COMPOSITION OF SOLAR SYSTEM
Sun: 99.85%
Planets: 0.135%
Comets: 0.01%
Satellites: 0.00005%
Minor Planets: 0.0000002%
Meteoroids: 0.0000001%
Interplanetary Medium: 0.0000001%
Asteroids are small rocky or metallic bodies that orbit the sun and range in size from meters to over 500 km wide. They are found predominantly in the main asteroid belt between Mars and Jupiter. Ceres is the largest asteroid at 940 km in diameter. Asteroids are classified according to their composition, with C-type asteroids being the most common at 75% and consisting of carbon and dust. It is believed that an asteroid impact was responsible for the extinction of dinosaurs 65 million years ago.
India launched its first mission to Mars, called MOM or Mars Orbiter Mission, on November 5, 2013. The mission objectives were to develop technologies for designing, planning and operating interplanetary missions, and to study the Martian surface, atmosphere and climate. The Mars Orbiter spacecraft was launched using the Polar Satellite Launch Vehicle. It weighed 1.35 tons and cost $73 million. After traveling 300 days, it successfully entered orbit around Mars, making India the fifth space agency to do so. The orbiter carried scientific instruments to study Mars' morphology, topography, mineralogy and atmosphere. While some saw the mission as putting India among the leading space-faring nations, others criticized the large cost when India faces
Comets are made of dust, rock and frozen gases that vaporize as they near the Sun, forming a coma and tail. Comets eventually break apart after passing by the Sun multiple times. Small pieces of comets are called meteoroids, which appear as meteors or "shooting stars" when burning up in Earth's atmosphere, or meteorites if they reach the ground. Asteroids are rocky bodies like planets that mainly orbit in a belt between Mars and Jupiter.
The outer planets are Jupiter, Saturn, Uranus, and Neptune. They are the largest planets in our solar system and are mainly composed of gases like hydrogen and helium, giving them low density. Most have a similar structure with an atmosphere of gases, a liquid hydrogen mantle, and a small molten rock core. Jupiter is the largest and has a prominent Great Red Spot storm and over 60 moons. Saturn is notable for its extensive ring system. Uranus and Neptune are both blue-green due to methane in their atmospheres.
This document discusses dwarf planets in the solar system. It defines dwarf planets as celestial bodies that orbit the sun, are massive enough to be rounded by their own gravity, but have not cleared their orbit of other objects. It provides details on the five officially recognized dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake. It describes their sizes, compositions, orbits, and discoveries.
Mercury is the planet closest to the Sun and the least explored. It is very difficult to study from Earth due to its proximity to the Sun, which means it never gets more than 28 degrees from the Sun's glare. Mercury is the smallest planet and fastest planet in its orbit, taking 88 days to revolve around the Sun. The Mariner 10 spacecraft was the first to visit Mercury in 1974 and photographed nearly half of its surface, finding a landscape scarred by impacts and wrinkled with great ridges.
The document is a presentation on the equation of time. It begins by defining key terms like apparent sun, mean sun, apparent solar time, and mean solar time. It then defines the equation of time as the difference between apparent and mean solar time, which can range from -14 to +16 minutes. The chief causes of this difference are the unequal speed of the earth in its orbit and the fact that the apparent sun is on the ecliptic while the mean sun is on the equator. Graphs and tables are shown to represent the equation of time. Finally, some applications are discussed, such as correcting sundial times and accounting for the equation of time in solar energy systems.
1. Mercury is the closest planet to the Sun and has extreme surface temperatures, ranging from 450 degrees C during the day to -170 degrees C at night.
2. Mercury's thin atmosphere contains hydrogen, helium, and oxygen as the three most abundant gases.
3. Mercury's surface temperature reaches a blistering 740 degrees kelvin during the day.
Astronomy is known as the science of the entire universe beyond the Earth. It includes the Earth’s gross physical properties: its mass and rotation, as they interact with other bodies of the solar system.
The document summarizes the terrestrial and Jovian planets of our solar system, as well as interplanetary debris. It describes the four terrestrial planets - Mercury, Venus, Earth, and Mars - as being made of rock and metal with solid surfaces. It then outlines the gas giants Jupiter and Saturn and ice giants Uranus and Neptune. The document concludes by defining asteroids, comets, and meteoroids as the three main types of interplanetary debris leftover from planetary formation.
The moon goes through eight phases in a cycle that repeats every 27 days and 8 hours. The phases are caused by the changing orientation of the moon in relation to the Earth and sun, and the amount of sunlight that reflects off the moon's surface and is visible from Earth. The moon does not produce its own light but shines due to reflected sunlight. The document discusses the moon's phases and cycle, how its appearance changes nightly, and how the moon rotates to always keep the same face toward Earth.
introduction to galaxies in space.
chapter 9 earth and space class.
about the scientist edwin hubble.
and his theories. The study of asstronomy. space study of planets and galaxies.
This document provides information about Uranus in 3 paragraphs and a conclusion. It notes that Uranus was named after the god of the sky due to its color, and was the first planet spotted through a telescope. The document describes Uranus' surface as made of gases like hydrogen, methane and helium with winds up to 200 mph. It states Uranus has over 25 moons with Ariel being the best known and Mab the smallest. The concluding paragraph compares Uranus and Earth, noting Uranus is colder, has rings, different composition and no solid surface.
Saturn is the sixth planet from the sun and named after the Roman god of agriculture. It is a gas giant with 18 known moons, the largest being Titan which is bigger than Mercury. Saturn's iconic rings are made of ice particles and span over 270,000 km wide, though they are only about 30 meters thick. The rings are composed of three main sections divided by darker gaps. Saturn orbits the sun every 29.5 years and spins rapidly on its axis, completing a day every 10 hours.
Eratosthenes, the director of the Library of Alexandria in the 3rd century BC, conducted an experiment to calculate the circumference of the Earth. He measured the shadow of a vertical stick in Alexandria at noon on the summer solstice and found it made an angle of 7 degrees with the zenith. He knew the sun was directly overhead in Syene at the same time, so the 7 degree angle represented 1/50th of the circumference. Knowing the distance between Alexandria and Syene was 5000 stadia, he calculated the circumference of the Earth to be 250,000 stadia, which is remarkably close to the actual circumference of 40,075 km.
Eratosthenes's experiment measuring the EarthHupenyu Mutoro
Eratosthenes, a Greek scholar living in the 3rd century BC, conducted an experiment to measure the circumference of the Earth. He noticed that on the summer solstice in Syene, now Aswan, an obelisk cast no shadow at noon, meaning the sun's rays were directly overhead. Meanwhile at the same time in Alexandria, 800 km north, the sun's rays formed a 7.2 degree angle with the surface. Using simple geometry and knowing the distance between the cities, Eratosthenes calculated the circumference of the Earth to be approximately 40,000 km, remarkably close to the modern measurement. His innovative experiment demonstrated the spherical shape of the Earth over 200 years before the time of
Eratosthenes calculated the circumference of the Earth using measurements from two cities in Egypt - Syene and Alexandria. He knew that on the summer solstice, the sun was directly overhead at Syene at noon. In Alexandria, 500 miles north, he measured the sun's shadow to be 7.5 degrees. Using this angle and the distance between the cities, he calculated the circumference of the Earth to be approximately 25,000 miles, with an error of only 4%.
outerspace, measuring distance of stars, parallaxMeasuring The Distance Of The Stars
Stellar Parallax Determinations
Spectroscopy And The Stuff Of The Stars
The Hertzprung-Russel Diagram
The Color Magnitude Relationship And Distance To Stars
The Cepheid Distance Scale
Eratosthenes, a Greek mathematician and astronomer from Alexandria in the 3rd century BC, devised a simple method to measure the circumference of the Earth. He noticed that on the summer solstice in Syene (now Aswan), Egypt, the sun was directly overhead at noon, while in Alexandria farther north, it cast a shadow. By measuring the angle of the shadow and knowing the distance between the two cities, he was able to calculate the circumference of the Earth. The document describes how students can follow in Eratosthenes' footsteps by measuring shadows and angles at solar noon to calculate the circumference and diameter of the Earth.
Apreciados Amigos de la Sociedad Julio Garavito para el Estudio de la Astronomía y de las Ciencias Espaciales en general. Reciban un cordial saludo. El sábado 8 de Junio de 2019 desde las 11:00 Am hasta las 1:00 PM. se tuvo la reunión de la Sociedad Julio Garavito en el Auditorio del Planetario de Medellín "Jesús Emilio Ramírez González"-Antioquia-Colombia con la Charla: EINSTEIN’S THEORY OF GENERAL RELATIVITY GRAVITATIONAL LENSING PHENOMENON SOBRAL (Brazil) – ISLA PRINCIPE OBSERVATION SITES OF TOTAL SOLAR ECLIPSE MAY 29, 1919" Por: Herman J. Mosquera Cuesta (PhD Astrophysics). Resumen: In this talk we will review the foundational physics arguments for the occurrence of the phenomenon of gravitational lensing as predicted by Einstein’s general theory of relativity (GTR). A short review of the Einstein’s equations formulated by 1915 and the successful observational confirmations of the theory, in particular the August 2017 spectacular direct detection of the spacetime curvature waves, i.e. gravitational waves, from merging of a neutron star binary, as seeing by LIGO and VIRGO gravitational-wave observatories. Some comments on Einstein’s pathway to predict such phenomenon will be offered, and the specific expression to short-hand computing the angular deviation of background stars around the Sun field of view, will be given. In the offing, we shall briefly digest on the overall implications of such an achievement on May 29, 1919 for our understanding of the universe we live in. https://www.slideshare.net/SociedadJu... Nota: Estas charlas promovidas por la Sociedad Julio Garavito son de entrada libre sin costo alguno. La Sociedad Julio Garavito agradece a los Directivos del Parque Explora por permitirle realizar sus reuniones quincenales que han sido tradicionales por más de 44 años en un lugar que se ha convertido en un referente de Ciencia, Ingeniería, Tecnología e Industria AeroEspacial en la Ciudad de Medellín. Por la atención prestada, muchas gracias. Sinceramente: Campo Elías Roldán. Director Sociedad Julio Garavito para el Estudio de la Astronomía Medellín-Antioquia COLOMBIA. sociedadjuliogaravito@gmail.com campoelias.roldan@gmail.com 3046633269
Transit of Venus Teacher Training Secondary School Session - History and ScienceSze-leung Cheung
The document provides details about a teacher training workshop on observing the transit of Venus. It includes the schedule, topics to be covered in lectures and demonstrations, and objectives of the workshop. The workshop aims to help teachers understand the importance of the transit, learn how to observe it safely and hold related activities, and discuss support options. It will cover the science and history of transits, observation techniques, and making observation equipment.
Hello guys, this ppt contains my project work on photometric analysis of Supernova 2008gj..with collaborators Ms. Komal Kabara and Manikandan K........Take a look.......looking forward for your suggestions...
Using radio observations, astronomers may be able to detect and characterize exoplanets by observing radio emissions from their magnetospheres. Planetary magnetospheres are theorized to produce bursts of decametric radiation through interactions with the solar wind that distort magnetic field lines and accelerate charged particles. While difficult to detect over a host star's emissions, observation of planetary radio signals could provide information on properties like the presence, size, and composition of a magnetosphere, as well as any orbiting satellites. The LOFAR radio telescope may enable the first detections of exoplanetary radio emissions within the next decade.
DETERMINATION OF THE EARTH’S RADIUS, MASS, AND GRAVITIONAL CONSTANT - PHYSIC...Ahmed Nassar
DETERMINATION OF THE EARTH’S RADIUS
In 200 B.C., the size of the Earth was calculated to within 1% accuracy! Eratosthenes used Aristotle's idea that, if the Earth was round, distant stars in the night sky would appear at different positions to observers at different latitudes. Eratosthenes knew that on the first day of summer, the Sun passed directly overhead at Syene, Egypt. At midday of the same day, he measured the angular displacement of the Sun from overhead at the city of Alexandria - 5000 stadia away from Syene. He found that the angular displacement was 7.2 degrees - there are 360 degrees in a circle, making 7.2 degrees equivalent to 1/50 of a circle. Geometry tells us that the ratio of 1/50 is the same as the ratio of the distance between Syene and Alexandria to the total circumference of the Earth. Thus, the circumference can be estimated by multiplying the distance between the two cities, 5000 stadia, by 50, equaling 250,000 stadia.
C equals circumference (5000 times 50 or 250,000)
the unit of the "stadium" was about 0.15 km. This means that Eratosthenes estimated the circumference of the Earth to about 40,000 km. He also knew that the circumference of a circle was equal to 2 times π (3.1415...) times the radius of the circle. (C = 2πr) With this information, Eratosthenes inferred that the Earth's radius was 6366 km. Both values are very close to the accepted modern values for the Earth's circumference and radius, 40,070 km, and 6378 km respectively, which have since been measured by orbiting spacecraft.
The diameter of a circle is twice the radius, giving us a diameter for Earth of 12,756 km.
Note: Eratosthenes was measuring the polar radius, and his value (using the 0.15 km/stadium conversion) lies between the polar and equatorial values.
DETERMINATION OF THE GRAVITIONAL CONSTANT
Isaac Newton expressed the Universal Gravitation Equation in 1687:
where
F is the force of attraction between objects
G is the Universal Gravitational Constant
M is the mass of the larger object
m is the mass of the smaller object
R is the separation between the centers of mass of the object
After that, there really wasn't much interest in G. Most scientists simply considered it a proportionality constant. they were more interested in gravity than gravitation.
In 1798, Henry Cavendish made an experiment to determine the Earth’s density. He used a torsion balance to measure the force of attraction between the two masses.
The Cavendish experiment uses a torsion equilibrium to measure the weak gravitational force between lead balls. A torsion equilibrium consists of a bar suspended at its middle by a thin wire. Twisting the wire requires a torque.
The way it works is that the gravitational force attracting the balls together turns the bar, overcoming torque resistance from the wire. That resistance is a function of angle turned and the torsion coefficient of the wire.
Pulsars in the Classroom: Presenter Stephen Broderick
"Let's do real world mathematics" The "Pulsar" project is designed to engage students in scientific projects that will give them a positive attitude towards science and mathematics, and appreciation of how maths is applied in the real world.
PULSE@Parkes allows students to directly control Parkes radio telescope over the Internet and use it to do real science. It is the only program of its kind in the world.
This document discusses refraction and astronomy. It defines refraction as the change in direction of a wave passing from one medium to another. There are two laws of refraction: 1) the incident, refracted, and normal rays are in the same plane, and 2) the sines of the angles follow a ratio called the refractive index. Astronomical refraction is the deviation of light caused as it passes through Earth's atmosphere in layers, making celestial objects appear higher than their true position. The amount of refraction increases for objects closer to the horizon.
The Big Bang model describes the origin and evolution of our universe. It postulates that approximately 13.8 billion years ago, the entire observable universe was only a few millimeters in size and extremely hot and dense. The universe has been expanding and cooling ever since. Evidence for the Big Bang includes the expansion of the universe, the cosmic microwave background radiation, and the relative abundance of light elements like hydrogen and helium.
The Big Bang model describes the origin and evolution of our universe. It postulates that approximately 13.8 billion years ago, the entire observable universe was only a few millimeters in size and extremely hot and dense. Since then, the universe has been expanding and cooling. Evidence for the Big Bang includes the expansion of the universe, the cosmic microwave background radiation, and the relative abundance of light elements like hydrogen and helium. The Doppler effect and redshift help astronomers measure the speeds at which distant galaxies are receding from Earth, leading to the discovery that the expansion of the universe is accelerating. Dark matter and dark energy are hypothesized to explain discrepancies in measurements of the density and expansion rate of the universe.
Eratosthenes Estimation of the Circumference of the Earth This que.pdfartimagein
Eratosthene\'s Estimation of the Circumference of the Earth This question investigates
something that is quite famous and amazing especially for its time. It briefly looks at the work of
Eratosthenes and what he did to estimate the circumference of the Earth. Now perhaps he
idealized the Earth as a perfect sphere to make it easier, but his estimate was pretty close to the
actual, modern value! In your answer, offer commentary and narration regarding what I have
given on the following pages. Please do NOT copy and paste answers and narration from the
Internet! I think YOU (yes YOU there reading this!!) will enjoy this famous mathematical
episode from history. Please make sure that you address and answer ALL questions in this
scenario. Please answer in paragraph form with excellent prose!
Solution
Answer:-
According to the statement
Eratosthenes calculated the circumference of the Earth without leaving Egypt. He knew that at
local noon on the summer solstice in Syene (modern Aswan, Egypt), the Sun was directly
overhead. He knew this because the shadow of someone looking down a deep well at that time in
Syene blocked the reflection of the Sun on the water. He measured the Sun\'s angle of elevation
at noon on the same day in Alexandria. The method of measurement was to make a scale
drawing of that triangle which included a right angle between a vertical rod and its shadow. This
turned out to be 1/50th of a circle. Taking the Earth as spherical, and knowing both the distance
and direction of Syene, he concluded that the Earth\'s circumference was fifty times that
distance.
His knowledge of the size of Egypt was founded on the work of many generations of surveying
trips. Pharaonic bookkeepers gave a distance between Syene and Alexandria of 5,000 stadia (a
figure that was checked yearly)Some say that the distance was corroborated by inquiring about
the time that it took to travel from Syene to Alexandria by camel. Carl Sagan says that
Eratosthenes paid a man to walk and measure the distance. Some claim Eratosthenes used the
Olympic stade of 176.4 m, which would imply a circumference of 44,100 km, an error of
10%,but the 184.8 m Italian stade became (300 years later) the most commonly accepted value
for the length of the stade,which implies a circumference of 46,100 km, an error of 15%. .It was
unlikely, even accounting for his extremely primitive measuring tools, that Eratosthenes could
have calculated an accurate measurement for the circumference of the Earth for three important
assumptions he made (none of which are perfectly accurate):
Eratosthenes later rounded the result to a final value of 700 stadia per degree, which implies a
circumference of 252,000 stadia, likely for reasons of calculation simplicity as the larger number
is evenly divisible by 60.Repeating Eratosthenes\' calculation with more accurate data, the result
is 40,074 km, which is 66 km different (0.16 %) from the currently accepted polar circumference
of the Earth.
Seventeen hun.
The document discusses the origin and evolution of models of the universe. It begins by describing early flat earth cosmologies from ancient civilizations like Egypt, India, and Mesopotamia. It then outlines the development of the spherical earth model in ancient Greece, including ideas proposed by Pythagoras, Plato, and calculations made by Eratosthenes to estimate the earth's circumference. The document also summarizes the geocentric model developed by the Greeks with the earth at the center, and revisions made by Aristotle and Ptolemy. Finally, it outlines the heliocentric model first proposed by Aristarchus, placing the sun at the center, and the further developments of this model by Copernicus.
The document discusses the Solar Wind Electrons, Alphas, and Protons (SWEAP) instrument suite aboard the Solar Probe Plus mission. SWEAP will make detailed measurements of solar wind particles to help solve mysteries like why the solar corona is so much hotter than the surface and how the solar wind is accelerated. Key measurements include particle velocities, densities, temperatures, and anisotropies to better understand kinetic physics processes and trace the flow of energy in the solar atmosphere.
Eratosthenes was a Greek scholar who calculated the circumference of the Earth using shadows from sticks in Alexandria and Syene. He observed that on the summer solstice, a stick in Alexandria cast a shadow while a stick in Syene did not. Knowing the distance between the cities, he calculated the circumference of the Earth to within a few percent of the actual measurement. Eratosthenes made several other contributions including accurately calculating the tilt of the Earth's axis and inventing the leap day.
Eratosthenes was a Greek mathematician who devised a simple method to measure the circumference of the Earth in the 3rd century BC. He noticed that on the summer solstice in Syene (now Aswan), Egypt, the sun was directly overhead at noon, casting no shadows, while in Alexandria shadows were cast. Using the known distance between the cities and basic geometry, he calculated the angle of the sun's rays and determined that this angle was approximately 1/50th of a full circle. Assuming the Earth was spherical, he estimated the circumference of the Earth to within a few percent of the actual measurement. The document describes replicating Eratosthenes' experiment to determine the circumference of the Earth by
The document discusses various methods and instruments used for celestial navigation. It describes tools like the sextant, astrolabe, and octant that were used to determine position by measuring the angle between celestial objects and the horizon. It also discusses coordinate systems and modern GPS technology used for navigation.
Similar to Cosmic Distance Ladder - Terrance Tao (updated 10-26-09) (20)
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3. Astrometry is the study of positions
and movements of celestial bodies
(sun, moon, planets, stars, etc.).
It is a major subfield of astronomy.
Solar system montage, NASA/JPL
4. Typical questions in astrometry are:
• How far is it from the Earth to the Moon?
• From the Earth to the Sun?
• From the Sun to other planets?
• From the Sun to nearby stars?
• From the Sun to distant stars?
Solar system montage, NASA/JPL
5. These distances are far too
vast to be measured directly.
D1 D1 = ???
D2 = ???
D2
Hubble deep field, NASA
6. Nevertheless, there are several ways to
measure these distances indirectly.
D1
D1 / D2 = 3.4 ± 0.1
D2
Hubble deep field, NASA
7. The methods often rely more on
mathematics than on technology.
v1 = H D 1
v2 = H D 2
v1 / v2 = 3.4 ± 0.1
D1
D1 / D2 = 3.4 ± 0.1
D2
Hubble deep field, NASA
8. The indirect methods control large
distances in terms of smaller distances.
From “The Essential Cosmic Perspective”, Bennett et al.
9. The smaller distances are controlled by
even smaller distances...
From “The Essential Cosmic Perspective”, Bennett et al.
10. … and so on, until one reaches distances
that one can measure directly.
From “The Essential Cosmic Perspective”, Bennett et al.
11. This is the cosmic distance ladder.
From “The Essential Cosmic Perspective”, Bennett et al.
12. 1 st rung: the Earth
Earth Observing System composite, NASA
13. Nowadays, we know that the
earth is approximately
spherical, with radius 6378
kilometers at the equator and
6356 kilometers at the poles.
Earth Observing System composite, NASA
14. These values have now been
verified to great precision by
many means, including modern
satellites.
Earth Observing System composite, NASA
15. But suppose we had no advanced
technology such as spaceflight,
ocean and air travel, or even
telescopes and sextants.
Earth Observing System composite, NASA
19. Aristotle (384-322 BCE) gave
a convincing indirect
argument that the Earth was
round… by looking at the
Moon.
Copy of a bust of Aristotle by Lysippos (330 BCE)
20. Aristotle knew that lunar
eclipses only occurred
when the Moon was
directly opposite the Sun.
21. He deduced that these
eclipses were caused by
the Moon falling into the
Earth’s shadow.
22. But the shadow of the
Earth on the Moon in an
eclipse was always a
circular arc.
23. In order for Earth’s
shadows to always be
circular, the Earth must
be round.
24. Aristotle also knew there
were stars one could see
in Greece but not in
Egypt, or vice versa.
Night Sky, Till Credner
25. He reasoned that this was
due to the curvature of
the Earth, so that its
radius was finite.
Night Sky, Till Credner
26. However, he was unable to
get an accurate
measurement of this
radius.
Night Sky, Till Credner
27. Eratosthenes (276-194
BCE) computed the
radius of the Earth to be
40,000 stadia (6800 km).
Eratosthenes, Nordisk familjebok, 1907
28. This is accurate
to within eight
percent.
Eratosthenes, Nordisk familjebok, 1907
29. The argument was
again indirect – but
now relied on looking
at the Sun.
Eratosthenes, Nordisk familjebok, 1907
30. Eratosthenes read of a well in Syene,
Egypt which at noon on the summer
solstice (June 21) would reflect the
overhead sun.
Syene
Tropic of Cancer, Swinburne University of Technology
31. [This is because Syene lies
almost directly on the
Tropic of Cancer.]
Sun directly
overhead
Syene
Tropic of Cancer, Swinburne University of Technology
32. Eratosthenes tried the
same experiment in his
home city of Alexandria.
Sun directly
overhead
Alexandria
Syene
Tropic of Cancer, Swinburne University of Technology
33. But on the solstice, the sun was
at an angle and did not reflect
from the bottom of the well.
Sun not quite
overhead
Sun directly
overhead
Alexandria
Syene
Tropic of Cancer, Swinburne University of Technology
34. Using a gnomon (measuring stick),
Eratosthenes measured the deviation
of the sun from the vertical as 7o.
7o
Sun directly
overhead
Alexandria
Syene
Tropic of Cancer, Swinburne University of Technology
35. From trade caravans and other sources,
Eratosthenes knew Syene to be 5,000
stadia (740 km) south of Alexandria.
7o
5000 stadia
Sun directly
overhead
Alexandria
Syene
Tropic of Cancer, Swinburne University of Technology
36. This is enough
information to compute
the radius of the Earth.
r 7o
7o 5000 stadia
r
2 π r * 7o / 360o
= 5000 stadia
r=40000 stadia
Tropic of Cancer, Swinburne University of Technology
37. [This assumes that the
Sun is quite far away,
but more on this later.]
r 7o
7o 5000 stadia
r
2 π r * 7o / 360o
= 5000 stadia
r=40000 stadia
Tropic of Cancer, Swinburne University of Technology
41. Aristotle argued that the Moon was a
sphere (rather than a disk) because the
terminator (the boundary of the Sun’s
light on the Moon) was always a
circular arc.
Merriam-Webster
42. Aristarchus (310-230 BCE) computed
the distance of the Earth to the Moon
as about 60 Earth radii.
[In truth, it varies from 57 to 63 Earth
radii.]
43. Aristarchus also computed the radius of
the Moon as 1/3 the radius of the
Earth.
[In truth, it is 0.273 Earth radii.]
44. The radius of the Earth was computed
in the previous rung of the ladder, so
we now know the size and location of
the Moon.
48. 2r
v = 2r / 3 hours
The maximum
length of a
lunar eclipse is
three hours.
49. 2r
v = 2r / 3 hours
= 2 π D / 1 month D
It takes one month for
the Moon to go
around the Earth.
50. 2r
v = 2r / 3 hours
= 2 π D / 1 month D
This is enough
D = 60 r
information to work
out the distance to the
Moon in Earth radii.
51. V = 2R / 2 min
2R
Also, the Moon takes
about 2 minutes to
set.
Moonset over the Colorado Rocky
Mountains, Sep 15 2008, www.komar.org
52. V = 2R / 2 min
= 2 π D / 24 hours 2R
The Moon takes 24 hours
to make a full (apparent)
rotation around the Earth.
Moonset over the Colorado Rocky
Mountains, Sep 15 2008, www.komar.org
53. V = 2R / 2 min
= 2 π D / 24 hours 2R
R = D / 180
This is enough information
to determine the radius of
the Moon, in terms of the
distance to the Moon…
Moonset over the Colorado Rocky
Mountains, Sep 15 2008, www.komar.org
54. V = 2R / 2 min
= 2 π D / 24 hours 2R
R = D / 180
=r/3
… which we have
just computed.
Moonset over the Colorado Rocky
Mountains, Sep 15 2008, www.komar.org
55. V = 2R / 2 min
= 2 π D / 24 hours 2R
R = D / 180
=r/3
[Aristarchus, by the way, was
handicapped by not having an
accurate value of π, which had to
wait until Archimedes (287-
212BCE) some decades later!]
Moonset over the Colorado Rocky
Mountains, Sep 15 2008, www.komar.org
56. 3 rd rung: the Sun
EIT-SOHO Consortium, ESA, NASA
57. • How large is the Sun?
• How far away is the Sun?
EIT-SOHO Consortium, ESA, NASA
58. Once again, the ancient Greeks
could answer these questions
(but with imperfect accuracy).
EIT-SOHO Consortium, ESA, NASA
59. Their methods were indirect,
and relied on the Moon.
EIT-SOHO Consortium, ESA, NASA
60. Aristarchus already computed
that the radius of the Moon
was 1/180 of the distance to
the Moon.
Zimbabwe Solar Eclipse 4 Dec 2002, Murray Alexander
61. He also knew that during a
solar eclipse, the Moon
covered the Sun almost
perfectly.
Zimbabwe Solar Eclipse 4 Dec 2002, Murray Alexander
62. Using similar triangles, he
concluded that the radius of
the Sun was also 1/180 of the
distance to the Sun.
Zimbabwe Solar Eclipse 4 Dec 2002, Murray Alexander
63. So his next task was to
compute the distance
to the Sun.
Zimbabwe Solar Eclipse 4 Dec 2002, Murray Alexander
64. For this, he turned to
the Moon again for
help.
Zimbabwe Solar Eclipse 4 Dec 2002, Murray Alexander
65. He knew that new Moons
occurred when the Moon was
BBC
between the Earth and Sun…
66. … full Moons occurred when the
Moon was directly opposite the
BBC
Sun…
67. … and half Moons occurred when
the Moon made a right angle
BBC
between Earth and Sun.
68. θ < π/2
θ
This implies that half Moons
occur slightly closer to new
BBC
Moons than to full Moons.
69. θ = π/2 – 2 π *12
hours/1 month)
θ
Aristarchus thought that half Moons
occurred 12 hours before the
BBC
midpoint of a new and full Moon.
70. θ = π/2 – 2 π *12 d
hours/1 month
θ
cos θ = d/D
D = 20 d D
From this and trigonometry, he
concluded that the Sun was 20
BBC
times further away than the Moon.
71. θ = π/2 – 2 π *12 d
hours/1 month
θ
cos θ = d/D
D = 20 d D
Unfortunately, with ancient Greek
technology it was hard to time a
BBC
new Moon perfectly.
72. θ = π/2 – 2 π /2 d
hour/1 month
θ
cos θ = d/D
D = 390 d D
The true time discrepancy is ½ hour
(not 12 hours), and the Sun is 390
BBC
times further away (not 20 times).
73. θ = π/2 – 2 π /2 d
hour/1 month
θ
cos θ = d/D
D = 390 d D
Nevertheless, the basic
BBC
method was correct.
74. d = 60 r r d
D/d = 20
θ
R/D = 1/180
D
R
And Aristarchus’
computations led him to an
BBC
important conclusion…
75. d = 60 r r d
D/d = 20
θ
R/D = 1/180
R~7r D
R
… the Sun was much larger
BBC
than the Earth.
76. d = 60 r r d
D/d = 20 390
θ
R/D = 1/180
R = 7 r 109 r D
R
[In fact, it is much, much
larger.]
BBC
77. He then concluded it was
absurd to think the Sun
went around the Earth…
NASA/ESA
78. … and was the first to
propose the heliocentric
model that the Earth
went around the Sun.
NASA/ESA
85. … but we’ll see much more accurate ways
to measure the AU later on.
Wikipedia
86. 4 th rung: the
planets
Solar system montage, NASA/JPL
87. The ancient astrologers knew that
all the planets lay on a plane (the
ecliptic), because they only
moved through the Zodiac.
Solar system montage, NASA/JPL
88. But this still left many
questions unanswered:
Solar system montage, NASA/JPL
89. • How far away are the planets (e.g.
Mars)?
• What are their orbits?
• How long does it take to complete
an orbit?
Solar system montage, NASA/JPL
90. Ptolemy (90-168 CE) attempted
to answer these questions, but
obtained highly inaccurate
answers…
91. ... because he was working with
a geocentric model rather
than a heliocentric one.
92. The first person to obtain
accurate answers was Nicholas
Copernicus (1473-1543).
93. Copernicus started with the records of
the ancient Babylonians, who knew
that the apparent motion of Mars (say)
repeated itself every 780 days (the
synodic period of Mars).
ωEarth – ωMars = 1/780 days
Babylonian world map, 7th-8th century BCE, British Museum
94. Using the heliocentric model, he
also knew that the Earth went
around the Sun once a year.
ωEarth – ωMars = 1/780 days
ωEarth = 1/year
Babylonian world map, 7th-8th century BCE, British Museum
95. Subtracting the implied angular velocities,
he found that Mars went around the Sun
every 687 days (the sidereal period of
Mars).
ωEarth – ωMars = 1/780 days
ωEarth = 1/year
ωMars = 1/687 days
Babylonian world map, 7th-8th century BCE, British Museum
96. Assuming circular orbits, and using
measurements of the location of Mars in
the Zodiac at various dates...
ωEarth – ωMars = 1/780 days
ωEarth = 1/year
ωMars = 1/687 days
Babylonian world map, 7th-8th century BCE, British Museum
97. …Copernicus also computed the
distance of Mars from the Sun to
be 1.5 AU.
ωEarth – ωMars = 1/780 days
ωEarth = 1/year
ωMars = 1/687 days
Babylonian world map, 7th-8th century BCE, British Museum
98. Both of these measurements are
accurate to two decimal places.
ωEarth – ωMars = 1/780 days
ωEarth = 1/year
ωMars = 1/687 days
Babylonian world map, 7th-8th century BCE, British Museum
99. Tycho Brahe (1546-1601) made
extremely detailed and long-term
measurements of the position of
Mars and other planets.
122. Using the data for Mars and
other planets, Kepler
formulated his three laws of
planetary motion.
Kepler’s laws of planetary motion
1. Planets orbit in ellipses, with the Sun as one of
the foci.
2. A planet sweeps out equal areas in equal times.
3. The square of the period of an orbit is
proportional to the cube of its semi-major axis.
NASA
123. This led Isaac Newton (1643-
1727) to formulate his law
of gravity.
Newton’s law of universal gravitation
Any pair of masses attract by a force proportional
to the masses, and inversely proportional to the
square of the distance.
|F| = G m1 m2 / r2
NASA
125. Conversely, if one had an
alternate means to compute
distances to planets, this would
give a measurement of the AU.
NASA
126. One way to measure such distances is by
parallax – measuring the same object
from two different locations on the
Earth.
NASA
127. By measuring the parallax of the transit of
Venus across the Sun in several locations
(including James Cook’s voyage!), the AU
was computed reasonably accurately in the
18th century.
NASA
128. With modern technology such as radar and
interplanetary satellites, the AU and the
planetary orbits have now been computed to
extremely high precision.
NASA
129. Incidentally, such precise measurements of
Mercury revealed a precession that was not
explained by Newtonian gravity…
NASA
130. … , and was one of the first experimental
verifications of general relativity (which is
needed in later rungs of the ladder).
NASA
133. However, one needs to know
it in order to ascend higher
rungs of the distance
ladder.
Lucasfilm
134. The first accurate measurements
of c were by Ole Rømer
(1644-1710) and Christiaan
Huygens (1629-1695).
Ole Rømer
135. Their method was indirect…
and used a moon of Jupiter,
namely Io.
Christaan Huygens
136. Io has the shortest orbit of all
the major moons of Jupiter. It
orbits Jupiter once every 42.5
hours.
NASA/JPL/University of Arizona
137. Rømer made many
measurements of this orbit by
timing when Io entered and
exited Jupiter’s shadow.
NASA/JPL/University of Arizona
138. However, he noticed that when Jupiter
was aligned with the Earth, the orbit
advanced slightly; when Jupiter was
opposed, the orbit lagged.
NASA/JPL/University of Arizona
139. The difference was slight; the orbit
lagged by about 20 minutes when
Jupiter was opposed.
NASA/JPL/University of Arizona
140. Huygens reasoned that this was
because of the additional distance
(2AU) that the light from Jupiter
had to travel.
NASA/JPL/University of Arizona
141. Using the best measurement of the
AU available to him, he then
computed the speed of light as c =
220,000 km/s.
[The truth is 299,792 km/s.]
NASA/JPL/University of Arizona
143. James Clerk Maxwell (1831-1879)
observed that the speed of light
almost matched the speed his
theory predicted for
electromagnetic radiation.
144. He then reached the important
conclusion that light was a form
of electromagnetic radiation.
sciencelearn.org.nz
145. This observation was instrumental
in leading to Einstein’s theory of
special relativity.
146. It also led to the development of
spectroscopy.
Ian Short
147. Both of these turn out to be
important tools for climbing
higher rungs of the ladder.
Ian Short
148. 6 th rung: nearby
stars
Northern Arizona University
149. We already saw that parallax from
two locations on the Earth could
measure distances to other
planets.
Northern Arizona University
150. This is not enough separation to
discern distances to even the
next closest star (which is about
270,000 AU away!)
Northern Arizona University
151. However, if one takes
measurements six months apart,
one gets a distance separation of
2AU...
152. … which gives enough parallax to
measure all stars within about
100 light years (30 parsecs).
153. This provides a lot of very useful
data – tens of thousands of stars
- for the next rung of the ladder.
Northern Arizona University
154. These parallax computations,
which require accurate
telescopy, were first done by
Friedrich Bessel (1784-1846) in
1838.
155. Ironically, when Aristarchus
proposed the heliocentric model,
his contemporaries dismissed it,
on the grounds that they did not
observe any parallax effects…
156. … so the heliocentric model would
have implied that the stars were
an absurdly large distance away.
158. 7 th
rung: the
Milky Way
Milky Way, Serge Brunier
159. One can use detailed observations
of nearby stars to provide a
means to measure distances to
more distant stars.
Milky Way, Serge Brunier
160. Using spectroscopy, one can
measure precisely the colour of a
nearby star; one can also
measure its apparent brightness.
Milky Way, Serge Brunier
161. Using the apparent brightness, the
distance, and inverse square law,
one can compute the absolute
brightness of these stars.
Milky Way, Serge Brunier
162. Ejnar Hertzsprung (1873-1967)
and Henry Russell (1877-1957)
plotted this absolute brightness
against color for thousands of
nearby stars in 1905-1915…
163. … leading to the famous
Hertzprung-Russell diagram.
Richard Powell
164. Once one has this diagram, one
can use it in reverse to measure
distances to more stars than
parallax methods can reach.
Richard Powell
165. Indeed, for any star, one can
measure its colour and its
apparent brightness…
Richard Powell
166. and from the Hertzprung-Russell
diagram, one can then infer the
absolute brightness.
Richard Powell
167. From the apparent brightness
and absolute brightness, one
can solve for distance.
Richard Powell
168. This technique (main sequence
fitting) works out to about
300,000 light years (covering the
entire galaxy!)
Milky Way, Serge Brunier
169. Beyond this distance, the main
sequence stars are too faint to be
measured accurately.
Milky Way, Serge Brunier
170. 8 th rung: Other
galaxies
Hubble deep field, NASA
171. Henrietta Swan Leavitt (1868-
1921) observed a certain class of
stars (the Cepheids) oscillated in
brightness periodically.
American Institute of Physics
172. Plotting the absolute brightness
against the periodicity she
observed a precise relationship.
Henrietta Swan Leavitt, 1912
173. This gave yet another way to
obtain absolute brightness, and
hence observed distances.
Henrietta Swan Leavitt, 1912
174. Because Cepheids are so bright,
this method works up to
13,000,000 light years!
175. Most galaxies are fortunate to have
at least one Cepheid in them, so
we know the distances to all
galaxies out to a reasonably
large distance.
176. Similar methods, using supernovae
instead of Cepheids, can
sometimes work to even larger
scales than these.
Supernova remnant, NASA, ESA, HEIC, Hubble Heritage Team
177. 9 thrung: the
universe
Simulated matter distribution in universe, Greg Bryan
179. With this data, he formulated Hubble’s law:
the red-shift of an object was proportional
to its distance.
NASA
180. This led to the famous Big Bang model of the
expanding universe, which has now been
confirmed by many other cosmological
observations.
NASA, WMAP
181. But it also gave a way to measure
distances even at extremely large
scales… by first measuring the
red-shift and then applying
Hubble’s law.
Hubble deep field, NASA
182. These measurements have led to
accurate maps of the universe at
very large scales…
Two degree field Galaxy red-shift survey, W. Schaap et al.
183. which have led in turn to many
discoveries of very large-scale
structures, such as the Great
Wall.
Two degree field Galaxy red-shift survey, W. Schaap et al.
184. For instance, our best estimate (as
of 2004) of the current diameter
of the universe is that it is at
least 78 billion light-years.
Cosmic microwave background fluctuation, WMAP
185. The mathematics becomes more
advanced at this point, as the
effects of general relativity has
highly influenced the data we
have at this scale of the universe.
Artist’s rendition of a black hole, NASA
186. Cutting-edge technology (such as
the Hubble space telescope
(1990-) and WMAP (2001-)) has
also been vital to this effort.
Hubble telescope, NASA
187. Climbing this rung of the ladder (i.e.
mapping the universe at its very
large scales) is still a very active
area in astronomy today!
WMAP, NASA