Polaris, also known as the North Star, appears fixed in the night sky from Earth's perspective as it spins. Before telescopes, people used constellations of stars to tell time and navigate. Telescopes allow astronomers to observe more light than the naked eye and use spectroscopes to analyze the wavelengths of light emitted by stars to determine their characteristics, compositions, and motions. Astronomers measure distances within our solar system in astronomical units but use light-years to measure farther distances, with 1 light-year equaling about 9.46 trillion kilometers.

1. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page1
Vocabulary
 Spectroscope (417) – an instrument that spreads light into different wavelengths
 Astronomical Unit (418) – the average distance between Earth and the Sun, about 150
million km
 Light-year (418) – the distance light travels in 1 year
 Apparent Magnitude (419) – a measure of how bright it an object appears from Earth
 Luminosity (419) – the true brightness of an object
Looking at the Night Sky
 If you look at the stars for a long time they seem
to________________.
 ________________is a star almost directly above the North
Pole.
 As Earth spins Polaris stays in place as stars near it seem to
circle around it.
 Polaris is commonly referred to as
the___________________________,
because it and the stars near it never
___________when viewed from the
northern hemisphere.
Naked-Eye Astronomy
 Naked-eye astronomy means gazing at the sky using just your eyes; no
___________________ or telescopes.
 Before telescopes, people used the stars to tell time, ___________________, and finding
directions.
Constellations
 When ancient cultures gazed at the night sky, they saw_______________________.
o They represented people, animals, and objects
 The Greek astronomer Ptolemy identified dozens of star patterns nearly
______________ years ago.
o These are called ________________ ____________________today
 Present-day astronomers use many ancient constellations to divide the sky
into ______________regions also called constellations
Telescopes
 Telescopes are able to collect much more _____________________than the human eye
 The _______________________ spectrum is a continuous range of wavelengths
o __________________ light is only one part of the spectrum

2. Chapter 12 Lesson 1 – The View from Earth – p414-419 - page2
o Longer wavelengths have ______________energy
o Shorter wavelengths have ______________energy
 Different objects in space can emit different types of wavelengths.
 The range of wavelengths a star emits is called its__________________________.
Spectroscopes
 Scientists study the spectra of a star using a___________________________________.
 A spectroscope ___________________ light into different wavelengths.
 This way, scientists can study a star’s characteristics, compositions, and______________.
 Newly formed stars emit mostly _____________and infrared waves. While exploding stars
emit high energy _______________________________waves.

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Measuring distance
 Astronomers use angles created by __________________ to measure how far objects are
from Earth.
o Parallax is the apparent change in an object’s
____________________ caused by looking at it from 2
different points.
o For example: Look at your pencil with only your left eye.
Then, without moving the pencil, look at it with only your
right eye.
 Astronomers create a parallax by using 2 points in Earth’s
____________________ around the Sun
Distance Within the Solar System
 Distances ________________ the solar system are measured using astronomical units or
AU.
 An astronomical unit is the average distance between Earth and _____________________ ,
about 150 million km.
Distances Beyond the Solar System
 Astronomers measure distances ___________________ the solar system using light-years.
o A light-year is the distance light travels in 1 year.
o 1 light-year equals about 10 _______________________km.
 The nearest star to our Sun is 4.2 light-years away. How far is that in km?
Looking Back in Time
 Because it takes time for light to travel, you see a star not as it is______________, but as it
was when light left it.
 At 4.2 light-years away, Proxima Centauri appears as it was
______________ years ago.
Measuring Brightness
 Astronomers measure the brightness of stars in two ways:
o By how bright they appear from Earth
o By how bright they actually are
Apparent Magnitude
 Scientists measure how bright stars appear from __________________ using a scale
developed by the ancient Greek astronomer Hipparchus
o Hipparchus assigned a _______________ to every star he saw in the night sky based
on its brightness.
 Today these are called __________________ _____________________
o The apparent magnitude of an object is a measure of how bright it appears from
Earth
 Hipparchus assigned the number __________ to the brightest star he saw in the night sky

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Absolute Magnitude
 Stars can appear bright or dim depending on their __________________ from Earth, but
stars also have actual, or absolute, magnitudes
 __________________________is the true brightness of an object
 This depends on the star’s _____________________and size rather than its distance from
Earth
 A star’s luminosity, distance, and apparent magnitude are all_____________________.
Thus, if a scientist knows two of these factors, he can mathematically determine the third.
Apparent Magnitude Scale