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.

1. By Prof. Liwayway Memije-Cruz
The History of Astronomy and Cosmology

2. Astronomy
 the science of the entire universe beyond
the Earth.
 studies the motions and nature of celestial
bodies.
 includes the Earth’s gross physical
properties: its mass and rotation, as they
interact with other bodies of the solar
system.
 includes the Sun, Moon, planets and
comets. stars, galaxies, nebula, and the

3. Celestial mechanics
 the science of the
motion of planets and
other solid objects
within the solar
system.
 became the first testing
ground for Newton’s
laws of motion and
helped in establishing
the fundamental
principles of classical
physics.

4. Astrophysics

the study of the physical properties and
the determination of the chemical
composition of celestial bodies.

5. Cosmology
 the study of the universe as a whole, including
its distant past and its future.
 studies the universe through observations by
looking at the universe; and theoretically
through using physical laws and theories to
predict how the universe should behave.
 involves a wide range of other sciences, such
as physics and chemistry.
 the study of the origin of the solar system.

6. About 350 B.C., Aristotle, A Greek
philospher
 proposed a
cosmology that was
held for thousands
of years.
 theorized that the
Sun, the Moon and
the planets all
revolved around the
Earth on a set of
celestial spheres.

7. Aristotle:
 celestial spheres were made
up of q uinte sse nce , which is
a perfect, unchanging,
transparent element.
 outermost sphere was made
of stars, which appeared to
be fixed in position. Early
astronomers called them
“fixe d stars ” to differentiate
them from planets. The
spheres inside the spheres
of the fixed stars held the
planets which astronomers
called them “wande ring
stars ”.

8. About 5250 B.C.: Greek astronomer,
Aristarchus of Samos:
 first known
astronomer to
assert that the
Earth moved
around the Sun, but
Aristotle’s model of
the universe
prevailed and was
accepted for almost
1,800 years after
his assertion.

9. Ptolemy, Greek scientist
 explained the retrograde
motion as the result of a set
of small circles, called
e picycle s, on which the
planets moved.
 hypothesized that the
epicycles moved on larger
circles called de fe re nts and
the combination of these
motions caused the
dominant forward motion
and the occasional
retrograde loops.

10. Nicolaus Copernicus, Polish
astronomer
 developed the model of a Sun-centered universe.
 explained the daily and yearly motion of the sun and
stars in the universe

11. Tycho Brahe, Danish
astronomer
 made the most scientific
and accurate observation of
the universe.
 discovered discrepancies
between astronomical
predictions and the actual
events.
 built a set of large
instruments that allowed
him to record the positions
of the planets and stars
with unprecedented
accuracy.

12. Johannes Kepler, German
astronomer
 discovered that
the planets
orbited around
the sun in
ellipses or
elongated circles
with the sun a bit
off-center at one
focus.

13. Galileo Galilei,
 the first astronomer to
use a telescope to
observe and recognize
everything he saw in
the sky.
 found out that the
Moon had craters, that
Venus went through a
full set of phases like
the moon and that
Jupiter had satellites,
or moons of its own.

14. Isaac Newton
 derived a wide
range of theoretical
results about
planetary orbits and
advanced the law of
universal gravity.
 Newton’s laws were
accepted as the
foundation of
cosmological field
until the 20th

15. Why is The Night Sky Black?

16. Olber’s paradox by Heinrich
Olbers
 why the sky was dark
at night if space is
indeed infinite
 why the stars are
distributed throughout
that infinite space.
 an infinite amount of
starlight make the sky
very bright at night.

17. Henrietta Leavitt
 relates distance to
variations in
brightness of
Cepheid variables, a
class of stars that
vary periodically in
brightness.
 Known for period-
luminosity of
Cepheid stars

18. Harlow Shapley
 measured the distance
of several groups of
stars known as globular
clusters.
 His observations made
the cosmologists
realized that the Earth
and the Sun do not
occupy any special
position in the universe.

19. Globular Cluster Orbit
 showed that the
clusters were
centered around a
point far from the
sun and the
arrangement of the
clusters was
presumed to reflect
the overall shape of
the galaxy, thus
realized that the sun
was not the center of
the galaxy.

20. Edwin Hubble
o Showed that the universe is
expanding
o Known for the Hubble Law
that the uniform relationship
between velocity of expansion
and the distance from the
Earth.
o The redshifts are not true
Doppler shift but rather the
result from the expansion of
space which carries the
galaxies along with it.