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ASTA01H3 Lecture Notes - Observable Universe, Milky Way, Cosmic Calendar

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Kristen Menou

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ASTA01-Chapter 1: The Scale of the Cosmos: Space and Time
1.1 From Solar System to Galaxy to Universe
Lecture 01
Astronomy is more than the study of planets, stars and galaxies.
Study of the the whole universe in which you live.
Humanity is confined to a small planet circling an average star.
No edge or an end in space of universe.
Universe may be infinite.
May extend in all directions without limit.
90 years ago: astronomers found that the universe expands.
13 years ago: astronomers found that it is expanding at an accelerating pace.
CERN- The European Organization for Nuclear Research
It is the home of the large Hadron Collider. The largest particle
accelerator in operation today, which was designed to simulate the
beginning of the universe.
Physicists study collision of objects on the scale
< 0.000000000000001 m
= 1 fm (femtometer or fermi)
We start using either prefixes (e.g., “kilo,” which means “one thousand”) or
scientific notation (i.e., using powers of 10).
For example:
101 = 10
102 = 10 * 10 = 100
103 = 10 * 10 * 10 = 1000 (kilo) ….
106 = 1,000,000 (mega)
109 = 1,000,000,000 (giga)
1012 = 1,000,000,000,000 (tera)
(…) peta, exa, ….
The Alps started forming 100 million years ago when the African tectonic plate
started to move toward the European plate, and the bottom of the sea rose to
form new mountains.
The Alps still gain about one millimeter in height every year, but since erosion
is faster, they will eventually round off and disappear.
Mountains and valleys are only temporary features on Earth that are slowly
but constantly changing.
As you explore the universe, you will come to see that it, too, is always
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the entire planet Earth, which is about 13 000 kilometers in diameter.
The rotation of Earth on its axis each 24 hours carries you eastward, and as
you cross the sunset line into darkness you say that the Sun has set.
Moon with a diameter only about ¼ that of Earth.
The average distance of the Moon from Earth of 380 000 kilometers.
We enlarge a picture not 10 times or 100 times, but 150 times in order to fit a
specific distance into the picture, the average distance from Earth to the Sun.
This distance is called the Astronomical Unit (AU).
It is 1.5 *8 km = 150 mln km = 1.5 * 11 m.
The average distance from Venus to the Sun is about 0.7 AU.
The solar system consists of the Sun, its family of planets,
and some smaller bodies, such as moons, asteroids, and
Like Earth, Venus and Mercury are planets small,
nonluminous bodies that shine by reflecting sunlight.
Venus is about the size of Earth, and Mercury is a bit larger than Earth’s moon.
The Sun is a star, a self-luminous ball of hot gas that generates its own energy.
The Sun is about 110 times larger in diameter than Earth, ~1.4 million km
Earth orbits the Sun once a year.
The Sun, Mercury, Venus, and Earth are so close together that we cannot
separate them at this scale.
Here you see the entire solar system, all the major planets, and their slightly
elliptical orbits.
Mars, the next outward planet, is only 1.5AU from the Sun.
In contrast, Jupiter, Saturn, Uranus, and Neptune are so far from the Sun that
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