ASTR 101 Lecture Notes - Lecture 1: March Equinox, Orbital Period, Lunar Month

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Published on 16 Oct 2017
Aug 21
What is astronomy
Natural science that tries to explain, understand and predict
observations of the world around us
Study of celestial objects (outside the earth’s atmosphere sun,
moon, stars, planets, galaxies)
Study of everything
Understanding the universe and our place in it
Astronomy with
Biology how we came to be
Chemistry formation of elements
Physics motions of planets and celestial bodies and predict the
Philosophy our place in the universe
Modern astronomy
How does matter work (dark matter, dark energy)
Our cosmic address
Earth (planet) > solar system (solar interstellar neighborhood) > milky
way > local group (galactic group) > virgo supercluster
(supercluster of galaxies) > observable universe
The observable universe
We can’t see things from 45.6 billion light years away
As we look further away, we look BACK in time
Constellations are in the milky way (in our own galaxy)
Aug 23
Unit of Measurement
SI system: international system of measurements
Easier to relate to
Astronomical Unit (AU)
Average distance between the Earth and the Sun
150,000,000 km
More manage to think about
Light Years (LY)
Distance that light travels in one year
How long does it take for light to travel through space
in one year
Time to denote a distance
Basically saying “I’m an hour away”
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Speed of light = c
2.99 * 10^8 m/s
Light Travel Time (Ltt)
Time it takes for light to travel from one place to another
Light coming from the moon LEFT the moon 1 seconds ago
(basically a delay)
Light from the sun takes 8 ½ minutes to get to us
The closer you are, the realer the time is
Look Back Time (Lbt)
How far back in time we see in years equals light travelled in
If you look at the sun, what you see is the sun 8.5 minutes ago
Andromeda is 2.5 million ly away so the image of Andromeda
that we see is 2.5 million years old
The nearest star is 4.4 light years away
The distance from one end of the milky way to the other is 100,000
light years
The distance to the nearest galaxy is 2,500,000 light years
Aug 28
Scientific Thinking
Science helps us predict using theoretical models (connecting
theories with behavior of complex systems to explain behavior)
Starts with a fact (statement that’s objectively true  not
necessarily obvious)
Then comes a hypothesis ( tentative explanation subject to
testing and revision)
Theory or law (a model whose prediction have been shown
to be true by repeated and varied testing  still subject to to
testing and revision)
Theory explains why something happens, uses words to
Law does not have an explanation, uses mathematical
Principles (general ideas or sense about how the universe if
that guides the construction of new theories)
Cosmological principle
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“There is absolutely nothing special about our
place in the universe”
Us existing can happen anywhere else and any
other time, which it does
Our view on earth is not special or unique
Being on earth doesn’t mean we see more or less
Distance objects act like objects near by
What happens here should happen
anywhere else
Matter and energy obey the same
physical laws everywhere
We make this assumption so we can study
distant objects even though they’re so far
Falsifiable statements
Statement that can be tested to determine if it is false
A theory can be true in millions of different ways, but if it’s false in
any way, it’s not useful
Written be proven false
Can’t be an opinion and should be able to test it
Patterns in the sky
Naked eye can only see ~6000 stars
Can only see them for half the day (aka at night)
Need good conditions
No smog, no light pollution, weather (rain, clouds)
Anywhere AWAY from the city
How do we locate things on earth
Continent > country > state > …
We do the same exact thing with the night sky
Constellations (regions of the sky)
88 total
Names are in Latin
Patterns that are recognizable in constellations
(big dipper is an asterism in ursa major)
Naming stars
Come from the transliteration of medieval greek to arabic to latin
Only a few stars have proper names
Bayer designation
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