2. What is Astronomy?
Astronomy is the study of anything we
see in the sky, and beyond
Overlaps with physics, chemistry,
geology, and other sciences
3. The Scientific Method in
Astronomy
Astronomy is one of the most difficult
sciences to do, because we can’t do very
many things in a lab
We have to combine our observations with
our understanding of other sciences to make
good predictions
Sometimes, our “lab” is a computer
4. Astrology
Astrology - the belief that the stars and planets
affect your life
Despite the –ology, it’s not a science!
Gravity of other planets is not as strong as the
gravity of your obstetrician!
Does not use the scientific method
It’s complete poppycock
5. Observing the Universe
Astronomy began with people observing
their surroundings
What did the sky look like when herds
moved? When a season changed?
When was it good to plant?
Planets, sun, moon, and stars all seemed
to move independently
6. What have you Observed?
An incomplete list:
Moon
Planets (Venus, Mercury, Mars, Jupiter, Saturn)
Stars
Meteors (shooting stars)
Aurora
Comets
7. What’s Out There, Anyway?
Atmospheric phenomena
Solar System
Sun and planets; comets, asteroids, etc.
Milky Way
Our galaxy
Extra-galactic
Other galaxies
Some objects like our galaxy
Some completely different phenomena
Things between galaxies
9. Solar System Objects and
Phenomena
The Sun
Eclipses
Planets & Moons
Asteroids
Comets
10. Galactic Objects and
Phenomena
Stars & star clusters
Nebulas
Supernova Remnants
Dead Stars
White Dwarfs
Neutron Stars
Black Holes
Dark Matter
55. Units for Measuring
Astronomical Distances
Astronomical Units (AU)
Defined as the distance from the Sun to the Earth
About 1.496x1011 m (about 150 million km)
Light-years
Defined as the distance light travels in one year
About 9.46x1015 m
Parsecs
Derived from the way stars appear to shift slightly
in the sky as the Earth orbits the Sun
Equal to about 3.26 light-years
56. How Big Is It?
Our Earth
12,756 km across
Earth to the Moon
384,400 km
Earth to the Sun
150 million km
= 1 AU
= 500 light-seconds
57. How Big Is It?, cont.
Sun to Jupiter
5.2 AU
Sun to Pluto
Between 30 and 49 AU
Oort Cloud
Theoretical, unobserved edge of the Solar
System
Out to about 50,000 AU (= 0.79 light-year)
58. How Big Is It?, cont.
Nearest star
4.2 light-years away
Our Galaxy
100,000 light-years across
To the nearest large galaxy
2.5 million light-years away
59. How Big Is It?, cont.
Virgo Cluster of Galaxies
Nearest cluster of galaxies to us
About 50 million light-years (debated)
Quasar 3C 273
One of the nearest and brightest quasars
About 2 billion light-years
Edge of the observable Universe
About 13.7 billion light-years away
60. Light travel times…
Across earth: 0.04 seconds
From moon: 1.3 seconds
From sun: 8 minutes
From Neptune: 4 hours
61. Light travel times…
From nearest star: 4 years
From galactic center: 25,000 years
From Andromeda galaxy: 2 million years
From hot early universe: 14 billion years