1. The document discusses various units of distance used in astronomy including the astronomical unit (AU), parsec, and light-year. 2. It provides conversions between these units, for example 1 AU = 149,597,870,700 m, 1 parsec = 3.086 x 1016 m, and 1 light-year = 9.460530 x 1015 m. 3. The document also contains information about constellations, galaxies, and how astronomers study distant objects that cannot be touched.

1. The Powers of Ten
and
Astronomical units

2. http://micro.magnet.fsu.edu/primer/java/scienceopti
csu/powersof10/index.html
Astronomical Unit: au, unit of distance adopted by
the General Assembly of the International
Astronomical Union in 2012:
1 au = 149,597,870,700 m (exactly)
The Earth – Sun distance is 1 au.
Parsec: unit of distance (pc)
1 pc = 3.086 x 1016 m

3. Parsec: corresponds to the distance at which the mean
radius of the earth’s orbit subtends an angle of one
second of arc.
Parsec: unit of distance (pc)
1 pc = 3.086 x 1016 m
1 pc = 3.261633 lt-yr

4. Light-year: A unit of DISTANCE not time. It is the
distance that light travels in a year.
1 lt-yr = 9.460530 x 1015 m
1 lt-yr = 6.324 x 104 au

5. Consider this situation:
Seems plausible but: Nothing can travel faster than the
speed of light. So is this leap correct?

6. Need a hint?

7. The Solution:
http://www.sciencelet.com/2012/10/light-year-long-
rod-to-beat-speed-of-light.html
In our hypothetical example, lets say the rod is made of steel.
Speed of sound in steel is 6100 m/s and the speed of light
is 299792458 m/s. So the pressure wave (that travels at the
speed of sound in steel) would take 49146 times more
duration to reach the other end. Thus in our example, Person
B would feel the nudge after nearly 49000 years. So much for
their attempt to beat the speed of light.

8. Other interesting data:

9. What will we study this semester?
Main Points:
1. Light
1. Optics
1. Our Solar System
2. planets and their satellites
3. orbits
3. inner small and rocky
3. outer large and mainly gas
2. Asteroid belt between Mars and Jupiter
2. Comets
3. Oort Cloud
2. Meteors
2. Sun
And a focus on “How did they find that, How did they do that?”

10. Your address in Galactical terms:
Street:
Town:
Indiana 4630?
USA
Earth
Solar System
Milky Way
Local Group
Universe

11. What about Constellations, Galaxies, Clusters
of Galaxies, Dwarf Stars, Super
Novas and all of that? Second Semester. But for now:
Galaxies are large collections of stars held together by
their mutual gravity.
Dwarf Galaxies might have only a few million stars,
many galaxies have hundreds of billions.
The Universe has around 100 billion galaxies.
Constellations hold groups of stars like the little dipper.
This is called an asterism.

12. Constellations like Orion are patterns of stars that remain
the same from night to night over the span of life-times.
Orion’s Belt

13. They do not appear in the same place in the night
sky. Why?

14. The constellations visible also depends on the time
of the year. Why?

15. What you see depends on where you are. Why?
The stars in a constellation are not flat but three
dimensional. Some are farther back than others.

16. The stars in a constellation are not flat but three
dimensional. Some are farther back than others.

17. How do Astronomers study what cannot be
touched?
1. Use the spectrum (from Radio waves to
Gamma rays)
2. Bigger and Better telescopes everywhere
including space. (Hubble telescope is only
one example.)

18. BHR 71 Nebula in visible
light.
BHR 71 Nebula in infrared
light.
Taken with NASA Spitzer Space telescope/Very Large Telescope in Chile.