The document discusses the structure of the solar system and universe. It begins by defining planets, moons, and stars. It then describes our solar system, including that the Sun is a star, and explains nuclear fusion as the process by which stars produce energy. Galaxies are described as containing billions of stars, with the Milky Way being our galaxy. The largest structures in the universe are superclusters containing millions of galaxies.

1. The Solar System

2. Planets: the larger bodies orbiting the Sun (or any other star)

3. The planets of our Solar System [& Pluto]

4. The biggest planet is….
-- but the biggest object in the Solar System, by far, is …..

5. Uranus
with 5 moons
A moon (a.k.a.
satellite): an object
of any size orbiting
a planet

6. Our star – the Sun

7. T/F: Our Sun is a star.
***********
Star: Large, spherical ball of gas…...
(…that’s just a partial definition)

8. Surface of Sun – Gas bubbles

9. Solar Flare – an explosive event on the Sun’s surface

10. A bit of the sky, showing stars

11. If the Sun is a
star, why does
it look so big
compared to
allof those
other stars?

12. Star
Large, spherical ball of gas that produces its own
energy by nuclear fusion.
Nuclear fusion
Atomic nuclei combine
to form larger nuclei,
releasing energy in the process

13. The Sun’s fusion reaction is called
Hydrogen Fusion:
H+H+H+H  He + energy (heat)
[ interpretation: 4 atoms of Hydrogen(H) combine to produce
one atom of Helium(He), plus a little bit of heat ]
The “fuel” for this reaction is atoms of hydrogen;
the “products” are helium atoms plus heat (energy)

14. Stars commonly appear clumped together as star clusters --
gravitationally-bound groups of stars, each one containing
hundreds to thousands of stars

15. Pleiades, a.k.a. “Seven Sisters”
- a nearby star cluster

16. Stars, star clusters, etc. collect into much larger
groups called galaxies.
The Sun is a star in the Milky Way Galaxy.

17. The Milky Way Galaxy is a so-called spiral galaxy. This picture of a
different spiral galaxy, one that is seen face-on.
All of the single stars (points of light) seen in this photo are stars that
are in our own Milky Way Galaxy

18. A spiral Galaxy seen Edge-on
-the actual 3D-shaped is like a pancake with a lump in the center

19. How big is a galaxy?
# of stars: about a billion or so (smallest)
- up to 100’s of billions for
large galaxies
Diameter: Very large: what units of distance should
be used?
-- using miles gives awkwardly
numbers.
-- a larger unit is needed.
-- for example…..

21. Light Year --is based on the “speed of light”: 186,000 miles/sec
Defn: 1 Light Year (1 LY) = the distance that light travels in one year.
*** - even YOU can figure it out! ***
Compute 1 LY from the (well-known??) equation:
“distance = velocity x time”
distance = speed of light x time (one year)
1 LY = (186,000 mi/sec) x (~31 million sec/yr)
= 5.86 Trillion miles ( roughly 6 trillion)
( = 5,860,000,000,000 miles )

22. Keep this point in mind about the connection between light-travel-time and
distances:
** It takes light one year to travel a distance of one light-year **
Try to make all 3 columns of the table below make good sense to you.

23. Light-Travel-Time from the Earth
TO TIME DISTANCE
a. the moon 1.25 sec 1.25 light-seconds
b. the sun 8.5 minutes 8.5 light-minutes
c. Pluto ~6 hours
d. Alpha Cen 4.3 yrs 4.3 LY
e. North Star 650 years 650 LY
f. M31 2.5 million yrs 2.5 M. LY
..so just keep in mind that all of those units of length
are based on the speed of light;
- for example: 1 light-minute = the distance that light travels in one minute

25. The
“Milky Way”
galaxy is a
spiral galaxy.
The Sun is in
a spiral arm
half-way out
from the
center.

26. Map of Milky Way
Our Sun(yellow dot) is in a spiral arm, ½-way out

27. Galaxies contain more than just stars. The irregular-looking blobs are either
hot (pink) or cold (dark) interstellar clouds

28. Galaxies occur in galaxy clusters.
This is M31 (the Andromeda Galaxy)…
…. and friends (2 smaller neighboring galaxies)
- sort of a “triple galaxy”

29. The “Local Group” is the name of the (small) cluster of galaxies to which the
Milky Way belongs. The map above shows about 2/3 of its members (fewer
than 40, total).

30. The galaxies closest to the Milky Way
The two Magellanic Clouds(LMC & SMC) are easily visible to the naked eye.

31.  LMC
 SMC
 comet

32. A “nearby” galaxy cluster: Distance = 280 Million LY

33. Distance = 500 million LY

34. Distance over 5 BILLION LY. The galaxies look progressively smaller as we
look at more distance clusters simply because of the increased distance. The
largest galaxies in large clusters are all about the same size.

35. This is a map
of
superclusters
out to
1 billion LY
from the
Milky Way
(which is at
the center)
*****
Supercluster:
– a cluster of
galaxy
clusters
******
# of galaxies
within 1 B ly
> 60 million;
*****
# of stars ~
250,000
trillion

36. What can you see with the naked eye? [outside of the Solar System]
- Milky Way stars! (meaning only stars in our own galaxy)
i.e., you cannot see any individual stars in any other
galaxy;-- they’re just too far and too faint
- 3 other galaxies, ALL in the Local Group:
M31, LMC, SMC
Note: Every star visible to your eye is part of the Milky Way!

37. • Numbers to Know
• Distance to nearest star ---------------- 4.3 Light Years
– ( typical distance between stars )
• Size of Milky Way Galaxy (a typical “big” galaxy):
• Number of stars -------- 400 Billion
• Diameter -------- 100,000 Light Years
• # of stars in ….
• our Solar System ------------- 1
• a star cluster ------------ 100’s to 1000’s
• a galaxy ------------ Billions: ( ~ a billion to
~ a trillion

38. Heirarchical structure of the Universe from largest to smallest
The Universe: includes all objects below
plus all of the space in between
Supercluster  largest; most stars
Galaxy cluster
galaxy
star cluster
planetary system (e.g., Solar System)  one star per system
stars
planets
moons  smallest (diameter)