Transcript The Sizes and Numbers of Objects in the Universe

Welcome to
Astronomy 210
Life in the Universe
“The Search for Life in
the Universe”
3rd Edition
Goldsmith and Owen
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Astronomy 210 Website is up
Pickup Powerpoint notes at the
beginning of class
Powerpoint presentations online
Possible field trip to MLO
Frequent Astronomy 100 refreshers
Reading list soon…
What should a
“Life in the Universe”
class cover??
The Sizes and Numbers of
Objects in the Universe
Solar System Inventory: 1 Star
Solar System Inventory:
9 Planets
The Terrestrial Planets
The Jovian Planets
Solar System Inventory:
91 + moons
Solar System Inventory:
Countless numbers of Asteroids,
Comets, Meteors, Dust
Terrestrial Characteristics:
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Metallic core
Oxygen dominated (silicates)
Material
Iron
Oxygen
Silicon
Magnesium
Nickel
Sulfur
% (by mass)
35
30
15
13
2.4
1.9
Terrestrial Characteristics:
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Thin (or nonexistent) atmospheres
Few (or no) natural satellites
Closely spaced orbits
Jovian Characteristics:
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Solid metallic-rocky cores
Hydrogen dominated
Material
Hydrogen
Helium
Water
Methane
Ammonia
Rock & Metals
% (by mass)
74
24
0.6
0.4
0.1
0.3
Jovian Characteristics:
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Thick gaseous atmospheres
Many natural satellites
Widely spaced orbits
Pluto-Like?
Cosmic Distances
Astronomical units of distance:
Astronomical Unit: The distance between the
Sun and the Earth
93 million miles
Light year: The distance light travels in a year
Speed of light: 186,282 miles/sec
Light year: 5.9 trillion miles
The Sizes of Stars in our
Universe
The Distribution of Stars in
the Universe
How do we know how many
stars there are in the Universe?
If we literally counted the
stars in each galaxy…
1 per second, 8 hours every day…
38,000 years!
How many stars are in the
Milky Way?
4
3
p 
d
G (m1  m2 )
2
2
4 d
m1  m2 
2
G p
2
4 d
mgal  msun 
2
G p
2
3
3
4 d

2
G p
2
mgal
3
How many stars are in the
Milky Way?
Orbital periodsun ~ 240 million years
Orbital distancesun ~ 28,000 light years
Mgal  100 billion Msun
Does this represent the actual
number of stars in our
galaxy?
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Our Sun is an “average star” in mass
and luminosity.
The galaxy has many more low mass
stars compared to high mass stars
Adjusted estimate of stars in Milky
Way: 300 – 400 billion stars
How are the galaxies
distributed in the Universe?
How do we know how OLD
the Universe is?
Edwin Hubble - 1929
It all depends on HO
HO – The “Hubble Constant”
 It is a measure of the slope of the line
in the Hubble Diagram
 Represents the expansion rate of the
Universe
1
Age of Universe 
HO
Current observations suggest:
km
sec
km
sec
70
20
H0 
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Mpc
Mly
Age of Universe ~ 14 billion years