Galaxies and the Universe. The Milky Way 31.1 Other Galaxies in the Universe 31.2 Cosmology 31.3. Chap. 31. Objectives. The Milky Way. determine the size and shape of the Milky Way, as well as Earth’s location within it. describe how the Milky Way formed. Discovering the Milky Way.
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The Milky Way 31.1
Other Galaxies in the Universe 31.2
Stars in the ‘giant’ branch of HR diagram that pulsate in brightness
Brightness pulsates between 1.5 hours and 1 day
Brightness pulsates between 1 and 100 days
The larger the period (time) of pulsation the greater the luminosity. (graph this)
If a star is really bright (__________ magnitude) but it appears to be dim (_________ magnitude), you know it’s far. The dimmer it looks the farther it is.
Remember that luminosity is related to mass. Stars that are bigger are also _________.
(M1 + M2)P2 = a3 Kepler’s 3rd law
M1 is sun’s mass (measured in “sun masses”)
M2 is universe’s mass (measured in “sun masses”)
P is orbital period (years) = 240 million y
a is distance (in AU)
1 ly = 63,200 AU
This center is about 2.6 million times the Sun’s mass
Notice the arrangement of the oldest stars.
He used variable stars to do it.
M74 in pisces
NGC 1300 – in Eridanus
Type a represents tightly wound arm with bright nucleus.
member of the local group
This is evidence for existence of dark matter
Light waves are stretched out due to relative motion of source and observer away from each other.
v = Hd
v = Hd
NGC 5128 -
Expansion of Universe never stops
Expansion stops and becomes a contraction
Expansion slows to halt in infinite amt. of time
Universe began with a fluctuation in expansion. For a brief instant its rate of expansion increased
Calculate the number of years since expansion of the Universe using Hubble’s constant: 1/H = time
H = 50 km/s / Mpc or H = 100 km/s / Mpc
1 pc = 3.1 x 1013 km
‘mega’ (M) = 1 000 000 units