The units of proper motion are km/s because proper motion is the motion of stars across the sky
a. True
b. False
Indicate whether the statement is true or false
False
RATIONALE: Units are not linear but angular so, for example, units of proper motion could be arc seconds/yr.
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Determine the steady-state temperatures of two radiation shields placed in the evacuated space between two infinite planes at temperatures of 555 K and 278 K. The emissivity of all surfaces is 0.8.
GIVEN
? Two radiant shields placed in the evacuated space between two infinite planes
? Temperature of the planes
? T1 = 555 K
? T4 = 278 K
? Emissivity of all surface (?) = 0.8
FIND
? The steady state temperatures of the shields (T2, T3)
ASSUMPTIONS
? All surfaces are gray and diffuse
SKETCH
When a gas is so dense that most of its electrons are not free to change their energies, it is called _______________
Fill in the blank(s) with correct word
Using an orbit size of 8 kpc, and a period of 225 million years, the mass of our Galaxy is found to be closest to:
A) 106 solar masses. B) 108 solar masses. C) 1010 solar masses. D) 1011 solar masses. E) 1012 solar masses.
On average, approximately how fast do plates move with plate tectonics on Earth?
A) a few centimeters per year B) a few millimeters per century C) a few centimeters per century D) They do not move at all, except during earthquakes. E) a few kilometers per hour