The Doppler radial velocity technique works best for
A) planets whose orbits are along are line of sight.
B) planets whose orbits are perpendicular to our line of sight.
C) planets whose orbits are nearly circular.
D) planets whose orbits are very eccentric.
A
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A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
GIVEN
• Long wire in still air
• Wire diameter (D) = 0.7 mm= 7*10-4 m
• Wire temperature (Ts) = 800 K
• Emissivity (?) = 0.9
• Air temperature (T?) = 270 K FIND
• The net rate of heat loss
ASSUMPTIONS
• The enclosure around the wire behaves as a blackbody enclosure at the temperature of the air
• The natural convection heat transfer coefficient is 18 W/(m2 K)
• Steady state conditions prevail
SKETCH
Which of the following was NOT a contribution of Galileo to astronomy?
A) Sunspots showed the Sun was rotating on its axis, like the Earth does. B) The four moons of Jupiter are a model for the solar system motions in general. C) The phases of Venus prove it orbits completely around the Sun. D) The changing appearance of Saturn's rings corresponds to our seasons. E) The craters and mountains of the Moon prove it a world in its own right.
Nearly every aspect of astronomy is related in some way to the existence of gravity and to the motions which are responsible for a balance against gravity. How does this balance play a role for the miscellaneous objects of the solar system (i.e
, the asteroids and comets)? How can some aspect of this be used as a tool to determine masses in the solar system?
Within cosmology, the critical density is
A. the density that determines whether the Universe expands forever or recollapses. B. the density of the Universe. C. the density of the most massive black hole in the Universe. D. the density of Universes in the multiverse. E. None of these choices is correct.