Two stars have apparent magnitudes of 0 and 5. If both stars are 117 parsecs away, which star is intrinsically brighter and by what factor is it brighter than the other?
What will be an ideal response?
Since both stars are at the same distance (it does not matter what the distance is), the magnitude 0 star is the brightest. It is intrinsically 100 times brighter than the magnitude 5 star because 5 magnitudes is always a factor of 100 in intrinsic brightness.
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A spherical communications satellite 2-m in diameter is placed in orbit around the earth. The satellite generates 1000 W of internal power from a small nuclear generator. If the surface of the satellite has an emittance of 0.3 and is shaded from solar radiation by the earth, estimate the surface temperature. What is the temperature if the satellite with an absorptivity of 0.2 is in an orbit in which it is exposed to solar radiation? Assume the sun is a blackbody and irradiation striking the satellite is 1366 W/m2 and state your assumptions.
GIVEN
• Spherical satellite
• Diameter (D) = 2 m
• Heat generation = 1000 W
• Emittance (?) = 0.3
• Absorptivity of satellite (?)=0.2
• Solar irradiation(G)=1366 W/m2
FIND
• The surface temperature (Ts)
• Surface temperature of satellite
ASSUMPTIONS
• The satellite radiates to space which behaves as a blackbody enclosure at 0 K
• The system is in steady state
SKETCH
PROPERTIES AND CONSTANTS
The Stefan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
A. +x direction B. -x direction C. +y direction D. -y direction E. +z direction F. -z direction T. The field is zero.
Since the rest energy of an electron and its antiparticle a positron is 0.511 MeV, a gamma ray must have an energy larger than 1.022 MeV to produce an electron-positron pair
Indicate whether the statement is true or false
Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating that they are orbiting one another?
A) spectroscopic binary B) double star C) eclipsing binary D) visual binary E) none of the above