Problem set 6C
The luminosity of Proxima Centauri is only about 1/500 that of the Sun, about 5x1023watt. Its surface brightness is 3.9x106 watt/meter2. What is Proxima Centauri's radius? Give the answer in km to two significant figures. (First find the answer in meters and then convert to km). Note: Your answer is assumed to be reduced to the highest power possible.
1.0 x 10^5 FEEDBACK: Use the formula for the radius derived in part V (Stellar Sizes). Proxima Centauri is a main-sequence star with mass about 1/10 the mass of the Sun. You should find a radius about 1/7 the radius of the Sun. EQUATION: Distance = 1/P Where P = parllax angle in arc seconds and D = distance in parsec Therefore, Distance = 1/4×10-1 = 2.50 × 10^0
What is the distance in pc to a star whose parallax angle is (4.0x10^-1) arc seconds? Give the answer to two significant figures as usual. Note: Your answer is assumed to be reduced to the highest power possible.
2.5 X 10^0 . Equation 1/4.0x10^-1 =2.5 x 10^0
Uranus is about twice as far from the Sun as Saturn is. The brightness of sunlight on Saturn is about 14 watt/meter2. What is the brightness of sunlight on Uranus? Give the answer as usual in scientific notation to two significant figures. Note: Your answer is assumed to be reduced to the highest power possible.
3.5 x 10^0 FEEDBACK: Brightness is proportional to 1/d2: Brightness at Uranus/Brightness as Saturn = 1/22 = 1/4. Brightness at Uranus = Brightness at Saturn/4
The brightness of sunlight at the surface of the Earth is 1400 watt/meter2. What is the brightness of sunlight on Jupiter, about 5 AU from the Sun? Give the answer in watt/meter2, in scientific notation to two significant figures. Note: Your answer is assumed to be reduced to the highest power possible.
5.6 x 10^1 FEEDBACK: Brightness at Jupiter/Brightness at Earth = (1AU/5AU)2 = 1/25. Brightness at Jupiter = Brightness at Earth / 25.
The luminosity of Betelgeuse is about 100,000 times that of the Sun, about 4x1031watt. Its surface brightness is 7.5x106 watt/meter2. What is Betelgeuse's radius? Give the answer in km to two significant figures. (First find the answer in meters and then convert to km). Note: Your answer is assumed to be reduced to the highest power possible.
6.5 x 10^8 FEEDBACK: Use the formula for the radius derived in part IV (Stellar Sizes) in the Notes for Week 9. You should find that the radius of Betelgeuse is about 1,000 times the radius of the Sun. If the Sun were a red giant that size it would engulf all the planets, extending out to Pluto's orbit. The Sun will become a red giant, but its surface will never extend much past the Earth. The difference is that Betelgeuse has a mass about 20 times that of the Sun.
