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| The Sun |
1. The luminosity is 4 x 1026 Watts. This is about 1019 dollars at current U.S. rates.
2. Solar constant is 1400 Watts/m2, so on 0.5 square meters about 700 Watts would fall.
3. About 700 km.
4. Granulation typically has a diameter of about 1000 km; this requires 1-2 arc second resolution to resolve at a distance of 150,000,000 km.
5. One check is helioseismology. Because the propagation of sound inside the Sun is sensitive to the helium concentration, a detailed analysis of the long-wavelength vibrations of the Sun (which are more sensitive to the deep interior) provides a test. These data suggest that the interior helium concentration is indeed not very different from that of the surface.
6. Helium is very difficult to excite or ionize because it is a noble gas. It cannot be seen in the Fraunhofer absorption spectrum because it is too cool in the photosphere to excite it. In the chromosphere the temperature is higher (10,000-15,000 K) and helium can be seen there in emission.
7. Calculate, but it would take a very long time to lose much mass at that rate.
8. The diameter of the Sun is 1.4 x 106 km, so its circumference is 4.4 x 106 km. In 25 days there are 3600 x 24 x 25 = 2.15 x 106 seconds. Thus, the velocity of a point on the equator is about 4.4 x 106 km / 2.15 x 106 s ~ 2 km/s.