PROBLEM SET #2

APAS 1040

1. Use Newton's Law to estimate the surface gravity of the Sun. Convert to gees. Then use simple scaling to estimate the surface gravity on a neutron star when the mass remains the same but the radius drops to just 10km.

2. Calculate the pressure of the Earth's atmosphere as we did in class. Set that equal to the formula for the magnet pressure. Solve for the magnetic field necessary to strongly affect the Earth's weather.

3. Use the definition of 1AU and the definition of one arcsecond to derive the length of the parsec.

4. How many times fainter would the Sun appear if it were moved from 1AU to 10pc?

5. What is the frequency of a "dental" x-ray having a wavelength of 0.1Å? What is its energy?

6. The star Zeta Puppis has a temperature of 30,000K. At what wavelength is it brightest?

7. A white dwarf star has a radius of 7x108cm and a temperature of 10,000K. What is its luminosity? Compare to the Sun.

8. A radio transmitter on a spacecraft emits a signal at a frequency of 108Hz. At Earth the signal is received and noted to be at 99,970,000Hz. How fast is the spacecraft moving? Is it receding or approaching?

9. The star Vega (featured in the movie Contact) has a parallax of 0.14" (arcseconds). How long will it take light to travel there and back?