ASTR 3730

Problem Set #1

READING: Chapter 3 of the textbook

1) UNITS
a) Neutral hydrogen emits radio waves with a wavelength of 21cm.
What is the frequency of this radiation?
b)What is the wavelength (in Å) of a 1000eV (1keV) x-ray?
c)An opaque spherical body of radius 1km has a uniform photon intensity of 1 ph/cm²/s/Hz/st between 10¹⁴ and 10¹⁵Hz. At all other frequencies it does not emit. What is its luminosity in ergs/sec? What is its luminosity in Watts?

2. An astronomer using a telescope discovers that a 12th magnitude star is actually a double binary consisting of four identical stars. What is the magnitude of each individual star?

3. After being struck by the phasers of an enemy starship, the Enterprise is left with a net negative charge of 10¹⁹ electrons. The Enterprise charges directly at its enemy, accelerating smoothly from rest to .33c in 5 seconds.
a) How much energy does it radiate? Calculate in cgs or mks (your choice). At the end, convert the answer to the other unit system.
b) How much of this flux does the enemy see?
c) To avoid a collision the Enterprise ceases forward acceleration and starts the same acceleration perpendicular to its motion. What is the maximum flux the enemy could detect (in ergs/cm²/s or W/m²) at 10⁵cm separation.

4. Do problem 3.2 of the text