User:Inconspicuum/Physics (A Level)/Astrophysics Questions

Radar and Triangulation
Regardless of (λ) wavelength, power density, or wavefront properties, the pulse would be absorbed with no reflection possible. Distances to pure energy sources are generally measured in terms of received light intensity, shifts of the light spectrum, and radio interferometry. The RF spectrum; and Laser (light) spectrum can be used to "listen" to radiation, but not bounce a pulse from an energy source having no true angle of incidence. Just as an observation, I will note that the sun can be seen on most radars either sunrise or sunset, usually when the sun is just above the horizon. But these receptions are unusable strobes (interference) and not a result of receiving a radar pulse from the sun. Radar technicians also use the sun as a "known" exact position to align the system to true north (and magnetic variations); this is called solar-boresighting and, again, only receives the radiation.
 * 1) A radar pulse takes 8 minutes to travel to Venus and back. How far away is Venus at this time?
 * 2) Why can't a radar pulse be used to measure the distance to the Sun?
 * 1) Radar is used to measure the velocity of a spacecraft travelling between the Earth and the Moon. Use the following data to measure this velocity:
 * 2) The angles between the horizontal and a star are measured at midnight on January 1 as 89.99980&deg; and at midnight on July 1 as 89.99982&deg;. How far away is the star?
 * 3) Why can't triangulation be used to measure the distance to another galaxy?

Large Units

 * 1) What is one parsec in m?
 * 2) Convert 3 light days into km.
 * 3) Convert 5.5 parsecs into light years.
 * 4) The difference in angle of a star on the perpendicular to the plane of the Earth's orbit which passes through the Sun when viewed from either side of the Earth's orbit is 0.1°. How far away is the star in parsecs?

Orbits

 * 1) The semi-major axis of an elliptical orbit can be approximated reasonably accurately by the mean distance of the planet for the Sun. How would you test, using the data in the table above, that the inner planets of the Solar System obey Kepler's Third Law?
 * 2) Perform this test. Does Kepler's Third Law hold?
 * 3) If T2 &alpha; R3, express a constant C in terms of T and R.
 * Io, one of Jupiter's moons, has a mean orbital radius of 421600km, and a year of 1.77 Earth days. What is the value of C for Jupiter's moons?
 * 1) Ganymede, another of Jupiter's moons, has a mean orbital radius of 1070400km. How long is its year?

Doppler Effect

 * 1) M31 (the Andromeda galaxy) is approaching us at about 120kms-1. What is its red-shift?
 * 2) Some light from M31 reaches us with a wavelength of 590nm. What is its wavelength, relative to M31?
 * 3) Some light has a wavelength, relative to M31, of 480nm. What is its wavelength, relative to us?
 * 4) A quasar emits electromagnetic radiation at a wavelength of 121.6nm. If, relative to us, this wavelength is red-shifted 0.2nm, what is the velocity of recession of the quasar?

Big Bang Theory

 * 1) What is the Hubble Constant in s-1?
 * 2) How old is the universe?
 * 3) What effect might gravity have had on this figure?
 * 4) Polaris is 132pc away. What is its velocity of recession, according to Hubble's Law?