Astronomy | Astrophysics Answers

The Earth effectively sits in a low-density H II region made up of the ionized solar wind. The wind
has is expanding constantly at about 400 kms−1 (i.e. the density decreases as r−2) and in the region of the Earth’s orbit, Ne = 10 cm−3. Estimate t and Tb at an observing frequency of 100MHz due to free-free absorption from this wind, at large angles from the Sun.

The same feed is used with a 1 megawatt transmitter at 2.3GHz for planetary radar. What is the on-axis power gain Gmax of this radar system?

The 2.3GHz feed at Arecibo illuminates an elliptical aperture 225m by 200m in size, and the aperture efficiency nA over this ellipse is nA about 0.70. What is the sensitivity of this system in K/Jy?

A convenient parameter for specifying the sensitivity of a radio telescope is its sensitivity in units of K/Jy; that is, the number of Kelvins of antenna temperature TA produced by an unpolarized point source whose flux density is 1 Jy.

(a) (3 points) What is the effective collecting area Ae of a radio telescope whose sensitivity is 1 K/Jy?

An electron is “wiggling” in one dimension such that its position is x(t) = Acos(wt). What is the average power radiated by the particle? Note how it scales with the wiggle frequency w?

It is a cool day in Green Bank (5 deg C), and you are observing a point-source calibrator with the GBT that has a flux density of 1 Jy. However, you measure a flux density of only 800 mJy.

(a) (2 points) What is the observed atmospheric opacity, tA?

Giant pulses from energetic pulsars have been observed with S5GHz = 10 kJy, but with durations of only 10 ns. The region from where a pulse of radiation originates must be no larger than the distance that light can travel during the duration of a pulse. If the pulsars are at a distance of 1 kpc, estimate the brightness temperature of these sources.

The surfaces of rocky planets aren’t perfect black bodies at radio wavelengths. Rocks reflect about 10% of the radio radiation incident upon them. Use this information to improve your estimate the 15 GHz brightness temperature and flux density of Mars.

Given the TM from above, what is the flux density of Mars at closest approach to Earth at an observing frequency of 15 GHz.

The Sun is a nearly perfect blackbody with temperature of T sun = 5800 K. Mars is also a
near-blackbody, with temperature TM, radiating about as much energy as it receives from the Sun at its orbital distance of 1.52 AU. At closest approach to Earth, Mars has an angular diameter of about 18 arcsec.
(a) (2 points) Compute the bolometric solar luminosity.