Astronomy | Astrophysics Answers

a) Approximately 9000 stars are visible to the naked eye in the whole sky (imagine that you could see around the entire globe and both the northern and southern hemispheres), and there are about 41,200 square degrees on the sky. How many stars are visible per square degree? Per square arcsecond? 

b) People are often bothered when they discover that reflecting telescopes have a second mirror in the middle to bring the light out to an accessible focus where big instruments can be mounted. “Don’t you lose light?” people ask. Well, yes, you do, but there is no better alternative. You can estimate how much light is lost by such an arrangement. The primary mirror (the one at the bottom in Figure 6.6) of the Gemini North telescope is 8 m in diameter. The secondary mirror at the top is about 1 m in diameter. Estimate what fraction of the light is blocked by the secondary mirror. 

Was there a beginning of time?

1- Approximately how many stars are visible with the naked eye in the night sky?2- Where in the night sky can you observe the famous double star system Mizar and Alcor?3- What kind of celestial object is Neowise C/2020 F3 and what makes it special?4- Which very intense meteor shower is taking place annually in December?

If you have a box of 10 cm of edge, how many grains of sand would fit in this box?

The star of a distant solar system explodes as a supernova. At the moment of the explosion, an resting exploration spaceship is 15 AU away from the shock wave. The shock wave of the explosion travels with 25000 km/s towards the spaceship. To save the crew, the spacecra makes use of a special booster that uniformly accelerates at 150 m/s2 in the opposite direction. Determine if the crew manages to escape from the shock wave. (Neglect relativistic eects.) 

The equation y = Asin (wt + kx) represents a progressive wave.

(a) What do the quantities A, w and k represent?

(b) In which direction is the wave moving? (Explain how you arrived at your conclusions) 

An astronaut working on the Moon tries to determine the gravitational constant G by throwing a Moon rock of mass m with a velocity of v vertically into the sky. The astronaut knows that the Moon has a density ρ of 3340 kg/m3 and a radius R of 1740 km.

(a) Show with (1) that the potential energy of the rock at height h above the surface is given by:

E = − 4πG 3 mρ · R3 R + h

(b) Next, show that the gravitational constant can be determined by:

G = 3 8π v 2 ρR2  1 − R R + h −1 

(c) What is the resulting G if the rock is thrown with 30 km/h and reaches 21.5 m?

(PLEASE SOLVE ALL PARTS)

A research team has discovered that a moon is circling a planet of our solar system: The moon orbits the planet once every 7 hours on a nearly circular orbit in a distance R of 48000 km from the centre of the planet. Unfortunately, the mass m of the moon is not known. Use Newton’s law of gravitation with G = 6.67 · 10−11 m3 /(kg·s 2 ) to approach the following questions: F = G · mM R2 (a) Based on the observations, determine the total mass M of the planet. (b) Which moon and planet of our solar system is the team observing? (Use literature.)

Radio telescopes are an essential tool for modern astrophysics. They played a crucial role in discovering a fascinating astronomical object: Pulsars - highly compact objects that periodically emit radiation. Pulsars are still an active part of astrophysical research. Explain how pulsars are formed and the causes for their pulsating behaviour.