Astronomy | Astrophysics Answers

About Earth's rotation speed:
Why does my shadow, cast by the Sun on Earth,
not move at 465 meters per second?

How is rocket stopped in the space after reaching its destination?

Anewstar lights up inside a cloud of atomic hydrogen with a constant number density of n atoms per unit volume. The star emits ionizing photons at a rate of Q¤ photons per unit time. The ionizing photons begin carving out a growing “Str¨omgren sphere” of ionized gas inside the neutral gas . a. At a distance r from the star, what is the timescale ¿ion over which an individual atom gets ionized, if the ionization cross section is ¾ion? b. If the recombination coef cient is ® ´ h¾vi, what is the timescale ¿rec for an individual proton to recombine with an electron?

I know the old ways of measuring radius of the Earth.
But I wan't to know what is the method that for example NASA uses nowadays to measure it ?
I want to know the best and most accurate way of measuring it.

Assume that the disk of the Milky Way has a radius of 20 kpc (20 thousand parsecs). It contains 100 billion stars, each with a radius similar to the Sun's, 6.96 x 1010 cm. What fraction of the galaxy's disk is covered by stars?

Two 10kg spheres are placed 500mm apart.Express the gravitational attraction acting on one of the spheres as percentage of its weight on earth

The “Opportunity” rover that just landed on Mars transmitted music back to Earth. If the distance to Earth at the time was 9x10^7 km and radio waves (a kind of “light”) travel with a speed of 3x10^8 m/s, how long did it take for the signal to reach listeners on Earth?

What do you understand by cosmic distance ladder? Explain how it is used to
estimate distance of stars.

What is an active galaxy? What is the source of its activity? Under what conditions
does an active galaxy emit synchrotron radiation?