# Astronomy Stack Exchange Community Digest

## Top new questions this week:

### How far away are the events that caused the gravitational waves that have been detected?

A certain number of gravitational wave events have been detected. Is it possible to know how far away the mergers that caused those gravitational wave events are?

black-hole gravitational-waves neutron-star

### Why does the sensitivity to GWs drops off inversely proportional to the distance?

This answer makes me wonder why the sensitivity to gravitational waves decreases proportionally to the distance. Since gravitational waves extend in all directions, my (uneducated) guess would be ...

gravitational-waves physics

### How would the sky look if Earth orbited a red giant at a safe distance?

Let's say that instead of the sun, we have a red giant, but are orbiting it at a safe distance, within the goldilocks zone. Would the sky actually look more red? Or would it be closer to ...

red-giant

### Why is Ganymede's aurora only visible in ultraviolet while Earth's is bright green and red?

GANYMEDE AURORAE NASA's Hubble Space Telescope observed a pair of auroral belts encircling the Jovian moon Ganymede. The belts were observed in ultraviolet light by the Space Telescope Imaging ...

hubble-telescope aurora electromagnetic-spectrum

### Is there a limit to the distance of detectable gravitational wave events?

This is somewhat a follow up question to this one. This article indicates that the binaries detected have a distance between 320 and 2840 Mpc. With the current technology, is there a limit to the ...

gravitational-waves instruments

### Gravitational field for oblate spheroid?

Consider a planet, described as an oblate spheroid. Assume that the spheroid is uniformly dense but not a point source. Outside of the object, do all vectors in the gravity field point through a ...

gravity

### Are Tharsis Montes and Hellas Basin a result of the same event?

Looking at Mars map: the highest, biggest mountains and their associated highlands are essentially antipodes of the deepest, huge basin. Roughly 180 degrees away, similar latitude except opposite ...

mars

## Greatest hits from previous weeks:

### Why did Venus not lose its atmosphere without magnetic field?

It is often stated that the magnetosphere not only shields the planet from cosmic radiation, but also prevents atmospheric loss. Why then did Venus not lose most of its atmosphere if it doesn't have a ...

atmosphere magnetic-field venus

### Will Earth lose the Moon before the Sun goes into supernova?

Ive read on some sites and saw on youtube videos that the moon is getting away from earth by 1-3 cm a year. Is this enough to make the Earth lose the Moon before the Sun goes into Supernova? Im ...

the-moon the-sun gravity earth supernova

### What is this rapidly twinkling red, blue, and white star I saw?

Last night, I was on my balcony at 1AM (PST) and I looked up and saw two stars near the horizon (I'd guess ~30 degrees above the horizon), and they were "twinkling" about twice as fast as other stars ...

star night-sky

### Does the Milky Way move through space?

Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?

galaxy universe milky-way

### How do we have photos of galaxies so far away?

A possible answer for this is that, light emitted from the galaxies travelled a billion miles all the way to earth, where the hubble space telescope picked up this light through its sensors, and was ...

galaxy light photography

### Does the moon have days?

As like Earth, does the moon have a day (24 hours). If it has, how many hours are in a moon day?.

time the-moon

### Is it safe to watch solar eclipse's reflection in water?

There will be a solar eclipse soon at my area... naturally I want to watch this with my son. Is it safe for us to watch the solar eclipse's reflection in the water? There is a swimming pool near my ...

solar-eclipse

## Can you answer these questions?

### Gravitational Slingshot

If a spacecraft slingshots around a planet P (with escape velocity V) at an angle $\theta$, I understand that the resulting velocity is { v }_{ 2 }=({ v }_{ 1 }+2u)\sqrt { 1-\frac { 4u{ v }_{ 1 ...

orbit newtonian-gravity

### Saint-Exupery describes visit to plateau where he easily finds several meteorites. Is this realistic?

In "Wind, Sand and Stars" Antoine de Saint-Exupéry describes a visit to a plateau where it is extremely easy to discern meteorites from stones, since there are no stones. I picked up one and then ...

meteorite