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  
asked by usernumber 21 votes
answered by antlersoft 14 votes

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  
asked by usernumber 14 votes
answered by Rob Jeffries 16 votes

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 ...

asked by Andrej Butić 8 votes

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  
asked by Bob516 7 votes
answered by Carl Witthoft 12 votes

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  
asked by usernumber 6 votes
answered by Sextus Empiricus 9 votes

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 ...

asked by medley56 6 votes
answered by Rob Jeffries 6 votes

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 ...

asked by SF. 6 votes
answered by David Hammen 11 votes

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  
asked by Irigi 22 votes
answered by MacUserT 14 votes

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  
asked by hawaii 16 votes
answered by David Hammen 27 votes

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  
asked by Gogeta70 8 votes
answered by Dr Chuck 8 votes

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  
asked by Mike 58 votes
answered by John Duffield 73 votes

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  
asked by K Split X 39 votes
answered by pela 51 votes

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  
asked by RANSARA009 17 votes
answered by CipherBot 20 votes

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 ...

asked by Rosdi Kasim 12 votes
answered by Dean 8 votes

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  
asked by DarkRunner 4 votes

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 ...

asked by Vashu 3 votes

How are Y-dwarf spectral subtypes defined?

It is often stated that the spectral subtype indicates the relative position between spectral types, e.g. G5 being halfway from the start of spectral type G to the beginning of spectral type F. Given ...

brown-dwarf classification spectral-type  
asked by antispinwards 1 vote
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