All Questions

118
votes
2answers
17k views

How much gold is there in our sun?

XKCD 1944 claims that there is "more gold in the sun than water in the oceans". Is this really true?
112
votes
2answers
11k views

How loud would the Sun be?

Sound can't travel through outer space. But if it could, how loud would the Sun be? Would the sound be dangerous to life on Earth, or would we barely hear it from this distance?
76
votes
6answers
5k views

Does the Sun rotate?

The planets rotate as an after effect of their creation, the dust clouds that compressed span as they did so and the inertia has kept it rotating ever since. It's fairly easy to prove that planetary ...
74
votes
2answers
11k views

Why is the discovery of merging neutron stars important?

I'm fairly certain people here will have heard about it, already, but apparently, two supernova leftovers clashed some 130 million years ago and some billion billion kilometres away ... What I haven'...
71
votes
12answers
17k views

Why don't astronomers use meters to measure astronomical distances?

In astronomy distances are generally expressed in non-metric units like: light-years, astronomical units (AU), parsecs, etc. Why don't they use meters (or multiples thereof) to measure distances, as ...
66
votes
1answer
8k views

How can there be 1,000 stellar ancestors before our Sun?

I've heard from a few sources* recently that the Sun is a 1,000th generation star, meaning it had a thousand stars that came before it based on its heavy-element content. I understand that earlier ...
64
votes
4answers
8k views

Is the moon only 60 pixels?

In doing research on vision, I have learned that "20/20" vision corresponds to a visual acuity of being able to resolve details 1 arcminute in size, that most people have around 20/15 vision, and that ...
61
votes
4answers
8k views

How does the Earth move in the sky as seen from the Moon?

I just want to be sure I am visualizing this correctly, because it seems odd. The Moon is tidally locked to the Earth but there are wobbles to its motion due to libration. So from a point on the ...
60
votes
6answers
7k views

Why is only one side of the Moon visible from Earth?

Why do we only ever see the same side of the moon? If this is to do with gravity are there any variables which mean we might one day see more than we have before?
58
votes
2answers
11k views

Could the dinosaurs have seen the asteroid that killed them?

Wikipedia says the Chicxulub impactor is thought to have been a 10-15 km diameter object. Would it have been visible to a (human*) naked eye before impact? And if so, would it have appeared like a ...
55
votes
4answers
14k views

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?
53
votes
5answers
8k views

When will the Sun end all human life on Earth?

If nothing else wipes out human existence prior to this, at what point will the Sun make Earth uninhabitable for humans?
50
votes
3answers
11k views

What would happen if an ice cube is left in space?

Recently I boarded a flight and noticed outside air temperature as -53°C at an altitude of 36860ft (11.23km). I don't know what causes such a freezing temperature in that altitude but was wondering ...
50
votes
3answers
7k views

Where did TRAPPIST-1a go?

According to the NASA announcement and the Wikipedia article on TRAPPIST-1, the planets around the TRAPPIST-1 star are named TRAPPIST-1 b through h. What happened to "TRAPPIST-1 a"?
49
votes
3answers
29k views

How many planets are there in this solar system?

So, in school (that's a long time age) they have been teaching us there are 9 planets in our solar system. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto But every now and then I keep ...
49
votes
5answers
10k views

Why is moon light not the same color as sunlight?

The light from the moon is light being reflected from the sun. The sun, in space, is white. But on Earth, when the light is filtered through an atmosphere, the light appears yellow. So then, why is ...
49
votes
5answers
13k views

If light has no mass, why is it affected by gravity?

Light doesn’t accelerate in a gravitational field, which things with mass would do, because light has a universally constant velocity. Why is that exception?
48
votes
4answers
10k views

Why does it take so long to transmit an image from New Horizons to Earth?

I just got the news that the New Horizons space probe has passed by some remote planet on the edge of the solar system. I was surprised that the guy from NASA says that it might take 24 months from ...
47
votes
5answers
6k views

Why hasn't the “9th Planet” been detected already?

In the comments to this question, there was considerable doubt placed as to the subject of if the so called "9th planet" really exists. That wasn't really the intent of the previous question, so I ask ...
45
votes
2answers
1k views

Two species of dark matter?

At this point in time, evidence for the existence of dark matter has accumulated in many ways: it affects galactic rotation curves plays a major role in cosmology, and the evolution of structure in ...
44
votes
3answers
22k views

How powerful a telescope would allow me to view the astronauts aboard ISS do a space-walk?

This arose from a comment posted against a question elsewhere on the stackexchange How powerful a telescope/binoculars would allow me to view the astronauts aboard the ISS do a space-walk? Aperture? ...
42
votes
2answers
8k views

How can 'HD 140283' be older than the universe?

Scientists have known about the star HD 140283, informally nicknamed the Methuselah star, for more than 100 years, since it cruises across the sky at a relatively rapid clip. The star moves at about ...
41
votes
11answers
16k views

Why do Black Holes in the middle of galaxies not suck up the whole galaxy?

As stated in several sources, it's supposed that in every galaxy there is a black hole in the middle. My question is, why do these black holes in the middle of galaxies not suck up all the ...
41
votes
2answers
2k views

Why has Venus's atmosphere not been stripped away by solar wind?

This answer on Space Exploration to a question about Mars says that one reason Mars has such a thin atmosphere is because it lacks a magnetic field to protect it from the effect of double solar winds. ...
40
votes
5answers
12k views

How old is the oldest light visible from Earth?

Because light can only travel so fast, all of the light we see in the sky was emitted at a previous moment in time. So if for example we see a supernova or some other great stellar event, by the time ...
40
votes
8answers
4k views

What is in the center of the universe?

If the universe has formed & originated by a Big Bang Explosion, then there must be empty space left in the center of the explosion site, as all the matter is travelling at tremendous speeds away ...
38
votes
5answers
8k views

Why does gas form a star instead of a black hole?

When a space gas gets pulled together a star is formed. On the other hand, when a massive star dies, it collapses to a black hole. You would think that the initial mass of the gas would be bigger ...
37
votes
2answers
9k views

Is it possible to achieve a stable “lunarstationary” orbit around the moon?

Is there a stable geostationary orbit around the moon? My feeling is, that the orbit would collide with earth, because of the moon's slow rotation.
36
votes
6answers
12k views

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 ...
36
votes
4answers
8k views

Why are we building larger land-based telescopes instead of launching larger ones into space?

This question is a follow-up to Do bigger telescopes equal better results? How much bigger does a ground-based mirror have to be to match what a space-based one can do? I guess I'm asking primarily ...
36
votes
4answers
9k views

Can the moon appear to be in any position in the sky?

It seems to me that the Moon has appeared in many locations - apparent locations - in the 'dome of the sky'. I know that the Sun follows an arc from east to west and that the arc is smaller in winter ...
35
votes
4answers
5k views

Where does the Solar System end?

This is a question I've heard many times in the past, and a quick search of the site says it hasn't been asked here, so I figured I might as well ask (and answer) it. I know that it is rare for ...
35
votes
5answers
5k views

9th planet location?

I've seen a number of news reports indicating there is likely a 9th planet in our Solar System, something with an orbital period of between 10k-20k years, that is 10 times Earth's mass. I haven't seen ...
34
votes
5answers
2k views

How are black holes found?

Black holes have so much gravity that even light can't escape from them. If we can't see them, and the suck up all electromagnetic radiation, then how can we find them?
34
votes
2answers
7k views

Do all stars have an Oort cloud or is it a rare occurence?

Do all stars have an Oort cloud like ours that will be filled with comets and other objects? If not, why are they not around every star?
33
votes
3answers
7k views

Did I see another planet?

A couple days ago, I zoomed in with my 30x optical zoom camera, and after some exposure adjustments, a bright star in the night sky turned into this: Are those other planets or other stars? Or is ...
33
votes
1answer
6k views

Considering our methods of exploration, how likely is it that there are unfound planets (not dwarf planets) in our solar system?

I think it's probably unlikely that there are more planets between Mercury and Mars, but out from Jupiter, there's lots of empty space between the planets. Could there be some small planet hidden out ...
33
votes
2answers
6k views

Why doesn't the moon twinkle?

Stars twinkle because their light has to squeeze through several different layers of the Earth's atmosphere. So why doesn't the moon twinkle as well?
32
votes
3answers
9k views

What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?

I assume that about 99.9% of the sun-rays that do not fall on any planet or any other celestial body keep on traveling farther and farther unto infinity. Apparently such rays get lost. Keeping in mind ...
32
votes
6answers
6k views

What did LIGO Actually See? (Gravitational waves discovery)

I am trying to find an original video/image of what LIGO actually saw, but all I can find is artist renditions of gravitational waves.
32
votes
7answers
4k views

Does matter accumulate just outside the event horizon of a black hole?

My understanding is that time slows and approaches stopping when approaching the event horizon of a black hole. I have seen this explained several places, including a brief explanation in the last ...
32
votes
1answer
3k views

How large can a ball of water be without fusion starting?

How large can a ball of water be without fusion starting? Peculiar question: some explanation might be necessary. My young son is into ‘space’ and astronomy. One of his posters says that Saturn could ...
32
votes
2answers
28k views

How does neutron star collapse into black hole?

We know the spectacular explosions of supernovae, that when heavy enough, form black holes. The explosive emission of both electromagnetic radiation and massive amounts of matter is clearly observable ...
32
votes
3answers
420 views

If you lived on the far side of the Moon, how could you infer the existence of Earth?

Suppose that you deposit an astronomer, armed with our current knowledge of orbital mechanics, on a dome on the far side of the Moon, so that the Earth is perpetually hidden from them. (And, of ...
31
votes
2answers
10k views

Can our Sun become a black hole

Does every star become a black hole? Is there any probability that our sun can become a black hole? If yes then is it on its way to become a black hole? what is the current state of sun as per the ...
31
votes
2answers
16k views

Why does Jupiter have so many moons?

Jupiter has a great many moons - in the hundreds, and they're still being discovered. What is the current theory for where all these moons came from? Are they rocks flying through space captured by ...
31
votes
2answers
911 views

How do I calculate the inclination of an object with an amateur telescope?

Suppose I would like to calculate the inclination of a satellite from the ecliptic. Would it be possible to do this with an amateur telescope? How would I go about doing so? Note: A good answer ...
30
votes
6answers
9k views

Why is the Sun's density less than the inner planets?

The density of the Sun is $1410~\frac{\text{kg}}{\text{m}^{3}}$ and Mercury's is $5430~\frac{\text{kg}}{\text{m}^{3}}$, but shouldn't the Sun be denser? Because when the Solar System was forming, ...
30
votes
5answers
18k views

What's the fastest moving object in the universe?

We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or ...
30
votes
4answers
9k views

How can we tell that the Milky Way is a spiral galaxy?

From Earth, we can distinguish the type of another galaxy very easily simply by observing the shape, colour, and structure of the galaxy when we image it. But since we are located inside the Milky Way,...

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