41
votes
3answers
1k 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 ...
35
votes
4answers
5k 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 ...
31
votes
4answers
4k 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 ...
30
votes
5answers
1k 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?
27
votes
3answers
2k 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 ...
25
votes
6answers
575 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?
25
votes
3answers
2k 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? ...
24
votes
2answers
341 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 ...
20
votes
4answers
4k 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 ...
20
votes
1answer
225 views

How could a hobbyist astronomer determine apparent magnitude of a star?

Apparent magnitude is a rather complex way to determine the brightness of a star. Quoting the introduction text from the linked to Wikipedia page: The apparent magnitude (m) of a celestial body is ...
19
votes
3answers
4k 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 ...
19
votes
2answers
1k views

Do all stars have an oort cloud or is it a rare occurance?

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?
19
votes
2answers
303 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 ...
18
votes
2answers
272 views

Why is the Hubble Telescope in space?

Why is the Hubble Telescope in space? Do we get enhanced clarity and range by placing it in space? What can it achieve from space that it could not achieve from Earth?
18
votes
2answers
337 views

What is a parsec and how is it measured?

Astronomical units of measurement are mostly pretty straight-forward: Astronomical Units refer to the mean Earth-Sun distance (~150 million km or 93 million miles) Light years are the distance light ...
18
votes
2answers
1k 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 ...
18
votes
2answers
316 views

How dense are Saturn's rings?

I assume that the A ring is the densest, but I might be wrong. Nevertheless, I failed to find any explicit information over the net about the minimum and maximum of densities for the different rings. ...
17
votes
4answers
1k 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 ...
17
votes
3answers
546 views

Pluto's orbit overlaps Neptune's, does this mean Pluto will hit Neptune sometime?

We know that the orbits of Pluto and Neptune overlap. This means that pluto sometimes crosses the orbit of Neptune; will Pluto hit Neptune in any circumstance?
17
votes
5answers
613 views

Can we (theoretically) spin the black hole so strong that it will be broken apart by centrifugal force?

I can't imagine the forces involved in black holes' lives. So please, help me to find out, if it is possible or not to destroy black hole in this specific way.
17
votes
2answers
2k views

Why do sunspots appear dark?

Sunspots, such as this one, appear dark: Why?
17
votes
3answers
462 views

Why can't light escape from a black hole?

I've heard that light can't escape from a black hole. Can it? If not, why?
17
votes
1answer
150 views

Why is there a matter/anti-matter asymmetry in the universe?

After the big bang occurred what biased the formation of particles over anti-particles? Why are particles more common than anti-particles?
17
votes
2answers
867 views

Why is our solar system “tipped” about 63° with respect to the plane of our galaxy?

Our own solar system is "tipped" by about 63 degrees with respect to the plane of the galaxy. Has it ever been researched or is there any scientific theory which could explain the reason why our solar ...
17
votes
2answers
163 views

Amateur observing targets for binary star systems?

Are there any easily resolvable, binary star, observing targets visible from ~N40°? I'd like to be able to show, in one observing session, Mizar and Alcor (naked eye resolvable), another with ...
16
votes
4answers
4k views

If Jupiter is a gas-giant then why don't its features change?

A naive question. When we look at Jupiter, we see that its features didn't change largely over many years, for instance, the red-spot. If it is composed of gases and liquids, then why aren't the ...
16
votes
3answers
387 views

Can small gas planets exist?

Most of the known gas planets (Jupiter, Saturn, etc.) are huge. They are even called "gas giants". is it possible to exist a gas planet around the size of Earth? If yes, why; if no, why?
16
votes
1answer
273 views

How distances are measured in the Solar System, in the Galaxy, and in the Universe?

Distances in our universe can be calculated in several ways: Stellar Parallax Standard Candles Redshift How are these methods linked, and how they are actually used to calculate distances are ...
16
votes
1answer
249 views

What causes a star to become a pulsar?

What processes does a star undergo to become a pulsar? Does it take a very specific star with a certain set of qualities such as "Just the right mass, diameter, and composition," or is it a freak ...
15
votes
4answers
614 views

How would the night sky look from inside a globular cluster?

When the weather is clear, we can look at the stars. And we normally would see several thousands of them, they all being more than a $\textrm{pc}$ away from us. Now, there are globular clusters, ...
15
votes
4answers
3k views

Does the Earth have another moon?

I was just wondering what are the chances that there is a small object (say less than 1 km but more than few meters) that orbits the Earth but has remained undetected by us? Are we actually ...
15
votes
3answers
276 views

Are we made of the stuff of one star or more stars?

[T]his coincidence enabled stars in the late stages of their lives to turn helium into carbon, oxygen and most of the other atoms that you and I are made of. [...] [W]e're made of star stuff. Max ...
15
votes
1answer
575 views

Milky Way Galaxy from Earth

I've seen a lot of beautiful pictures of the Milky Way from Earth such as this: ...but I can't understand what the cloudy ribbon at the bottom the horizon is. Is it a super-large nebula? Or is it ...
15
votes
3answers
726 views

Do all the objects in the universe exert force on all other objects?

Do all the objects in the universe exert force on all other objects? Like a type of gravity; also, how much does it decrease as it gets farther away?
15
votes
1answer
179 views

I live in an area with a lot of light pollution, how can I view the stars without building an observatory?

I live in an urban area with a lot of light pollution and very little garden space. On a clear night I can see most of the sky and the brighter stars are visible. I can't build an observatory - I ...
15
votes
1answer
844 views

Can you see man-made lights on the dark side of the Earth from the surface of the moon with the naked eye?

This question is prompted from a comment on this answer: Could a person on the surface of the moon see man-made lights on the dark side of the Earth with the naked eye? If not, how much magnification ...
15
votes
2answers
290 views

What are practical considerations for backyard radio-astronomy detection of black holes?

Evidently, direct observation of a black hole for an amateur astronomer, such as described for what professionals do in the question "How are black holes found?" would be nigh on impossible, so the ...
14
votes
3answers
517 views

Could someone explain RA/dec in simple terms?

The equatorial coordinate system isn't too complicated. However, for people new to this, it seems rather intimidating at first. Is there an easy way to explain it?
14
votes
2answers
115 views

Near-Earth supernova

There are 51 stars within 17 light years of the Earth (source). If one of these stars was to become a supernova, how would they effect the Earth?
14
votes
5answers
389 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 ...
14
votes
1answer
128 views

Why is the Sun's atmosphere (the corona) so hot?

The visible surface of the Sun is 6000 degrees Celsius but the gas in the solar corona is at least 1 million degrees. What heats the solar corona?
13
votes
4answers
201 views

What is Gravitational Lensing?

What is the effect known as gravitational lensing? How does it work? What objects would be able to cause this effect?
13
votes
4answers
716 views

Is the light we see from stars extremely old?

Our nearest star Proxima Centauri is 4.243 light years away from Earth. Does that mean we are seeing light that is 4.243 years old everyday?
13
votes
4answers
520 views

Doesn't gravity attract objects in space until they collide?

If the formula to calculate the force of gravity of two objects is: $$F1 = F2 = G * (M1 * M2/r^2)$$ Why do planets stay in orbit? Or is there another formula at work?
13
votes
3answers
686 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 ...
13
votes
3answers
126 views

When will we be able to detect Earth-sized exoplanets?

I have heard that the only planets able to be seen outside the Solar system are Jovian-sized planets with the occasional detection of planets three times the Earth's size. But, as far as I know, we ...
13
votes
4answers
240 views

What are the differences between a Black Hole and a Supermassive Black Hole

From what I understand, the mass of a black hole should be nearly infinite, how much more massive can something get? Is the name to be literally interpreted such that a Supermassive Black Hole just ...
13
votes
3answers
978 views

Should I focus more on Aperture or Focal Length for a telescope?

Let's assume there are three types of telescopes with the following specifications: ...
13
votes
2answers
285 views

What physical features determine if a planet is a major, minor or dwarf planet?

Like many, when I was growing up, we always were taught, hence always learned that there were 9 planets. However, recently, decisions were made and all of a sudden there were 8 major planets and a ...
13
votes
3answers
101 views

Why is the Oort cloud presumed to be spherical?

Most descriptions of the Oort cloud depict it as a mostly spherical distribution of planetesimals, with occasional allowance for an inner component that is more donut-shaped. This is slightly at odds ...

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