All Questions

5
votes
2answers
68 views

How did the Mars satellites “take cover” from the recent comet flyby?

After comet Sliding Spring's Oct. 19, 2014 close flyby of Mars, NASA reports that All three NASA orbiters around Mars confirmed their healthy status Sunday after each took shelter behind Mars ...
8
votes
1answer
133 views

If we count Avogadro's Number of stars that are closest to Earth, how big that space would be?

I posted this as a question to Scientific Imagination (Area 51 proposal) a while ago. And it was suggested that this question "is perfectly acceptable on Astronomy SE", since "it's about stellar ...
1
vote
1answer
39 views

Free neutrons and stellar nucleosynthesis

Both the R-process and the S-process of stellar nucleosynthesis rely on absorbing 1 (S) or more (R) neutrons. Where do they come from? I thought there are no free neutrons in stars. (Also the ...
10
votes
5answers
5k views

What will happen to life on Earth when Andromeda and Milky Way galaxies collide?

It is said that, Andromeda and Milky way galaxies are coming close to each other with the speed of approx $400000 \ km/hours$. They will be together in the next $4 \ billion years$. What will ...
3
votes
4answers
154 views

Where can I find a catalog of all stars in the Milky Way?

Is there a catalog of all known stars or brightest stars in our galaxy? Preferably with some sort of galactic coordinates instead of just night sky coordinates (right ascension, etc.) I'm trying to ...
3
votes
1answer
77 views

Is early life required for life?

I was watching the new Cosmos and Neil DeGrasse Tyson said something that made me go hmmm... He mentioned that the only reason that the Earth did not experience the runaway greenhouse effect like ...
3
votes
1answer
100 views

What is the correct ratio of Newtonian to General Relativistic gravitational effects for Sun + single planet orbital system

For a hypothetical orbital system (Sun + single planet) the Newtonian model and the General Relativity (GR) model produce different expressions for the gravitational effect of the Sun on the planet. ...
0
votes
3answers
37 views

How near to Earth do comets pass?

Siding Spring now passes about 10 Earth diameters away from Mars. What are the estimates of how often comets fly by Earth at different distances? Are the distances to some famous historical comets ...
9
votes
2answers
118 views

Might Oort cloud comets be exchanged between solar systems?

Considering their distance from their parent stars, might Oort cloud object such as comets be exchanged between passing stars (assuming that other stars have similar Oort clouds)?
3
votes
2answers
246 views

Diameter of any galaxy

I've been trying to figure out how to find the diameter in kpc of any galaxy given that one knows the distance to it in Mpc (d) and also the angular diameter/size (A) in arcsec. I had a formula before ...
18
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?
1
vote
2answers
103 views

Is there enough hydrogen left after a star dies so another star will have enough to light up?

A star consumes quite a lot of hydrogen in its life, and is pretty much "vacuuming" everything in its vicinity. After it dies (eventually by supernova which will spread all its composition over light ...
10
votes
3answers
402 views

How do we know that the speed of the influence of gravity is instant?

When I was in college, I posed to my astronomy professor a thought experiment that had been puzzling my mind for some time: "If the sun magically disappeared, instantly, along with all its influences, ...
0
votes
4answers
116 views

Question about the Sun's Motion

My name is Chris, I am a junior and I'm taking an Astronomy class in my high school. For a homework assignment, I have to explain how the Sun would move across the sky from September 1st through ...
1
vote
1answer
41 views

Star class according to initial mass

Studying the stars classes for my homework (school) i learned that stars are classified by the spectral types (Harvard) and luminosity class (MKK) .. So the sun is a star class ...
4
votes
1answer
112 views

What is the bluest narrow band filter mounted on ground based telescopes?

If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that? I mean under the circumstance that its lyman alpha shifts to 3300A.
0
votes
1answer
60 views

Time-density and time-temperature functions of the Universe since the Big Bang

I am looking for these... functions. I want to be able to say, "at a 1873. second there were around 54230000000 K temperature and 0.00435 kg/m^3 density". On the net I could find only tables or ...
2
votes
3answers
117 views

How much would you weigh if Earth stopped orbiting the Sun? [on hold]

I have a curious question. The reason why astronauts are weightless in space is because they are orbiting Earth. If they suddenly stopped orbiting they would fall directly into Earth. Earth is doing ...
2
votes
5answers
95 views

Evolution of Life

Since life evolved here on Earth does that mean that life had to have existed before or in the future elsewhere in the Universe or could it be a one time only freak accident ?
5
votes
2answers
114 views

Planets and Pluto? Neptune?

If one of the rules to be a planet is that it needs to clear ALL objects from their orbit, does this also make Neptune a non-planet? Since it has thus far failed to clear Pluto (and based on an answer ...
-2
votes
2answers
88 views

Could we actually freeze a star?

I read an article recently that said NASA has discovered a brown dwarf that has frozen. Given we had the technology, resources, and supplies, could we actually freeze a star and stop it from burning ...
0
votes
0answers
6 views

How will they mine asteroids? [migrated]

Say we find an asteroid that is rich in ores and we would like to mine that asteroid. How could this be done? The gravity on an asteroid is so minimal that pushing a drill into the asteroid would ...
4
votes
1answer
116 views

What is the difference between Sphere of Influence and Hill sphere?

Wikipedia's definition of Hill sphere is: An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit ...
2
votes
1answer
45 views

why do we look at dark energy as an energy?

We call dark matter dark matter, because of the way it acts on galaxies, but why do we look at dark energy as an energy? With $E = m c^2$, can't dark energy be mass as well? Why dont we look at dark ...
1
vote
2answers
105 views

How can a planet not rotate at all and yet have 1 year that is day and 1 year that is night?

A mercury day if you consider its solar day is 2 mercury years. Now if you consider just 1 half of mercury, in 1 of those years it is facing towards the sun and in another one of those years it is ...
0
votes
1answer
45 views

what is a MIA satellite

I came across this sentence in a magazine: We sit outside the Lorne Community Hall, Victoria, watching the MIA satellite overhead. I wonder if the author is talking about an artificial ...
5
votes
2answers
42 views

Are epicycles and mean Earth/Sun actually useful astrophysical concepts?

Copernicus put the Sun in the center of the Solar system. This turns the Moon's orbit into an epicycle around Earth orbit. And the Jovian moons (later discovered) have orbits which are epicycles ...
6
votes
1answer
73 views

Time period in which a planet rotates

I notice that Wikipedia give two contradictory terms for the time period in which a planet rotates in relation to an infinitely-distant object. In one place this is called a "sidereal day" and in ...
2
votes
1answer
37 views

Could dark matter be considered a medium?

Long ago, it was theorized that light had to travel through a medium, until the particle/wave duality of light was discovered. Then it changed to the idea that light can travel through the vacuum of ...
1
vote
4answers
145 views

What happens if gravity shuts down for only one second?

Question has it all.What happens if total gravitational force in the universe shuts down for only one second?
2
votes
0answers
19 views

Mapping selenographic coordinates onto a sphere

I have a 3D rendering of the moon, which is represented as a sphere with a radius of N pixels. I also have selenographic coordinates. For example, the coordinates of the Apollo 11 landing site are ...
1
vote
2answers
44 views

length of Star lifetime

In a star, the fact that not all the hydrogen is used up, not all the helium is used up etc. is a little counterintuitive. Shouldn't it be that a star looses the hydrogen layer passively, in other ...
2
votes
2answers
46 views

Why objects are uniquely defined by their right ascention and declination?

I've just started studiyng Astronomy. I understood how I would measure Right Ascention and Declination: for the first one I'd trace an Hour cirlce to the Celestial Equator, and then, compute the ...
1
vote
0answers
25 views

A question about stellar magnitude and the pogson's equation

Well surely the eye has different sensitivity to various wavelengths... will the pogson's equation not be affected if say I compare Betelgeuse and Rigel( both having a marked difference in spectral ...
1
vote
1answer
21 views

Binary star not exceeding Roche Lobe?

Is it possible that a binary star doesn't exceed its Roche lobe and so when the second star becomes a red giant, instead of accreting some of its plasma onto the white dwarf that it becomes a white ...
4
votes
2answers
252 views

When will all eight planets in our solar system align?

Ignoring expansion of the universe, entropy, decaying orbits, and interference from any bodies colliding with or otherwise interfering with their orbits, will the eight planets known planets in our ...
2
votes
1answer
57 views

Why does iron consume more energy in the fusion process than it produces?

I understand that once a star starts fusing iron, it's doomed to collapse because iron fusion requires more energy than it releases in the process, allowing the opposing gravity of the star to cause ...
4
votes
2answers
141 views

Can we see individual stars in other galaxies?

Just wondering if we can examine individual stars from other galaxies, or if we are pretty much stuck with the billions that are in the Milky Way?
5
votes
1answer
79 views

Red cresent moon

Yesterday night i witnessed something very strange when i looked outside the window. I saw the moon (crescent) but it was dull red and right on the horizon ,which is strange considering that it is ...
2
votes
0answers
28 views

Why didn't Johannes Kepler use data about more planets?

In Astronomia Nova (1609) Johannes Kepler used observations of Mars in order to refute circular orbits. Throughout Astronomia Nova he hardly even mentions other planets than Mars, Earth and the Sun ...
3
votes
1answer
70 views

Calculate telescope orientation based on RA, DEC and Lat/Long

I'm parsing FITS files for a project based on data from a telescope. These files include 'DEC', 'RA' and lat long values. I understand roughly the concept of celestial coordinates and I assume that ...
6
votes
3answers
221 views

What is a singularity? What is at the center of a black hole? Specifically regarding space-time

So because I can only really think of space-time in 2-dimensions like a sheet of something, my assumptions might be wrong to begin with. I was watching a YouTube video on black-holes and there was a ...
1
vote
1answer
53 views

What is the danger for Ceres of collision with other asteroids?

In the context of possible colonization of Ceres, would not such colony be totally impossible because of high probability of collision of Ceres with other asteroids in the Asteroid Belt?
1
vote
2answers
187 views

Fate of the Universe

Which scenario will be worse for the ultimate fate of the Universe , forever expanding or the "Big Crunch" ? Will the Universe be destroyed in both scenarios ? At the present time does it appear that ...
1
vote
3answers
76 views

How would we detect a planet behind the Sun?

Let's assume hypothetically that Earth has a twin planet on the opposite side of Earth's orbit. Its orbital period would be exactly the same as Earth's and it would always be behind the Sun so ...
1
vote
2answers
36 views

Is the whole universe is rotating on an axis?

Most of the celestial bodies we know are rotating or spinning on its axis.Is there any chance for the universe to rotate on its axis?
0
votes
0answers
56 views

Compute the colour in the AB photometric system

I have a question for homework and don't get it at all: Consider two filters as shown in the figure below. Compute the colour S1 - S2 in the AB system for a star with flux: where is a constant ...
3
votes
1answer
57 views

Classification of a Comet

Google's definition of a comet is: a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun. This ...
7
votes
3answers
193 views

Do parallel universes exist?

Do other universes like ours exist? If they exist, how do we know that they exist when we have even not seen the ends of our own universe?
2
votes
1answer
36 views

Can Hubble red shift be interpreted as time dilation?

Can we interpret the de Sitter universe as a spherical cosmic horizon null surface of finite radius, centered at Earth, and containing the Hubble volume of space where time is dilated and radial ...

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