3
votes
1answer
152 views

Why is the Color scheme of natural satellites in our solar system based of light shades of grey?

What is the explanation of the color similarity that the majority of natural satellites obtain?
1
vote
0answers
48 views

What would be the maximum theoretically possible angular resolution?

I have studied some basic astronomy, but I have difficulty conceptualizing the physics of luminosity and optics. We use electromagnetic spectra to detect existence and properties of distant planets, ...
4
votes
2answers
241 views

Can we compress any object to create black Holes?

In general, when a star runs out of nuclear fuel, gravity gets the upper hand and the material in the core is compressed even further and creates black holes. I am clear till here. Now the question ...
0
votes
1answer
63 views

could dark energy be a force coming from the hyperspace outside the universe?

It seems to me that the expansion of the universe is only being looked at one way. a repelling force, basically being the opposite of gravity. After pondering this for many nights, I began to wonder ...
3
votes
1answer
73 views

Estimates of exoplanets distribution consistent with current data

I am interested in current estimate of distribution of planets of various radii in various distances from their parent star. There is many sources, where one can find database of presently known ...
2
votes
2answers
125 views

Does all of time exist and if so where is it?

I've recently learned about the theory of relativity and time. I'm trying to understand it more. My (basic) understanding is that there is no distinction between past present and future and that ...
0
votes
0answers
27 views

Does all of time already exist if so why can't we see it? [duplicate]

I've recently become fascinated with the theory of relativity and time. If all of time already exists, and there is no difference between past, present and future then what is preventing us from being ...
0
votes
1answer
59 views

TIME TRAVEL-Can it be really done? [closed]

Is it posssible for us to time travel? Is light essential factor or the dark matter and dark energy?
1
vote
1answer
42 views

What exactly is a stellar association?

What exactly is a "stellar association" in the strict kinematic sense?
1
vote
2answers
108 views

Gravitational red hift vs Doppler redshift: Is the universe really expanding?

Is it possible that the redshift observed by Edwin Hubble is really from a gravitational redshift and the universe isn't expanding as he has predicted? What I think I know thus far is this: ...
4
votes
1answer
43 views

Do sungrazing comets leave a field of meteoroids near the Sun?

A large fraction (a third?) of all comets found (with observational bias thanks to SOHO) have been sungrazers, breaking up with perihelion of a few of Sun's radius. Is there reason to believe that ...
3
votes
1answer
107 views

What is the color of Venus if it has no atmosphere?

Mars looks reddish and Mercury looks gray because they lack thick atmospheres and we can see their "real color" easily, how about Venus? Is the surface of Venus really yellowish in color?
15
votes
1answer
175 views

Why does a mirror bent 'like a potato chip' allow space telescopes to be smaller and have a wider field of view?

I was browsing NASA featured items and came across this - Out With the Old, In With the New: Telescope Mirrors Get New Shape Called freeform optics, this emerging mirror technology, brought about ...
0
votes
1answer
60 views

Could the Earth use gravitational lensing / bending of light to see it's own bottom?

Specifically, I have often wondered whether gravitational lensing might be able to (theoretically) be used in order to see light reflecting off the Earth that has zoomed off into space and been bent ...
2
votes
2answers
53 views

Astronomical telescope making

I am thinking about making a telescope. I have a 100cm focal length lens which I can use as objective lens in my telescope. So which is the best focal length I can use as eyepiece in my astronomical ...
3
votes
5answers
188 views

Why does gravity increase in star formation?

When a star ignites ( ie. fusion starts ), the star maintains its form by balancing gravity's inward pressure, and radiation's outward pressure. I get that the fusion of hydrogen atoms releases ...
4
votes
3answers
318 views

Is a black hole a perfect sphere?

I know all about how black holes form and why their gravity is so strong. However, is the gravity equally powerful in all directions? Will the event horizon appear as a perfect sphere?
1
vote
0answers
47 views

How to use spectral profiles to determine luminosity class?

I know the luminosity classes are: Ia-0 ( Hypergiants ), Ia ( bright supergiants ), ... , VII ( white dwarf ). I also have learned that you can use the presence of absorption lines ( ie. use spectral ...
4
votes
1answer
32 views

What parameters determine whether galaxies colliding will result in a merger or a hit and run?

Colliding galaxies sometimes merge and sometimes pass through each other. Either way, there are huge changes as a result. What are the parameters that matter in determining whether a collision will ...
1
vote
2answers
87 views

Gravitation - Pulling or Pushing force?

According to Newton, gravity is the pulling - or in fact the attracting - force of any heavenly body towards any object to its center. But, to the contrary, Einstein once said that the four dimensions ...
1
vote
1answer
155 views

Does the Moon capture radiation pressure from the sun causing momentum from photon propulsion? [closed]

Could a planet's main use for natural satellites be that of a photon sail?
3
votes
2answers
86 views

What are the stars/constellations a beginner/enthusiast can easily identify?

I was just wondering what are some of the stars, constellations or any other things that one can just identify by looking up at the night sky. For example, when ever i look up, I immediately see ...
1
vote
4answers
160 views

Does time slow down because the universe is expanding at an accelerating rate?

If the universe is expanding at an accelerating rate, such that the galaxies' moving away from each other is accelerated, then time should also slow down. And when universe will accelerate to the ...
1
vote
1answer
82 views

Are hot stars like O-type stars entirely composed of helium?

Hot stars like O-type stars show no hydrogen in their spectra. Does this mean they are made entirely of helium? Any explanation would be really helpful.
2
votes
1answer
47 views

Math for calculating the terrestrial longitude directly under the sun with time

I'm trying to calculate the longitude on the earth where it's noon at some time. (That is, the longitude which is coplanar with the plane defined by the sun and the earth's axis.) Here is my python ...
2
votes
0answers
18 views

What are the implications if the Sun was formed in a warm nebula?

Molecular oxygen O2 has been found on comet 67P/C-G in a ratio of 3.8% to water, which is much higher than expected. An explanation proposed is that the Solar System formed from a molecular cloud ...
5
votes
3answers
201 views

Is extraterrestrial mining more difficult or impractical for bodies without plate tectonics?

This article talks about the possibility of mining Uranium on the moon. Since the Moon lacks the geological forces that have created veins of concentrated minerals on Earth, would extraterrestrial ...
2
votes
0answers
45 views

Are there equal number of planets, stars, galaxies etc in observable universe spinning in both directions?

Just because we observed that our milky way galaxy is spinning in a certain direction therefore we assume it is applicable to all other galaxies, I am curious to find out if hypothetically most of the ...
4
votes
2answers
278 views

What happens to oxygen produced on the Sun (or other stars)?

Through nuclear fusion, the Sun can (or at the very least, someday will) produce atoms of all elements up to and including oxygen. And in terrestrial chemistry at least, when you combine oxygen, ...
2
votes
2answers
62 views

Linear extent of an accretion disk

I have a homework assignment question on accretions discs (essentially an estimation of the number of electron scatterings, but this is just for background). There are a few parameters, one of them ...
5
votes
2answers
99 views

Was that actually a shooting star during the supermoon eclipse on September 27th 2015?

During the super-moon total lunar eclipse on September 27th a meteor-like streak passed very close within view of the event. It appeared to happen at the very middle, the maximum eclipse. ...
4
votes
1answer
93 views

Conversion between Astronomical Frames, ex. IRCF, FK5, FK4, etc…

I'm a little bit confused about reference frames, and I was wondering if someone could help clarify a few things? So let's say I have equatorial coordinates that refer to the mean equator and equinox ...
4
votes
1answer
121 views

Where are we in an approximate timeline of the possibly habitable universe?

Our universe is supposedly 13+ billion years old and our Sun is a third generation star. It seems to me that we are now in a relatively young stage of the universe. How many generations of stars will ...
8
votes
3answers
140 views

How do scientists name space objects?

I am curious that there are lots of celestial objects (planets, comets, stars, galaxies, etc.) in space. How do we name them?
11
votes
2answers
460 views

Is there a ninth planet?

After Pluto's demotion as a planet, we have currently eight planets in our solar system. But Sun's gravitational pull can be felt well beyond Pluto, so is it possible to have a ninth planet beyond ...
2
votes
1answer
98 views

Is this a wet moon?

Tonight around 12:20 AM I realized that the top part (instead of the side) of the moon was missing. I live at a country in the tropics. I took this picture with my phone so it isn't very good. ...
2
votes
1answer
42 views

Where can I look up the 3D positions of the closest stars? [duplicate]

The problem: I want to simulate a travel from Earth to the closest 15-25 stars. Which is the fastest way to accomplish this? What i have: I currently have the distance between Earth and the nearby ...
3
votes
1answer
43 views

I can't find Rigel on Tycho 2 catalogue

I'm trying to develop a planetarium using Tycho 2 catalogue. To read it I use the WCSTools. But I have a problem. On Wikipedia I have found that Rigel star has RA: 05h 14min 32,3s and Dec: -08º 12’ ...
3
votes
1answer
36 views

Astrophysical “unitised” version of the Gravitational constant

This question relates formalising the gravitational constant, $G$, (which in S.I. units is usually quoted as $\sim6.67\times10^{-11}\,\mathrm{m}^{3}\,\mathrm{kg}^{-1}\,\mathrm{s}^{-2}$) in units which ...
7
votes
3answers
1k views

What is a dead comet?

How is a Dead Comet different from the normal comet? How are they formed? And why is the Halloween asteroid 2015 TB145 called a dead comet?.
1
vote
0answers
52 views

Gravitational Propulsion [closed]

I am not a physicist, in fact I am just a family doctor, so I beg of you to excuse me of anything I say that you may find outrageous :) But I came to this forum to see if anyone would be able to ...
2
votes
1answer
34 views

What does oxygen on comet 67P/Churyumov-Gerasimenko mean?

Recently, the Rosetta mission found oxygen on the comet 67P/Churyumov-Gerasimenko. According to theories, oxygen should not be in the state in which it is on the comet. What are the previous theories ...
2
votes
1answer
41 views

How long New Horizons will remain operational? [closed]

As of now the New Horizons probe is well beyond the orbit of Pluto, moving towards the Kuiper belt. In an article I read that New Horizons will eventually follow the path of Voyager probes to the ...
1
vote
1answer
50 views

Which are the best American universities/colleges for observational astronomy? [closed]

I'm a French student and I'm planning to go to the United States for a graduate program in astronomy. When I will arrive in the U.S. I will begin by the first year of graduate. Then I will pursue ...
3
votes
0answers
37 views

Linear limb darkening coefficient, u

I was wondering if anyone knew of any resources to understand the linear limb darkening coefficient, $u$. That is to say, how the $\theta$-dependent coefficient $u$ (or sometimes $b_{\nu}$) varies ...
6
votes
2answers
123 views

Acquirable Raw Data in Amateur Astrophotography

What raw data can I possibly acquire from an 8" Classical Dobsonian Telescope, and a DSLR? Could anything eye-opening to amateur astronomers be computed or calculated first-hand with such equipment? ...
1
vote
0answers
9 views

What makes small interferometers useful? Like NIRISS on JWST

NIRISS is an instrument on the James Webb Space Telescope. It has a "non-redundant aperture mask" which obviously covers most of the area of the sensor. It seems to be advantageous for high contrast ...
1
vote
1answer
114 views

How gravity works in a black hole? [closed]

In astronomy class, we have to state how gravity work in the black hole? I know for one fact is that black hole is strong enough to stretch you thin enough like a noodle. Any ideas?
4
votes
1answer
30 views

Beamsize in radio/microwave observations

In radio/microwave observations, I understand the beamsize is the response of the telescope to a point source - effectively, the telescope's resolution. Now, the Planck satellite (par exemple) ...
2
votes
1answer
115 views

Is there any difference between rotation axis 90 degrees and 270 degrees? [closed]

Is there meaningful reason to distinguish 90 and 270 degree rotational axis?

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