The science dealing with objects and phenomena located beyond Earth. In particular, this applies to observations and data. At its core, astronomy is the physically informed cataloging and classifying of the contents of the universe in order to better understand what is out there.

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Why are Lunar Eclipse more common than Solar Eclipse?

Why are Lunar Eclipse more common than Solar Eclipse? Chapter from Light My thoughts; Eclipse can only occur at new moon and moon orbit is inclined at an angle of about 5 degrees to the earth's ...
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28 views

Finding the distance a spaceship would travel given a time of departure and velocity

Let's say a spaceship leaves Earth at a day t and with velocity v. Is there a way to know how many kilometers it will cover to arrive on Mars? This would be a trivial question were it not by the fact ...
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47 views

Can an absorbed photon be emitted as two photons?

I am taking an intro to astronomy class, and have touched upon absorption and emission lines and etc, the prof asked this question in class and got me thinking. I would want to say no, because one ...
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9 views

Would we expect the space between different Oort clouds to be empty?

If we consider a few solar systems to be like to image below (yes, I know it's overly simplistic), and each solar system has a cloud similar to the Oort cloud (the yellow globes), would the space ...
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25 views

Finder scope on telescope [closed]

I was just reading something on your site about finder scopes for telescopes. My ExploraScope came with a plastic scope that looks like that on a rifle. It has a red laser light inside the tube that ...
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3answers
374 views

What is the cosmological redshift of SN 1987A?

I haven't found any literature on SN 1987A, which provides me with its cosmological [not gravitational, wrong in inital question, thanks for the remark] redshift. Is it larger or smaller than $z=0.1$, ...
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1answer
38 views

A question on Jeans's instability

I am a Physics student and I'd really appreciate if anybody could help me with an exercise my professor gave me a couple of weeks ago. It goes like this: Let us consider a spherical symmetrical gas ...
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6k views

How can we see planets thousands of light years away but don't know if there are more planets in the solar system?

That is basically my question, it arose when I saw an article (here is the scientific paper, which should be free to read) saying two Caltech scientists might have found the 9th planet of the solar ...
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1answer
40 views

Have cosmic rays and the CMB affected Earth's history?

Do cosmic rays and the cosmic microwave background carry with them enough energy to have a macroscopic effect on events on Earth? The most obvious example I can think of is by giving animals cancer. ...
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31 views

Is a deviation from the equal flavor ratio of neutrinos ruled out experimentally?

Neutrinos have a lifetime which exceeds the lifetime of our universe. Therefore we measure an equal ratio of all three neutrino flavors, 1:1:1. However, lets assume that the heavier neutrinos can ...
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1answer
21 views

Finding radius of an exoplanet's orbit knowing orbital period and star's mass [closed]

I've been stuck on this question in an assignment for a while now, and I can't seem to find anything on the internet that either deals with a question in which more values are provided, or where the ...
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1answer
70 views

What is the limit of the deep field exploration?

The deep field exploration is quite fascinating, first the Hubble Deep Field (HDF) showing a small piece of the Univers one billion year after the Big-Bang, next the Hubble Ultra-Deep Field (HUDF), ...
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17 views

Dust mass-loss rate from a massive star given a set of parameters?

I've been looking for examples at how mass-loss rates are determined. I'm studying a circumstellar dust shell ejected from a Wolf-Rayet star. I have some parameters like, expansion velocity of the ...
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29 views

Given a focal length and an aperture of the telescope, what is its field of view?

While I know FOV of scope is equal to FOV of eyepiece divided by magnification. How can one find FOV given only the focal length and aperture of the telescope?
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1answer
32 views

About the ratio of the density of dark energy at the time of cosmic microwave background emission to the current density of dark energy [closed]

In a question, I am given the current densities of dark energy, dark matter and normal matter and am asked to find the ratio of density of dark energy at the time of CMB and now. The answer is 1. Is ...
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0answers
91 views

Observation of a dying star

Looking far away mean looking back in time. Stars evolve and then after long time they die. Some of them evolve in supernova. Other than this case, when looking at the sky with telescopes, are there ...
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36 views

Visible Mass Distribution in a Galaxy [closed]

Is there any known relationship between stellar density and distance from the galactic centre? I want to know how the visible matter is distributed in the galaxy, especially at the bulge.
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2answers
65 views

We say Light is Red-Shifted or Blue-shifted from faraway stars and galaxies [closed]

We say Light is Red-Shifted or Blue-shifted from faraway stars and galaxies. Can we find out the distance at which it changed its frequency. So in another solar system, it might seem to be Green ...
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2answers
99 views

How can I convert Right Ascension and declination to distances?

I am calculating galaxy rotation curves for various galaxies in Ursa Major cluster and I want distance of those galaxies from the centre of Cluster. The values referred as coordinated are RA and dec ...
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109 views

Why are the jets of the “light saber” star slightly curved?

Why don't the jets of the HH-24 object follow a straight line? In the image below, notice how they bend towards left from the expected straight line. Is it an optical distortion, or some nearby ...
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Can the average length of the day and night of a planet be different?

At one point in "Marvel's Agents of S.H.I.E.L.D.", some agents are on a planet where the day, defined as the length of time where the sun shines on the planet, occurs only once every 18 years for a ...
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1answer
55 views

Reconciling geosynchronous orbits and why the moon is moving away

First time on PSE, and forgive me if the question doesn't make sense. Everything I've read, and the explanations make perfect intuitive sense, for why the moon is moving away from the earth is ...
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1answer
51 views

If there were infinite many stars [duplicate]

If there were infinite many stars, is the sky then always full of light so is there than even night?
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22 views

Why dark matter do not gather together? [duplicate]

Stars and planets were gathered together by gravity, thus emit light. Why dark matter doesn't behave that way? Why they won't be gathered together by gravity and form stars?
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31 views

Is there any evidence of black holes existing? [duplicate]

Yes, I am aware of observations of "massive objects", for example near the center of the galaxy. But is there any evidence that the object in question is a black hole, with all its commonly attributed ...
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1answer
63 views

How should I interpret a Chi-Squared Result?

I've got a Model A with a reduced chi-square of 1.28. I've got a Model B with a reduced chi-square of 0.70. Which is a better model? The model closest to 1 or the model closest to zero? (Yes, I ...
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30 views

Gravity effect of a star behind the sun during a solar eclipse [closed]

We know that stars blocked by the sun during a solar eclipse may still be observable as if they are not behind the sun but rather visible to the side unblocked by the sun (because the photons are ...
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65 views

Matter and dark energy

So dark energy is the biggest thing in the universe, it keeps accelerating the expansion. But it's a constant so at some point there was a matter - dark energy equivalence. My question is how can you ...
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1answer
39 views

How long was the universe radiation dominated?

Using the Friedmann metric I've been trying to calculate how long the universe was radiation energy dominated. I've reduced the metric to: $c.dt$ = $a(t).dr$ where a is the scale factor. I can work ...
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1answer
47 views

Why aren't pictures of Pluto darker than those of other planets?

Just as the intensity of the light from a candle decreases with distance, I would expect the light from the sun to illuminate the distant planets less than the closer ones. However, the pictures of ...
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1answer
52 views

Here's a fun question, what would happen if Venus was thrown off in a highly elliptical orbit? [closed]

I'd like to know what would happen if Venus was flung into a highly eccentric orbit like Sedna (except maybe with its current perihelion) with an orbital period measured in thousands of years by a ...
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0answers
47 views

Can a spheromak propagate in vacuum?

I recently learned about (and am now fascinated by) spheromaks. I am no expert on plasma physics, but as I understand they are analogous to propagating toroidal vortices (smoke rings), but with plasma ...
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2answers
45 views

Sound speed vs Speed of sound

Are 'sound speed' and 'speed of sound' the same thing? If not, what is the difference? If they are, could you clarify how the speed of sound applies in the below description of gaseous clouds? ...
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95 views

Why doesn't the Cosmic Microwave Background heat my food like a Microwave?

I know the reason we have a CMB is because the photons don't react with any of the matter in the universe, or the mean distance between interactions for photons generated since decoupling is now the ...
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20 views

Reduced Chi-Square - How to compare values?

I've got two models of velocity curves fitting a Low Surface Brightness (LSB) galaxy: one is MOND-like, the other ΛCDM. I've fit them both with Chi-Square minimization. I understand the winning ...
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2answers
314 views

How accurately could we theoretically see into far space?

Travels to different galaxies are strongly limited by the speed of light. Unless we find a way to travel through space with some wormholes, we will never reach planets in another galaxy. But what ...
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1answer
48 views

Have we observed sufficient extra-solar planetary systems to establish a planetary distribution pattern? [duplicate]

From Kepler And Extra-Solar Planetary Observations As of January 2015, Kepler and its follow-up observations had found 1,013 confirmed exoplanets in about 440 stellar systems, along with a further ...
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143 views

Why is “gravitational” red-shift neglected in galaxy and galaxy cluster scales?

The red-shift of the light of a star in a galaxy or that of a galaxy in a cluster of galaxies is generally interpreted as how fast the star or the galaxy is moving, i.e. it is interpreted in a purely ...
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2answers
45 views

How we are able to see stars in night, even if they are light years away from earth? [closed]

I am wondering, how we are able to see so much stars in the sky even though they are light years away from us. Even light take years to reach from those stars to earth? Then, how we are seeing those ...
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3answers
2k views

Are there any exact data about Earth's orbit?

Wikipedia says that the Earth's orbit's axis is $a=149\ 598\ 000\ \mathrm{km}$ and its eccentricity is $e=0.016\ 7086$, but if we use these values to find distance at aphelion and perihelion we get ...
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1answer
43 views

How do space probes identify molecules?

How does a space probe identify molecules without actually obtaining the molecules? The common identification techniques I can think of are spectroscopy and magnetic resonance, but for both of them, ...
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1answer
98 views

What is the curve that describes the Daytime line in a Day and Night World Map?

A Day and Night World Map shows which parts of the Earth are in daylight and which are in night at a given instant. At one side of the Daytime line they are in daylight and at the other side they are ...
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0answers
47 views

Bulge-Disk decomposition in galaxies

I'm starting a new project on dark matter astrophysics in which I have to extract from some data (I will write some below) the surface brightness, to later construct the mass density profiles of de ...
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2answers
239 views

How long would it take to see the nearest star die?

If you were in the general proximity to the nearest star to Earth (besides the Sun) and you saw it turn to a neutron star or black hole at the very end of it's star cycle, how much longer would it ...
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1answer
94 views

Gas Mass Calcuation in Galaxy Cluster

Rob Jeffries found this document for me that describes how the X-Ray emissions from galaxy clusters are used to calculate the mass of the cluster. I'm unable to follow the steps to calculating the gas ...
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2answers
81 views

What is meant by the velocity of a star?

I recently read somewhere that among other things like size, radius, distance from earth, luminosity, age, etc of a star, velocity was another variable. What is exactly meant by the velocity of a ...
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1answer
86 views

Are we looking at single stars, or solar systems?

When looking at the night sky, the stars we can see just look like single dots. Are they alone in space- each one a single object? Or, when we look at a star, are we actually looking at a distant ...
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24 views

What type of observational constraints are there for reionization?

What type of observational evidence is used to constrain reionization? At what redshift?
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28 views

Information Brought by Electromagnetic Waves

Is it possible for a Technologically Advanced Civilization to watch in "Real Time" events of the Earth History? Let me be more specific: Let us suppose a civilization who resides on a sphere in the ...
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1answer
35 views

Earth precession

I got a bit confused while studying the tropical and sidereal years. I noticed that the Earth's precession is in the opposite direction than that of a top's precession, when their rotational direction ...