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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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
38 views

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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30 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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1answer
49 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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11 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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3k views

Is it possible to 3D print a mirror to create a high quality telescope?

Is it possible to 3D print a mirror with todays available materials? If so, would there be a reduction in image quality?
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2answers
115 views

How stellar aberration is measured?

A simple calculation shows that stellar aberration due orbital motion of earth is roughly 20 arcseconds. My questions are: Practically how this small value is measured? Does this value is in the ...
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1answer
187 views

Planetary alignment of the gas giants?

There is this nice and new applet of the orbits of the planets around the sun: Solar System Orrery You can click and drag any planet and watch their relative orbits evolve in time. I was curious ...
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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
39 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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3answers
608 views

Parallax, obliquity, precession, and Orion?

Today, the obliquity of the earth is about 23.4°. 6500 years ago, it was about 24.1° Imagine the blue square is the constellation of Orion, and the yellow star is the sun. Viewpoint B is you, on ...
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1answer
294 views

Suntan: UV absorption vs daytime

I guess that these questions were being asked by many people on the Northern Hemisphere during this summer (and other summers) and someone may give a nice, coherent answer. The general question is how ...
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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
808 views

What are the alternative theories of dark energy? ($w \neq -1$)

There has been a lot of related questions about dark energy around here but these are usually 2-4 years old and the closest question to mine hasn't really been answered, so I am going to proceed. ...
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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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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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0answers
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
5k views

How much sky do we see at any one moment?

When we look at any particular point the sky, what percentage of the celestial sphere do we see? This question arises from the notion that on average there passes one meteor per hour overhead. So ...
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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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6answers
5k views

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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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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1answer
143 views

Do the arms of a spiral galaxy spin around like a candy bar in long spirals?

Because the arms of a spiral galaxy have a cylindrical-linear center, perhaps they have a cyilindrical rotation around their center same as a vortex of smoke? Have similar movements within galaxies ...
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1answer
159 views

What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...
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0answers
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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0answers
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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2answers
735 views

How to calculate the amount of night time during a flight?

I have been asked to find a way to calculate the amount of time that a flight takes during night time. So far, I have the departure latitude and longitude and the time of takeoff, the arrival ...
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0answers
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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1answer
614 views

How do we know that these radio bursts are from billions of light-years away?

NASA just announced that they detected the first radio bursts from outside of our galaxy. Astronomers, including a team member from NASA's Jet Propulsion Laboratory in Pasadena, Calif., have ...
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1answer
339 views

CMB parameter, what's the meaning of the matter power spectrum normalization $\sigma_8$?

Most CMB experiments like WMAP and Planck include a certain cosmological parameter called $\sigma_8$. My understanding is that normalization of the matter power spectrum is not a theoretical ...
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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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3answers
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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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
243 views

How did Kepler infer three-dimensional positions from Tycho Brahe's data?

This has bugged me for some time. Tycho Brahe's data on planetary observations, presumably, consisted of the direction in which a planet was observed at a given date and time, but not the distance to ...
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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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6answers
361 views

Given a photo of the Moon, taken from Earth, is it possible to calculate the position of the photographer's site?

Given a photo of the Moon, taken from Earth, is it possible to calculate the position (Earth longitude and latitude) of the photographer's site? I am thinking about photos taken with a normal camera ...
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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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0answers
32 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 ...
5
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1answer
536 views

Why are solar eclipses more common in the southern hemisphere?

I've seen the claim that solar eclipses are more common in the southern hemisphere than the northern hemisphere and would like to understand why and if that is the case? Does it relate more to the ...
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0answers
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
53 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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2answers
828 views

Is there a simple, accurate formula for calculating transit times from rise and set times?

I have access to "rise" and "set" times for astronomical objects, and want to determine the corresponding times of culmination. Is there a reliable and accurate way to do this? It isn't clear to me ...
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0answers
22 views

Do the arms of spiral galaxies differ based on the speed of which the galaxy is rotating?

If I were to take a circle with strings attached to it and spin it, the strings would behave differently based on how fast the circle is rotating. Do galaxies behave the same way?
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2answers
46 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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2answers
96 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 ...