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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4
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3answers
125 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 ...
20
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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 ...
1
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1answer
57 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 ...
-2
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1answer
55 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?
0
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0answers
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?
0
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0answers
40 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 ...
0
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1answer
84 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 ...
0
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0answers
86 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 ...
0
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1answer
71 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 ...
1
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1answer
60 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 ...
1
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1answer
76 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 ...
1
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0answers
48 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 ...
1
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2answers
54 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? ...
0
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2answers
127 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 ...
0
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0answers
32 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 ...
2
votes
2answers
322 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 ...
3
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1answer
60 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 ...
3
votes
2answers
153 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 ...
1
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2answers
95 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 ...
16
votes
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 $...
4
votes
1answer
49 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, ...
1
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1answer
162 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 ...
2
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0answers
64 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 ...
1
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2answers
273 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 ...
0
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1answer
101 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 ...
2
votes
2answers
120 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 star?...
3
votes
1answer
96 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 ...
1
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2answers
28 views

What type of observational constraints are there for reionization?

What type of observational evidence is used to constrain reionization? At what redshift?
0
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0answers
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 ...
2
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1answer
45 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 ...
2
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0answers
44 views

SOHO solar observatory, comet numbers and composition

SOHO discovered its 3,000th comet, cementing its standing as the greatest comet finder of all time. Prior to the 1995 launch of the observatory, commonly known as SOHO, only a dozen or so comets ...
0
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2answers
31 views

How to measure the spectra of the stars

I recently made a mini spectrometer using a CD. I have used that to measure the spectrum of the Sun, moon and various artificial light sources. My question is how can I use it or modify it to measure ...
0
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0answers
25 views

Size of meteor-made crater [duplicate]

I am reading "What if" piece https://what-if.xkcd.com/20/ and I am very interested in how can one ever estimate the size of a crater? How can you ever know, it must depend on energy of a falling body ...
0
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1answer
108 views

Can the Earth be seen to transit the sun from the outer planets?

Transit of Mercury as seen from Mars The Curiosity rover on the planet Mars observed the planet Mercury transiting the Sun, marking the first time a planetary transit has been observed from a ...
0
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1answer
56 views

NED vs. SIMBAD: Which is more accurate?

I'm doing some research on M33. NED lists the luminosity as 6.27. SIMBAD gives it as 5.27. First, it looks odd to me that the difference is exactly 1. Second, I've seen other differences comparing ...
1
vote
1answer
124 views

SDSS spectra FITS format: what do the rows mean?

This might be in the FITS Header, but I couldn't find it. I am looking at the FITS files for SDSS 1D spectro images from DR7 using the SDSS Data Archive Server at das.sdss.org (there might be an ...
28
votes
3answers
6k views

Why are there no stars visible in this photograph?

Pluto and Charon, photo taken by New Horizons on July 8, 2015 from a distance of 6 gigameters. it's hard for me to believe there were no stars behind the twin dwarf planets in the field of vision. ...
1
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2answers
181 views

What is the definition of $[\alpha/H]$?

The notation $[A/B]$ denotes \begin{equation} [A/B] = \text{log}_{10}\Big[\frac{\text{(number of A atoms/number of B atoms)}_{\ *}}{\text{(number of A atoms/number of B atoms)}_{\ \odot}}\Big] \end{...
1
vote
2answers
87 views

Why do so many galaxies in clusters have a near zero velocity?

I'm looking at a velocity chart of the Coma Cluster: And the question occurred to me: why are there so many galaxies that have a zero velocity (relative to the core of the Coma Cluster which is ...
3
votes
1answer
114 views

The James Webb Telescope, why are there 5 levels of protecting foil?

From simple curiosity, does anybody know why there are around 5 layers of solar radiation reflecting foil on the James Webb Telescope, rather than one or two? Is it to save weight, or (probably) ...
1
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1answer
73 views

How to start using IDL in 2015?

Unfortunately it looks like I have to run a bit of old astronomy software on IDL. I keep running into statements that "I need to buy a license" in order to run IDL. Is this true? How can I ...
1
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0answers
49 views

What is the definition of the “stellar angular diameter” in stellar astronomy?

(Following the definitions here: http://arxiv.org/pdf/astro-ph/0509535.pdf ) What is the "stellar angular diameter", as measured by astronomers specializing in stellar astrophysics? Using the ...
1
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0answers
61 views

Using stellar spectroscopy to measure stellar parameters, why is it log g?

Stellar spectroscopy can in principle measure the stellar surface gravity, radii, effective temperature, and stellar rotation. Why is it that surface gravity g is ...
0
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0answers
23 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?
1
vote
1answer
73 views

What is Drake equation?

I was reading an article on aliens, where I found something called Drake equation. I tried to understand it, but just couldn't get it in my head, as I belong to class 11. So, can anyone explain me it ...
45
votes
2answers
6k views

Why are gold mirrors yellow?

Why are golden mirrors yellow? Do they add a yellow component to the spectrum or absorb non-yellow components? If they absorb, then why are they used in telescopes being imperfect? If they add a ...
1
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1answer
249 views

How to calculate tide times?

How do I calculate the time of the tides at a given location? I'm not interested in the amplitude of the tides, just the times when they occur.
0
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1answer
67 views

Best telescope for value per dollar? [closed]

recently I'm thinking of buying a telescope for recreational purposes. I'm looking for telescopes that have the highest performance/cost ratio, and I'm willing to spend around $200 on this. Anyone ...
2
votes
1answer
34 views

Definition of a Supercluster

A group of astronomers in September 2014 redefined what classifies a supercluster. Before this, the supercluster where the Milky Way resides was the Virgo Supercluster. Now, the Virgo Supercluster &...
1
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1answer
48 views

How to begin using SDSS data?

SDSS has gone through so many updates, it's difficult to find out how to access the data today in 2015. How can I use SQL and Python to access SDSS data, e.g. the photometry and spectra of quasars, ...