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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8
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1answer
71 views

How close would Earth have to be for us to detect it was habitable, and then inhabited?

Given our current technology (or technology that is near implementation), how close would a clone of our Solar System (and so also Earth) have to be to us in order to detect that the cloned Earth was ...
3
votes
2answers
341 views

How is the Earth heated by a Full Moon?

While the moon is certainly not a good reflector of solar radiation, surely the radiation it reflects back heats the Earth (even if it is a terribly small amount). How would one go about calculating ...
2
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3answers
205 views

How early might a moon-sized asteroid be detected?

If an enormous asteroid, approximately the size of our moon (~2000-mile diameter), was passing close to Earth, how early might we detect something that large? Or alternatively, how close could ...
1
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0answers
37 views

Calculus used by Gaus to find Ceres' position?

With very little data, the great mathematician Gauss was able to predict the exact location of where the asteroid Ceres, having only few data. If possible I would like-a-reconstruction of his work, ...
13
votes
3answers
357 views

Winter solstice, sunrise and sunset time

We all know the Winter Solstice comes on December the 20th or 21st, which is (by definition) the shortest day of the year. The Winter Solstice day is not the day of the year the Sun rises later (that ...
2
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3answers
230 views

Converting between Galactic and Ecliptic coordinates

I was hoping someone would be able to tell me the formula to convert between ecliptic and galactic coordinates. I've been able to convert values using ...
2
votes
2answers
75 views

Emission and absorption spectra of sun

I heard in a documentary that the elements of the sun can be read out from the absorption lines. But I have also heard that an elements absorption lines and emission lies coincide. That means the sun ...
1
vote
1answer
52 views

Radio vs optical telescope imaging

As I understand, the visible light from an optical telescope is focused on a sensor which correlates light exposure to an electrical voltage, which is then converted to an image. A single antenna ...
11
votes
3answers
1k views

Is it possible to see satellites with the naked eye?

Every now and then I notice some very bright "stars" in the sky. They tend to be very few (one or two, usually), and are quite much brighter than any other star out there. Often they're perfectly ...
14
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2answers
370 views

Why don't any of the gas giants have moons of Earth's mass (or greater) that orbit them? Is this generalizable to exoplanet gas giants?

Now, we know that the composition of the outer planets tend to contain a much higher ratio of ice over rock. [1] So the lack of Earth-like moons around the outer planets that this could be an artifact ...
0
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0answers
143 views

Reference request: Hollow concave Earth hypothesis

Reference request concerning the Hollow concave Earth hypothesis. I am searching for this paper: A Geocosmos: Mapping Outer Space Into a Hollow Earth authored by M. Abdelkader and published in ...
2
votes
5answers
872 views

Recommended first accessories for starblast 4.5

My son got an orion starblast 4.5 for Christmas. It comes with orion explorer II 17mm and 6mm eyepieces. We are looking at some additional accessories and wondering what you would recommend as "first ...
0
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2answers
255 views

Shining object in the sky resembling a star

From last 2 days I am observing a shiny star like shining object in the sky in almost same place at same time. Is there any possibility that it could be a satellite? Will satellite shine like a star ...
4
votes
2answers
205 views

Do green stars exists?

I asked a university lecturer why we don't observe green stars, and he said the blackbody curve averages at that frequency such that the cones in our eyes don't recognise it. I have a hunch that ...
19
votes
3answers
9k views

How long does it take to travel 36 light years with tolerable acceleration and deceleration?

The recent discovery of HD85512b only 36 light years from Earth has promising attributes to harbor life. Assuming we want to travel there, we cannot instantaneously jump to light speed, (StarTrek ...
1
vote
0answers
44 views

When viewed from a telescope, does an object get more magnified if its angular diameter is increased?

and if yes, how can the diameter be increased? Lets say I want to view saturn from a small telescope. Increasing the angular diameter will give a better magnification if the answer to the above ...
0
votes
2answers
70 views

Length of solid part of object shadow

Little background first: I take part in preparing environmental reports for wind turbines/farms and now I'm exploring shadow flickering effect of moving blades. From some sources (in Polish) I got ...
3
votes
1answer
60 views

What is the space between galactic arms called?

Is there a term referring to space that is inside the plane of a galaxy, but not part of the center/bar/arms/spurs, etc? What's the filler called? The space between two spiral arms (if it isn't a ...
0
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0answers
54 views

How to calculate max/min Right Ascension and Declination in telescope field of view

I have a telescope with focal length 1200mm. My camera has 5184x3456 pixels with size 4.3um. This combination should give me a resolution of 0.74"/pixel and thus a field of view of 1.06° x 0.71°. ...
5
votes
0answers
119 views

Does it make sense to continue searching for dark matter on Earth?

The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of ...
1
vote
4answers
6k views

How does the moon reflect light?

We can see the moon in the night because it reflects sunlight. But the light is incident on the opposite side of moon with respect to the observer in the night. In this case, how does the moon ...
7
votes
1answer
177 views

How did Eratosthenes know the suns rays are parallel?

Eratosthenes famously observed that the suns rays were perpendicular to the ground in one location, yet non-perpendicular to the ground at a location some miles to the north. On the assumption that ...
10
votes
5answers
779 views

How is it possible for astronomers to see something 13B light years away?

In a NPR News story from a few years back: "A gamma-ray burst from about 13 billion light years away has become the most distant object in the known universe." I'm a layman when it comes ...
1
vote
0answers
37 views

Estimating the Hubble constant of Virgo Cluster questions?

Im estimating the $H_0$ (Hubble constant) using the calculated distance to galaxy (M100) in the Virgo cluster, but given that the cluster is about 1-2 megaparcecs in diameter, what issues can I expect ...
3
votes
1answer
571 views

At what temperature does water become a liquid on Mars? On the asteroids? And in a vacuum?

I know that I can just read off the phase diagram for water (for the surface atmospheric pressure on each object). But could there possibly be some nuances that someone might miss just from viewing ...
5
votes
1answer
119 views

About the hump on galaxy rotation curves

The past days I have been studying the rotation curves of disk galaxies and I am currently trying to understand how we can extract information about the dark matter of a galaxy by looking its rotation ...
2
votes
1answer
108 views

Finding Interstellar Extinction Coefficient

I have the following problem for an astrophysics course: A star is seen through a rather dusty region of space has its brightness dimmed by +1 magnitude/kpc, which makes it seem further away ...
0
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0answers
35 views

Are there any programs or codes widely used for computing spherical multipole expansion, especially for CMB?

I have data of coordinates and values of a part of sky, and I'm supposed to calculate multipole expansion, change some components between some $\ell$s, and finally calculate back to values. The ...
5
votes
1answer
162 views

Calculate sunrise, where does the magic numbers come from?

In this question about how to calculate sunrise, there is a link to a page that describes a algorithm to calculate sunrise sunset. But when I start to follow the instructions I find that there is a ...
1
vote
0answers
46 views

Present experimental status of Moffat's Modified theory of Gravity

Modified theories of Gravity have been discussed before in this 2-year old question, Are modified theories of gravity credible? I was going through Moffat's modified gravity, given in ...
3
votes
1answer
113 views

Tycho's stellar parallax measurements

How, exactly, did Tycho Brahe do his measurements of (no) stellar parallax? All the descriptions of parallax that I have been able to find seem to talk about the change in position of a nearby star ...
0
votes
1answer
148 views

Validity Of the Drake Equation [closed]

The Drake Equation is designed to estimate the number of Planets possibly having intelligent life forms existing in our Galaxy. But I don't see how it's justified. As far as we know, Earth is the only ...
1
vote
0answers
32 views

Where can I get latest full updated list of supernovae candidates from the SDSS-II Supernova Survey?

I am doing a project where I need the list of supernovae candidates from the Sloan Digital Sky Survey II (SDSS-II) supernova survey. One list is available as part of the data-release-7 (DR7) website. ...
10
votes
2answers
281 views

Does the Milky Way have dark matter satellite galaxies?

This recent paper by Weinberg et al. discusses that one potential problem with our current model of Cold Dark Matter (CDM) is that is predicts a greater number of satellite galaxies for the Milky Way ...
1
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0answers
44 views

How do you calculate the radiant for Kreutz Sungrazer comets? where in the sky do I look?

According to wikipedia: All known members of the [Kreutz Sungrazer] group up until 1965 had almost identical orbital inclinations at about 144°, as well as very similar values for the ...
9
votes
4answers
713 views

How big should a lens of a telescope be so we can see the American flag on the Moon from the Earth's surface? [duplicate]

How big in diameter should the lens of the imaginary telescope to be so we can see the American flag from e.g. some observatory in Hawaii?
4
votes
1answer
114 views

Why do comets have tails?

There is no atmosphere for comets to get hot and burn and show tails but they still have tails. Why do they? Edit: Isn't the answer "acceleration"?
1
vote
0answers
35 views

When sun is exactly overhead in my place in the tropics [closed]

What formula to use to find dates and times when the sun is exactly overhead in my place in the tropics?
6
votes
2answers
310 views

How does dark matter halo outside a galaxy help to explain galaxy rotation curve?

How does a dark matter halo outside a galaxy help to explain a galaxy rotation curve? Suppose for simplicity we use a model of a star rotating about a more massive star in a fixed circular orbit. For ...
1
vote
1answer
108 views

Does the Sun orbit a much larger nearby star?

EDIT: I got thumbed down, so I removed the details. The question is already crystal clear, IMO.
12
votes
2answers
126 views

Is there a fundamental limit to the temporal resolution of signals from space?

In Earth-based experiments, we can measure phenomenon very rapidly in an experiment given appropriate equipment. Clearly if something takes a long exposure to see (due to a weak signal), then the ...
6
votes
3answers
198 views

How do people work out the trajectories of planets and stars just by looking at them?

I've been thinking about how astronomers can look at bright dots in the sky and deduce a whole bunch of things from their movements. I'm particularly interested in how people like Kepler and Galileo, ...
5
votes
2answers
102 views

When did we learn that stars die?

As we all know, the stars we see in the night sky might already be dead. I was wondering though, when was this fact or conclusion commonly established? Today, most people (let's assume with an above ...
9
votes
2answers
538 views

If the Earth didn't rotate, how would a Foucault pendulum work?

How does the Foucault pendulum work exactly, and would it work at all, if the Earth didn't rotate?
1
vote
2answers
344 views

What is the highest useful magnification todays largest telescopes can offer?

I know that the maximum (useful) magnification is limited by the diffraction limit, but I was not able to find numbers for the highest useful magnification factors using modern large telescopes. How ...
4
votes
1answer
236 views

Can an asteroid have a magnetic field?

Some M-type asteroids are believed to be metallic, even possessing Nickel-Iron. Given the proximity of the asteroid belt to Jupiter's magnetosphere, the regularity of motion of any given M ...
5
votes
5answers
10k views

Why can I never see any stars in the night sky?

I have always lived near a large city. There is a stark contrast between the picture linked below for example, and what I see with the naked eye. Sometimes I can see a few stars here and there, but ...
3
votes
0answers
86 views

Maximum-Entropy Method deconvolution implementation?

I am looking for an implementation of the Maximum Entropy Method for image deconvolution, ideally in MATLAB or Mathematica. I'm trying to reconstruct an image from fringe visibilities, as is often ...
0
votes
1answer
94 views

How would a very nearby supernova shockwave and remnants affect the earth?

I've been reading about supernovae for a while, and I noticed how incredibly fast their shockwave and remnants travel shortly after the explosion. So I thought about how this would affect the earth if ...
6
votes
2answers
466 views

Galaxy Spectra: Emission and Absorption Lines

Spectra from galaxies include both absorption and emission lines. I do understand how both types of spectral lines are produced but I am not quite sure where each type is coming from when we observe a ...