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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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
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2answers
86 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
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1answer
73 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 ...
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0answers
72 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°. ...
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1answer
279 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 ...
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2answers
2k views

Amateur moon laser ranging

Questions first, then my rough estimations: 1) Is it possible to perform moon laser ranging with amateur motorized 114mm telescope? My calculations suggest that for 1mJ laser it should receive ~2 ...
8
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1answer
363 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 ...
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0answers
43 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 ...
5
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1answer
172 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
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1answer
471 views

Calculate the latitude / longitude coordinates of the location where the Sun is at the zenith

There are plenty of resources showing how to calculate zenith and azimuth of the Sun when the time and the location are given. However, I need to calculate the location where the sun is at the ...
5
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1answer
182 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 ...
2
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1answer
158 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 ...
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2answers
247 views

What are the demographics of stars visible to the naked eye?

Of the stars that can be seen with the naked eye, what are the distributions of each type? For example, how many are main sequence? how many are Super Red giants/white dwarfs/neutron stars...etc. ...
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0answers
57 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 ...
2
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1answer
184 views

Analyse astronomical data

Recently I was told of a job offer to analyse astronomical data. The job offer states that they want somebody with knowledge of astronomical data analysis software and it will be a plus somebody who ...
2
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0answers
52 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. ...
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0answers
51 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 ...
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4answers
842 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?
6
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1answer
158 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"?
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0answers
43 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?
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1answer
129 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.
5
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2answers
112 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 ...
4
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1answer
364 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 ...
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3answers
234 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, ...
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2answers
679 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 ...
3
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0answers
113 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 ...
4
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1answer
147 views

Identifying the position of the moon

I encountered the following question in a previous year paper of a graduation-based test. On a certain night the moon in its waning phase was a half-moon. At midnight the moon will be (choose one ...
6
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2answers
931 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 ...
5
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2answers
291 views

Is a total solar eclipse a common phenomenon?

Is our moon "special" for creating a total solar eclipse? Is it common or rather rare for a moon to create a total solar eclipse the way our moon does, with corona and such?
4
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2answers
164 views

How to measure declination of sun and moon?

I came by some graphs showing the declination for sun and moon (between angles of -30° and +30°). The graphs look very much like sine waves. I googled a bit and read about what the declination is, ...
3
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1answer
138 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 ...
1
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1answer
201 views

Weather difference on Mars compared to Earth

How the weather on Mars differs from here on Earth? In here you see that weather on Earth is Hurricanes, typhoons and tornadoes a real problem. Disgustingly interminable fog in coastal ...
4
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1answer
1k views

When does a planet become a star?

How big can a gas giant become before it's considered a star? How does the theoretical maximum compare the observed maximum?
6
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1answer
96 views

Are there rogue planets between Sun and Proxima Centauri?

Would we be able to detect (via emitted radiation, or its gravity) a rogue planet between us and Proxima Centauri? How big would that planet need to be?
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1answer
73 views

Does the sun's bearing at a given time vary, and if so, how?

More an astronomy question, but Physics is the closest stack exchange category I could find and Google doesn't have the answer. Granted, the sun's elevation changes for a given time of day throughout ...
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2answers
133 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 ...
1
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1answer
142 views

Why does earth spins? [duplicate]

I understand the governing force causing the earth's cycle around the sun is gravity. It can be described by Keplar's law. But what causes the earth's spin? what is its governing law?
0
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1answer
298 views

What is the 1977 Wow signal? [closed]

Can someone explain about the 1977 Wow signal? I know that it is a signal received from space in 1977, in the form of a series of code "6EQUJ5". I would like to know if there is any thing or event ...
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2answers
134 views

Galaxy rotation equation problem

I would like to know if in this equation for the rotation of galaxies: $$v^2=\frac{GM}r.$$ Is $M$ the mass of the black hole at the center of our galaxy? Someone said to me that No, $M$ is the ...
1
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1answer
275 views

Calculate exact time of Solar midnight

I want to calculate real time of midnight (Solar midnight), but I am unable to find any formula or algorithm for that. I have times of sunrises and sunsets for every day of year. How can I get Solar ...
4
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2answers
247 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 ...
5
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1answer
238 views

Red Giant branch and Asymptotic Giant branch

What's the difference between the RGB and the AGB? I can't seem to find an clear distinction anywhere. Thanks.
1
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1answer
328 views

What is the correct Orientation of Earth's Rotational-axis w.r.t Ecliptic at Equinox?

I am boggled with the position of earth relative to the sun at the "Equinoxes". According to the wikipedia: an equinox occurs twice a year (around 20 March and 22 September), when the tilt of ...
3
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3answers
276 views

Dark age of universe when all fusion process ceases?

Some say we live in the golden age of the universe because there exits countless number of stars that shines in the dark universe. As the supply of gas for star formation is steadily being exhausted, ...
5
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0answers
173 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 ...
5
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2answers
103 views

How many watts of light do instruments in modern telescopes need?

I just calculated that if the European extremely large telescope(978 m^2 area) would be pointed at the Andromeda galaxy once it is built, it will only get mere 1.2*10^-6 Watts of power from Andromeda. ...
26
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4answers
2k views

Why are there no asteroids or meteoroids with relativistic speeds?

Cosmic rays can have energies going into the $10^{20}$ eV domain. Asteroids and meteoroids originating in the solar system are probably limited in their speed because they all started out from the ...
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1answer
79 views

Is the fraction of radioactive isotopes on the near side of the moon higher than on the far side?

As time passes more slowly in a region of space close to the source of a gravitational field, shouldn't the moon, which always has one side facing towards the earth, have a higher fraction of ...
16
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4answers
869 views

How would we see a near-lightspeed object emitting light?

Consider an object travelling near the speed of light relative to us (let it be a spaceship or a star), which is emitting light (consider it monochromatic resulting from a two level electronic ...
3
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1answer
398 views

Center of Mass of two planets

The formula for calculating the center of mass is $$ r_{center} = \frac{m_1 \cdot r_1 + m_2 \cdot r_2}{m_1+m_2} $$ Why can't I use it to calculate the barycentre of two planets? I understand how ...