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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115 views

Dividing two star spectra

I am doing some work that involves dividing two stellar spectra from the same star. Those stellar spectra are constructed by summing random samples of multiple spectra from the same star to improve ...
9
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1answer
288 views

What dark matter can AMS currently find (or exclude)?

The rumor mill is running again, this time it's about the AMS experiment (Alpha Magnetic Spectrometer) that's going to make a major announcement soon. I suppose they are looking for peaks in gamma ...
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2answers
180 views

Why do astronomers never put a scale on their photographs?

Why do astronomers never put a scale on their photographs? I have been looking at images of the Bird nebula, a collision of three galaxies, but in none of the dozen or so that I have found, nor in the ...
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257 views

Mirrors and light beam divergence technology limits

There are many applications for orbital space mirrors in astronomy (better telescopes) and space propulsion (solar power for deep space probes), but this is limited by the minimum beam divergence ...
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2answers
193 views

Is there a map of the particles in outer space?

Since outer space is not quite a vacuum, and the distribution of various heavenly bodies is locally inhomogeneous, it seems reasonable to expect that the density and variety of particles ...
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1answer
281 views

Relationship between Mars and Earth rotation

Is it by pure random chance that Mars and the Earth have nearly the same day duration (Mars day is barely 40 minutes longer, which is just 3% difference), or there is some causal relationship between ...
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2answers
503 views

Why aren't gas planets and stars fuzzy? [duplicate]

The edge of Jupiter looks very sharp. Even more bothersome, the edge of the sun looks sharp, aside from kind of a soup of particles floating above it. The sun's surface has an incredibly low ...
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1answer
217 views

Could a planet ever end up with a doughnut hole in it?

If there was an asteroid that happened to be made out of something really solid (iron, titanium?) and it got enough velocity (sling shot around the sun?), is it conceivable that it could hit a planet ...
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1answer
1k views

Where to find the current positions and velocities of the planets?

I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in ...
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199 views

If there was no Earth, what would be the acceleration of gravity from here from the Sun?

Suppose there were no Earth to pull us back and we're hanging in the solar system. Assuming no other force of gravity from other bodies, what would be the $g$ from the Sun?
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81 views

What is the furthest object from which fermion rays were detected?

What is the furthest object from which non-electromagnetic cosmic rays were detected?
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35 views

How do stars look like from space? [duplicate]

Possible Duplicate: Optical explanation of images of stars? What are these rays that appear in photograph of sun? I thought stars should look round shaped (similar to a sphere, or oblate ...
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2answers
104 views

Approach of the Andromeda Galaxy

So, it's theorized that Andromeda will collide with the Milky Way some time in the next 3 billion years... I don't get how galaxies can collide with each other. What is the cause of their movement? ...
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1answer
553 views

What is the apparent diameter of the sun as seen from earth?

I know this may not be physically accurate. For my purposes, basically 3D renders, I am assuming the sun rays are parallel rays from an infinitely far lamp. If the sky is clear, what size would that ...
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3answers
563 views

How far are constellations recognizable?

A novel of the 'Foundation' series mentioned that the universe being 3-D the shape of a constellation is recognizable only in the near vicinity of a given planet. In other words move out from the ...
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1answer
351 views

Determine date of birth from “astrological” signs?

Suppose someone tells me what constellation the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn were in when they were born, and the information is astronomically accurate (ie, not astrological ...
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2answers
2k views

Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
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2answers
2k views

Dumbed-down explanation how scientists know the number of atoms in the universe?

It is often quoted that the number of atoms in the universe is 10$^{70}$ or 10$^{80}$. How do scientists determine this number? And how accurate is it (how strong is the supporting evidences for ...
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1answer
155 views

Do stars appear to move with uniform motion?

The Ancient Greek astronomers had quite an obsession over uniform circular motion; I was wondering if there was a logical reason for this. Did it develop through actual observations of the stars? Do ...
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1answer
301 views

The Moon is slowly moving away from the earth. Does this mean that a total solar eclipse wasn't possible at some point in earth's history?

When the moon was closer to earth, was it still possible to witness a total solar eclipse millions of years ago? Or was the view-able space so small that it was impractical to even witness it?
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1answer
88 views

Could a bipolar nebula be produced by a time gradient?

M2-9 is an example of a bipolar nebula that resembles two back-to-back rocket nozzles. Is it possible that this shape (somewhat unusual for an explosion) is the result of a time gradient? A rotating ...
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1answer
95 views

Other than the motion of the Earth, what else would cause parallax?

Wikipedia has this to say about the discovery of the aberration of light: In 1728, while unsuccessfully attempting to measure the parallax of Eltanin, James Bradley discovered the aberration of ...
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1answer
79 views

Atmospheric hydrogen in Titan

In 2005, some astrobiologists proposed that methanogenic life on the surface of Titan would consume both hydrogen and acetylene from the atmosphere, causing a downward gradient in the concentrations ...
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1answer
193 views

Why is the Hubble Space telescope able to see farthest in the universe?

What determines how far a telescope can see in the universe? How does recording data for a very long time (~10 years) help? If we could build a telescope which work at microwave region, will it be a ...
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2answers
723 views

How deep is the Great Red Spot?

The Great Red Spot (GRS) is a very persistent storm system that's easily visible through a telescope on the surface of Jupiter. But what is the three-dimensional structure of the GRS, and how deep ...
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0answers
318 views

Why is my approach to the equation of time off by a constant?

I'm trying to better understand the causes for the equation of time by deriving an approximation from first principles. My naive approach, $EOT_{NAIVE}$, is to take the difference between the right ...
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3answers
940 views

How many percent of the visible light reaching the Earth are from other stars than the Sun?

How many percent of the whole visible light reaching the Earth are from other stars than the Sun? Is it maybe 0,5 - 1% or is my guess already too much? I am interested mainly in visible light, but ...
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578 views

What is the difference between UT0, UT1 and GMT time?

Every reference I find says that they are "essentially" the same, which we all know really means that they are not the same, but different only by a some small amount that someone else other than me ...
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1answer
299 views

When calculating the local apparent sidereal time, which time scale should I use?

UT1, UTC, TAI, TDB, or what? I need to determine the time difference between a given observation and the epoch from which certain constants apply. I typically work with the J2000.0 epoch. This is to ...
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3answers
519 views

Tidal force on far side

I have a question about tidal forces on the far side of a body experiencing gravitational attraction from another body. Let's assume we have two spherical bodies $A$ and $B$ whose centers are $D$ ...
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2answers
265 views

What does “equinox of date used” mean?

The documentation for an API I often use for quick astronomical modeling and figure drawing says Positions are given in FK5 heliocentric coordinates in the equinox of the date used. What does ...
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4answers
473 views

Are galactic stars spiraling inwards?

Are the stars in our galaxy spiraling inwards towards the center, or are they in a permanent orbit? And if we are heading towards the center then what is the rate of this process? I started ...
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4answers
6k views

Is it possible for the planets to align?

We've all heard the statement that on the 21st of December, the planets in the solar system will "align" from the point of view of the Earth. I assume this means that they would all be in the same ...
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2answers
1k views

When is the right ascension of the mean sun 0?

I understand that the right ascension of the mean sun changes (at least over a specified period) by a constant rate, but where is it zero? I had naively assumed that it would be zero at the most ...
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2answers
273 views

The validity of the Longitude of Perihelion

As I understand it from Astronomical Algorithms, by Jean Meeus, the Longitude of Perihelion is a very common numeric value associated with planets, even used as one of the planetary orbital elements. ...
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2answers
624 views

How did pre-Copernican astronomers accurately predict planetary position?

Copernican elements (circular orbital elements) are not very accurate. But Copernicus simplified our understanding a great deal by placing the Sun at the center of the system. Im astonished by the ...
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1answer
129 views

Polaris distance correction and implications for cosmological measurements

Polaris has been a guiding light of navigation for centuries. But Polaris also happens to be the closest cepheid variable to our sun. These, together with the type II-A supernovae constitute standard ...
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3answers
486 views

How much of the universe is observable at visible wavelengths?

Knowing that: The Zone of Avoidance (Looking towards the center of the Milky Way) blocks roughly 20% Each Milky Way star has an angular size, depending on proximity, that obscures a certain ...
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5answers
779 views

Why cant one see tidal effects in a glass of water?

Why cant one see the tidal effect in a glass of water like in an ocean?
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4answers
3k views

View of the Sun from Voyager 1

Today Voyager 1 is approximately 122 AU distance from the Sun. What does the sun look like from this distance? How much brighter does the sun appear to the naked eye compared to other stars in the ...
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2answers
2k views

What is the farthest-away star visible to the naked eye?

My girlfriend and I were watching Cosmos, and something Carl Sagan said got us wondering what the farthest-away visible star is. Obviously "visible to the naked eye" is a fuzzy concept that might have ...
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4answers
364 views

How accurate are Mayan astronomical “ephemerides”?

Because of the hype surrounding the "end" of the Mayan calendar (along with the usual cultural relativism and Western guilt) it is nearly impossible to find an objective quantitative assessment of the ...
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1answer
177 views

How do physicists and astronomers handle leap seconds?

I'm confused by the many contradictory descriptions I see about how UTC leap seconds are accounted for. I understand that there are various ways to handle them in common practice, and I've seen a ...
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5answers
352 views

Why relative positions of stars and other objects in a galaxy do not change over the year

Though the identifiable stars in a constellation(say andromeda) and galaxy(say andromeda galaxy) are situated light years apart, why isn't the galaxy appearing at different positions(with respect to ...
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1answer
197 views

What time scale is used by the JPL HORIZONS system?

I'm confused by the ust of the term "UT" in the description of time scales used by the JPL HORIZONS system. Their manual states that UT is Universal Time This can mean one of two non-uniform ...
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2answers
324 views

Exploding Earth

I have always heard that the Earth, due to its structure, cannot explode. Now, I'm quite fascinated by astronomy physics but I admit I only hold some more than basic knowledge. In any case, even ...
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0answers
68 views

Elimination of the node

Recently I have been reading a lot of astronomy papers on reductions in models of the solar system. A reoccurring concept is the elimination of the node. However, they never explain what the node is ...
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1answer
211 views

How long in advance can dates of moon phases be accurately predicted?

When researching an article on Chinese New Year I found a few websites that predict the dates of Chinese New Year (CNY) tens - or sometimes even hundreds - of years in advance. I´m wondering how many ...
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772 views

How distorted does the Andromeda Galaxy appear to us due to the speed of light?

The Andromeda Galaxy appears to us at an angle to the galactic disk, i.e. we are not in the Andromeda Galaxy disc's plane, nor are we near the direction that the galaxy's pole points. Therefore, due ...
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174 views

Is there an “authoritative” source for ephemeris data?

I find some variation in the values reported for ephemeris by the various sources I have access to. For example for 2012-11-27T03:31:55 UTC I get solar declination values of -21.1828°, -21.18296°, ...