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.
13
votes
2answers
268 views
Why aren't gas planets and stars fuzzy?
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 ...
4
votes
1answer
140 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 ...
2
votes
1answer
187 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 ...
1
vote
1answer
99 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?
3
votes
1answer
71 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?
0
votes
0answers
28 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 ...
0
votes
2answers
74 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? ...
1
vote
1answer
144 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 ...
4
votes
3answers
128 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 ...
3
votes
0answers
129 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 ...
8
votes
2answers
615 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 ...
0
votes
0answers
136 views
A book for IOAA [closed]
Hello I am preparing for the International Olympiad on Astronomy and Astrophysics. However my knowledge of constellations and practical astronomy is very poor. I was looking for a book which would ...
8
votes
1answer
170 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 ...
0
votes
1answer
105 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 ...
2
votes
1answer
148 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?
4
votes
1answer
69 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 ...
0
votes
1answer
70 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 ...
0
votes
0answers
91 views
Theoretical early-universe cosmology [closed]
I wanted to know what are the cutting edge/recent papers to read w.r.t theoretical early universe cosmology.
I would like to know of recent review papers
I would like to know of areas which use ...
4
votes
1answer
66 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 ...
6
votes
1answer
111 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 ...
14
votes
2answers
274 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 ...
5
votes
0answers
213 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 ...
5
votes
3answers
261 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 ...
-4
votes
1answer
154 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 ...
1
vote
1answer
131 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 ...
6
votes
3answers
230 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 $D$ ...
1
vote
2answers
94 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 ...
4
votes
4answers
260 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 ...
2
votes
3answers
709 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 ...
3
votes
2answers
262 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 ...
2
votes
1answer
98 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. ...
3
votes
1answer
160 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 ...
4
votes
1answer
96 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 ...
6
votes
3answers
271 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 ...
10
votes
5answers
558 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?
6
votes
3answers
609 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 ...
6
votes
1answer
266 views
what is the farthest-away individual star that is visible with 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 enough concept that ...
8
votes
0answers
179 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 ...
2
votes
1answer
126 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 ...
0
votes
0answers
34 views
Rainbow moon halo [duplicate]
Possible Duplicate:
What causes a ring-like image around light of the moon?
Right at this moment I am observing a fascinating meteorological phenomenon.
The Moon is surrounded by a halo, ...
4
votes
5answers
181 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 ...
4
votes
1answer
136 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 ...
7
votes
2answers
246 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 ...
2
votes
0answers
63 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 ...
1
vote
1answer
51 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 ...
4
votes
1answer
81 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 ...
0
votes
1answer
102 views
What size will the sun become once it is a red giant?
How big will the Sun be once it becomes a red giant? How much of the solar system will it engulf?
1
vote
1answer
92 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°, ...
5
votes
5answers
230 views
How is distance measured to far away stars and galaxies?
What I need is an accurate description of the methods used to determine the distance to Andromeda. The Parallax method is for nearby objects as I presume. The red shift method applies, but how do you ...
2
votes
1answer
92 views
Fractal Cosmology and Misner's Chaotic Cosmology
I have a question pertaining to the ideas behind the considered homogeneity and isotropic nature of the universe (at a grand scale) versus the theory of a chaotic and anisotropy structure of the ...
