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.
6
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6answers
808 views
Is rotational motion relative to space?
Let's assume that there is nothing in the universe except Earth. If the Earth rotates on its axis as it does, then would we experience the effects of rotational motion like centrifugal force and ...
9
votes
1answer
184 views
How vacuous is intergalactic space?
You often hear intergalactic space is an example for a very good vacuum. But how vacuos is space between galaxy clusters and inside a huge void structure? Are there papers quoting a ...
4
votes
2answers
508 views
How do you measure distance to stars within the galaxy?
I know that for close by stars (<50 LY) we can use the parallax effect. And for distant galaxies we use red-shift (& hubble's constant). So how do we measure how far is a star lets say 50,000 ...
7
votes
2answers
2k views
Why does Venus rotate the opposite direction as other planets?
Given: Law of Conservation of Angular Momentum.
Reverse spinning with dense atmosphere (92 times > Earth & CO2 dominant sulphur based).
Surface same degree of aging all over.
Theoretical large ...
7
votes
2answers
202 views
Why don't we see solar and lunar eclipses often?
Since we see the new moon at least once in a month when the Moon gets in between of the Sun and the Moon at the night and as far as I know if this happens during the day, you'll get to see a solar ...
22
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4answers
2k views
Why is a new moon not the same as a solar eclipse?
Forgive the elementary nature of this question:
Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse ...
21
votes
9answers
4k views
Can Jupiter be ignited?
Our solar system itself contains two candidate "Earths"
One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
7
votes
6answers
976 views
What methods can astronomers use to find a black hole?
How can astronomers say, we know there are black holes at the centre of each galaxy?
What methods of indirect detection are there to know where and how big a black hole is?
3
votes
1answer
364 views
About binary stars and calculating velocity, period and radius of their orbit
I saw somewhere about being able to measure the velocity, period and radius of a binary star orbit by looking at red shift and blue shift.
I understand it but can someone give me an example of ...
28
votes
8answers
5k views
Would it matter if the Earth rotated clockwise?
In the Futurama episode "That Darn Katz!" they save the world by rotating the Earth backwards saying it shouldn't matter (which direction Earth rotates). If Earth rotated clockwise and remained in ...
12
votes
4answers
3k views
How do astronomers measure the distance to a star or other celestial object?
How do scientists measure the distance between objects in space? For example, Alpha Centauri is 4.3 light years away.
7
votes
2answers
350 views
How did Halley calculate the distance to the Sun by measuring the transit of Venus?
What numbers did Halley, Cook, et al. have? What was the strategy by which they calculated the AU?
4
votes
4answers
545 views
Optical explanation of images of stars?
Very often when viewing pictures of the cosmos taken by telescopes, one can observe that larger/brighter stars do not appear precisely as points/circles on the image. Indeed, the brighter the light ...
2
votes
2answers
771 views
What are good books for graduates/undergraduates in Astrophysics?
There are no book recommendations for Astrophysics here. I will write my own answer, but I am also interested in what are others' views on the question (I will NOT mark my own answer as the best one).
...
5
votes
2answers
229 views
Is dark matter really present around the sun?
Recently I read an article that there is dark matter around the sun but if it is so, than why can we see it clearly.
If it is called matter than it shall show some hindrance in radiation we receive ...
4
votes
1answer
134 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
4answers
489 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 ...
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 ...
3
votes
2answers
109 views
What is a good introductory text to astronomy
What is a good and easy to read introductory text for an adult with limited basic scientific knowledge to astronomy for someone without a telescope and lives in a big city and why do you think that ...
1
vote
2answers
123 views
What's the evidence supporting 1 singular Big Bang? [duplicate]
Possible Duplicate:
What has been proved about the big bang, and what has not?
I love to dabble with science, I'm by no means a scolar in this field. One thing that haven't seen proven yet ...
13
votes
1answer
382 views
What percentage of the sky is occluded by stars?
If you drew rays from the center of the earth out to infinity at every angle, what percentage of them would intersect a star?
Extra details:
Assume the rays are mathematical rays, or that they ...
17
votes
3answers
427 views
Direct observations of a black hole?
I'm not very knowledgeable about physics generally, but know that nothing can escape a black hole's gravitational pull, not even light (making them nearly invisible?).
My question is: What has been ...
10
votes
3answers
295 views
Is there a limit to the resolving power of a mirror telescope?
Like, if you flattened out Ceres to a 1 mm iron foil telescope mirror with 20x the surface area of the Sun, could you resolve details on the surface of an exoplanet? Could you make it arbitrarily ...
5
votes
0answers
209 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 ...
3
votes
2answers
1k views
How is the speed of light calculated?
How is the speed of light calculated? My knowledge of physics is limited to how much I studied till high school. One way that comes to my mind is: if we throw light from one point to another (of known ...
12
votes
9answers
168 views
In astronomy what phenomena have theory predicted before observations?
As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought ...
10
votes
5answers
676 views
Anti-Matter Black Holes
Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a ...
8
votes
4answers
736 views
How can I stabilize an unstable telescope?
I have an 80 mm refractor telescope on a tripod, but it shakes on every touch. It's very hard to see via 6 mm (x120) ocular. Even a little wind causes the image to become too unsteady.
How ...
6
votes
2answers
4k views
How is distance between sun and earth calculated?
How has the distance between sun and earth been calculated by scientists?
and size of sun?
Thanks,
5
votes
1answer
57 views
Is there an established standard for naming exoplanets?
I understand that exoplanets are named by adding a lowercase letter to the a designation of the planet's parent star or stellar system, beginning with 'b' (the star itself is 'a') in order of ...
5
votes
1answer
43 views
Is there an Algorithm to find the time when the sun is X degrees above the horizon for a given latitude B at date C
Is there an accurate algorithm / method to determine the precise time of day/night when the sun is X degrees above (or below) the horizon for a given latitude Y at date Z?
Is this the same question ...
3
votes
2answers
258 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 ...
3
votes
1answer
232 views
When and how were relative distances to the planets first measured?
I understand that the absolute distance to a planet can be measured using earth-baseline (e.g., diurnal) parallax, and that the first reasonably accurate such measurement was made for Mars by Cassini ...
2
votes
1answer
124 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 ...
2
votes
2answers
293 views
Does the length of the sidereal day vary systematically?
I'm confused about some properties of the sidereal day, in particular whether its duration varies systematically over the course of the year.1 It seems to me that that must be the case, but the ...
2
votes
1answer
225 views
How did Copernicus establish the relative distance to the superior planets?
I understand that the relative distances to the planets had been calculated using various methods since ancient times, and, in particular, that the assumptions of the Copernican model of the Solar ...
1
vote
3answers
4k 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 ...
-2
votes
5answers
256 views
Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events? [closed]
Does the rotational speed of a planet consistently become faster and faster given that there are no conflicting events?
8
votes
1answer
186 views
How to explain the Moon halo phenomenon?
Today, here in Brazil, I have observed (and is still observing) an interesting phenomenon.
The Moon is near to a big star in the sky, but this is normal. The interesting part is what's around them.
...
8
votes
3answers
254 views
Why is this radio telescope's reflector spherical and not parabolic?
This is the Arecibo Observatory in Arecibo, Puerto Rico. Its reflector is spherical, measuring 1,001 ft. in diameter. It is considered the most sensitive radio telescope on Earth, but the fact that ...
7
votes
2answers
176 views
How would one navigate interstellar space?
Headed out from Earth within the Solar System, Sol and Earth both may be used as reference.
When traveling in interstellar space with stellar systems themselves traveling at varying velocities even ...
7
votes
6answers
436 views
Can any telescope be used for solar observing?
Can any telescope, such as a 8" reflector, that is normally used at night to look at planets be used or adapted for solar observing?
What kind of adapters or filters are required or is it better to ...
7
votes
2answers
439 views
What does the sky look like to human eyes from orbit?
There are numerous pictures, obviously, of the blackness of space from the shuttle, the space station, and even the moon. But they all suffer from being from the perspective of a camera, which is not ...
6
votes
1answer
435 views
How do we know the masses of single stars?
I have recently read that we can only know the masses of stars in binary systems, because we use Kepler's third law to indirectly measure the mass. However, it is not hard to find measurements for the ...
6
votes
2answers
101 views
What's the best way to start out with astrophotography on a tight budget?
I'm new to astronomy and I don't have a great deal of cash to spend. I currently have a 3" reflector telescope which I've had great fun with. I also have a Pentax DSLR which I've been using to take ...
6
votes
2answers
215 views
Are there planetary systems where the planes of orbits vary greatly?
Inspired by this question, are there any known planetary systems with largely varying planes of orbit? For example a system where two planets have perpendicular planes?
5
votes
3answers
493 views
Is a water world possible, and for how long could it be stable?
I have several questions regarding this topic.
First, could a water world be stable for thousands of years with most of its surface remaining covered in water. What would it take for this to be ...
5
votes
1answer
1k views
How much sky do we see at any one moment?
When we look at any particular point the sky, what percentage of the celestial sphere do we see?
This question arises from the notion that on average there passes one meteor per hour overhead. So ...
4
votes
0answers
151 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 ...
4
votes
2answers
220 views
How much thrust would be needed to turn a hobbyist satellite into a deep space probe?
I was reading the article Weather Balloon Space Probes that says you can put your own satellite at 65,000 ft temporarily.
Is it even remotely possible to raise the probe high enough using ...
