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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49 views
What information about a meteor's trajectory, size, or height can be derived from a single location?
If one sees a meteor, is there any way to get even a rough approximation of its height, entry angle, size, or other characteristic without triangulation from another position?
If it appeared as a ...
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2answers
78 views
I want the Saturn's position in terms of Declination and Right Ascension?
I want the Saturn's position in terms of Declination and Right Ascension for a couple of month in the interval of 1 hour in a text file to do a simulation. Which site can provide me these data?
Or ...
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2answers
96 views
Curiosity Rover (MSL): current coordinates
I'm looking for information on the current coordinates of Mars Science Laboratory's Curiosity Rover.
I've only found the landing site coordinates 4.5895°S ...
7
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3answers
83 views
Parallax, obliquity, precession, and Orion?
Today, the obliquity of the earth is about 23.4°.
6500 years ago, it was about 24.1°
Imagine the blue square is the constellation of Orion, and the yellow star is the sun. Viewpoint B is you, on ...
5
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1answer
64 views
Do all known planets and moons have magnetic field?
In this Wikipedia article it is stated, that magnetic field of Earth is caused by currents in her core. The same origin is for Jupiter magnetic field.
For Moon (article) there is a magnetic field, ...
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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 ...
3
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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 ...
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5answers
680 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 ...
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3answers
108 views
Distance away from earth to see it as a full disk [duplicate]
This question is more space-related than physics-related, but here goes...
How far away the earth would I have to be in order to see the earth as a full disk? What I'm looking for is a distance in ...
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0answers
19 views
What's an equation for two astronomical entities both of 4000 tonnes in weight, colliding? [duplicate]
I have next to no knowledge of any physics, but would be happy if you could answer my question...
I want to know an equation for two astronomical entities such as the star Sirius (2.02 solar mass) ...
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0answers
22 views
Aligning images of starfields
I have two images taken within 30 minutes of each other in the same part of the sky. They are very similar but are slightly offset due to the Earth's rotation and other factors.
I know: the X, Y ...
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4answers
461 views
What is the typical career path to become a professional Astronomer? [closed]
Here is a typical question which I have been asked many times while giving public lectures in various places. While I know one of the paths like Diploma, Masters and PhD but sometimes this is not so ...
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2answers
91 views
Is it possible that universe might not be speeding up expansion?
I'm not sure but I was thinking of galaxies shrinking with time while still moving apart from each other at almost a constant speed or less (i.e: uniform/slightly decelerating expansion). This may ...
4
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1answer
45 views
What planets are visible to the naked eye from Mars?
Here on Earth we are blessed with being able to see some other planets, Mars & Venus etc, with the naked eye on a fairly regular basis thanks to the distance between the planets.
What about from ...
2
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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. ...
7
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6answers
989 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?
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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 ...
10
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1answer
368 views
What accounts for the discrepancies in my calculations of year lengths?
A common exercise in many introductory astronomy texts is to use the lengths of various kinds days to calculate the approximate length of the corresponding year.
For example, ratio $k$ of the length ...
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1answer
115 views
What happens to the electron companions of cosmic ray protons?
If primary cosmic rays are made mostly of protons, where are the electrons lost, and does this mean that the Earth is positively charged?
Does the sun eject protons and electrons in equal number?
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0answers
117 views
Optimal telescope size?
Consider a diffraction-limited telescope with unobstructed aperture $D$. Such a scope is capable of yielding an angular resolution $\alpha$ that scales as $\lambda/D$, with $\lambda$ denoting the ...
8
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3answers
85 views
How do we measure the range of distant objects despite relativistic effects?
When we observe astronomical objects like distant galaxies there are several complicating factors for estimating the distance:
Relativistic speed result in length contraction
Relativistic speed ...
4
votes
1answer
267 views
Is there a simple yet accurate formula for where on Earth the Sun and Moon are directly overhead?
I'm trying to improve a site that shows the region of the Earth currently under daylight, and I
need a formula that, given the current time, tells where
(latitude/longitude) the sun and moon are ...
3
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1answer
265 views
Magnitude of New Comet C/2012 S1 (ISON)
A new comet (magnitude 18.8) has been discovered beyond the orbit of Jupiter.
Comet ISON will get within 0.012 AU of the Sun by the end of November 2013 and ~0.4 AU from of Earth early in January ...
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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 ...
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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,
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5answers
6k views
Gravity on the International Space Station
We created a table in my physics class which contained the strength of gravity on different planet and objects in space. At altitude 0(earth), the gravitational strength is 100%. On the moon at ...
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0answers
288 views
Strange things about new moon [duplicate]
I have some strange and infantile questions about new moon. I want to know how is it possible that the Moon is not visible at night and also at day it is not Sun eclipse?
I will explain the problem in ...
7
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2answers
203 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 ...
2
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3answers
108 views
Why wasn't the moon visible during the day a few decades ago?
I was born in 1949. When I was young we played outside and watched the clouds and the sky a lot, and I don't remember ever seeing the moon during the day. Is the sun closer to us now so we see it more ...
2
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1answer
58 views
Alpha Centauri Bb: Comparing astrometric precision vs doppler precision
How do you compare astrometric precision vs doppler spectroscopic precision?
In particular will the Gaia spacecraft to be launched next year be able to confirm the existence of Alpha Centauri Bb? ...
5
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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 ...
10
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5answers
2k views
What is an asterism compared to a constellation?
I'm doing an astronomy exam tomorrow and in the practice paper it asks for the difference between constellation and asterism. It seems asterism is a group of recognizable stars; however I thought that ...
2
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1answer
127 views
Find temperature of surface (Blackbody Radiation)
An astronomer is trying to estimate the surface temperature of a star with a radius of $5 \times 10^8\ m$ by modeling it as an ideal blackbody. The astronomer has measured the intensity of ...
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2answers
49 views
Has anyone studied a statistical scaling law for the universe? [closed]
How do named objects in the universe scale? Is there a predictable curve for an ordered list, say {atom, animal, planet, solar system, galaxy, etc}? Can you then use the analysis to predict when the ...
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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 ...
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5answers
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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 ...
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0answers
28 views
Information-theoretic limits in observational astronomy
It seems to me that with ever larger and better telescopes and powerful statistical methods, humans are gleaning surprising amounts of information from observations of distant stars. I am especially ...
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2answers
135 views
Why does a blue sky at dusk appear nearly black through a telescope?
Earlier this evening I was looking at the Moon through my cheap toy telescope (x150 magnification) when I noticed a (rather mundane) optical effect I couldn't explain. The Sun had just dipped below ...
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2answers
513 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 ...
3
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1answer
57 views
Where can I search for high quality telescope images of Earth's moon?
I am developing a sensor calibration capability that compares a telescope lunar observation to a physics-based radiometric model. I'd like to find some high quality lunar images to test our ...
3
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2answers
180 views
Smithsonian Astrophysical Observatory (SAO) star catalog
Is a Smithsonian Astrophysical Observatory (SAO) star catalog, 4 volumes, dated 1977, worth keeping in a library or is it too outdated? Can it be used for epoch 200?
9
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1answer
223 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 ...
5
votes
1answer
80 views
How is celestial navigation done on a low-level?
When we send a probe off to Jupiter or Saturn, or even Earth orbit, how are the rocket firings timed and coordinated?
For instance, when I want to drive to another city I pull onto the highway and ...
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0answers
45 views
What is the observable Earth we can see? [duplicate]
Yes I know we can see the whole earth, but how far can we see left to right waving out the limitations of sight.
Because it's impossible to see the whole earth right? because it's spherical?
So is ...
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0answers
72 views
Doubts about NASA's announcement of collision between Milky Way and Andromeda [closed]
Andromeda is one of the nearest big gallaxies out there.
We can estimate the distance to the Andromeda Galaxy measuring the apparent brightness of Cepheid variable stars; its distance is currently ...
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2answers
96 views
Is there anyone calculate the probability of extrasolar planets?
After reading an recent news "Stargazers capture first picture of a planet with two suns – just like Luke Skywalker’s home planet of Tatooine in Star Wars", I am thinking that: can we calculate the ...
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5answers
1k views
Why is the solar noon time different every day?
If you check the local time for solar noon is different every day. Why is it so? Is it because Earth doesn't make a complete rotation in exactly 24 hours?
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3answers
133 views
How old is SUN ☉?
How do we know/calculate the exact age of sun ☉ ? ie. 4.57 billion years. What is the way to calculate it?
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0answers
67 views
Calculating distance to an asteroid on a given day
I'd like to calculate the distance between the Earth and an asteroid at a given date. Is this possible using the data from JPL's small-body database? Is there a better way?
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0answers
176 views
Why are solar eclipses more common in the southern hemisphere?
I've seen the claim that solar eclipses are more common in the southern hemisphere than the northern hemisphere and would like to understand why and if that is the case? Does it relate more to the ...
