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.

learn more… | top users | synonyms

3
votes
1answer
88 views

Galaxy Kinematic Fitting: How to deal with Point Spread Function (PSF)

The past few months I have been studying astronomy and Integral Field Spectroscopy (IFS). What I want to do is to fit a galaxy kinematic model to data (ie: estimate the model parameters that give the ...
8
votes
1answer
182 views

How can one get the eccentricity of the orbit of the Sun around center of the Milky Way?

How can one get the eccentricity of the orbit of the Sun around center of the Milky Way? Can it be measured?
1
vote
2answers
128 views

starlight flux on earth

I want to calculate if it is possible to photograph a subject lit only by starlight. I found one website claiming that a starlit scene is lv = -15 (daylight is lv 15, or 2^31 times brighter), but he ...
6
votes
1answer
92 views

Astronomical-wavelength radio (AWR) transmissions between cosmic plasmas?

My son asked me if electromagnetic waves longer than radio exist. I told him that even though physics permits such waves, there are no antennas long enough to radiate or detect them. However, on ...
7
votes
1answer
426 views

Distribution of star colours in a galaxy

I'm trying to randomly generate a representation of a galaxy. I have some Idea on the spatial distribution of stars within a galaxy, and I can find plenty of material on the colour of stars, but ...
4
votes
2answers
448 views

Recent Planck probe results: how unexpected?

The data from the Planck probe's observations are in, and according to the European Space Agency they show a "hemispheric asymmetry in the cosmic microwave background (CMB)". Quote: an asymmetry ...
0
votes
0answers
42 views

Estimating the present state of stars [duplicate]

Many time while reading through astronomy articles on the stars most of then thousand of light years away from earth. I have wondered how do astronomer know about the present state of star if we are ...
-5
votes
1answer
87 views

What would happen if the moon was in perpetual opposition of the sun [closed]

What would happen if an artificial force made the moon to stay at a perpetual opposition from the sun? Assume that the artificial force necessary is possible, and capable of making the moon stay at ...
-1
votes
1answer
278 views

How do you calculate the Milky Way’s galactic year? [closed]

The Solar system moves at a speed of 220 km / s around the galaxy. It’s about 27,000 light years from the Galactic Centre. How long does it take for the solar system to orbit around the Milky Way? ...
1
vote
1answer
130 views

How far to the 'edge' of the galaxy?

Wikipedia lists the average thickness of the milky-way to be about 1,000 LY - but where (roughly) within that is the sun currently? In asking this, I'm fully aware that there's no well-defined edge - ...
0
votes
2answers
246 views

Planet in which satellite(moon) and star(sun) appear together once a year

With a hypothetical system, where the moon would be always on the opposite side of the planet than the sun, in a way that the moon would only be visible at night on the planet. I don't know if this ...
7
votes
1answer
854 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, ...
7
votes
3answers
237 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 ...
2
votes
3answers
459 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 ...
0
votes
0answers
25 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) ...
1
vote
2answers
309 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 ...
1
vote
2answers
125 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 ...
5
votes
1answer
275 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 ...
1
vote
2answers
283 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 ...
17
votes
3answers
179 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?
8
votes
3answers
140 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 ...
19
votes
2answers
608 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 ...
11
votes
0answers
300 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 ...
2
votes
3answers
399 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 ...
0
votes
2answers
69 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 ...
1
vote
0answers
34 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 ...
2
votes
1answer
1k 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 ...
3
votes
1answer
72 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 ...
0
votes
0answers
46 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 ...
2
votes
3answers
166 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?
1
vote
2answers
139 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 ...
2
votes
2answers
69 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 ...
2
votes
1answer
910 views

Telescope size to view saturn

What is the properties (size, etc) of required lenses for minimal telescope to see the Saturn rings clearly?
6
votes
1answer
374 views

What is the frequency of occurrence of stellar classifications off the HR main-sequence?

An alternative version of this question would be: "if was to pick a star from the $10^{11}$ or so in our galaxy at random, what are the probabilities of it being various kinds of star?" (and I do mean ...
5
votes
1answer
105 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 ...
1
vote
1answer
62 views

Initial separation of neutron star/black hole binaries?

How would I go about finding the distribution of initial separations (i.e. the lengths between the centres of mass) of stars that make up binary systems. I am interested in neutron stars and stellar ...
2
votes
1answer
68 views

Have we observed another supernova explosion since SN 2008D?

I read the wikipedia article about SN 2008D which says: "Now that it is known what X-ray pattern to look for, the next generation of X-ray satellites is expected to find hundreds of supernovae every ...
5
votes
3answers
451 views

Why planets are rotating only in one plane? [duplicate]

Since gravity is three dimensional why planets are rotating only in one plane around sun.
4
votes
1answer
248 views

Very large absorption lines in stellar spectrum

I was puzzled by the wide absorption lines in a stellar spectrum I found. The following is what I expect absorption lines to look like - thin, crisp lines: However, I found this stellar spectrum, ...
1
vote
1answer
67 views

How is Doppler redshift of distant galaxies established?

Doppler redshift of distant galaxies gave first hint that the universe is expanding. I am curious to know how this redshift is actually measured and interpreted from observation. Suppose I observe ...
0
votes
0answers
34 views

What is the formula for calculating the length of any given day (sunrise to sunset)? [duplicate]

In a specific date what law gives us perfect measurements and how will we measure if latitude is given?
4
votes
2answers
188 views

How/why can the cosmic background radiation measurements tell us anything about the curvature of the universe?

So I've read the Wikipedia articles on WMAP and CMB in an attempt to try to understand how scientists are able to deduce the curvature of the universe from the measurements of the CMB. The Wiki ...
1
vote
1answer
74 views

How “big” objects can WISE and NEOWISE detect?

I mean WISE is monitoring near-Earth objects, but cannot see the latest Russian meteor and others. Why can it not detect small objects? What is the limit of it's infrared detectors?
1
vote
2answers
390 views

Could we survive if the sun were a black hole?

Ignoring the impossibility of the sun suddenly collapsing, and the energy release (which would kill us): If the sun suddenly turned into a black hole, could we survive if we had sufficient energy for ...
2
votes
2answers
455 views

Which way does a black hole spin?

As far as I understand, and from what I have been shown in renderings of black holes, they spin (like water going down a drain). My question is, firstly, does the matter being pulled into a black ...
3
votes
1answer
120 views

How is it the Voyagers are a few seconds closer to Earth than earlier?

The Voyager 2 tweet of March 01, 2013 put it's distance at 14 hrs 04 mins 23 secs of light-travel time from Earth. A more recent (earlier today) tweet says it is 14 hrs 04 mins 22 secs of light-travel ...
8
votes
3answers
493 views

What made us think that Earth moves around the Sun?

Trying to observe the night sky for a few weeks, the motion of the Sun and the stars pretty much fits into the Geocentric Theory i.e. All of them move around the Earth. What then, which particular ...
4
votes
1answer
110 views

How to track the visual path of a LEO satellite as seen from the ground

I have been struggling with this problem for a while so I decided to ask. I'm new here and I'm not sure where this type of question belongs, so forgive me if this isn't the right section. I am ...
0
votes
3answers
777 views

EM waves: How do they travel for billions of km without damping

If a star is 1 billion light years away, it means that the light we see from the star is emmitted billions of years ago. How does this light not undergo a frequency change or get damped inspite of ...
4
votes
3answers
82 views

Length of day of a gas giant

How can the rotational speed, or the length of a day be determined or estimated in a planet which is composed entirely of non homogeneous fluids? There must be internal forces (pressure gradients, ...