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

0
votes
1answer
32 views

Simplifying Friedmann's Equation

So we have one of Friedmann's equation: $$\rho_c = \frac{3H^2}{8\pi G}$$ Using This website, resources where gathered for specific times in the universe. The resources being the Hubble constant at ...
1
vote
0answers
8 views

Why does the Zodiacal light vary between dawn and dusk?

According to several pages, in the Fall the Zodiacal light is better seen at dawn than at dusk: In the mid-latitudes, the zodiacal light is best observed in the western sky in the spring after the ...
10
votes
2answers
1k 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 ...
11
votes
4answers
4k 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. Hypothetical large ...
1
vote
1answer
42 views

Data/signal from a black hole to observe a singularity

I wonder if a situation is possible where, we measure some signal/property concerning a black hole. Supposing the measurement we make with some telescope, gets us the Fourier transform coefficients of ...
1
vote
1answer
60 views

Radial and tangential velocities of a star

(source) Early in this piece it states that the radial and tangential velocities are: $$V_r = V_c \cos(\alpha) -V_{c,0} \sin (l)$$ $$V_t = V_c \sin(\alpha) -V_{c,0} \cos (l)$$ but I am struggling ...
2
votes
1answer
44 views

Import of Celestial Effects on Satellite Radio Interference

Some internet (among other) infrastructure comprises satellites, which beam communications in radio frequencies. These satellites, to ground observers, appear as very small solid angles in the sky. ...
1
vote
0answers
34 views

Sharpness of starlight

I am interested in argument that the observed lack of blurriness in starlight refutes the "tired light" theories. I have not been able to find this argument expanded in detail. There are two ways ...
7
votes
3answers
1k views

Rocky Planet in the center of System [duplicate]

We all know that mostly stars are at the center of planetary systems, but is it possible that instead of star there was a rocky planet in the center with stars (and other planets and moons) orbiting ...
2
votes
1answer
78 views

Could a Class A Stellar Engine Use A Brown Dwarf

Could a class A stellar engine (or maybe a class C one) be built using a brown dwarf (for argument's sake, a T-dwarf like Gliese 229B)? Would it be capable of enough thrust to move itself any ...
11
votes
6answers
2k views

Where can I find public domain astronomical pictures?

Where can I find public domain astronomical pictures of nebulae, stars, etc. that can be freely used?
0
votes
1answer
36 views

What can be seen with a 114mm Aperture 675x Zoom Telescope?

I choose to post this question on the physics exchange seeing there would be a bigger audience for answers than the astronomy exchange still in BETA. But i'm looking to buy a telescope and was ...
0
votes
1answer
28 views

How much has the Milky Way moved since it's forming?

What i really want to ask how much has the Milky Way moved, relative to where it was "at the big bang" or the soonest time that makes sense (since i doubt "at the big bang" makes much sense in this ...
0
votes
0answers
21 views

Why is metallic hydrogen degenerate matter?

Why is metallic hydrogen considered a form of degenerate matter, akin to neutronium and electron-degenerate matter? I can understand that for the other two, degeneracy pressure is the only force ...
6
votes
2answers
508 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 ...
1
vote
0answers
27 views

Sun reaching zenith at a particular latitude

I need to find when the sun reaches the Zenith at a given latitude. What I've done so far: $L=23.5 \cdot \sin(\frac{2\pi}{365.25}\cdot D) $ Here L is the latitude (<23.5) and D is number of days ...
11
votes
1answer
267 views

Does it make sense to continue searching for dark matter on Earth?

The Large Underground Xenon Detector (LUX) recently released results1 that they have found no signs of dark matter2 after a ~3 month search this spring and summer. The LUX group plans to spend all of ...
1
vote
1answer
103 views

Magnification of an astronomical telescope not in normal adjustment?

I am stuck on this question: A telescope consists of two thin converging lenses of focal lengths 100cm and 10cm respectively. It is used to view an object 2000cm from the objective. What is the ...
3
votes
3answers
267 views

Dark age of universe when all fusion process ceases?

Some say we live in the golden age of the universe because there exits countless number of stars that shines in the dark universe. As the supply of gas for star formation is steadily being exhausted, ...
2
votes
1answer
170 views

Analyse astronomical data

Recently I was told of a job offer to analyse astronomical data. The job offer states that they want somebody with knowledge of astronomical data analysis software and it will be a plus somebody who ...
8
votes
1answer
2k 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, ...
4
votes
5answers
927 views

Are telescopes with a concave lens useful for astronomy?

Are telescopes with a concave lens (instead of convex ones) ever useful for astronomy? And if so, where are they used? Do they ever affect resolving power?
26
votes
4answers
2k views

Why are there no asteroids or meteoroids with relativistic speeds?

Cosmic rays can have energies going into the $10^{20}$ eV domain. Asteroids and meteoroids originating in the solar system are probably limited in their speed because they all started out from the ...
1
vote
0answers
39 views

Sedna, VP113 and the likelihood of the PX/Tyche/Thelistos hypotheses

The recent discoveries in exoplanetary science (specially those findings of planets orbiting far far away from its parent star/stars) raise questions about how much we know about the (true, AIU ...
1
vote
3answers
58 views

astronomy & light pollution

If you were staring to the sky in a big city and electricity is turned off in a big area around you, would you be seeing the sky with little light pollution instantly?
3
votes
1answer
421 views

Ephemeris calculations: Light time correction of the moon

I am currently trying to calculate apparent positions from raw JPL data. I've got it pretty much figured out, but there is one thing that's bugging me: Has the light time correction of the moon to be ...
2
votes
3answers
153 views

How does the evolution of a solar system not break the second law of thermodynamics?

Please forgive: I am a layman when it comes to physics and cosmology, and have tried finding an answer to this that I can understand, with no luck. As I understand it, the solar system evolved from a ...
3
votes
1answer
108 views

How is UT1 being computed?

I've recently read up about time standards and now understand that UTC is a second-corrected version of international atomic time so that it is kept within 0.9s from UT1. And then UT1 is defined as ...
5
votes
2answers
211 views

How to explain the existence of heavier elements in Population I stars and in Population II stars contain lighter one

Recently I read Astrophysics Notes where I found a statement that young stars are classified as Population I stars and relatively older one as Population II stars. Population I stars contain ...
0
votes
2answers
170 views

Gyrochronology, the formula is empirical ?

The formula used in Gyrochronology that relates a star's Period of Rotation-Mass-Age is empirical? This news How to Learn a Star’s True Age "“A star’s rotation slows down steadily with time, ...
11
votes
2answers
2k views

Is it possible to 3D print a mirror to create a high quality telescope?

Is it possible to 3D print a mirror with todays available materials? If so, would there be a reduction in image quality?
1
vote
0answers
30 views

How to prove the Hubble law is the unique expansion law compatible with homogeneity and isotropy?

In the book physical foundations of cosmology, it saids that Hubble law is unique and a problem seems to be a hint of proving that. In order for a general expansion law,v=f(r,t), to be the same ...
0
votes
1answer
34 views

What is the power of the most powerful quasar found?

Trying to find an answer to this question, I came across many sources that are in complete in contradiction. For example Wikipedia states that a typical quasar has a power of $10^{40}$ watts while ...
2
votes
1answer
85 views

Adding matter to make galaxies bigger

What are the actual factors that play a role in the accretion of matter into galaxies? I read about Accretion Disks but I don't quite understand how they work yet.
0
votes
1answer
65 views

Deflection of light by the Sun

Can you give details of a recent experiment of deflection of light by the Sun? What is the distance from the surface of the Sun and what is the exact value of the angle of deflection?
3
votes
2answers
89 views

Direct rocky planet formation without protostellar disk?

Inspired by this question, which sort of asked what I'm asking, but emphasized a different point (and the answers accordingly addressed that). Can a rocky planet form directly from the collapse of ...
0
votes
1answer
151 views

What are the conditions around Sgr A* for a space ship trying to plunge into the central black hole?

The possible problems for a space ship near an active galactic nucleus are the following: tidal forces, hot plasma accreting into the black hole and "jetting" out, radiation, and magnetic fields. If I ...
18
votes
6answers
3k views

Why are the orbits of planets in the Solar System nearly circular?

Except for Mercury, the planets in the Solar System have very small eccentricities. Is this property special to the Solar System? Wikipedia states: Most exoplanets with orbital periods of 20 ...
6
votes
1answer
120 views

What prevents stars in globular clusters from merging over time to form a black hole?

Globular clusters are apparently very very old, and the density of these clusters appears to increase as one approaches the center of a cluster. Orbits are bound to be chaotic, since there is no ...
8
votes
6answers
2k 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?
0
votes
2answers
81 views

Sun's Right Ascension appears to be wrong in my Stellarium

The Stellarium version 0.12.4 I have shows the RA of the sun at 22.5 Hour while Google says it is 19h 4m 31s. I am confused. Please help.
11
votes
1answer
817 views

Why don't the black holes appear black in color in images of galaxies taken from HST?

According to NASA a black hole is anything but empty space. Rather, it is a great amount of matter packed into a very small area According to the documentary Space Unraveling The Cosmos about ...
2
votes
2answers
81 views

Could two identical stars revolve around each other in a common orbit if we only account for Newtonian physics?

Both a parent star and its planet revolve around the center of mass of the system, the reason we see stellar wobble. But if we take this to be true, which it is, there can be a configuration in which ...
0
votes
3answers
502 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 ...
5
votes
3answers
92 views

How to measure the effects of the rotation around the Sun?

It is well know that we can measure the spinning of the Earth with a Foucault pendulum. But, is there a similar experiment for the rotation of the Earth around the Sun? I would like to know if we ...
3
votes
1answer
66 views

What is the origin and nature of the “hydrogen envelope” located on the sun side of a comet coma?

It is tempting to assume the origin of the hydrogen is water vapor from the comet, in which case, what process "breaks up" the water molecule (or perhaps ammonia molecule?)? Is the hydrogen actually ...
4
votes
0answers
72 views

Calculus used by Gauss to find Ceres' position?

With very little data, the great mathematician Gauss was able to predict the exact location of where to find the asteroid Ceres. If possible I would like a reconstruction of his work, from the data ...
11
votes
1answer
265 views

What are the alternative theories of dark energy? ($w \neq -1$)

There has been a lot of related questions about dark energy around here but these are usually 2-4 years old and the closest question to mine hasn't really been answered, so I am going to proceed. ...
5
votes
6answers
260 views

Are there free data available online from cosmology (or astrophysics) experiments that anyone can analyse?

One can understand a subject better in physics by trying to solve as many problems as one can from a textbook say. When it comes to experimental physics and data analysis, no book on experimental ...
0
votes
2answers
41 views

For a planet which has a temperature gradient, hot in the center and cooler on the surface, why do we get absorption lines?

For a planet which has a temperature gradient, hot in the center and cooler on the surface, why do we see absorption lines? Similarly, why do we see emission lines if the planet is hot on the ...