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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11
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3answers
2k views

What on Earth is this drawing of Venus?

The Wikipedia article for Venus's alleged moon Neith has this picture: And a tantalizing remark regarding paramecia (vandalism?). I know the grey ball is supposed to be Neith, the white is Venus, ...
2
votes
2answers
31 views

The difference between sub-Eddington and super-Eddington accretion disk models

I am studying accretion disks around active galactic nuclei (AGN). I have seen two sets of models, sub-Eddington and super-Eddington accretion disks. What do these terms refer to in this case? I ...
-3
votes
0answers
25 views

Book on galaxy formation and theoretical astrophysics for physics graduate [on hold]

I am looking for a graduate level book on galaxy formation and theoretical astrophysics and also numerical relativity for a graduate student who has completed quantum field theory and general ...
0
votes
1answer
70 views

Using starlight to create a fire

It is easily experimentally demonstrated that a focussed image of the Sun can be used to start a fire. Furthermore, by thermodynamic considerations or the conservation of étendue, it can be shown that ...
1
vote
1answer
51 views

Resource: Star map which show current actual positions versus current observable positions?

Light travelling from stars and galaxies takes some time to reach us here on Earth - when we observe stars or galaxies in the night sky, we see their positions as they were when the light left on its ...
0
votes
0answers
25 views

How dense is the material in the core of a black hole? [duplicate]

If I would like to find out the answer of this question, I get two different one: The material is collapsed into a tiny dot. This density is called planck density, and it is so dense, all of the ...
17
votes
6answers
5k views

Why can we see the moon when it is between the Earth and the Sun? [duplicate]

A rather stupid question, why can we see the moon when it is between the Earth and the Sun?
2
votes
2answers
45 views

Juno probe's speed is in relation to what frame of reference?

When describing the velocity of space probes in general (the Juno probe in particular) what frame of reference is the velocity quoted in? This is in relation to the news of the Juno Satellite ...
-4
votes
1answer
28 views

What changes in the moon light (spectrum, intensity, etc…) after the spring equinox? [closed]

There must be a correlation between the earth moon system and the sun during spring, just after the spring equinox.
0
votes
0answers
18 views

What is meant by Hydrogen dilution in Plasma?

I was going through the paper of methanol masers and it says that for a strong maser the geometrical dilution factor of HII emission should have low values. What is the meaning geometrical dilution ...
1
vote
1answer
43 views

What is the meaning of a negative Galactic longitude?

What is the meaning of negative longitude in Galactic coordinate system, for instance in this article? Does the longitude $-65^\circ$ equal $295^\circ$?
6
votes
2answers
69 views

How are coherent astronomical objects imaged?

I am studying astronomical imaging, and am curious about how to image astronomical objects which are coherent. Stellar interferometry measures the mutual coherence function of a star, and then uses ...
-1
votes
0answers
35 views

Books for someone interested in physics/space [duplicate]

As an avid reader of more realistic SF and someone who has always been interested in physics and astrophysics, I was wondering if someone could suggest both some introductory books on the subject, and ...
1
vote
2answers
122 views

Can astronomers observe neutron stars optically?

Are there any neutron stars near enough for astronomers to observe them optically? If not, then how close are we to having the technology to do so?
0
votes
1answer
37 views

Any good statistics books under the context of astronomy? [closed]

I just started a position as a research aide with the cosmology group at Argonne National Lab, and am working on creating and finding correlations within velocity dispersions of galaxy clusters. After ...
4
votes
2answers
115 views

Determining Mass of Spectroscopic Binaries

I know that the mass of a binary star system is given by Kepler's Law: $$\mathrm{m_1 + m_2 = \frac{4 \pi^2 r^3}{GT^2}}$$ Further we know that: $$\frac{r_2}{r_1} = \frac{v_2}{v_1} = \frac{m_1}{m_2}$$ ...
0
votes
0answers
17 views

How does Torque from tidal forces scale with distance

I read in a paper a while back that the torque on a body caused by differential rotation and tidal forces scaled with distance to the power of 6. That struck me as odd since the tidal force scales ...
0
votes
1answer
39 views

Why don't solstices coincide with temperature extremes? [duplicate]

In northern hemisphere, the highest temperatures are usually in July — in the middle of calendar summer. See e.g. the climate chart on this wikipedia page. But the solstices are on 20-21 of June, ...
1
vote
1answer
36 views

What is exactly the “progenitor bias”?

I am taking a course in astrophysics and my teacher mentioned different biases that are present when taking a sample of galaxies: the progenitor bias and the Malmquist bias. I understand very well the ...
3
votes
1answer
135 views

How to read numbers reported in this LIGO paper?

I am not sure how to read the numbers in this excerpt from the abstract of GW151226: Observation of Gravitational Waves from a 22-Solar-Mass Binary Black Hole Coalescence: Are the +/- small ...
3
votes
1answer
68 views

Uncertainty in the distance between Sun and other planets

I have read about the orbit distances between Sun and the planets and have come to know for example: Earth is around 150 million km away from the Sun. However I have seen that tht value is only an ...
14
votes
2answers
2k views

What is the farthest planetary body or star system object we have observed using visual light?

What is the farthest object which we can get a direct Detailed visual image of using visible light which appears more than just a dot and falls into one of the following categories: Planet Satellite ...
0
votes
1answer
30 views

Sloan Digital Sky Survey (SDSS) spec file headers

I downloaded spectra from Sloan Digital Sky Survey (SDSS), which has the following column headers flux, loglam, ivar, and_mask, or_mask, wdisp, sky and model (...
0
votes
1answer
27 views

Short gamma ray burst redshift

I would like to know what kind of methods are being used to infer the redshift distance of GRBs. Some background: I recently went on two sites; grbweb by IceCube and Fermi GRB database. On grbweb ...
2
votes
1answer
54 views

GR Verification for a Charged Black Hole

For a charged ($Q$) rotating ($L$) mass ($M$), the Kerr-Newman equations give the angular deflection of light. Has there been observational verification (I would prefer to use only the angular ...
-1
votes
1answer
43 views

How can i estimate the apparent size of an object?

I would like to be able to estimate, the apparent size of some object. The motivation behind this, is to use the correct numbers, in a sci-fy novel i am writing. Só, i want to be able to calculate, ...
1
vote
1answer
42 views

How do we filter out radiation from galaxies from the cosmic background radiation?

When a whole sky view is done to get a picture of the cosmic background radiation the radiation from our Galaxy is filtered out, and we are left with a picture which show radiation coming, more or ...
0
votes
1answer
34 views

How to interpret these gravitational lensing data?

The data I am trying to understand this gravitational lensing data in the link above. However, unfortunately I don't have an extensive knowledge in physics. Could someone please tell me what each of ...
2
votes
1answer
46 views

Do satellite galaxies have the same proportion of dark matter as “ordinary” galaxies

My question is relatively straightforward: Do we know if satellite/ dwarf galaxies contain the same proportion of dark matter to ordinary matter as "regular" sized galaxies? The Milky Way, for ...
1
vote
0answers
39 views

Very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth

I need a very precise calculation of the heliocentric position coords (X, Y, Z) the point of coordinates (N/S, W/E degrees) on Earth. Currently, thanks to the algorithm which generates the position ...
1
vote
0answers
75 views

World's Largest Radio Telesope : How accurately does it need to be figured?

In Guizhou Province, China, the worlds largest radio telescope is almost complete, measuring 500 metres across. I am aware that todays largest optical telescope require very accurate figuring and ...
3
votes
1answer
54 views

Error measurement barycenter of the Solar System - NASA data

What are the possible measurement error barycenter of the Solar System in NASA data? In the data JPL's HORIZONS system for NASA (http://ssd.jpl.nasa.gov/?horizons): Target Body: Solar System ...
0
votes
1answer
25 views

Translational Velocity

Is the translation velocity equivalent to its real velocity or radial velocity? Online sites and textbook are saying different things, So Im not too sure what is going on
2
votes
2answers
60 views

Why don't reflector telescopes place their reflectors at an angle?

To avoid placing a secondary mirror in front of the objective mirror, why not tilt the objective and design the eyepiece in such a way that comatic aberration is minimized?
0
votes
0answers
9 views

What is the estimator that used to de-rotation of CMB polarization? [duplicate]

For de-rotation of CMB polarization we need to use of estimator for rotation angle. and used many estimator for this process.
0
votes
2answers
46 views

The impact of the Oort cloud to change the barycenter of the solar system

Is the Oort cloud changing the position of the barycenter of the solar system? Does it affect in a significant way? How significant?
3
votes
2answers
39 views

Different width of spectral lines for different groups of stars

As seen in an HR-diagram, a certain stellar classification can correspond to more than one group/sequence of stars (G5 could for instance be either a giant, main sequence star or a white dwarf and so ...
2
votes
0answers
45 views

Calculating the Diameter of Jupiter through Image [closed]

I was trying to calculate the diameter of Jupiter from a picture I took of it. Here's the information I was able to get that I needed to calculate the diameter: Focal Length of Telescope: 1.2 m ...
0
votes
1answer
104 views

Can you see yourself in space? [closed]

Can one see them self in space if no near by star was in view? Is there enough star light to read once your eyes adjust?
1
vote
1answer
38 views

Gamma Ray Burst data

I wanted to know if there was some database for gamma ray burst (GRB) data. I would like to get the luminosity and duration of recorded GRBs. So far, I have come across this website, but since I do ...
1
vote
1answer
33 views

The observation of changes barycenter of the solar system

Is it possible to observation changes in the barycenter of the solar system? There are graphics showing changes barycenter but they are made on the basis of computer simulation (E.g.: here and here). ...
1
vote
1answer
26 views

Stellar classifiaction and metals

I have recently started to study astronomy and there is a thing with stellar classifications I can't get my head around: The colder the star the more absorption lines from metals are present in its ...
0
votes
0answers
37 views

Blurry image in a Celestron 8SE

We have a Celestron 8SE. Last night we were looking at the quarter moon. The moon was in focus. We switched viewers & 2nd viewer only saw a blurry white blob, not the surface of the moon. When ...
2
votes
0answers
40 views

Would a black hole cast a shadow? [duplicate]

Okay, so I've been wondering and this is a simple question and I cannot find an answer anywhere. Would a blackhole the size of the Moon (event horizon) black out the Sun in a "Lunar eclipse"? My ...
4
votes
1answer
72 views

Hubble time and age of the universe

I'm having trouble with the following derivation of the 'age of the universe': http://imgur.com/gRvLWX8 The parts I'm struggling to conceptualize is what a 'universe expanding' means, and also why ...
0
votes
1answer
45 views

Are planets and galaxies being discovered from earth?

I wonder how new planets and galaxies can be discovered from earth. I mean, there are not inifinately many directions to look with the telescope, right? Is it really so many different directions to ...
1
vote
1answer
46 views

Surface brightness

I have to compute the surface brightness as a function of the radius from the following set of data: {right ascension ($\alpha$), declination ($\delta$), magnitude (m)}. I also know the center of the ...
0
votes
0answers
32 views

Is it possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR?

I'd like to know if it is possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR (digital single lens reflex camera) mounted on tripod. Maybe, when shooting ...
0
votes
1answer
51 views

Calculating the diameter of Jupiter through an image

I took an image of Jupiter through my 8" Dobsonian Telescope, attaching a DSLR and a 1.25" Barlow Lens where the eyepiece goes, as shown in this video: https://www.youtube.com/watch?v=reFxoF3XoaU ...
4
votes
2answers
76 views

A question about the Fermi acceleration

In high school physics, we know that a charged particle cannot gain energy from a magnetic field. But, it seems that in the so-called Fermi acceleration, the particle is accelerated by the magnetic ...