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 (2)

10
votes
3answers
1k 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 ...
4
votes
3answers
1k views

What is the formal definition of a stellar day?

I'm having trouble understanding precisely what a stellar day is. Neither the USNO nor the IERS sites provide a definition. And Wikipedia's description as the "rotation period relative to the fixed ...
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?
10
votes
2answers
4k views

Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
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 ...
37
votes
8answers
30k views

Why CAN we see the new moon at night?

I understand that the Moon's phases are determined by its position in orbit relative to the Sun. (See: Full Story on the Moon). The "shadow" is not cast by the Earth (a common misconception - this is ...
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 ...
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?
-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.
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 ...
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 $295^\circ$?
15
votes
1answer
380 views

Relationship between Mars and Earth rotation

Is it by pure random chance that Mars and the Earth have nearly the same day duration (Mars day is barely 40 minutes longer, which is just 3% difference), or there is some causal relationship between ...
-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 ...
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
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 ...
0
votes
0answers
47 views

Negative Parallax

I am constructing a Hertzsprung-Russel diagram for stars within a radius around Pleiades and have repeatedly come across stars that have negative parallaxes. For example, http://vizier.u-strasbg.fr/...
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 ...
22
votes
5answers
3k views

What do the colors in false color images represent?

Every kid who first looks into a telescope is shocked to see that everything's black and white. The pretty colors, like those in this picture of the Sleeping Beauty Galaxy (M64), are missing: The ...
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
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, ...
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 ...
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 ...
7
votes
3answers
2k views

Why does the light side of the moon appear not to line up correctly with the evening sun?

I live at roughly $(52.4^\circ,-2.1^\circ)$. On sunny evenings I've often looked at the Moon and the Sun and noticed that the light part of the Moon does not appear to line up with the Sun. For ...
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 ...
7
votes
2answers
2k 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 ...
8
votes
2answers
626 views

“Reverse engineering” of a horoscope?

I'll start with a disclaimer -- this is not a question about astrology itself, I'm neither trying to refute nor to defend astrology. I'm interested in purely technical things, which are mostly ...
6
votes
0answers
80 views

How do we decode the image formed by a gravitational lens?

Using our own sun as a gravitational lens, we can scrutinize planetary surfaces in distant solar systems with a good deal of accuracy. How do we translate this smeared out and curved image into a ...
5
votes
2answers
348 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 ...
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 ...
17
votes
5answers
37k views
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 ...
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 ...
6
votes
1answer
272 views

About the hump on galaxy rotation curves

The past days I have been studying the rotation curves of disk galaxies and I am currently trying to understand how we can extract information about the dark matter of a galaxy by looking its rotation ...
-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, ...
15
votes
4answers
12k 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 ...
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 ...
3
votes
1answer
2k views

How to determine day/night based on latitude, longitude and a date/time?

Is there a simple method of determining, given a UTC date/time, whether it is day or night at a given lat/long coordinate? I am currently using a formula based on a Sunrise/Sunset Algorithm from the ...
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 ...
7
votes
1answer
600 views

Determine date of birth from “astrological” signs?

Suppose someone tells me what constellation the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn were in when they were born, and the information is astronomically accurate (ie, not astrological ...
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 ...
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 ...
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?