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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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 ...
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3answers
3k 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?
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1answer
117 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?
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1answer
88 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.
14
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1answer
2k 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 ...
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2answers
978 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 ...
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1answer
404 views

Can life exist in intergalactic space?

A terrifying idea I think, to be so utterly alone. Do you recon life could exist in intergalactic space? A lot of cosmic radiation is shielded from us by the Milky Way's magnetic field, but the ...
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2answers
57 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 ...
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2answers
313 views

Possible intergalactic celestial objects

We know there are rouge stars floating in intergalactic space, thought to be caused by galactic collision. What other other classes of celestial object could be found floating around in intergalactic ...
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1answer
97 views

Classification of small extra-solar system bodies

A Small Solar System Body (SSSB) is an object in the Solar System that is neither a planet, nor a dwarf planet, nor a satellite. This encompasses all comets and all minor planets, as well as all ...
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1answer
97 views

how to measure the age of light?

We measure distances in universe by the units of light year/s or parsec. Which means distance traveled by light in one year equals one light year. Thus the lights we receive from the distant stars or ...
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2answers
74 views

How are the distances to the most distant $\gamma$-ray bursts measured?

This question came to my mind when I read on NASA's website that an explosion (gamma ray burst, GRB 080913) took place 12.8 billion light years away from us. How do they measure such large distances?
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2answers
168 views

Is redshift a reliable means to know how fast an object is moving away or towards an observer?

Does wavelength change with distance? How do they know that the change in wavelength can only be caused by the change of speed of the object to the observer? What if it is an intrinsic property of ...
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1answer
68 views

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy?

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy? Galactic-sized - or larger - gravitating halos seem to get all the attention. I'm ...
6
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1answer
377 views

BBC radiation: What is it?

I'm reading articles about blazars, and in a discussion about models concerning Blazar SEDs (Spectral Energy Densities) there are mentions of different processes: Sychrotron scattering, inverse ...
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2answers
3k views

Day/night cycle in Greenland

I have heard that in Greenland there is day for 6 months and night for 6 months. Is this true? If so, how does it happen?
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1answer
46 views

Prior binary star system as possible explanation of high-velocity Type II Supernovae remnants

From wikipedia(http://en.wikipedia.org/wiki/Supernova) :- "A long-standing puzzle surrounding Type II supernovae is why the compact object remaining after the explosion is given a large velocity away ...
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2answers
496 views

Optically thick media

What does "optically thick media" mean? Does this property depend on the length of an enclosure? Why is the diffusion approximation for the radiative transfer equation applied to optically thick ...
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4answers
154 views

Drake's equation

Some years ago i read about this equation that helps us estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy. Now, i am wondering if there are results ...
4
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1answer
145 views

Absorption lines in the context of identifying elements in far away celestial objects

I understand that absorption lines are used to identify elements but how are individual absorption spectrums identified in the light that is received by a telescope?
17
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1answer
916 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. ...
2
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2answers
280 views

Would it be possible to detect nuclear explosion on exoplanet?

How strong would have to be nuclear explosion on exo-planet that orbits some other star for it to be detectable outside of that system. Or it would be impossible due to amount of radiation coming from ...
2
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2answers
150 views

Can a point source be located more accurately out-of-focus or in-focus?

Let's say I am taking a picture, and I know a priori that the image is of a single ideal point source of light at infinity. With a perfect imaging system in focus, the image shows an Airy disk. I ...
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1answer
73 views

Why 21cm line observations is more helpful compared to other radiation?

Why 21cm line observations is more helpful compared to other radiation? Is it only because of its abundance in whole universe or anything else?
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3answers
129 views

How stellar aberration is measured?

A simple calculation shows that stellar aberration due orbital motion of earth is roughly 20 arcseconds. My questions are: Practically how this small value is measured? Does this value is in the ...
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1answer
70 views

Are galaxies “disk” shaped?

When you look a sphere from a fixed observation point, you can easily mistake it for a circle, so I was wondering: are galaxies really "disk" shaped or we just don't have the means to detect the ...
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1answer
79 views

Why is solar eclipse so important for sunlight spectrum analysis?

People wait for decades to catch the chance of a solar eclipse to observe the sun. Why cannot they do it every noon?
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29 views

How does intensity differ from apparent luminosity in the context of photometry?

Context: photometry in astronomy. Background: The total luminosity $L$ of a star is the energy that radiates in all spatial directions in all wavelengths and is given by the following formula, where ...
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1answer
181 views

Absorption line detected with a significance of $2.2\sigma$

What do we mean by the following statement? The SV $\lambda$ 786.46 line is detected with a equivalent width of $W = 22.7\pm10.2$ corresponding to a significance of $2.2\sigma$ How does one ...
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2answers
258 views

Redshift 1+z - CMB Temperature lower?

I know that $\frac{\lambda_2}{\lambda_1} = 1 + z$ Suppose a galaxy had redshfit $z=3$. Does this mean that the wavelength becomes $4\lambda$? Then by wien's law where $\lambda \propto \frac{1}{T}$, ...
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1answer
206 views

Calculate the maximum variation in brightness of a star due to the presence of a planet in orbit

Background: As a planet orbits around a star, the star's brightness periodically dims as shown in the following picture. By measuring the variation of brightness, we are able to deduce information ...
2
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1answer
90 views

Current map of galaxies' z's and distances?

So, here's a diagram with some galaxies. I realize there are 500 billion galaxies out there (likely many more), but is there are fairly up-to-date diagram of all the galaxies, or a representative ...
5
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2answers
686 views

Abundances of the light element of the Big Bang Nucleosynthesis

This question is related to the Big Bang Nucleosynthesis of light elements, more concretely I do not understand some features of the graph Why do the $^3$He and D abundances go down with ...
6
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4answers
629 views

How does the formation 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 ...
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0answers
45 views

Milky way rotation data

Can anyone tell me where I can download sample rotation curve data for the Milky Way in csv format?
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2answers
151 views

What is the error in the measured value of the Hubble Constant?

I've found on the internet that the Hubble constant has been measured to be about $2.3\times 10^{-18} \, \mathrm{s}^{-1}$ Does anyone know what the current error bounds are on this value?
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2answers
68 views

Size of objects and variations in brightness?

My textbook says talking about Cygnus X-1 (the first black hole to be identified as such) has variations in brightens of the order of 0.01 seconds and that this means that it's dimeter must be on the ...
5
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2answers
829 views

Are there any astronomical objects at night that are dangerous to look at (through a telescope)?

Are there any astronomical bodies that would be dangerous to my vision to view through a telescope? Obviously the sun is dangerous, but are there other bodies at night I should avoid?
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1answer
216 views

Factors in predictions for Tolman's Surface Brightness Test?

http://en.wikipedia.org/wiki/Tolman_surface_brightness_test It says: In a simple (static and flat) universe, the light received from an object drops inversely with the square of its distance, but ...
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1answer
115 views

Approaching of Milky way to M87

The Andromeda Galaxy is approaching the Milky Way at about 110 kilometres per second (68 mi/s). What is the velocity that Milky way is approaching M87 ?
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2answers
105 views

Quick question on astronomical units

I'm trying to solve for $\frac{M*}{M_0}$ and $p''$ using these two equations: Here is the lecturer's working, I worked it out several times and I got a different answer! Surely when you use ...
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1answer
110 views

Quick question on parallax and parsec

I know that 1 parsec (pc) is the distance of star at which 1 AU subtends 1 arcsecond. so $1 pc = \frac{1 AU}{1"}$ Now, if two stars in a binary with a separation of 3" and have a trigonometric ...
5
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1answer
225 views

Hubble time and its derivation? [duplicate]

I know the derivation of Hubble time goes something like this (I am an a-level student so this may not be the actual derivation): Two galaxy that is moving away from each other at speed v are now D ...
4
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1answer
56 views

No tremendous neutrino-flux for SNIa?

Why do neutrino account for 99% of the energy release for a SN II, while it is not expected to be the case for SN Ia? Is it because the densities are not high enough to induce inverse beta-decay? ...
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2answers
34 views

Are combined masses in space, such as galaxies, considered to be uniform bodies? *In addition, a related question about force

If we were to calculate the force that one galaxy exerted onto another, would we consider the individual masses within the galaxies, or the masses of the galaxies as a whole? Do the individual stars ...
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0answers
68 views

Why are other universes in the picture of Dark Flow?

It seems to me that the popular suggestive explanation of dark flow is another universe interacting with ours. Isn't there other alternative explanations?
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2answers
100 views

The reason(s) of seasons on earth

This maybe simple and usual question, although there is a lot of confusion about it over internet and even in some books, so I want from an astronomer / astrophysicist to fill the gaps for me ...
2
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3answers
169 views

Astronomical Constant in Astronomical units?

I'm doing a computer simulation of the solar system and I'm having trouble working with big numbers (implementation specific problem). So what would be the Newtonian gravitational constant $G$ in ...
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1answer
104 views

Why are no CMB experiments able to measure the whole range of multipole moments?

Have a look at the following diagram: This shows measurements of the CMB by various experiments, with multipole moment $l$ on the x-axis and the temperature of the corresponding moment on the ...
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393 views

if the universe is flat does it mean it exists only in our mind as math? [closed]

My dad, who is a retired mathematician, has this attitude, which I think we all have as kids, that ultimately reality is made of stuff. End of story. If you look around yourself in the world, ...