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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4
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1answer
110 views

From how far away could Earth's telescopes detect Earth like radio signals?

The Earth has been broadcasting human generated radio signals for about 100 years now. If a nearby civilization were broadcasting similar radio signals, could we detect them with our own radio ...
9
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4answers
14k views

What are good books for graduates/undergraduates in Astrophysics?

There are no book recommendations for Astrophysics here. I will write my own answer, but I am also interested in what are others' views on the question (I will NOT mark my own answer as the best one).
2
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2answers
315 views

Planetary alignment of the gas giants?

There is this nice and new applet of the orbits of the planets around the sun: Solar System Orrery You can click and drag any planet and watch their relative orbits evolve in time. I was curious ...
1
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0answers
59 views

What could this star-like object in the morning sky have been?

At sunrise this morning and yesterday morning, around 6:45 am in Chicago, a bright light appeared in the eastern sky over Lake Michigan. It twinkled like a star, but it was much larger and brighter ...
2
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2answers
2k views

What is the difference between UT0, UT1 and GMT time?

Every reference I find says that they are "essentially" the same, which we all know really means that they are not the same, but different only by a some small amount that someone else other than me ...
0
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0answers
32 views

I have a fits file. I need to find the brightest pixel?

When I use astropy.fits to read the data of the fits file, I get a numpy array of values of shape(64,32,32). I am not able to understand what does this array contain. Ofcourse they are not RGB values ...
0
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1answer
25 views

What is the possibility of using the ionosphere or van Allen belts as a source of propellant for ion engines especially for orbital station keeping?

Just like how a jet engine uses the air it moves through to propel it self forward. In this case energy for ionizing the propellant won't be needed because we already have ions. How viable is my ...
2
votes
1answer
166 views

What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...
0
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1answer
42 views

Light curve analysis: how to estimate temperatures of Binary star system

I'm stuck at a binary star system lightcurve analysis. I have to set initial values for the bodies temperatures and then improve their accuracy by fitting. I know that the system type is WUMa. How ...
5
votes
3answers
1k views

How would I calculate celestial body characteristics without a priori knowledge?

Without any a priori knowledge of the mass, speed, distance, and size of local celestial bodies (aside from Earth's size), what can I calculate and how from my "backyard" through observation? Edit: ...
2
votes
3answers
132 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 ...
11
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1answer
2k views

How vacuous is intergalactic space?

You often hear intergalactic space is an example for a very good vacuum. But how vacuos is space between galaxy clusters and inside a huge void structure? Are there papers quoting a measurement/...
1
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0answers
26 views

Where can I find data for the masses/component velocities of galaxies in the Local Group?

I am trying to run an N body simulation to see how galaxies in the Local Group gravitationally interact for my thesis, but I can't find any data for the masses of the galaxies in the Local Group, or ...
1
vote
1answer
61 views

Does solar eclipse have impact over increase of earth's temperature?

Does a solar eclipse have an impact on global temperature? Wired theory : When I jump, does the Earth recoil? Yes, the Earth has to move in some way for momentum to be conserved. However, since ...
9
votes
2answers
1k views

Why don't we see solar and lunar eclipses often?

Since we see the new moon at least once in a month when the Moon gets in between of the Sun and the Earth during the evening ( and as far as I know if this happens during the day, you'll get to see a ...
2
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0answers
38 views

What are the main issues limiting resolution of gamma ray detectors?

Current gamma ray detector resolution is far from diffraction limited. For example, Swift's Burst Alert Telescope has a resolution of 1-4 arcminutes for gamma ray bursts (Wikipedia:Swift). My ...
2
votes
3answers
143 views

Gravitational wave detection and electromagnetic counterpart

Background Referring to this article on Fermi EM signal, 0.4 s after the gravitational wave detection by LIGO, FERMI detected an electromagnetic signal (poorly localized) with a false alarm ...
1
vote
0answers
54 views

Current length of the solar day?

As can be seen in this diagram, the length of the solar day has varied Question considerably the last century. But the diagram is incomplete and doesn't show the very last years. Can anyone tell me ...
5
votes
1answer
2k views

Formula for getting time of sunrise at a particular location?

Is there a formula that can get sunrise at a particular latitude and longitude (and elevation from sea level)? If so, what it is? (Why does it work?)
3
votes
1answer
186 views

Calculating telescope detection rate

I am working through a paper from Inoue et al. 2013. In section 6.1, pg 18 it states, ... assuming a whole sky rate of ∼ 600 GRBs/year, a 5◦ diameter FoV and a 10% duty cycle, the telescopes ...
14
votes
2answers
4k views

What is the largest observed celestial body?

I'm not referring to phenomena such as galaxies or clusters but rather, what is the largest discrete celestial body that has been observed in the universe?
1
vote
0answers
42 views

Why In Thermosphere is He and O divided as measured? [closed]

If we look Thermosphere a bit closer. we found out that Helium and Oxygen is divided peculiarily. This picture below shows the Earth looked below the south pole. So the orbiting direction is shown in ...
0
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0answers
46 views

Gravity difference on earth?

Would gravity on earth be any different if the earth were in intergalactic space rather than interstellar space?
0
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0answers
13 views

How much pressure would be on Mars if the icecaps melted?

I was wondering, The martian polar ice caps are made of water and CO2. All documentaries say that melting the poles can add pressure. How much pressure would there be? I know that every summer they ...
13
votes
2answers
320 views

Suntan: UV absorption vs daytime

I guess that these questions were being asked by many people on the Northern Hemisphere during this summer (and other summers) and someone may give a nice, coherent answer. The general question is how ...
0
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0answers
18 views

Relevant Archemidan Spiral Theorems: An Enquiry

Basically what I'm doing is investigating the solar wind's outflow. As part of this investigation is included a fairly crude application of a more complex outflow solution to that of basic archemidian ...
2
votes
1answer
230 views

Is there anything special about the Sun's photosphere in terms of density?

The Earth has a definite boundary between rocky/ watery surface and gaseous atmosphere. The same cannot be said of the sun. Even though the photosphere gives an apparent "edge" to the sun via the ...
0
votes
1answer
54 views

How can one tell how much light is blocked by a secondary mirror in a reflecting telescope?

I've been reading about reflecting telescopes and I understand how the secondary mirror doesn't cause any obstruction to the image itself, but I've read that it does dim the image by blocking the ...
1
vote
2answers
36 views

Redshift Versus Luminosity

I understand that there is a relation between the proper distance of a cosmic object and its "measurable" redshift, i.e. once you know the value of the redshift parameter z, then you actually know how ...
8
votes
1answer
143 views

How many galaxies could be the source of the recent LIGO detection?

The recent LIGO detection is pretty exciting, and a lot of people are asking whether there is a chance of optical detection of the black hole pair that created the signal. From a cursory reading of ...
11
votes
3answers
3k views

Is it possible to see satellites with the naked eye?

Every now and then I notice some very bright "stars" in the sky. They tend to be very few (one or two, usually), and are quite much brighter than any other star out there. Often they're perfectly ...
2
votes
1answer
87 views

Why do we assert Hulse–Taylor binary system's orbital decay to gravitational waves and not radiation?

From https://en.wikipedia.org/wiki/PSR_B1913%2B16#Star_system The Hulse–Taylor system's orbit has decayed since the binary system was initially discovered, in precise agreement with the loss of ...
5
votes
1answer
722 views

Velocity distribution in Plummer's models and others mass distributions

The Plummer's sphere is an model for the mass density in a globular cluster of stars. For an $N$-body simulation I have initialized the position of $N$ masses with a Monte-Carlo technique but cannot ...
13
votes
1answer
624 views

What is the status of existing measurements of the speed of gravity?

In replying to a recent question I stated: Gravitational waves have not been yet experimentally observed so as to have their velocity measured. Which after the fact prompted me to try and verify ...
2
votes
2answers
1k views

Size of a photon

When detecting radio waves in space, we use very large telescopes or arrays of telescopes. But according to QM, aren't photons point particles when measured? Does a photon with a large wavelength ...
0
votes
2answers
2k views

Shining object in the sky resembling a star

From last 2 days I am observing a shiny star like shining object in the sky in almost same place at same time. Is there any possibility that it could be a satellite? Will satellite shine like a star ...
0
votes
3answers
112 views

How do we determine the pressure at the surface of a star?

Is there any means to do so? I know there are some means to determine the surface temperature.
0
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0answers
23 views

photometric redshifts - the origin of 1 / (1+ zspec) in photometric accuracy

i have a training sample of sources with known spectroscopic redshifts ($z_{\rm spec}$) and i run a photometric fitting code that uses a template to determine the photometric redshifts ($z_{\rm phot}$)...
1
vote
0answers
24 views

solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.
0
votes
0answers
22 views

Trouble using my Celestron Astromaster 130

I am having trouble viewing objects clearly. I can find them but they look the same as with the naked eye. I have tried a few different lenses. Sometimes when I zoom I can see the reflection of the ...
1
vote
0answers
49 views

Can a spheromak propagate in vacuum?

I recently learned about (and am now fascinated by) spheromaks. I am no expert on plasma physics, but as I understand they are analogous to propagating toroidal vortices (smoke rings), but with plasma ...
1
vote
2answers
75 views

Why are Lunar Eclipse more common than Solar Eclipse?

Why are Lunar Eclipse more common than Solar Eclipse? Chapter from Light My thoughts; Eclipse can only occur at new moon and moon orbit is inclined at an angle of about 5 degrees to the earth's ...
2
votes
1answer
74 views

Can an absorbed photon be emitted as two photons?

I am taking an intro to astronomy class, and have touched upon absorption and emission lines and etc, the prof asked this question in class and got me thinking. I would want to say no, because one ...
1
vote
0answers
16 views

Would we expect the space between different Oort clouds to be empty?

If we consider a few solar systems to be like to image below (yes, I know it's overly simplistic), and each solar system has a cloud similar to the Oort cloud (the yellow globes), would the space ...
14
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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?
2
votes
3answers
394 views

What is the cosmological redshift of SN 1987A?

I haven't found any literature on SN 1987A, which provides me with its cosmological [not gravitational, wrong in inital question, thanks for the remark] redshift. Is it larger or smaller than $z=0.1$, ...
1
vote
1answer
49 views

A question on Jeans's instability

I am a Physics student and I'd really appreciate if anybody could help me with an exercise my professor gave me a couple of weeks ago. It goes like this: Let us consider a spherical symmetrical gas ...
8
votes
3answers
712 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 ...
58
votes
6answers
6k views

How can we see planets thousands of light years away but don't know if there are more planets in the solar system?

That is basically my question, it arose when I saw an article (here is the scientific paper, which should be free to read) saying two Caltech scientists might have found the 9th planet of the solar ...