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Questions tagged [astronomy]

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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Several disscussions and questions made on black holes [duplicate]

This isn't a duplicate question, this is revisting the whole black hole model: If an object with mass M is compressed to radius r, where r ∈ (0,Rs] such that Rs is the Schwarzschild's radius of the ...
2
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1answer
57 views

Would the Doppeler effect be incorrect to use as evidence to support an expanding universe?

In our science class we have a question to answer, which is 'explain how redshift supports the idea of an expanding universe'. I am not sure how to answer this question, as I know that there are '...
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6answers
140 views

Why are we looking for alien signals from radio waves?

Is the only reason we are scanning the radio frequency bands for signs of aliens simply as this is all we have technologically able to do? It seems that any civilization capable of interstellar ...
4
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2answers
334 views

Where can I find visible/radio telescopic observations of the center of the Milky Way galaxy?

I recently stumbled across this time-lapse telescopic image (radio image, I believe) of the center of the galaxy. Here's a still image. Link to time-lapse video below. I haven't been able to find ...
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0answers
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Deriving equations for Equatorial -> Galactic transformation via Euler Angles

As the title suggests, I'm looking for a derivation of the transformation equations between the equatorial and galactic coordinate systems via Euler angles. $\cos{b}\cos{(l-l_{0})} = \cos{\delta}\...
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0answers
16 views

What is the relationship between the colour of a star and its mass to light ratio

We were talking about methods to measure the mass of a galaxy and one way was to measure the mass to luminosity ratio and multiply by the luminosity. That seems like a trivial equation but apparently ...
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2answers
63 views

Why is most of the star formation that goes on in the milky way occurring in the spiral arms?

This fact was mentioned by our astrophysics lecturer and I can't seem to understand why. Isn't the densest and hottest part of our galaxy the central bulge? I would've thought star formation would ...
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0answers
29 views

Do space-borne cosmic ray experiments publish all-particle spectra?

I was trying to gather data to produce my own cosmic ray (CR) spectrum plot. I have relied on this very useful French database collecting past space-based CR measurements. If I try to insert the ...
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1answer
21 views

Where can I Find position vs time data for the star S2?

Does anyone here know where I can find the actual position versus time data for the orbit of the star S2 around the supermassive black hole Sagittarius A*? I have tried googling it with all possible ...
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0answers
42 views

How is V838 Moncerotis Expanding at 10x the speed of light? (It isn't - but sure looks like it)

The first picture from the Hubble Telescope was on May 20, 2002. A subsequent set of pictures culminating in October 2004 showed that it had expanded at about 1 LY per month. Now as we know there is ...
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0answers
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Do super dense objects smear instead of colliding?

I am watching a video (https://www.youtube.com/watch?v=C1mmTwjHhHs) and it is discussing a pair of neutron stars colliding and how the LIGO detected them. In this video and other videos on such ...
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1answer
44 views

Query about using HR diagram to determine stars progression through its main sequence

There was a problem in my astrophysics lecture which showed a cluster of stars (M92), the apparent magnitude was plot against the B-V colour for each star in the cluster: Along with other graphs, we ...
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0answers
41 views

How does a Thorne Zytkow star die?

A Thorne-Zytkow star is one where a red giant or supergiant contains a neutron star at its core, formed from the collision of the giant with the neutron star. It is believed that one has been found in ...
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0answers
29 views

A book about extragalactic astrophysics?

I'm an undergraduate student, writing my thesis. And I look for an advanced book of extragalactic astrophysics that contains information about Line Emission Galaxies. I already read "Extragalactic ...
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0answers
94 views

Do we really need a new physics? [closed]

I have heard many times in news that a new discovery has taken place, and we need a new physics. It has recently been announced in scientific news that the world is apparently expanding faster. And ...
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1answer
66 views

Moving moon explanation

I saw the moon moving in a fast pace several times with the naked eye, even during day time when its cloudy. How is that possible? I asked my teacher about it and he said its just an illusion, but ...
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1answer
27 views

What imparts the linear motion or the tangential velocity to natural satellites like the moon to enable them to be in orbit around the earth?

From Newton's laws of motion & gravitation, it is clear that the force of gravitation provides the necessary centripetal force which acts along the line joining the centre of masses of the earth &...
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1answer
77 views

How much in the past are we viewing the accretion disk of a black hole?

Sine the gravity near a black hole is so high, the time moves slower than the observer(in our case we from the earth).In that case, imagine if are viewing a black hole's accretion disk(the innermost ...
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0answers
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How does signal and background depend on declination

Considering a neutrino telescope, such as the ANTARES, how is the signal and background dependant on the declination.
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0answers
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What does the line strength mean in terms of spectral lines?

In my previous astrophysics lecture we were discussing the spectral types of stars. We were looking at the absorption features of dwarf stars in different spectral classes at a particular luminosity ...
2
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1answer
46 views

Why do stars appear so close in universe photos?

I saw an extremely sharp picture (from NASA/ESA) of the Andromeda Galaxy recently, and it made me wonder why the stars appear so close together, when I know in fact that they are not. Is it simply ...
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2answers
138 views

Why can't I see whole galaxies with the naked eye?

I have read these questions: At what distance could you see andromeda with the naked eye? Do all the individual stars that we can see in the night sky belong to Milky Way? I look at the night sky ...
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5answers
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Can anything be seen from the center of the Boötes void? How dark would it be?

Let's say I was at the very center of the enormous Boötes void, way out in deep, deep space. What could I see with the naked eye? I assume I could see no individual stars, but could I resolve any ...
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1answer
46 views

Are pressureless, collisionless and self-interacting dark matter all synonymous?

Is there any distinction between pressureless, collisionless and self-interacting dark matter or does being one imply the other?
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0answers
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Precise Event Horizon Telescope locations?

Presumably, in order to perform their interferometry, the Event Horizon Telescope correlator needs to know (i) exactly the time of an observation, which I understand is accomplished by timestamping ...
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2answers
58 views

Axis of rotation of the earth

It is known that the axis of rotation of earth is tilted with respect to the perpendicular to the plane of orbit. Is there a way to measure this tilt from earth without the aid of pictures taken from ...
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0answers
48 views

Moonlight reflection on ocean [duplicate]

I am trying to explain physically what is happening in the picture below: My gut explanation is that we are observing the reflection of a cone of light emanating from the moon, it explains the form ...
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0answers
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What molecular distribution models apply for nonequilibrium systems as cold stars?

Maxwell-Boltzmann distribution function describes well the distribution of ideal particles in thermal and chemical equilbrium (the concentration of the species is constant). Which models would apply ...
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1answer
234 views

Orange ring in a black hole image

What exactly is the origin of the orange ring around M$87$? I understand that the image was not taken in the visible light range. The colors are therefore artificial. I also read that the image ...
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3answers
544 views

Is the black hole image in false color?

The first-ever image of a black hole released this week was taken with radio telescopes, suggesting that it is a false-color image and doesn't represent what a person would see in reality, or visible ...
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5answers
7k views

Did the new image of black hole confirm the general theory of relativity? (M87)

How can we do it just by looking at the image. But I heard in news saying "Einstein was right! black hole image confirms GTR. The image is so less detailed that I can't even make some pretty good ...
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1answer
53 views

Light emission from the vicinity of a black hole [duplicate]

The photograph of the black hole, at the centre of galaxy M87, is now a part of human history. We are told that the red-colour is caused by hot gas, matter & radiation around the "edge", the Event ...
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2answers
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How do you calculate the black hole diameter of M87*?

The recent data from the EHT Consortium on the size and mass of the central black hole of M87, named M87*, are telling us that the diameter of the event horizon ...
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0answers
303 views

Putting the importance of the blackhole image into perspective [closed]

The recent astonishing achievement of obtaining an actual image of a blackhole, resulted from a massive collaborative work using 8 different telescopes and the equally on par efforts in developing the ...
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1answer
143 views

How did the first image of a black hole test the general relativity?

Recently, the event horizon of the black hole at the center of M87 was directly imaged by the EHT. My college professor said this could serve as another test of the accuracy of general relativity. ...
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1answer
211 views

First Black Hole Picture Takeaways [closed]

We just have obtained the first "picture" of a black hole, the supermassive blackhole at the center of galaxy M87. As spelled in this approved answer, there were multiple unsolved questions to be ...
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1answer
5k views

Why was M87 targeted for the Event Horizon Telescope instead of Sagittarius A*?

The first image of a black hole has been released today, April 10th, 2019. The team targeted the black hole at the center of the M87 galaxy. Why didn't the team target Sagittarius A* at the center of ...
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3answers
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Why isn't the circumferential light around the M87 black hole's event horizon symmetric?

After the revelation of the first black hole images, it seems there is a bias towards the south side. Is it because of measuring it from earth or is it something more fundamental in the understanding ...
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1answer
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black dwarf stars and dark matter

Today we understand that a black dwarf star represents a hypothetical star that is the result of the complete consumption of the energy of a white dwarf which is the remnant of a star of little or ...
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1answer
248 views

Picture of Sgr A* [duplicate]

As a lot of you may know, on April 10th we'll get to see the so said "first picture of a black hole" from the EHT. I'm no expert in observational astrophysics, so my questions are: how are they taking ...
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2answers
1k views

Schwarzschild Radius of the Universe

According to the Wiki on the Rs, the Rs of the observable universe is 13.7BLY. https://en.wikipedia.org/wiki/Schwarzschild_radius (The observable universe's mass has a Schwarzschild radius of ...
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3answers
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Why do we have to wait half a year to measure stellar parallax

To measure distance of astronomical objects, often we may use parallax, the angle it makes with the earth-sun and trigonometry to determine the distance. The thing I don't get is why do we need to ...
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0answers
56 views

In what ways can gravitational wave research help particle physicists? [closed]

Old content (put on hold as too broad) I was massively ill-informed about the experiments that shape the modern particle physics research. For example, I believed that most of the information that ...
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1answer
146 views

Black hole photography

I recently read an article that said that the event horizon telescope took a picture of a black hole (Sagitarius A*) and it will be presented on the 10th of April. I was wondering how this picture is ...
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4answers
12k views

How can a day be exactly 24 hours long? [closed]

The longest solar day of year is approximately 24 hours 0 min 30 seconds (occurs at mid to late December) while the shortest solar day of year is approximately 23 hour 59min 38 seconds. If I average ...
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3answers
3k views

Would a galaxy be visible from outside, but nearby?

We all know the typical sci-fi image of a guy standing on the ship deck and able to see a full galaxy. If you somehow were able to stand a few lightyears away from a galaxy would you be able to see it ...
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1answer
54 views

How do I know that I am observing a quasar?

When I find a faint object on the sky that looks like a star or a far away galaxy how do I know that it really is a quasar? I guess that I could first compare the apparent magnitude (how bright it ...
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3answers
98 views

Why is a gibbous moon possible?

This could be a silly question to ask, but I would like to know why is a gibbous moon shape possible. From the few cases I've drawn here, I could not think of a configuration where the Earth's shadow ...
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0answers
59 views

What is the co-moving distance to a point, at which the late-time acceleration of the universe began?

First of all sorry for my English - it is not my native language. According to the following wonderful diagram made by Pulsar, the late-time acceleration of the universe began at $t_{acc}=$ 7.7 ...
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0answers
74 views

Query about the ion tail of a comet

I understand that the solid gas coating the nucleus of a comet is melted and that this gas is ionised by the UV rays from the sun. This makes the gas particles charged. What I dont understand is why ...