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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Projecting a star at the elongation between a point on the earth and the center

I am trying to find the alt/az of a ' infinitely' far fake star that would exist right above a certain point on the earth. So let's say we want a point above Stockholm at 58, 18 deg and then observe ...
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How do we know the Moon has a 0.50 angular degree from us?

Before we knew the distance to the moon, how can you get the exact angular degree of it without knowing the distance to it? Obviously you can just guess or assume but how was it first calculated?
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On the Rømer experiments and the speed of light

In 1676, Rømer determined that the speed of light must be finite. His experiment consisted on observing the eclipses of Io, one of Jupiter's moons, by Jupiter itself. He timed these eclipses over a ...
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Determining accurate value of Hubble constant [closed]

All the methods for determining the value of Hubble constant are based on the received lights redshifts from distant galaxies. my question is why can't we do the experiment locally? we have a ...
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Is the observable universe equivalent to 'our' light cone?

All the objects we can observe (stars, galaxies, ...) must be in our past light cone, since otherwise we couldn't see them. Presumably there are more objects located outside of our observable universe ...
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Can we determine the date just from sky observations?

Assuming everyone "freezes" for several thousand years. Then everyone unfreezes at the same time. Could we tell how much time passed based on sky observations without fancy telescopes? (Just started ...
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Spectrograph difference between cross disperses and echelle gratings?

In echelle spectrographs, the presence of echelle gratings and cross-dispersers is common. What task does each one perform? Why are the cross-dispersers needed?
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How do we get the image of a black hole? [duplicate]

According to Einstein's theory, nothing can travel faster then light and also a black hole doesn't allow light to escape but recently scientists got an image of a black hole. Here I am confused: if ...
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Does the direction of Earth's axial tilt change over time? In relation to the sun? What about the 'pointy ends' of our ellipse?

Does the direction we are tilted change in relation to the background stars? And the points where our ellipse is pointiest? (most elongated?) Does this change the timing of our aphelion and ...
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Consistency with calculating the Solar Azimuth Angle

I am struggling to find consistency regarding the calculation of the Solar Azimuth Angle. The equations across multiple publications have similar terms, but differ significantly. These differences ...
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Can a planemo turn into a star?

I read this question Why is planet CFBDSIR2149-0403 hot? and wonder what will happen to this "planemo". Will it attract more mass as it flows around in the gas clouds in space and eventually light ...
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Relation between distance, sizes and angular diameter?

If we pick up a ruler and look at it and at the sky at the same time we can have the moon be completely inside the ruler or if we add distance between the ruler and us the moon will become apparently ...
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Is there a way to see the sun's outer layers from earth outside a solar eclipse using polarization?

¿Is there a way to filter sky light using light polarization? in https://en.wikipedia.org/wiki/Coronagraph#Invention it says: High Altitude Observatory's Mark IV Coronagraph on top of Mauna Loa, use ...
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How do I transform flux density into temperature?

I have flux density data from Planck mission (in Jy) - measure in a certain frequency - and I would like to transform it to temperature data (Kelvin). I'm not sure if I should use Stefan Boltzmann's ...
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Angle $\phi$ in astronomical coordinate transformations

I was reading about the transformation between horizontal coordinates (Alt-Az) and equatorial coordinates (RA-Dec) from Fundamental Astronomy by H.Karttunen. In the image, one can see the angle $\phi$...
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How do we determine both the distance to and speed of distant stars?

My understanding is that we can measure the distance to far away stars by using their color to infer the absolute magnitude of the light they emit and compare that to the observed magnitude of the ...
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How can I deduce a probability using a Kroupa IMF and a set of observed stars along a model isochrone?

I’m plotting a colour magnitude diagram for an open cluster and setting it against a few model isochrones. I want to deduce the probability that the cluster belongs to one or the other isochrone, but ...
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Why were pulsars not discovered in the visual spectrum?

In 1967, the first pulsar was discovered at a radio observatory in Cambridge. Radio astronomy started around the 1930s, but astronomy in the visible part of the spectrum had been done for a long time ...
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Could a soft telescope be created?

Everyone knows of the issues the Hubble had with its primary mirror. But could a space telescope be created that used a reflective material such as Mylar or other very reflective material? Would it ...
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How can a non-rotating black hole or singularity be created?

Every star or other massive body in the universe rotates, if only a little. If such a body collapses, its spin, any spin at all, and thus, angular momentum approach infinity as r approaches 0. Angular ...
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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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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 ...
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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 ...
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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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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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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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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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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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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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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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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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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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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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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 ...