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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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Atmospheric Optical Thickness from flux

Is it possible to calculate or estimate the atmospheric optical thickness given a measured flux? And if so, how?
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Is there a bound on the number of sterile neutrinos from cosmological observations?

The right-handed sterile neutrinos $\nu_{R}$ are electroweak singlets. They do not contribute to the electroweak anomaly, and therefore, their number is not fixed by the requirement of the anomaly ...
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What's equation for average daily amount of solar energy per $m^2$ by latitude and time of year? [on hold]

It feels like it should be fairly simple math problem, but I forgot all trigonometry.
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1answer
25 views

What is the least energy trajectory in Astronomy?

Hi I wanted to know what the least energy trajectory is in relation to astronomy as I can't seem to find a good answer on Google. I want to know because I am trying to answer this question: A ...
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3answers
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Thought experiment. Earth orbital motion if we stopped Earth spinning

This is a thought experiment that puzzles me. Imagine we could magically stop Earth’s rotation around its own axis (and locally verify it by disappearance of inertial forces generated by the spin ...
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Doubts with the formation of bullet cluster

The bullet cluster is formed by the collision of two clusters of galaxies. After the collision, the stars and galaxies in those two clusters passed through each other. But the intergalactic gas clouds ...
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What is the most measurable electromagnetic wave coming from a small, dark, and not necessarily hot object in sky? [closed]

Optical fibers are recently used to generate some spectroscopic surveys of the universe map based on some projects such as DESI, MOONS, SDSS-V, etc. The current fibers are often sensitive to visible ...
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1answer
88 views

Did Eratosthenes make his measurements on the same day?

Erasthosenes measured the circumference of the earth on the summer solstice by observing the sun at Alexandria and Syene. Was this done on the same day in one year or on the same day in two ...
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What are the starting units to perform the Gauss method?

To calculate the Gauss method, we need : the respective geodetic latitude the equatorial radius of the body (here earth) the respective local sidereal time the respective declination the respective ...
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1answer
36 views

What is Earth's current true anomaly from j2000?

I enjoy amateur astronomical calculations. I calculate earth true anomaly and noticed a bug in my software just as earth passing through j2000 point and instead of going to 0 degrees it subtracting ...
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1answer
77 views

'Harmony of the Spheres' or 'Harmony of the World' - is it debunked? [closed]

I sincerely apologise for this vague question but I'm writing an essay for my music class on musical harmony and it's historical origins. I came across the Pythagorean notion of Harmony of the Spheres ...
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Show me how the sky is like in Jupiter (but not mars)

Assuming someone is "standing" on the "surface" of Jupiter (ok, in a stable position deep inside the gas giant's gravity field analog to standing on the surface of a rock planet) where the moons can ...
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1answer
38 views

Does cosmological homogeneity imply that density is also the same?

So I know that at sufficient scales, the universe looks the same (Same average amount of galaxies, clusters, stars, etc). Does this mean that at these scales the density of the universe is also the ...
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Strength of core-envelope coupling in stars

For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope? I understand that the core-envelope boundary is only (...
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1answer
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What do “broad” and “narrow” mean in the context of spectral lines?

For example, at this page: http://pages.astronomy.ua.edu/keel/agn/spectra.html it talks about some lines being broader than others. But they all look the same width to me. I feel like this is ...
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Stellar aberration: distal or local? Experimental proof?

Stokes put forward the theory (I am simplifying here.) that stellar aberration takes place out in space and that light from stars is already fixed in direction with respect to the Earth's surface by ...
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Where did the energy from the CMBR go? [duplicate]

Basically the title. The wavelength of light from the CMBR has expanded as the universe expanded and so it has lost energy since it is inversely proportional to the wavelength. Where did this energy ...
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2answers
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Does the Sun cause star to appear in the sky on two different positions?

So, I was reading A brief history of time and it was talking about the sun bending the light of a star causing it to appear on a different place from where it actually was located. I was wondering if ...
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1answer
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What is the solar wind speed as function of distance from the Sun?

Someone must have calculated at least a "zero-order approximation" of the behavior of solar wind speed, density, and pressure as a function of distance from the Sun, but the heck if I can find it. ...
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2answers
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Why do we say the three-dimensional space is flat (in Physics)? [closed]

This is quote from Hawking's book: The surface of the Earth is what is called a two-dimensional space. That is, you can move on the surface of the Earth in two directions at right angles to each ...
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2answers
39 views

Introduction to Astronomy books

I am looking for a book that covers an introduction to astronomy. Currently, I am reading Introductory Astronomy and Astrophysics, by Zeilik and Gregory. However, I quickly noticed that it is much too ...
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1answer
28 views

Optics of an all-sky camera

I'm curious about the optics of an all sky camera like this one or this one. My suspicion is that the sensor has an inherently wide field of view - the former has a lens that's 1.55, which doesn't ...
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1answer
92 views

Milky Way Density

It seems to be a simple question, but I wasn't really able to find an appropriate answer: How dense is the Milky Way? I am certain that there are reliable statistic, maybe even new ones from the GAIA ...
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1answer
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Difference between Airy disk and seeing disk

In the diffraction pattern for a circular aperture, instead of just having a circle, we have a central disk and several faint rings around the circle. Does the Airy disk consist of only the central ...
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1answer
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What will be the expression between conformal time and scale factor for $\Lambda$ CDM model (for $k=0$, $\Omega_M + \Omega_\Lambda = 1$)?

An approximation of the relationship between the scale factor and time for our universe is given by the following expression: $\displaystyle a \approx \left (\frac{\Omega_{M_0}}{\Omega_{\Lambda_0}}\...
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2answers
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Why are there so many different “colors” in the line spectra of simple elements?

I understand that atoms emit photons of wavelength $\lambda$ when electrons transition to lower orbitals according to the equation $E = \frac{hc}{\lambda}$. Based on my understanding, those orbitals ...
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How massive is the Sun compared to other stars?

I was just reading "Rare Earth" by Peter Ward and Donald Brownlee and they claim that $95\%$ of stars are less massive than the Sun. But, I was always told the Sun is an average star. Which is it?
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Convergence of Milky Way and Andromeda

It is definitely a certainty that Andromeda will collide directly with the Milky Way in ~4 billion years. Has it been estimated how long the two galaxies have been attracted to each other to the ...
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1answer
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How is red colour from from rainbow hotter than blue (W. Hershel) if it has lower frequency than the latter?

We know that blue light has a smaller wavelength and higher frequency than red light, which is a consequence of higher energy in the former, then how is it true that, when scattering light from the ...
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UVES relevance in science?

What has been to this date the most important discoveries/breakthroughs brought on by UVES (VLT) data? What is the most relevant research using UVES at this time?
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1answer
80 views

If the Sun moves across the ground at 0.25 nautical miles per second, why do shadows move very much slower? [closed]

This title has been discussed previously on this site here. Question: Shadows from the sun moves fairly slow across the ground. Maybe a centimeter per sec. however, I calculated that the sun is ...
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1answer
44 views

Speed of solar system through dark matter halo

How is the speed of the solar system through the dark matter halo determined? Direct dark matter detection experiments rely on this speed estimate. Assuming the sun/earth travel through the dark ...
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Bose-Einstein distributions when combining different sources of photons

In a telescope, the photons coming from the object you want to observe will pass through a lens, which emits its own photons from heat. It's possible to calculate a B-E distribution from both these ...
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Can amateurs use the retroreflector on the moon? [duplicate]

There is a retroreflector on the moon, placed there, I believe, by astronauts in the 1970s. I think there is at least one station (in France?) that continuously beams a laser at it to measure the ...
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1answer
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Transit of Venus and the computation of the Atronomical Unit

I have searched for the computation of the AU. The two best websites I found about it were https://sunearthday.nasa.gov/2012/articles/ttt_75.php How did Halley calculate the distance to the Sun by ...
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2answers
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Why does transforming from equatorial coordinates to galactic coordinates require 3 equations?

My question seems self explanatory but still: In transforming equatorial coordinates to galactic coordinates or the reverse you have to solve a well known system that has three equations. Since ...
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1answer
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What is the diameter size of the umbra shadow cone of the Earth when the Moon passes through it on a lunar eclipse?

I am sure this varies given the distance from moon to earth varies, but a range would be sufficient. I am trying to explain to a flat earther how there is not a lunar eclipse every full moon. My ...
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2answers
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How to tell if the moon is waxing or waning?

Imagine you are placed in an unknown location in the middle of the ocean. You see the moon at its half. Which are the different "sets of information" which, if provided to you, would allow you to ...
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1answer
127 views

Convert sexagesimal to decimal

I've been studying astronomy and I've encountered 3 different (sexagesimal) ways to write angles. hh mm ss - hours minutes and seconds dd '' '''' - degrees, arcminutes and arcseconds. +/- dd mm ss -...
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Nature of peaks in the CMB power spectrum and the underlying physical processes giving rise to them

The power spectrum is the Fourier transform of the two-point correlation function of a noise $X(t)$ where $t$ is time. It gives us the frequency content of a noise or in other words, tells how much ...
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Are there stars that wouldn't look white to the naked eye? [duplicate]

I have a small YouTube channel in which I make videos about topics relating science and things I find interesting. The topic I'm working on recently is on the color of the sun. What I thought at the ...
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1answer
67 views

Calculating the Earth-Sun distance

Using just the facts that the period of earth around the sun is 1 year. that the distance of 1 degree of latitude on earth is 100km . that the acceleration due to gravity on earth is 10m/s^2 and that ...
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Arago spot on terrestrial object

Here is a question that occurred to me considering Fresnel's theory and Arago spot: Is there a bright spot on the surface of the moon in a lunar eclipse? If No Why? If Yes, have we ever make an ...
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1answer
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star gazing from the bottom of a well

I have read that it is a myth that you can see stars in daylight if you stood at the bottom of a well, however, if you stood at the bottom of a well at night, or built a long non reflective tube and ...
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1answer
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Triangulating Sol's position from another star

Let me pose this question as a hypothetical. Your ship makes a warp/jump through space. There's a malfunction. You're definitely not at your intended destination. You've warped to an unknown star, ...
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1answer
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How does TESS focus on bright nearby stars?

How does the Transiting Exoplanet Survey Satellite "focus on" bright nearby stars, in contrast to the Kepler Mission's focus on dim distant stars? I understand that the fields of view of the two ...
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2answers
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Why does the Sun appear more round while distant stars can appear more pointed?

In a minute physics video about the shapes of stars, it mentions that stars in the night sky appear star-shaped due to imperfections in our eyes known as suture lines which cause diffraction. Then ...
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1answer
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Living at the equator (Colombia), how to figure out the orientation towards north using the sun falling through a window?

The real life issue is this: A friend is moving to a new apartment. What is bad here, is if the apartment is getting full sun in the morning or afternoon. So the Sun goes from east to west, right? If ...
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2answers
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Is the astronomical magnitude identical to the distance? [closed]

Why do astrophysicists use Magnitude rather than the actual distance to calculate intergalactic parameters? The magnitude is the relative brightness and has no units, the typical distance requires the ...
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1answer
75 views

Is there any moon without its planet?

Is there any planet without its star? Is there any moon or any planet wandering in outer space without a definite orbit? (The name moon or planet used here serves only for size and spherical shape ...