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 reason we originally and still use the non-SI unit, the Jansky?

The Jansky is the unit for spectral flux density. It is defined as $1 Jy = 10^{-26} W m^{-2} Hz^{-1}$ in terms of Watts per square meter per Hertz. I've never quite understood why this unit was ...
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13 views

How exactly does a solar flare cause a power line surge?

I'm sure we nearly all know about the occasional electrical blackouts caused by solar flares. My question is what affects the severity of the problem? It obviously depends on the energy of the flare, ...
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23 views

Precession of Mercury (Python simulation)

I was trying to simulate the precession of Mercury based on the perturbed solution, and my questions about its implementation in python can be seen here: ...
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1answer
67 views

How is “little h” measured in cosmology? The dimensionless parameter from the Hubble constant, H_0

Hubble's law has been well-know for close to a century now. It is written as $v = H_0 d$ where the Hubble constant $H_0$ is the constant of proportionality between recession speed $v$ and distance ...
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19 views

Magnification: Microscopes Telescopes

What is the difference between the way a microscope magnifies say a star and a telescope say a cell? Why is it, that the eyepiece of a telescope magnifies stronger when it is smaller and with a ...
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834 views

How many observations are needed to determine a comet's orbit?

Based on the following facts: We have Kepler's laws of planetary motion. We have a good knowledge of the positions and orbits of the gravitationally significant objects in the Solar System. We can ...
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21 views

observational-astronomy

I am looking for the current location of the line of apsides in tropical astrological coordinates; I tried using the sun's position at the time of earth's perihelion, but the results vary too much. ...
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16 views

Have we any reliable means of predicting solar flares or CME's

Helioseismology is the study of solar waves (and not solar seismic activity), as per Wikipedia. My question is: Can sound waves within the sun be correlated with flare activity or solar mass ...
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1answer
70 views

Drift of Earth's orbit?

How much has Earth drifted (inwards or outwards) from its orbit about the sun? Or has Earth has not moved at all, compared to, say, 1000 years ago? 10,000 years ago?
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140 views

Mass and distance of the bodies of the solar system?

This might be a bit of a historical question in nature. Obviously given that we know the constant G, the mass of the sun, and the distance between a solar body and the sun we can calculate it's mass. ...
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15 views

How do I compute the galactic cooridinates of the Earth for a given date?

The question is simple enough, but I wasn't able to find any tools online. Does anyone know of one, or a simple formula?
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1answer
10 views

numerical galaxy morphology classification scheme

For an assignment, I've been told to divide up the galaxies with a Virgo Cluster Catalog number into early and late-type galaxies using the GOLDMine database, http://goldmine.mib.infn.it:8080/ ...
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2answers
40 views

Explain relationship between angular diameter distance and luminosity distance, Etherington Theorem

I have a question relating to the Etherington Theorem. The luminosity distance is defined by the equation for flux, i.e. $F=\frac{L}{4\pi D_L^2}$ where flux is in units energy per unit time ...
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22 views

Can you explain in mathematical term of how the moon makes the earth spin stable?

I heard that our moon keeps the earth's rotation at the same angle. This is, as the Science Channel explained, is essential for regular seasons on earth. I am not interesting in the fact why it is ...
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1answer
56 views

What is the precise definition of “cadence” in astronomy?

I'm finding it difficult to find a precise definition of "cadence" in astronomy. This term is commonly used to describe the data of astronomical surveys. For instance, one of the data products for the ...
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2answers
64 views

Olbers Paradox Solution

Olbers’ Paradox says that in an infinite universe every line of sight will end on a star. Surface brightness is independent of distance (moving a star further away makes it smaller and reduces its ...
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0answers
27 views

How accurately do Airy discs need to be superimposed in an optical interferometer to create fringes?

In an astronomical optical interferometer, what is the largest amount of error in the alignment of the Airy disks of point source star images from different arms of the interferometer that will still ...
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30 views

Need help with which books I should buy [duplicate]

I need some help with witch books i should read. I would like to study science, physics, quantum physcics, astrophysics and all other kind of physics. Hit me with the best books inside of thoes ...
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2answers
81 views

How do we measure distance using parallax?

This is a quick mock-up of how stars are measured using parallax method. My question is : How on earth (literally) do we measure the anfle $\theta$? Is theta measured from the zenith of Earth? ...
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13 views

How do I calculate the right ascension of the ecliptic at the points where it intersects the horizon?

Given an observer's location on the Earth's surface, and time, how do I calculate the right ascensions of the points along the ecliptic where it intersects the observer's horizon?
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25 views

Accretion disks on neutron star binaries

Why does hydrogen gas from accretion disks not constantly get sucked onto/into a neutron star or into a black hole? I understand that some gets sucked into the black hole and some may come down and ...
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0answers
24 views

Who orbits who? Earth or Sun [duplicate]

We always say that the earth orbits the sun, but how can we prove this? Could we not say that the sun orbits the earth or that the earth orbits Mars?
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1answer
59 views

Can you use pulsar observations to determine absolute time? How long can you go without anything else?

In this old answer of Steve Allen's, he quotes this nice passage Imagine for a moment what would happen if, just as a practical joke, someone found a way to stop all atomic clocks, just for a ...
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1answer
68 views

Do the arms of a spiral galaxy spin around like a candy bar in long spirals?

Because the arms of a spiral galaxy have a linear center, perhaps they rotate around their center same as a candy bar spiral or a spiral of smoke? Have similar movements within galaxies been measured? ...
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1answer
90 views

Do we actually measure distances in light years?

The cosmic distance ladder has a wide range of length scales, which are quite difficult to measure and to conceptualize. These distances are commonly quoted, particularly in less technical articles, ...
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38 views

Color of objects in Yellow sun

The sun appears yellow but the objects on the earth appear as if they have been illuminated in white light. Are all objects that we see in sunlight actually in a yellow shade, and would appear ...
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26 views

Perturbations of planetary Orbits

I have, for years, been an Astronomy and physics nerd. For the first while, I was a total astronomy nerd. Then I slowly transitioned into physics and have been, for less than a year, a physics nerd. ...
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1answer
90 views

Is there a map which shows all the black holes in our galaxy?

I am looking for a map which shows all black holes in the Milky Way. See this exoplanet map for what I mean. If it is not existing (yet). Is there at least an online catalogue which summarizes for ...
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1answer
40 views

Why is the lyman alpha line asymmetric at high redshift?

If someone could explain this to me I'd be very grateful, thanks.
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5answers
1k views

Why is the sky of the moon always dark?

Why is the sky of the moon always dark compared to the sky of the earth, doesn't it have day and night like earth?
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34 views

Which technique is used to measure huge astronomical distances which are in terms of billions of light years? [duplicate]

I know what a "light year" means. However, I am very curious to know about the technique through which scientists are able to calculate the distance of various astronomical bodies from earth which are ...
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1answer
57 views

Redshift of supernova light curve

I am trying to understand how the width of a supernova light curve depends on the redshift of its component frequencies. Let us make the simple assumption that the light curve is Gaussian. The ...
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1answer
55 views

Where else is there fire?

Apart from on Earth, where else does fire occur in the universe? I'd hazard a guess that it is quite rare for oxidation to occur naturally, could someone elaborate on this?
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1answer
92 views

Using nuclear bombs to detect near earth orbit objects

This question is based on an article written some years ago by A. C. Clarke, in which he attempted to solve two problems with one solution. His idea was to remove the Earth's stockpile of nuclear ...
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30 views

Structure formation: growth of density perturbations in sub-horizon vs super-horizon scales

I've always had difficulty visualizing how sub-horizon scales work versus super-horizon scales. Inflation causes perturbations due to quantum fluctuations. These are under-densities and ...
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1answer
56 views

Calculating the area of region of the sky

I am given the right ascensions ($\alpha_1$ and $\alpha_2$) and declinations ($\delta_1$ and $\delta_2$) of a specific region of the sky. How can we find the area of this region? I know that there ...
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1answer
66 views

Photometric surveys vs. Spectroscopic surveys

I consistently read about certain astronomical surveys which are either described as "photometric surveys" or "redshift surveys". I'm still unclear as to how these two methods differ. Photometry ...
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1answer
81 views

Mass-to-light ratio and rotation curve from brightness profile

This should probably be basic but I've been looking for days and I can't find how to (I'm probably over complicating, but still). I want to calculate a rotation curve for some spiral galaxies. From ...
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1answer
66 views

If there were intelligent life in another galaxy, would we notice? [closed]

I've read that once intelligent life successfully achieves interstellar travel, it could populate the galaxy in tens of millions of years, likely populating the most habitable planets and preventing ...
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0answers
57 views

What prevents Digital interferometry in an optical telescope array?

I understand it is common to combine an array of radio telescopes in to a single instrument using interferometry. This has the photon collecting area of the combined radio telescopes but an aperture ...
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1answer
313 views

How to tell if a star is in a galaxy?

An astronomer is studying a star that appears to be in a galaxy. How does the astronomer know the star is actually in the galaxy and not just on the same line of sight as the galaxy? I'm guessing ...
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3answers
88 views

What is meant by a “sodium line”?

What speed should a galaxy move with respect to us so that the sodium line at $589.0\ \mathrm{nm}$ is observed at $589.6\ \mathrm{nm}$? In the above question what's meant by a sodium line? The ...
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0answers
17 views

For a Plummer model mass distribution, what is the timescale of dissolution?

Given an initial system of masses distributed in a Plummer model close encounters cause stars to gain enough energy to leave the system. What is the timescale over which the whole cluster with N ...
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0answers
23 views

from right ascension and declination to angle from semi-major axis

I am working on a research project and having trouble converting from ascension and declination to angles with respect to the semi-major axis. The target coordinate system has its origin at the ...
5
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1answer
83 views

Experimental Data for Mass Distribution of a Galaxy

My goal here is not to discuss dark matter in general. I know there are many other observational clues that hint us towards Dark matter. My goal is simply to understand this argument here a little ...
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0answers
67 views

CMB parameter, what's the meaning of the matter power spectrum normalization sigma_8?

Most CMB experiments like WMAP and Planck include a certain cosmological parameter called $\sigma_8$. My understanding is that normalization of the matter power spectrum is not a theoretical ...
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1answer
80 views

What is the direction of our solar system in the Milky way galaxy and in the universe?

What is the direction of our solar system in the Milky way galaxy and in the whole universe? Are we heading toward another constellation, not including Andromeda?
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1answer
233 views

Difference between Gunn Peterson trough and the Lyman Alpha Forest? Cosmological implications?

I'm having difficulty understanding the full implications of the Lyman alpha forest and its use in cosmology. My understanding is this: we detect features in the Intergalactic Medium (IGM) by very ...
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3answers
150 views

Are some sources of electromagnetic radiation theoretically (or perhaps technically!) more challenging to detect than others?

In a previous question, I learned that in order to detect an object in space, what matters is how much electromagnetic radiation it is giving off, and what sources of EM radiation the sensor can pick ...
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78 views

What are the coordinates of the center of rotation of our galaxy, relative to ourselves?

So standing outside in the garden, can we physically point to the center of rotation of the galaxy? I understand that from our viewpoint on Earth, it would be a moving point, so allowing for Earth ...