Thomas
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Why doesn't the Sun produce an emission spectrum?
12 votes

The photosphere of the sun does produce an emission spectrum (a Planck spectrum according to its temperature of about 6000K). It is only that the atmosphere above the photosphere (the chromosphere) ...

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Density of Plasma in Solar Corona
7 votes

It depends on which region you consider. The lower corona has a plasma number density of the order of $10^9 cm^{-3}$, the upper corona about $10^5 cm^{-3}$. This is all quite variable though, ...

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How does NASA figure out orbital period and mass data for planets and other celestial bodies?
7 votes

Yes, NASA uses indeed Kepler's 3rd law to calculate the orbital periods of planets and other objects in the solar system. If you go to NASA's Horizons Website and generate orbital data for a planet ...

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What does the Sun "look like" below 100 MHz?
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7 votes

Below about 300 MHz you can only see the sun's corona as the frequency is too low to penetrate the coronal plasma from further below. In Wikipedia's Solar radio emission you can see images of the sun ...

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Would we have spotted the ascent stage of Apollo 11's Eagle if it was still in orbit around the Moon?
7 votes

There are a couple of inconsistencies with theory presented in the video and the paper it is based on. Apparently, the author(s) are suggesting that Eagle did not crash as it was/is in a 'frozen' ...

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What are the experimental limits to the residual charge of the Sun?
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6 votes

Some of the comments here seem to be suggesting that there should not be any residual charge of the Sun at all because of the fact that in a conducting medium no electric fields can exist. This ...

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Could someone explain what is wrong with my telescope, and what should I be able to see with it?
5 votes

Even if your telescope is correctly set up, its short focal length of 650mm is not ideal for observing details of the moon and planets. You should get one or two more eyepieces with a shorter focal ...

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How was the speed of the Sun (around the Milky Way Galaxy) calculated?
5 votes

The rotation of our Milky Way in general is derived from observations of the kinematics of gas and stars throughout our galaxy. See for instance a recent compilation of Milky Way rotation curve data ...

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When could solar eclipse happen in a way that Sun's disk is diminishing from below?
Accepted answer
5 votes

If you regularly observe the moon, you know that it rises later each day (by about 50 minutes) due to the fact that it orbits earth in the same direction as earth's rotation (so earth has to rotate a ...

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Is there molecular hydrogen in the Sun's atmosphere? If so, how much, and how was that first determined and measured?
Accepted answer
5 votes

According to Formation of the UV Spectrum of Molecular Hydrogen in the Sun (S. A. Jaeggli et al. 2018 ApJ 855 134, also here) molecular hydrogen in the sun was first spectroscopically discovered in ...

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How big is the Lorentz force on the Sun?
4 votes

Due to the fact that electrons can escape the gravitational field of the sun more easily than ions, the sun is positively charged by an amount $q=77$ Coulombs (see https://www.aanda.org/articles/aa/...

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How did Astronomers mostly(?) agree to publish arXiv preprints along with peer-reviewed Journals? Was there pushback?
3 votes

It is the usual policy of publishing companies (as per their terms and conditions) that you can publish preprints of the submitted manuscript on non-commercial websites, not only on arXiv but also ...

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Spectrum of stars
Accepted answer
3 votes

'Absorption' lines are caused by resonance scattering (scattering the radiation out of the line of sight, see illustration below), and resonance scattering has a very large cross section of roughly $...

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What is precision of planet periods data?
2 votes

The planetary orbits can not strictly be described by the usual Kepler elements anymore as they are disturbed by the other planets (Saturn in particular will for instance be heavily affected by ...

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Massive star formation
2 votes

The crucial point here is that the initial large cloud does not have a constant density throughout but contains many random smaller blobs with a higher density. Because of the higher density, these ...

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Are there stars with an average density greater than the central density?
2 votes

A density increasing with distance from the center is impossible for a star in hydrostatic equlibrium, regardless of the temperature profile (assuming the ideal gas law holds). In fact, the density ...

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Would we have spotted the ascent stage of Apollo 11's Eagle if it was still in orbit around the Moon?
2 votes

I first wanted to edit this into my other answer here, but since this, even though being highly relevant for the issue, does not directly address the OP's question(s), I decided to add this as a ...

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Is the barycenter of the solar system usually outside of the sun?
2 votes

Not a direct answer to your question (which others have given already), but maybe still worth considering here: The dynamics of the solar system can to a high degree of accuracy be calculated by ...

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Kepler's Law, focal points - Heliocentric or Barycentric?
2 votes

Kepler's laws and the associated orbit only hold for a two-body problem, so the 'barycenter' in the question can only be understood as the center of mass of the sun and a particular planet (ignoring ...

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If an orbit is shifting due to orbital precession, is it still a Keplerian orbit?
2 votes

It depends how you define 'Keplerian orbit'. A precessing orbit can obviously not be represented by a stationary ellipse anymore, but it is essentially still the same ellipse, merely uniformly ...

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How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?
1 votes

The jump occurs at the redshifted wavelength of the Lyman-$\alpha$ line, so this is the Gunn-Peterson trough, which is caused by neutral hydrogen in the intergalactic medium suppressing any radiation ...

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Was the young Sun cooler or hotter than it is today?
1 votes

You are asking the wrong question for the problem at hand. It is the luminosity of the sun that determines earth's temperature, not its temperature. And you can see from the diagram below that during ...

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Lunar Eclipse and relativity
1 votes

A lunar eclipse as seen from the moon is actually a solar eclipse (by the earth). This should definitely be better to time than the lunar eclipse from the earth (which is a very 'fuzzy' event). Still, ...

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How is space a vacuum when there are planets, gases, etc?
1 votes

Space isn't an absolute vacuum. Even in intergalactic space there a few atoms in a sufficiently large volume (like a $m^3$). In some respects you can approximate it with an absolute vacuum but in ...

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Spin-down of gas-giants during formation
1 votes

The slowdown is due to 'angular momentum transfer' from inner regions of the rotating cloud to outer regions via magnetic fields. You can find a detailed mathematical explanation in terms of a ...

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What Causes the Large Radiation Fields Around Jupiter?
1 votes

The mechanism that produces Jupiter's magnetic field is in principle not any different to that which produces Earth's magnetic field. Only that in the latter case it works with liquid iron instead of ...

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Is expanding universe adding potential energy?
1 votes

A gravitationally or otherwise bound system does not expand together with the universe. The effect of the expansion is much too small to affect such systems. Our solar system had the same size as ...

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Solar wind, Earth wind and planetary winds?
1 votes

All planets lose a small amount of atmospheric gases due to some atoms/molecules (even neutral ones) having an energy high enough to escape the gravitational field of the planet. This tends to affect ...

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Is there a formula to calculate the angular speed at which the Sun apparently moves around the Earth?
1 votes

Since you said in a comment that you want to calculate astronomical twilight, here some links that may help. Some general info https://skyandtelescope.org/astronomy-blogs/astronomical-twilight/ Online ...

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Problem regarding the absorption lines of the sun
1 votes

The atmospheric layer that produces the absorption lines acts somewhat like a mirror at these frequencies and scatters the light back into the sun (although this is diffuse reflection not specular ...

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