eshaya
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Can lightning occur in stars like the Sun?
38 votes

Stars are not actually gaseous, they are plasmas, i.e., highly ionized. Hence, the entire star is highly conductive and does not easily develop the voltage difference via friction needed for lightning ...

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What is the cause of all of these sharp, concentric rings around bright stars in this HST image?
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8 votes

The diffraction pattern at the focal plane created by a circular aperture is called an Airy Disk or Airy Pattern. Both the outer opening and the inner hole plus secondary contribute to the exact ...

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Age of the universe and time dilation
8 votes

In the standard model, the universe looks the same for all locations moving in the local rest frame. This includes its apparent age. You can tell if you are in the local rest frame if the expansion ...

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Is it possible to break apart a neutron star?
8 votes

One problem is if you split a NS into too small pieces, the gravity of each piece becomes weaker, and with the pressure reduced, it may no longer be highly degenerate. The minimum neutron star mass ...

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Could light be dark matter?
7 votes

Most of the light energy in the universe is still in the cosmic microwave background (CMB). Spring 2011 UC Berkeley Physics 250 class materials calculate from the fact that $T=2.73$ for the CMB: It ...

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Is there an equivalent of the red shift effect for cosmic rays?
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6 votes

Yes, there is a "retardation of the co-moving velocity" of particles. It is important to take it into account to understand the time history of peculiar velocities of galaxies and for ...

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Does this amateur observation hold a record even including robotic searches for supernovae?
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5 votes

No, supernovae have been observed earlier and with better cadence than this one. The Kepler Satellite has been observing galaxies at a 30 minute cadence from months before the supernova explosion to ...

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Why is carbon so rare on the Moon and on Mars?
5 votes

Although carbon is highly abundant in the universe, it is not homogeneously distributed. Some regions of the interstellar medium could be rich in carbon and others rich in silicon or oxygen, ...

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On (minuscule) dark matter production in supernovae
5 votes

There are several types of supernova and ways that the core can collapse. Lets take an extreme case in which gamma-ray photodisintegration destroys all of the heavy elements (Si, Fe and Ni, etc) and ...

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How bright are the outer planets, when at close range?
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4 votes

There is a rule about average surface brightness: it is conserved as you change distance or magnification. For the gory details see. Telescopes make unresolved objects brighter, but for resolved ...

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Origin of heavier elements on earth?
4 votes

Supernova ejecta expand at velocities between 5,000 km/s and 30,000 km/s. Lets take 10,000 km/s as typical. The speed of light, c, is 300,000 km/s, so 10,000 km/s = c/30. So, it would take 120 years ...

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What kind of a visual trajectory would an asteroid have if it were to hit Earth?
4 votes

There is no simple answer to this question other than: you have to do the math. Most often you would see the asteroid brightening more rapidly and moving across the sky faster as the days pass, but ...

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Are exo-meteoroids possible?
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4 votes

Most, and perhaps all, stars form in stellar clusters. Most likely, the sun formed in a open cluster. In clusters the density of stars is quite high, therefore close encounters are common. So, I ...

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Do Noctilucent clouds cause problems with telescopes?
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4 votes

Noctilucent clouds are not a problem for space telescopes because their orbits are always more than 85 km. The Hubble Telescope orbits at about 570 km. Noctilucent clouds are a problem for ground-...

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Why aren't secondary mirrors offset to get rid of diffraction spikes due to the support vanes?
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4 votes

There is a 1.6 meter off-axis telescope for solar observation at Big Bear Observatory called the New Solar Telescope (NST). Off-axis is particularly helpful in solar observations because it reduces ...

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Standardized "constellation" regions?
4 votes

Modern astronomers are not instructed on the constellations and pay little attention to them except as a naming convention for stars. Positional information is nearly always either equatorial (ra,dec)...

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How many new galaxies enter the observable universe each day/year/decade?
4 votes

What we see at the outer reaches of the observable universe is a surface of the cosmic microwave background (CMB), which is at the time when the universe, still quite homogeneous (perturbations were a ...

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Could supermassive black holes form in dwarf galaxies?
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4 votes

The prediction was that dwarf galaxies have SMBHs, but with smaller masses than regular galaxies. This was based on the idea that regular galaxies were built from dwarf galaxies and the BHs need to ...

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Dark Flow: statistical limits on existence
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4 votes

The dipole in the microwave background indicates motion of the Milky Way and thus of the whole Local Group, at least, at about 600 km/s in a certain direction. The straightforward explanation is that ...

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Deep space radiation distribution
3 votes

If you were in deep space, i,e., a spot somewhere between galaxies, then the night sky would look a lot like the sky seen by astronauts in the ISS, when they look away from both the ecliptic plane ...

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Light pollution and apparent magnitude of objects in solar system
3 votes

The answer is yes: dust is highly constrained to the ecliptic plane and so viewing from above the plane would result in less light that needs to be subtracted from observations of the solar corona. ...

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Real images (not "artist concept") by NASA
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3 votes

NASA mission data is archived at a handful of NASA archives. If you do not know which archive a data set is in, then you can search the Master Catalog at the NASA Space Science Data Coordinated ...

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How do you calculate length of day in a multiple-star system?
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3 votes

Are you asking how to measure a day for an exoplanet? Because that is pretty hard given that they are far away and hard to image their surfaces. But, if you are asking how to define the day, say for ...

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Is the angular resolution of a telescope irrespective of used eye-piece?
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3 votes

The resolution of a telescope is the resolution of the image created by the primary mirror at the focal plane. It provides the minimum separation between two equal brightness stars that appear ...

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Do Roche limits apply to black holes?
3 votes

Because the density of the matter at the center of a black hole is infinite (or nearly so) the Roche Radius is 0 (or nearly so). Two black holes in orbit spiral in towards each other because they ...

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Why does Jupiter break comets apart?
Accepted answer
3 votes

It is. Tidal disruption occurs when $\rho_{Jup}(R_{Jup}/R)^3$ > $\rho_{comet}$ where R is the separation and $\rho$ is the density. The density of Jupiter is 1.33 g/$cm^3$ and the comet was ...

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Could a space radio telescope fill multiple purposes?
3 votes

See http://en.wikipedia.org/wiki/HALCA and http://en.wikipedia.org/wiki/Spektr-R. HALCA was a Japanese 8 meter radio telescope satellite used for Very Long Baseline Interferometry (VLBI) from 1997 to ...

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Fate of lone spiral galaxies?
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2 votes

I think there are a few misconceptions floating around here. The Hubble Sequence is not a sequence in time. Hubble did not mean to imply that galaxies flow from one side to the other in the sequence ...

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Does the Zwicky Transient Facility only run when triggered by a cell phone?
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2 votes

The ZTF is operating on most clear nights on an automated queue of pointings. When they discover transients, they inform TNS which may trigger other observatories to point at the same object, just as ...

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Is this the best non-radio image of whatever's at the center of M87? How was it taken?
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2 votes

Your top image is this from Dr Jean Lorre stock science images. Just a photo showing stars and the optical jet with a 22 MB CCD camera through a small telescope. It is unfortunate that he chose a ...

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