Peter Erwin
  • Member for 6 years, 8 months
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Where do we have it from that the Moon is migrating away from Earth?
66 votes

There are, I think, at least four parts to this argument: the first being the theoretical argument that ties it all together and the remainder being observational evidence for the Moon's orbit ...

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Is oxygen really the most abundant element on the surface of the Moon?
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59 votes

Yes, that's correct; it's also true for the Earth's crust. The reason is that "rocks" are typically made up of components containing combinations of silicon or one or more metals (e.g., ...

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Is Earth's Surface "In orbit"?
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52 votes

1. Is material on Earth's surface not in free fall around Earth's center? No. Material on the Earth's surface -- or inside it -- is not in orbit, and so is not in free fall. You can temporarily put ...

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Are there any old/ancient star maps that we can compare to today’s and see drastic differences?
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43 votes

In practice, you're probably not going to get anything useful from ancient star maps, for several reasons: Very few of them actually survive from more than a few hundred years ago. Maps (and visual ...

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Are there observable changes in a star about to become supernova, minutes or hours before the explosion?
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42 votes

I think your best bet would be detecting neutrinos generated by nuclear burning inside the star (as we do for the Sun). Once the star hits the carbon-burning stage, it's actually putting out more ...

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Is it possible that the Sun and all the nearby stars formed from the same nebula?
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25 votes

There are three main reasons why we can tell that local stars did not, for the most part, form from the same molecular cloud that the Sun formed from. The first is that unless stars are born in a very ...

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Which are stars and which are noise in this comet photo?
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18 votes

Is that right? Yes. Is the fuzzy one an extended object? That would certainly be my guess (probably a distant galaxy). What causes so many isolated pixels to be so much brighter ...

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Why isn't most hydrogen in the universe molecular (diatomic), instead of atomic (monoatomic)?
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16 votes

Yes, the atomic hydrogen is probably mostly left over from the Big Bang. [Edited to add: Not sure how much that is true and how much present-day atomic hydrogen is the result of recombination.] And, ...

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Why is Starlink polluting the night sky a big concern if we have space telescopes?
15 votes

To expand on the "space telescopes are expensive" aspect: Space telescopes cannot be maintained or repaired. This applies not just to things like optics and instruments, but also to space-...

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How can the (in my eyes quite ridiculous) conjecture of Sheldrake be disproven?
14 votes

To be fair, Sheldrake credits Greg Matloff (2015) for this "dark matter is really the motions of 'volitional stars'" idea. It's easy enough to show this won't work (I mean, aside from all ...

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Is a kilonova bigger than a supernova?
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13 votes

Although it's a little tricky to say what "bigger" means in this context, the answer is, in most senses, no. A supernova puts out about ten to a hundred times as much energy in the form of light, and ...

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Radius to which all hydrogen-burning stars are known?
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12 votes

Your best bet is probably a distance-limited catalog designed to include everything within a specific distance. The most recent such compilation I'm aware of is Reylé et al. (2021), which has a limit ...

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Calculate the true diameter of stars from photographic plate
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12 votes

Let's pretend for the moment that this is possible (it's generally not, as I'll explain below) and see how we would go about it. In principle, this is basic trigonometry: you have a measured angle ($\...

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Conventional matter to dark matter ratio, outside of galaxies
12 votes

Let me see if I can answer at least some of this. Yes, there is dark matter between galaxies. This is demonstrated by the fact that in galaxy groups and clusters, you need more dark matter than is ...

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What is the name of our Solar System?
12 votes

It's just called "the Solar System". (Plenty of places and objects have names like that; it's no different from "the Arctic" or "the Moon" or "the Sun".) ("Sol system" is an invention of science ...

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Question: By design, JWST cannot observe in the anti-sun direction. Is this due to Gegenschein backscatter?
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10 votes

I'm going to say no. Gegenschein is, as you note, reflected sunlight, and is the brightest part of the (reflected component of the) zodiacal light. It's not very bright in the optical (there are no ...

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Using masers to measure rotational velocity of a galaxy
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10 votes

Masers tend to be extremely bright, compact sources with line emission at cm wavelengths (usually from OH or H$_{2}$O molecules; this is a technique for gas clouds, albeit one that only works in ...

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Are Brown and Sub-Brown Dwarfs secretly more common than stars?
10 votes

The answer to your first question is (now) fairly simple: No, brown dwarfs are not more common than red dwarfs. A crude approximation is that stars (which are indeed mostly red dwarfs) outnumber brown ...

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What is the application of pseudorandomness in astrophysics?
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10 votes

The primary advantage of pseudorandom numbers is speed (as Cristiano mentioned) and convenience: they're what are available in almost any software package or library, whereas true random number ...

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What are the chances of a star colliding with another during a galactic collision?
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10 votes

Let's see what we get from some back-of-the-envelope estimates. Imagine throwing one star (e.g., the Sun) at the other galaxy. How likely is it we'll hit a star in the other galaxy? Well, it's ...

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Can "rogue" supermassive black holes be made this way?
10 votes

I assume you're asking about central supermassive black holes (SMBHs, one per galaxy), not stellar-mass black holes. The answer is yes, but what actually happens is the two SMBHs have to merge first, ...

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Why aren't ground-based observatories using adaptive optics for visible wavelengths?
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10 votes

There's a pretty good discussion at this page. There are several factors at work: The smaller isoplanatic angle, as you note. This limits how much of the sky you can observe with AO, since your ...

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How do astronomers know that distant galaxies aren't actually nearby star clusters?
9 votes

Other answers have provided general ideas about how to confirm that individual sources are distant galaxies and not clusters, so I'll focus on the question of how astronomers in the Dark Energy Survey ...

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Has Hubble photographed Venus in near IR? If so how does it compare to the new and exciting Parker Solar Probe image?
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9 votes

This web page -- "Here is why the Hubble Space Telescope only looked a few times at Venus (and why it looked at the Moon instead)" -- seems like a pretty good answer to your main question (...

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How does a galaxy in Abell 2261 exist without a black hole in the center?
9 votes

The Brightest Cluster Galaxy (BCG) in Abell 2261 ("Abell 2261-BCG") is a massive elliptical; these almost always seem to have supermassive black holes in their centers. In addition, the ...

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What cluster of stars is this with a "dark donut" to one side?
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9 votes

OK, having (finally) actually looked at the video, it's clear that Szymanek is looking at the center of M33. There is in fact a nuclear star cluster in the center of that galaxy; not knowing the field ...

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What is the "lost light" in this unusual Hubble Deep Sky image?
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9 votes

Let me see if I can explain the main aim and accomplishment of this work. First off: the picture you're puzzling over is a "luminance RGB" image, in which the bright regions are represented by color (...

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Why aren't there any images of Sun-orbiting bodies by Spitzer?
8 votes

In addition to the target list linked to by @planetmaker in their answer, there are two recently published review articles (from Nature Astronomy) summarizing the many different aspects of Solar ...

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Degrees of freedom in restricted circular coplanar three body problem
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8 votes

In the most general case, there are three (spatial) degrees of freedom for each body, for a total of 9 degrees of freedom. The circular restricted three-body problem forces the two larger masses to be ...

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Can an average person see stars from the bottom of a well or through cardboard tubes? Definitive answer required!
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8 votes

This article (Hughes 1983, "On Seeing Stars (especially up chimneys") from the Quarterly Journal of the Royal Astronomical Society seems like a pretty good account of the "phenomenon&...

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