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48 votes

Is there any planet bigger than a star?

The answer depends on whether you mean is any planet bigger than any star, or whether the planet and star have to be in the same system and have been discovered/measured, rather than just that they ...
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26 votes
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Relatable comparison of VY Canis Majoris to the Sun?

After some playing around with wolfram alpha and google my best comparison has been The sun compared to VY Canis Majoris is like a donut compared to the London Eye. The London Eye is about 120m in ...
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  • 499
22 votes

Relatable comparison of VY Canis Majoris to the Sun?

On the banana scale, it's an ore freighter. Every physicist worth their salt knows that the most important scale in the galaxy is the banana. Now, your average banana is between 7-8 inches in length. ...
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  • 413
19 votes
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Is the Sun really a medium size star?

It is true that a surprisingly large number of stars are smaller (and thus less massive) than the Sun. However, the stars that are bigger than the Sun are often much bigger. Look at this chart: ...
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16 votes
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How many earths fit in the observable universe?

Without checking the numbers in detail, according to Wikipedia, the volume of the observable universe is about $3.5\cdot 10^{80} \mbox{ m}^3$, and the volume of Earth is about $1.08321\cdot 10^{21} \...
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15 votes
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Which is the largest planet ever observed?

Yes, there is a limit. Anything with a mass larger than about 13 times that of Jupiter would be called a brown dwarf (a failed star), though whether such an object would consist entirely of gas, or ...
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15 votes
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How can the universe be infinite?

What I mean is, even if it is capable of expanding, if everything originated at the big bang how can that space turn to be infinite in a finite time - the age of the universe. In the standard ΛCDM ...
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  • 7,674
14 votes

Is there a theoretical maximum size limit for a star?

A decent part of this answer is based on the introduction to Kroupa & Weidner (2005), though I’ve obviously gone into a lot more depth on all of the references. Our story starts, as do many ...
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14 votes
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Size and mass of comet ATLAS (C/2019 Y4)

The confusion comes from the difference between the nucleus and the coma. The nucleus is a small icy body, only a few km across. The coma is the cloud of gas and dust released from the nucleus as it ...
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  • 87.6k
12 votes

Logically, how can the universe be infinite in size?

Something infinite can expand. Consider an infinite length of elastic. There are (infinitely) beads attached to it at 1m gaps. You might label one of the beads "0", then the next one is &...
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  • 87.6k
10 votes

How can the universe be infinite?

I think the source of confusion between the two concepts - the Big Bang singularity and an infinite universe - is the misconception that the universe began as a finite expanse originally. This ...
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  • 398
10 votes
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Size of Saturn's ring material

The vast majority of the particles in Saturn's rings are small, on the order of $\sim10^{-1}$ m or lower. The columnar number density, according to data from Voyager 1 and Earth-based observations, ...
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9 votes
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How big is one arcsecond at various distances?

How big is one arcsecond at various distances? An arcsecond is a small angle, 1/3600 of a degree or about 5 millionths of a radian ($4.85\times10^{-6}$). To estimate the size of something that ...
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  • 87.6k
8 votes

Regarding the age / size of the Universe

The expansion rate of space is not itself the reason that the radius $R_\mathrm{Uni}$ of the observable Universe is larger than 14 billion lightyears (Gly). Just the fact that space expands is the ...
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  • 31.9k
8 votes

How can the 13.8 billion years old universe have a radius of 46 billion light years?

You assumption is wrong. Universe can( and is ) expand faster than the speed of light. The photon emitted towards our planet in the early universe, had to traverse a universe that is expanding. That ...
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  • 427
8 votes

Relatable comparison of VY Canis Majoris to the Sun?

An airplane flying along the surface of the sun would take about 6.6 months to circle it once. The same airplane would take 787 years to complete one trip around VY Canis Majoris. Aircraft's speed: ...
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8 votes
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Can a habitable planet be smaller than 0.58 Earth radii?

Short Answer: In part Two of the long answer below, it is stated that a planetary mass object needs to have a mass of at least 0.1, 0.12, 0.23, or 0.25 Earth mass to be habitable. Worlds with those ...
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8 votes

Is there any planet bigger than a star?

If by "bigger" you are referring to mass, disregarding radius, then the answer is strictly no for a regular "star" A star is a body that has reached a stable state in which ...
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  • 87.6k
7 votes

How can the 13.8 billion years old universe have a radius of 46 billion light years?

Far away galaxies are receding from us faster than $c_{0}$ = 299 792 458 m/s, but it does not mean that they are breaking the speed of light limit. These galaxies would still measure the speed of ...
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  • 101
7 votes
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Do more massive stars become larger or smaller white dwarfs?

More massive stars have a more massive core and produce more massive white dwarfs. The relationship between the initial mass of the main sequence star and the final mass of the white dwarf is ...
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  • 114k
6 votes
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How much larger would a star have to be to cause thermonuclear reactions if it was made out of mostly rock like Earth, instead of gases?

It really depends what you mean by "rock". At the temperatures and pressures at the cores of stars (and at which nuclear fusion reactions are possible), "rocks" as I suspect you are thinking of, do ...
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  • 114k
6 votes
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If the Milky Way galaxy is as big as planet earth, how big is Earth?

Well, they are different shapes, but we can get a rough answer by doing a ratio calculation based on their radii. Let $g$ be the radius of the galaxy, about $5\times 10^{20}\ \mathrm m$. Let $e$ be ...
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  • 8,912
5 votes

Relatable comparison of VY Canis Majoris to the Sun?

Depends a bit on whether you want to compare diameters or volume (3D). For radius, consider that it's approximately 6.6 A.U., so if you dropped it into the Solar System it'd extend out to well past ...
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5 votes

How can the 13.8 billion years old universe have a radius of 46 billion light years?

To expand on self.'s answer - Derek from Veritasium on Youtube explains the "(and is)" portion - ...This doesn't violate Einstein's theory of relativity since nothing is moving through space ...
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  • 51
5 votes

How can the universe be infinite?

It is known that the universe that we can see in our telescopes is less than the total universe. Since we cannot see what is beyond the visual edge, we cannot determine if the universe is infinite or ...
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5 votes
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Why haven't more captured small moons been found?

Encounters between small planetesimals and the larger core of planets (especially Jupiter) transfer momentum between the two. But momentum is conserved. Momentum is: $p = m v$, where $p$ is momentum ...
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5 votes
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When was the diameter of Titan first measured?

Discovery of Titan, 1655: Unknown diameter. Dollfus, 1970: 4,850$\pm$300km (1). Measured by Filar micrometer (2) and diskmeter / double-image micrometer (3). (Apparently a summary of earlier ...
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  • 611
5 votes
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What if you 'placed' the Chicxulub asteroid onto the Earth?

An asteroid resting on Earth would be a mountain. Or, for smaller asteroids, a pile of gravel. Mountains are limited in altitude by the strength of stone to resist compression: a too tall mountain ...
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