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50 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 ...
ProfRob's user avatar
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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 ...
Jacxel's user avatar
  • 499
21 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. ...
corsiKa's user avatar
  • 403
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 ...
ProfRob's user avatar
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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 ...
James K's user avatar
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13 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 ...
HDE 226868's user avatar
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13 votes
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What is the apparent size of Earth from the Sun?

The calculation of the apparent size of Earth as seen from the Sun is pretty straight forward. Just consider the triangle: from your observation point the distance to the center of the object, to the ...
planetmaker's user avatar
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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 &...
James K's user avatar
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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, ...
HDE 226868's user avatar
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10 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 ...
James K's user avatar
  • 123k
10 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 ...
James K's user avatar
  • 123k
9 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: ...
Dhruv Saxena's user avatar
9 votes
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Existence of planets larger than their host star?

The answer to the question depends on the exact definition of planet that is used. A possible example is the L dwarf 2M 0746+20 (2MASS J07464256+2000321) and its planet 2M 0746+20 b. The radius of ...
aventurin's user avatar
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9 votes
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Size of the Unobservable Universe

The article Applications of Bayesian model averaging to the curvature and size of the Universe cited in the question is from 2011. It is now 2023 and we have much better data, in particular from the ...
Albert's user avatar
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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 ...
M. A. Golding's user avatar
8 votes

What is the apparent size of Earth from the Sun?

According to space.com 109 earths could be lined up across the face of the sun. Therefore, if you were at the sun, the earth would look 109 times smaller than the sun does from the earth. This answer ...
Ken Mercer's user avatar
8 votes

How was the size of the earth determined 100/200/300 years ago?

The same principle, but with better equipment. To measure the size of the Earth you need to know the angular distance between two points (in degrees) and the curved distance (in km). If you choose ...
James K's user avatar
  • 123k
8 votes

About angular diameter, parallax and image of the nearest neutron star RX J185635-3754

With very few exceptions of the biggest and most nearby sources (like Betelgeuze with <~50mas) we cannot resolve the angular diameter of stellar-type sources by direct imaging means. Precision of ...
planetmaker's user avatar
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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 ...
ProfRob's user avatar
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7 votes
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What is the maximum size for a solid celestial body such that it still can be tunneled down to the core?

Such tunnels might be possible for objects up to a few hundred kilometres in size. Larger objects could be tunnelled if the tunnels are lined with high strength materials. Assuming the centre of the ...
David Bailey's user avatar
7 votes

About angular diameter, parallax and image of the nearest neutron star RX J185635-3754

All images of stars (bar one or two of the closest or largest) are effectively those of point sources. The image we see is the convolution of a point with the instumental "point spread function&...
ProfRob's user avatar
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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 ...
PM 2Ring's user avatar
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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 ...
Bill Lee's user avatar
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 ...
Carl Witthoft's user avatar
5 votes
Accepted

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 ...
IronEagle's user avatar
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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 ...
Anders Sandberg's user avatar
5 votes

Logically, how can the universe be infinite in size?

Being infinite doesn't keep something from expanding. The expansion of space can be thought of as similar to the stretching of a coordinate plane by multiplying every coordinate by a constant, which ...
zucculent's user avatar
  • 1,758
5 votes

Does "Angular Diameter Turnaround Point" solve the Great Wall Problem?

Expansion of the Universe, not of small structures It is true that large "structures", such as unvirialized clusters, and voids, scale with the expansion of the Universe, but smaller ...
pela's user avatar
  • 38.6k
5 votes

Size of the Unobservable Universe

Yes, you are right. It refers to the Hubble volume rather than the Hubble radius, specifically it is 251 times the Hubble volume, but based on the volume, we can calculate the radius of the whole ...
Arjun's user avatar
  • 1,464

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