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Questions tagged [size]

Questions regarding the physical dimensions of a celestial object.

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27 votes
4 answers
16k views

Is there a theoretical maximum size limit for a star?

Some stars are simply huge. Eventually, though, wouldn't there be simply too much pressure or mass for the star to sustain itself? Wouldn't it eventually collapse into a black hole? Is there a ...
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25 votes
4 answers
10k views

Is there any planet bigger than a star?

Or a star smaller than a planet? Which star and planet would be an example of this?
asker223's user avatar
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20 votes
1 answer
1k views

How small can a spiral galaxy be?

The smallest observed spiral galaxies I can find are NGC 2976 and NGC 4605, both with a diameter of 20 kly, but I don't have anything like an exhaustive source to search. I've also found a mention ...
Elukka's user avatar
  • 301
19 votes
3 answers
4k views

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

The universe is about 13.8 billion years old. Assume at the big-bang it starts from a small region and the maximum possible speed according Einstein is the speed of light how can the universe got a ...
Wernfried Domscheit's user avatar
18 votes
5 answers
12k views

How can the universe be infinite?

I've heard from renowned astrophysicists that we don't yet know whether or not the Universe is infinite. How is that possible regarding the big bang theory is accepted (as they all do)? Are they ...
harogaston's user avatar
  • 1,037
17 votes
1 answer
6k views

Is the Sun really a medium size star?

It is often said that the Sun is a medium size, or even dim star. Is this true? According to this list of stars within 21 light years, there are, out of the closest 121 stars, only six brighter than ...
SE - stop firing the good guys's user avatar
14 votes
2 answers
696 views

How thick can planetary rings be?

This arose from a comment on Worldbuilding. We have data from four planets in the Solar System with rings, which doesn't make for a very good sample size. Observations of exoplanets could change that,...
HDE 226868's user avatar
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13 votes
7 answers
4k views

Relatable comparison of VY Canis Majoris to the Sun?

I was trying to describe how vast the largest known star is to someone and felt I wasn't quite able to relate the scale difference. I know it's roughly 1500 times larger than the sun. Anyone know of a ...
Jacxel's user avatar
  • 499
12 votes
3 answers
708 views

Existence of planets larger than their host star?

The mass region of objects between ~ 0.5 Jupiter masses and 80 Jupiter masses (gas giants through to brown dwarfs and red dwarfs) is typified by an almost flat relationship with object diameter. There ...
Ingolifs's user avatar
  • 4,155
11 votes
1 answer
337 views

Why haven't more captured small moons been found?

Shouldn't captured moons have the same size distribution as asteroids? And asteroids are more common the smaller size they are. Moons are likely captured if they are in highly inclined orbits, and ...
LocalFluff's user avatar
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9 votes
1 answer
215 views

What was the greatest spatial extent of the Asteroid Belt prior to the Late Heavy Bombardment?

Reading the article On the asteroid belt’s orbital and size distribution (Gladman et al. 2009), there is an interest point made: asteroids a few kilometers and smaller in size are recent ...
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9 votes
1 answer
439 views

How to determine the scale on astronomical images?

I've always been amazed at the many beautiful images of objects in the night sky. The Andromeda galaxy is a superb example. But it was only a few years ago that I discovered that Andromeda in those ...
Roger Wood's user avatar
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9 votes
1 answer
1k views

What is the smallest diameter black hole that can be formed naturally?

I was watching the video I Put a 1mm Size Black Hole Next to Earth and This Happened - Universe Sandbox 2 discussing what would happen if a 1 millimeter black hole is orbiting the earth, and I began ...
Chico3001's user avatar
  • 193
8 votes
2 answers
1k views

Size of the Unobservable Universe

If you search that question on Google, the answers will be "250 times the size of the observable universe" or "more than 15.000.000 the size of the observable universe". Both of ...
jack_O'Dim's user avatar
8 votes
1 answer
3k views

Size and mass of comet ATLAS (C/2019 Y4)

I read some news about this new comet and some unreliable sources said it is twice as big as Jupiter. I tried to find a reliable estimation of its size or mass, but I couldn't find anything. Would you ...
abbassix's user avatar
  • 365
8 votes
2 answers
4k views

Size of Saturn's ring material

How big are the chunks of rock ice that make up Saturn's rings? Are there many objects larger than pebble size?
joseph.hainline's user avatar
8 votes
1 answer
1k views

If we were to see the Sun with our naked eyes from the Orion belt, would all planets be encompassed inside the star? Is this calculable?

When we see a star it looks much bigger in diameter to us than it really is, this picture (extracted from here) explains what I mean: Notice that the point we see in the skynight, represented by the ...
Eduardo Serra's user avatar
6 votes
3 answers
3k views

What is the apparent size of Earth from the Sun?

Heatwaves have been in the news in recent years. I found it amazing to consider that the energy from the Sun is enough to kill you, when only a tiny fraction of its radiation reaches Earth. Then I ...
albertoeda's user avatar
5 votes
1 answer
17k views

How many earths fit in the observable universe?

I was pondering our insignificance, when I wondered - how much smaller is our planet then the (observable) universe? And being as I don't know how to do the math, I'm asking it here. So how many of ...
Math chiller's user avatar
5 votes
1 answer
550 views

Which is the largest planet ever observed?

I don't know much about planets outside our solar system. Do we even know the limit of the size of how large a planet or satellite can be? The largest planet I know of is Jupiter, but could there be ...
Niklas Rosencrantz's user avatar
5 votes
1 answer
954 views

Can a habitable planet be smaller than 0.58 Earth radii?

According to the below image, the lowest escape velocity a planet can have in order to still be able to retain water on its surface and have a temperature above freezing is 6.5 km/s minimum. With ...
Xi-K's user avatar
  • 403
5 votes
3 answers
203 views

Why are there gaps in the size distribution of solar system moons?

Looking at the moons natural satellites in the solar system, the larger ones appear to fall in a few groups of sizes. Eyeballing the above picture, there appear to be a bunch of big moons (the ...
JanKanis's user avatar
  • 591
5 votes
1 answer
399 views

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

According to Wikipedia, The Hercules–Corona Borealis Great Wall is the largest known structure in the observable universe, measuring approximately 10 billion light-years in length. But since it's ...
Monster196883's user avatar
5 votes
1 answer
333 views

What is the current size of the SN1006 supernova remnant?

I was enamored by the wikipedia article of SN1006. Esp. the fact that it was so bright, it could cast shadows on the ground. (Even this idea that you could have possibly read parchment with just the ...
Sid's user avatar
  • 51
5 votes
1 answer
341 views

Surface Brightness Definition

I know the surface brightness is calculated by taking the apparent magnitude of an object and then divide by the size of the thing. But this is more of "observed" surface brightness, how do ...
JOAQUÍN HERNÁNDEZ's user avatar
4 votes
1 answer
275 views

What is the maximum size for a solid celestial body such that it still can be tunneled down to the core?

Old science fiction had lots of stories that involved people exploring the center of Earth, like for example Journey to the Center of the Earth, by Jules Verne. As Earth sciences advanced, this sort ...
ksousa's user avatar
  • 1,201
4 votes
6 answers
6k views

Logically, how can the universe be infinite in size?

Many people have told me that the “universe doesn’t care what you think” in my regards to it being infinite in size, and I know something that seems logical doesn’t mean anything when measured by ...
Max's user avatar
  • 59
4 votes
1 answer
70 views

Long-lived supernova remnants?

We cannot see the supernova remnant of the star that triggered the formation of the Sun and the Solar System, as the remnant dispersed and became mixed into the interstellar medium. So I am wondering, ...
WarpPrime's user avatar
  • 6,683
4 votes
1 answer
41 views

How do pressure, temperature, and gravity affect a smaller body than Earth with the same bulk composition?

Earth has a density of about ${\rm 5.513 ~g/cm^3}$ with one Earth radius and one $g$. Venus, a very similar planet to Earth and likely with about the same bulk composition, has a density of about ${\...
Xi-K's user avatar
  • 403
4 votes
1 answer
524 views

Volume of Galaxies

Pretty much awkward question though. I would like to ask how is the volume of a Galaxy X is measured? For example consider milky way, what are the techniques to measure the same? How accurate and ...
Pranay's user avatar
  • 783
3 votes
3 answers
367 views

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

I have a big doubt about our allegedly nearest (X Ray isolated) neutron star, also known as the Walter star, one of the members of the "Magnificent Seven stars": RX J185635-3754. So I came ...
omivela17's user avatar
  • 201
3 votes
1 answer
585 views

Do more massive stars become larger or smaller white dwarfs?

I wonder whether e.g. stars more massive than the Sun (but below the mass where they'd go supernova) would become larger or smaller white dwarfs than a white dwarf Sun. Since Procyon B is larger than ...
Greenhorn's user avatar
  • 293
3 votes
1 answer
365 views

If the Milky Way galaxy is as big as planet earth, how big is Earth?

If the Milky Way galaxy is as big as planet earth, how big is Earth?
larry909's user avatar
  • 141
3 votes
2 answers
169 views

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?

I assume it would have to be considerably larger since rock isn't as flammable as gases are? But it's also more dense to begin with.. Do we know of any suns that are made like this? Is it even ...
Eric's user avatar
  • 133
3 votes
2 answers
308 views

Best way to simulate star sizes to scale in celestial sphere

Using the Hipparcos catalogue, I am trying to create a celestial sphere. As all the stars are a fixed distance from the centre of this sphere, the only way to differentiate the distances and magnitude ...
SidS's user avatar
  • 225
3 votes
2 answers
2k views

Finding the radius of a star in arcsec

If i know the radius r of a star in cm, how can I convert it to arcseconds? For example, if I have a star with r = 3.18e13 cm, and distance to the star d = 220 parsecs, what is the relation to ...
S. Mas's user avatar
  • 69
3 votes
1 answer
632 views

How big and how far away would the moon be if earth was the size of Jupiter?

If the earth were the size of Jupiter, what would its 'moon' be in both relative size and distance? I did some quick figuring and think I roughly figured out that if placed at the position of the sun, ...
Steven Stutzman's user avatar
3 votes
2 answers
924 views

How to Find the Viewing Size of a Star

The sizes of the stars in the picture below have more to do with their brigtness than the actual size of the star. I'm looking for a formula that relates the viewing size of a star with its ...
David Elm's user avatar
  • 403
3 votes
1 answer
120 views

Why doesn't star size distribution conform to space rock size distribution?

The number of space rocks is exponentially related to the size of the rocks. There are more small space rocks than big ones. Stars are most commonly the size of the sun, big and smaller stars are rare,...
bandybabboon's user avatar
  • 4,268
3 votes
0 answers
65 views

Is there a minimum size for a galaxy to have spiral arms?

Is there a minimum size or mass for a galaxy to present spiral arms? I don't remember many small galaxies with spiral arms. Does the mechanism responsible for producing spiral arms no longer hold if ...
Elismar Lösch's user avatar
2 votes
2 answers
941 views

What would be the apparent magnitude of Betelgeuse if it were as close to Earth as Sirius?

How large and bright would Betelgeuse appear if it were as close to Earth as Sirius, before and after it goes supernova?
Justin Waters's user avatar
2 votes
1 answer
165 views

When was the diameter of Titan first measured?

Titan is enshrouded in a thick opaque cloud of methane : with a telescope, you can't see the moon's surface. Because of this, from a distance, you can only see the diameter of the moon + its ...
usernumber's user avatar
  • 17.6k
2 votes
2 answers
4k views

Is there some upper limit in the moon size distribution?

The planets range hugely in sizes, Jupiter is more than 300 times as massive as Earth. But the sizes of the large moons seem to be uncorrelated with the sizes of the planets they orbit. Why doesn't ...
LocalFluff's user avatar
  • 11.4k
2 votes
1 answer
260 views

How do we know what the biggest star is?

Kurzgesagt claims that the largest (observable) star in the universe would be Stephenson 2-18 which is in line with Wikipedia: It is among the largest known stars, if not the largest, and one of the ...
B--rian's user avatar
  • 5,626
2 votes
1 answer
217 views

Yet another Question about the expansion of universe

A galaxy 13 billion light-years distant is 94% of the way to the big bang. The universe was 800 million years old when the light was emitted. That galaxy today is traveling away from us at 94% of the ...
David Wilson's user avatar
2 votes
2 answers
708 views

Retrieving input effective radius from Sérsic profile

I'm playing around with Sérsic profiles, and would like to retrieve the effective (half-light) radius that I put in by integration of the profile. I'm not managing to, so perhaps someone can help me ...
user1991's user avatar
  • 844
2 votes
1 answer
48 views

Largest projected images (such as shadows) observed

Serpens Nebula around the star HBC 672 (source: heic1819b) Which are the largest observed images projected onto interstellar bodies (such as nebulae) by means of electromagnetic radiation? By “largest”...
Incnis Mrsi's user avatar
2 votes
2 answers
496 views

What increases or decreases the mass and density of a fixed radius star?

Assuming a relatively even proportion of mass and radius, a 0.25 solar masses and radii star would have a density of 22.5003 g/cm³, or about 16 times our Sun's density. Keeping the radius of 0.25 ...
Xi-K's user avatar
  • 403
2 votes
0 answers
68 views

How big could a regular star in supergiant/hypergiant phase theoretically get, not counting quasi-stars?

For clarity, I'm not asking about the super-behemoths that are quasi-stars. I'm interested in knowing how large a regular star could theoretically get once it reached supergiant/hypergiant phase, ...
zucculent's user avatar
  • 1,758
2 votes
0 answers
321 views

How big is the Andromeda galaxy in the night sky? [duplicate]

If divide the distance to the sun by its diameter, I get the number 107.517 Likewise, if divide the distance to the moon by its diameter, I get the number 110.650 Both numbers are quite similar which ...
GetFree's user avatar
  • 121