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Questions tagged [size]

Questions regarding the physical dimensions of a celestial object.

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76 views

If the whole observable Universe is as big as planet Earth, how big would Earth be?

If the whole observable Universe is as big as planet Earth, how big would Earth be?
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1answer
83 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?
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0answers
97 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 ...
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1answer
43 views

Do celestial bodies actually appear larger along the horizon? [duplicate]

Whether it be the moon (especially when full) or tonight, as Mars is closer than it has been in decades, it appears that these bodies are larger when close to the horizon than overhead. Is this an ...
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1answer
106 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 ...
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2answers
149 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 ...
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1answer
52 views

Inconsistent online radius value for Proxima Centauri

I was looking up the radius of Proxima Centauri and got a funny result. Google says it's about 100,000 km, while WolframAlpha says its about 200,000 km. Are the error bars that big, or does someone ...
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0answers
192 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 ...
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2answers
268 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 ...
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1answer
211 views

Why could a gas planet not get much larger than Jupiter? [duplicate]

What is the maximum size for a gas giant?
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3answers
763 views

How big is one arcsecond at various distances?

I've been reading this article https://en.wikipedia.org/wiki/Celestial_coordinate_system and a question came to my mind. The minimum units are seconds ( ″ ). I picture an angle of 1 second as being ...
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2answers
217 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 ...
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7answers
3k 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 ...
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1answer
261 views

How do we get the angular size of a crater without lens?

Suppose I want to calculate the diameter of the crater. I apply the small angle formula $$diameter=\frac{\theta_{diameter}}{206265''}\times D$$ where $\theta_{diameter}$ is the angular size of the ...
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2answers
900 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?
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1answer
461 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 ...
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2answers
374 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?
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1answer
653 views

The moon: how to determine its size, speed and distance from earth using a simple telescope?

Assuming I only have a simple telescope, how can I determine the size of the moon, its angular velocity and distance from earth?
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2answers
102 views

Regarding the age / size of the Universe [duplicate]

I believe the current estimated age of the Universe is around 14 billion years. I just read in another post on here that the diameter of the Universe is around 90 billion light years. This doesn't ...
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1answer
4k 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 ...
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1answer
590 views

If earth were the size of a marble would it be smoother than a marble? [closed]

As the title states, If earth were the size of a marble would it be smoother than a marble?
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2answers
1k 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 ...
13
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2answers
406 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,...
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2answers
143 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 ...
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1answer
78 views

Do astronomers and astrophysicists more often use diameters or radii when discussing about planets, dwarf planets, exoplanets and stars?

Mathematicians much more often use radii over diameters when discussing about circles and spheres, because in mathematics the radius is more fundamental than the diameter (the sphere is defined using ...
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1answer
533 views

Relationship between temperature of nebula and size of star

I was wondering, in the process of star formation, does the temperature of the nebula that produces a star play a role in the size of that star? I mean, it's only logical that the size would depend on ...
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1answer
173 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 ...
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3answers
2k 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 ...
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1answer
4k 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 ...
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5answers
4k 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 ...
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1answer
235 views

What are angular sizes of thin and thick disks in our Galaxy?

What are diapasons of galactic coordinates for thin and thick disks of our Galaxy?
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1answer
765 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 ...
7
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1answer
114 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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3answers
6k 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 ...