Questions tagged [size]

Questions regarding the physical dimensions of a celestial object.

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

How was the size of the earth determined 100/200/300 years ago? I know that by then the had better methods then the simple sticks and shadow experiment.
blademan9999's user avatar
5 votes
3 answers
169 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
  • 491
7 votes
2 answers
804 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
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
278 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
260 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
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5 votes
1 answer
336 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
1 vote
1 answer
191 views

How much energy to shorten a synodic month by about 1.56%?

Suppose the moon underwent a single, massive, large-object bombardment event. About what number (or range) of about what mean mass of objects could shorten the synodic month by about 1.5633%? (Assume ...
Peter Heffner's user avatar
9 votes
1 answer
418 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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26 votes
4 answers
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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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4 votes
6 answers
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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
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2 votes
0 answers
63 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
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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
0 votes
0 answers
146 views

Volume of the observable universe [duplicate]

What about the volume of the observable universe? Can we find it? And what is the result in cubic light years?
Panagiotis Makris's user avatar
0 votes
3 answers
867 views

How big can a planet get, with respect to its star for it to sustain life? [closed]

Earth is 108 times smaller than the sun in terms of its diameter while Jupiter is 10 times. Assuming Jupiter was located such that it could sustain life, theoretically how big a planet can get with ...
Abhay Bhai's user avatar
4 votes
1 answer
68 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
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3 votes
1 answer
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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
1 vote
0 answers
51 views

Is a star with 2/3 solar masses and 9/10 solar radii still in the main sequence?

As far as I know, K-type and G-type stars (among others) grow in radius as they age, eventually leading to red giant phases. My question is, would a star that is about 0.66 solar masses and 0.94 solar ...
Xi-K's user avatar
  • 403
1 vote
0 answers
84 views

Is is possible for a main sequence star to have 0.77 solar masses yet only be 0.54 solar radii?

I know ordinarily a star's mass and radius tend to be proportional, so a 0.5 solar masses star tends to be about 0.5 solar radii and have a density of 4.82 g/cm³, 3.42 or about three and a half times ...
Xi-K's user avatar
  • 403
2 votes
2 answers
481 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
0 votes
2 answers
817 views

What factors influence a star's temperature and density?

Assuming a relatively even proportion of mass and radius, a 0.25 solar mass and radius star would have a density of 22.5003 g/cm³, or about 16 times our Sun's density. However, there is obviously a ...
Xi-K's user avatar
  • 403
5 votes
1 answer
861 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
4 votes
1 answer
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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
1 vote
1 answer
131 views

What if you 'placed' the Chicxulub asteroid onto the Earth? [closed]

We all know what sort of devastating impact an asteroid could have if it collided with the Earth. But I'm curious to know what the effects would be if you removed the speed element from it, and were ...
user avatar
3 votes
1 answer
114 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
  • 4,242
2 votes
1 answer
251 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
  • 5,616
3 votes
1 answer
563 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
0 votes
2 answers
207 views

Why are event horizons described in Schwarzschild radii rather than diameters, and either way can they change equator to pole?

I never heard of Schwarzschild diameters, only of Schwarzschild radii. Why is it like this? Wouldn't it be better to portray the (possible) size of a black hole in a diameter? Either way, can we use ...
John's user avatar
  • 113
2 votes
1 answer
157 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
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0 votes
1 answer
202 views

Is a literal instance of Russell's teapot possible?

Much has been said about Russell's teapot, and I accept as obvious that a teapot would be too small to be detectable in an orbit around the Sun by any reasonable method today, or by any method that ...
Veky's user avatar
  • 111
-4 votes
3 answers
2k views

Why is the Moon's volume so small compared to the Earth's?

The Moon has 27.3% of the Earth's radius/diameter but only 2% of the Earth's volume. I don't quite get it why the Moon's volume is that small despite having more than a quarter the 2-dimensional size ...
Ioannes's user avatar
  • 1,090
3 votes
2 answers
297 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
1 vote
1 answer
164 views

can we calculate the velocity of galaxies at the edge of the observable universe?

I read this post Does the edge of the Universe travel faster than the speed of light? but there was no calculation, so I tried it thusly: The observable universe is 28.5 Gpc (gigaparsecs) = 28500 ...
aquagremlin's user avatar
-1 votes
1 answer
182 views

What are the necessary steps required for calculating the size of a star? [closed]

Title pretty much says it all. Basically, what exact variables are used, and what steps need to be taken, in the calculation of the size of a star? Preferably, some example data for how a the size of ...
B''H Bi'ezras -- Boruch Hashem's user avatar
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
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 ...
Mehdi Abbassi's user avatar
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
4 votes
1 answer
505 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
  • 793
1 vote
1 answer
44 views

Different sizes of bow shocks

In this image of LL Ori bow shock, there is a smaller bow shock at the upper right. Is that second bow shock substantially smaller than the LL Ori bow shock, or is it just much further away? If ...
Bob516's user avatar
  • 1,467
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
1 vote
0 answers
80 views

Expansion of space - how do we end up with an unobservable region?

I've just been answering a question on this issue,in physics SE,and realised that my answer conceals a point I don't myself understand. I understand that The expansion of metric isn't affected by ...
Stilez's user avatar
  • 1,022
13 votes
3 answers
691 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
  • 4,157
1 vote
1 answer
613 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?
larry909's user avatar
  • 141
3 votes
1 answer
351 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
11 votes
1 answer
332 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
  • 11.4k
1 vote
1 answer
78 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 ...
Jason P Sallinger's user avatar
2 votes
1 answer
216 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
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
1 vote
1 answer
67 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 ...
David Elm's user avatar
  • 403