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What causes the dimensions of a star increase when its hydrogen fuel is exhausted?

What causes the dimensions of a star increase when its hydrogen fuel is exhausted? For example, the Sun is expected to increase its radius 250 times. What causes this if its temperature is expected to fall? How gas can expand if the temperature…
Anixx
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Is there enough hydrogen left after a star dies so another star will have enough to light up?

A star consumes quite a lot of hydrogen in its life, and is pretty much "vacuuming" everything in its vicinity. After it dies (eventually by supernova which will spread all its composition over light years), is there enough hydrogen left in that…
Andrei
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Is it possible that a ultra-large portion of the space we live in is already inside a black hole? How could we refute this?

Trying to wrap my head around some concepts involving the very large gravitational fields of black holes, and what the gravitational gradients look like on a cosmic scale. I'm familiar with the Great Attractor, and wondered if it were possible if…
Ian Moriarty
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How was the Earth-Sun distance originally calculated?

AFAIK it was possible long before the first interplanetary probes. Who did it?
peterh
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Earth is Tilted, but in reference to What Object / relative to what?

I am asking basic question on trying to understand on tilt. I know if I (as a human) tilt when standing on feet, my tilt will be in relation to gravity. For Earth, I am not able to understand, what is the relative object of the earth tilt is. I am…
puzzled
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What does the Earth look like when viewed from Saturn?

Are there any data from spacecraft that visited that planet? How large the Earth is when viewed from that planet?
user53098
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Why can't a half-illuminated planet support life at all?

Here is my own translation of the Polish version of the Drake equation article in Wikipedia: (...) They must provide the right amount of heat. The smaller the star, the less heat it gives off and the closer the planet must be until it reaches a…
trejder
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Why do white dwarfs cool down so slowly?

I read that when white dwarfs do not proceed with nuclear fusion, the heat radiation from it is solely based on heat it retained in the past But then, it floats in an almost 0 K empty space. So, why does it take a million (or many many more) years…
Zoli
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How one can establish that the Earth is round?

I am asking this question out of curiosity. Currently, I am reading the book: A Brief History of Time. In Chapter 1, the author discusses about Aristotle's conclusions about spherical Earth. For example: At horizon, one sees the top of the ship…
YII
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What telescope is Polish astronomer Kazimierz Kordylewski holding in this April 1964 photo at the Jagiellonian University Observatory in Krakow?

The following questions touch on Kordylewski clouds Can dark matter accumulate at Lagrange points? Are dust-dust collisions necessary to explain Kordylewski clouds at Earth-Moon L4/5? Aren't the cross-sections, number density timescales too…
uhoh
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Could it be possible to detect planets from stars that went supernova through the resulting nebula shape?

It ocurred me, if a star with at least one planetary companion undergoes a nova or supernova, we shoud expect the debris to be deflected to some degree, on exit. To ilustrate it, first let's take the example of a lone star exploding in a unlikely…
ksousa
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What Causes the Large Radiation Fields Around Jupiter?

I had heard that the large radiation belts around Jupiter may be formed by liquid metallic hydrogen in (or around) Jupiter's core (which Wikipedia says haven't been observed in labs yet due to the immense pressure required), but I don't understand…
Sarah Szabo
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What is going on with this (sub?) brown dwarf WISEPA J174124.26+255319.5?

In this Wikipedia article, it details about a T9 class brown dwarf named WISEPA J174124.26+255319.5. Apparently, this brown dwarf has 0.95 Jupiter masses, and 0.4 Jupiter radii (with rather low error). Its mass is already weird in the first place,…
Max0815
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Strange bump in solar spectrum taken with home-made spectrograph

I am an astronomy teacher, and made some kind of spectrograph with a difraction grating, a 3D printed slit, water pipes and a reflex camera. With a group of students we got this picture of the solar spectrum: Then we created a luminosity profile…
Luis López
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Does a measuring stick with a size of a billion lightyears in intergalactic space keep the same length in expanding space?

Imagine a measuring stick (a rod or ruler) made of ordinary matter which has a length of a billion lightyears. The space surrounding the ruler expands. Will the ruler keep the same length by the accumulating electromagnetic forces opposing…
Gerald
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