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1500 questions
24
votes
6 answers
What will happen to life on Earth when the Andromeda and Milky Way galaxies collide?
It is said that the Andromeda and Milky Way galaxies are coming close to each other with a speed of approximately 400000 km/hour. They will be together in the next 4 billion years.
What will happen to life on Earth or human beings on Earth?
If we…
AmitG
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Would a black hole evaporate via Hawking radiation before you fall past the event horizon?
It takes an infinite amount of time for something to fall past the event horizon of a black hole from the perspective of someone outside the event horizon. Black holes also evaporate after a finite amount of time from an outsider's perspective due…
Thomas
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24
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3 answers
Why can't moon light (reflected sun light) turn the sky blue?
Does turning the colour of the sky blue need more luminous light? Does it depend on luminosity or some other factors are also responsible for this phenomenon? Why can't the moon light turn the sky blue even a little bit (at least the area near the…
Sirius
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23
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How distances are measured in the Solar System, in the Galaxy, and in the Universe?
Distances in our universe can be calculated in several ways:
Stellar Parallax
Standard Candles
Redshift
How are these methods linked, and how they are actually used to calculate distances are measured in the Solar System, in the Galaxy, and in…
leonard vertighel
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23
votes
6 answers
How does Titan maintain its atmosphere?
Titan, which is smaller than Mars, has an atmosphere but Mars is not able to maintain its atmosphere. Even Luna (the Moon) doesn't have an atmosphere. Why is Titan able to hold an atmosphere, despite being smaller than Mars?
Strikers
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23
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3 answers
Why is the Oort cloud presumed to be spherical?
Most descriptions of the Oort cloud depict it as a mostly spherical distribution of planetesimals, with occasional allowance for an inner component that is more donut-shaped. This is slightly at odds with the fact that most protoplanetary clouds and…
Emilio Pisanty
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23
votes
3 answers
From an outsider's perspective, how can a black hole grow if nothing ever crosses the event horizon?
Due to time dilation, an outside observer never sees a falling object actually cross the event horizon. I'm not referring to the optical illusion of red-shifted light making objects appear to fade away before crossing the event horizon. I'm…
user52416
23
votes
3 answers
When and how was it discovered that Jupiter and Saturn are made out of gas?
Was it due to appearance only or spectroscopic methods were used? Venus also has a thick cloud cover, how was it determined to be a rocky planet?
Astrodhan
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23
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4 answers
What's the difference between an exoplanetary transit and eclipse?
This article states
Their data contained eclipses for all 25 exoplanets, and transits for 17 of them.
This page from NASA explains the difference between an eclipse and a transit:
Like an eclipse, a transit occurs when one object appears to pass…
usernumber
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23
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2 answers
Why did the Comet Shoemaker-Levy-9 fragments cause such large explosions on Jupiter?
In July 1994, the comet Shoemaker-Levy 9 (D/1993 F2) tidally fragmented and these fragments collided into Jupiter, as per the image below.
Image source
The question is, what mechanisms resulted in these small fragments causing such large explosions…
user8
23
votes
3 answers
How can I measure the angle between two stars?
This is a backyard astronomy question.
My middle-school-aged son and I would like to measure the apparent angle between two easily-visible stars more precisely than measuring with our outstretched hands and fingers. Our current technique gives…
Wyck
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23
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4 answers
Why is Neptune a darker blue than Uranus?
If Neptune and Uranus have similar composition then why is Neptune a darker blue than Uranus?
sno
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23
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2 answers
What ground-based observational evidence is there that the Moon doesn't have an atmosphere?
The Moon doesn't have any significant atmosphere (surface pressure is $3\times10^{-15}$ bar). Can the absence of atmosphere on the Moon be determined with ground-based observations? When was it first determined that the Moon doesn't have an…
usernumber
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23
votes
10 answers
Is the closest planet to another planet always the innermost planet?
In our Solar system Mercury is not only the closest planet to Earth on average but also, for the same reason, the closest planet on average to all other planets (Jupiter, Neptune, etc...).
Does that always apply for any planetary system? For…
Gerardo Furtado
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23
votes
1 answer
Why can't observatories just stop capturing for a few seconds when Starlink satellites pass though their field of view?
Given that the positions and trajectories of the Starlink satellites are public, why can't the telescopes just ignore the photons they receive when the satellites pass through the field of view?
It seems that they could "just" stop image capture for…
Alexis Delrieu
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