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Can "tired light theory" explain the observed redshifts of galaxies?
(Intermediate)
Could photons be dark matter?
(Intermediate)
Does a photon observe other photons moving past it at the speed of light?
(Intermediate)
Has there been an experiment that measured speed faster than the speed of light in vacuum?
(Advanced)
How are photons created and destroyed?
(Advanced)
How do photons from distant objects maintain enough energy to reach us?
(Intermediate)
How do scientists slow light down?
(Intermediate)
How do we feel heat?
(Intermediate)
If light has no mass, then what draws it into a black hole?
(Intermediate)
If photons have zero mass, why do they feel the effects of gravity?
(Advanced)
Is light blueshifted when it is gravitationally lensed?
(Intermediate)
Is light of different colors affected differently by gravity?
(Intermediate)
What is the photoelectric effect? Why can't multiple low-frequency photons free an electron?
(Intermediate)
Where did the matter in the universe come from?
(Intermediate)
Where did the Universe come from?
(Intermediate)
Why doesn't light from distant galaxies reach us instantaneously?
(Intermediate)
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How does the Earth compare in size to the entire universe at the present epoch? (Intermediate)
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Is speed of light the same everywhere ? (Beginner)
How does Venus have sulphuric acid in it's clouds? (Beginner)
Earth's Bow Shock (Advanced)
How much does the Earth "wobble" on its orbit due to the Moon's gravity? (Intermediate)
Why is the sun red? During sunset, Northeastern US, Summer 2021 (Beginner)
Why do rays from Sun appear to converge at a point? (Beginner)
But seriously: what was there before the Big Bang? (Beginner)
How far can photons move freely in the early universe (Advanced)
How likely is it that the Solar System has had or will have a close encounter with another star? (Intermediate)
How do we know what we observe is x light years away? (Beginner)
Editor's Pick
What is the universe expanding into? (Intermediate)
What do I need to do to become an astronomer? (Beginner)
What's the difference between astronomy and astrology? (Beginner)
Why is looking out into space the same as looking back in time? (Beginner)
Can we find the place where the Big Bang happened? (Intermediate)
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What kind of eyepieces do I need to look at planets? (Intermediate)
How far is each planet from Earth? (Intermediate)
What was the bright, smoothly moving star that I saw? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
What would happen if the Moon fell out of its orbit around Earth? (Intermediate)
Which planet is most similar to Earth? (Intermediate)
Why do the planets orbit the sun? (Beginner)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
Why do all the planets orbit in the same plane? (Intermediate)
Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
What was the bright, smoothly moving star that I saw? (Beginner)
How far is each planet from Earth? (Intermediate)
Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
What would happen if the Moon fell out of its orbit around Earth? (Intermediate)
Earth's Bow Shock (Advanced)
How do you measure the distance between Earth and the Sun? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
Which planet is most similar to Earth? (Intermediate)
Why do the planets orbit the sun? (Beginner)
How are light and heavy elements formed? (Advanced)
Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
How are light and heavy elements formed? (Advanced)
What was the bright, smoothly moving star that I saw? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
Which planet is most similar to Earth? (Intermediate)
How far is each planet from Earth? (Intermediate)
Why is the moon in a different place every night? (Beginner)
What would happen if the Moon fell out of its orbit around Earth? (Intermediate)
How does the position of Moonrise and Moonset change? (Intermediate)
Earth's Bow Shock (Advanced)
What's going to happen on December 21st 2012? (Intermediate)
What color is each planet? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
How far is each planet from Earth? (Intermediate)
How do you measure the distance between Earth and the Sun? (Intermediate)
Is the Moon moving away from the Earth? When was this discovered? (Intermediate)
Why do the planets orbit the sun? (Beginner)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
When was the last time all of the planets were aligned? (Beginner)
How long does it take for the Sun's light to reach us? (Beginner)
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Telescopes
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Physics
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The Theory of Relativity
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Space Exploration & Astronauts
The History of Astronomy
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