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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 different would the night sky have looked in 40,000 B.C.? (Intermediate)
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If I were hypothetically wearing a spacesuit and sitting on one of the Voyager space probes at their current positions in space, how much light would I have? (Intermediate)
What makes certain lunar eclipses so special? (Beginner)
Why is Earth's core molten? (Intermediate)
What will happen to Earth's tides as the moon moves away from us? (Intermediate)
How can spiral galaxies keep their shape? (Advanced)
Does a black hole have a "surface"? (Intermediate)
How can you link telescopes to make a bigger "effective telescope"? (Intermediate)
What should I know about the upcoming Solar Eclipse (2017)? (Beginner)
Do galaxies that are receding from us faster than the speed of light disappear from our observations? (Intermediate)
Why are astronomers interested in gravitational waves? (Intermediate)
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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 color is each planet? (Intermediate)
Why are the Moon and Sun sometimes orange or red? (Beginner)
Why do the planets orbit the sun? (Beginner)
At what speed does the Earth move around the Sun? (Beginner)
How does the position of Moonrise and Moonset change? (Intermediate)
Is the Moon moving away from the Earth? When was this discovered? (Intermediate)
Why are there high tides during a Full Moon? (Intermediate)
Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
What is the difference between a "star" and a "sun"? (Beginner)
Can a person go into a black hole and come out alive? (Beginner)
What color is each planet? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
Why do the planets orbit the sun? (Beginner)
How far is each planet from Earth? (Intermediate)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
What would happen if an asteroid 10 kilometers across hit the Earth? (Beginner)
Is the Moon moving away from the Earth? When was this discovered? (Intermediate)
How do you measure the distance between Earth and the Sun? (Intermediate)
Is the distance from the Earth to the Sun changing? (Advanced)
What are the requirements for being a planet? (Beginner)
What color is each planet? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
Why do the planets orbit the sun? (Beginner)
Is the distance from the Earth to the Sun changing? (Advanced)
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)
What are the names of the earth, moon, sun, and solar system? (Beginner)
What are the requirements for being a planet? (Beginner)
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)
Is the Moon moving away from the Earth? When was this discovered? (Intermediate)
How do you measure the distance between Earth and the Sun? (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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Physics
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