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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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Can life exist on the recently discovered extrasolar planets? (Beginner)
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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)
Can two galaxies move away from each other faster than the speed of light? (Intermediate)
What is a graviton? (Intermediate)
Why are there high tides during a Full Moon? (Intermediate)
Why is Neptune still considered a planet when Pluto crosses its orbit? (Intermediate)
Could there be objects orbiting interior to Mercury? (Intermediate)
Have the inner planets cleared their neighborhood? (Intermediate)
What caused the Big Bang and created the Universe? (Beginner)
If spacetime is curved, is it possible for us to look into space and see light from Earth from long ago? (Intermediate)
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What should I know about the upcoming Solar Eclipse? (2017)
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)
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What color is each planet? (Intermediate)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
How far is each planet from Earth? (Intermediate)
Where did the name 'Earth' come from? (Beginner)
Does your weight change between the poles and the equator? (Intermediate)
When was the last time all of the planets were aligned? (Beginner)
How does the location of sunrise and sunset change throughout the year? (Advanced)
How are light and heavy elements formed? (Advanced)
What is the difference between a "star" and a "sun"? (Beginner)
Can artificial gravity be created in space? (Intermediate)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
What color is each planet? (Intermediate)
How are light and heavy elements formed? (Advanced)
How far is each planet from Earth? (Intermediate)
When was the last time all of the planets were aligned? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
How does the location of sunrise and sunset change throughout the year? (Advanced)
What is the difference between a "star" and a "sun"? (Beginner)
Why do airplanes take longer to fly West than East? (Intermediate)
How is it proved that the Universe is expanding? (Intermediate)
What color is each planet? (Intermediate)
How are light and heavy elements formed? (Advanced)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
How far is each planet from Earth? (Intermediate)
When was the last time all of the planets were aligned? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
Why do airplanes take longer to fly West than East? (Intermediate)
What is the difference between a "star" and a "sun"? (Beginner)
How does the location of sunrise and sunset change throughout the year? (Advanced)
How is it proved that the Universe is expanding? (Intermediate)
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)
How long does it take for the Sun's light to reach us? (Beginner)
What is the significance of the Tropic of Cancer, Tropic of Capricorn, Arctic Circle and Antarctic Circle? (Beginner)
What is the universe expanding into? (Intermediate)
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The History of Astronomy
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