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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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Why are astronomers interested in gravitational waves? (Intermediate)
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What what a black hole merger look like from a telescope? (Advanced)
Do galaxy mergers have a major impact on star formation rates within the galaxies? (Intermediate)
Our universe is still expanding, does that mean things in our daily life are expanding? (Intermediate)
What was the bright, smoothly moving star that I saw? (Beginner)
What happened to the Arecibo Telescope? (Beginner)
Can I buy or name a star? (Beginner)
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)
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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 are the advantages and disadvantages of using a telescope in space? (Intermediate)
Is it possible to see the full Moon and the Sun simultaneously in high northern latitudes when the Sun doesn't set? (Intermediate)
Why is looking out into space the same as looking back in time? (Beginner)
What is the observational difference between a star and a planet? (Beginner)
Can you fire a gun on the Moon? (Intermediate)
Why do planets rotate? (Intermediate)
Does the Sun have a scientific name? (Intermediate)
How long does the supernova stage of a star last? (Intermediate)
Is the speed of light constant? (Beginner)
What what a black hole merger look like from a telescope? (Advanced)
What is the difference between a "star" and a "sun"? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
Which planet is most similar to Earth? (Intermediate)
How long could life on Earth survive if the Sun stopped shining? (Beginner)
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)
What color is each planet? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
How does the position of Moonrise and Moonset change? (Intermediate)
How do you measure the distance between Earth and the Sun? (Intermediate)
What is the difference between a "star" and a "sun"? (Beginner)
How long could life on Earth survive if the Sun stopped shining? (Beginner)
How are light and heavy elements formed? (Advanced)
Why do the planets orbit the sun? (Beginner)
Which planet is most similar to Earth? (Intermediate)
At what speed does the Earth move around the Sun? (Beginner)
What color is each planet? (Intermediate)
Are there telescopes that can see the flag and lunar rover on the Moon? (Beginner)
How does the position of Moonrise and Moonset change? (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)
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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People & Astronomy
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Space Exploration & Astronauts
The History of Astronomy
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