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A line drawn perpendicular to a line through the tips of the horns of the crescent moon doesn't point to the Sun! Why not?
(Advanced)
Can we look back far enough in time to see the Big Bang?
(Beginner)
Can we look back in time and see our galaxy forming?
(Intermediate)
Can you use an infinite line of reflectors to send light to the edge of the Universe?
(Intermediate)
Could dark energy come from matter anti-matter pairs forming spontaneously and then annihilating?
(Advanced)
Could photons be dark matter?
(Intermediate)
Has there been an experiment that measured speed faster than the speed of light in vacuum?
(Advanced)
How can we see galaxies if their stars are so faint?
(Intermediate)
How do we know that nuclear fusion is still going on in the Sun?
(Intermediate)
How has light from 13 billion years ago not passed us by?
(Beginner)
How long does the supernova stage of a star last?
(Intermediate)
How much power is contained in a beam of light?
(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 it possible to measure the temperature of the Sun?
(Beginner)
Is light blueshifted when it is gravitationally lensed?
(Intermediate)
Is the green flash real?
(Beginner)
What color would Mars be if you were standing on it?
(Advanced)
What do a galaxy's colors mean? Are they its true colors?
(Intermediate)
What is a star's "spectrum"?
(Beginner)
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What is the difference between the "Doppler" redshift and the "gravitational" or "cosmological" redshift? (Advanced)
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Do galaxies that are receding from us faster than the speed of light disappear from our observations? (Intermediate)
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Why are there high tides during a Full Moon? (Intermediate)
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Have the inner planets cleared their neighborhood? (Intermediate)
What caused the Big Bang and created the Universe? (Beginner)
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What should I know about the upcoming Solar Eclipse? (2017)
What is the universe expanding into? (Intermediate)
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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)
When was the last time all of the planets were aligned? (Beginner)
Can artificial gravity be created in space? (Intermediate)
Why do airplanes take longer to fly West than East? (Intermediate)
Is the universe expanding faster than the speed of light? (Intermediate)
What is the difference between a "star" and a "sun"? (Beginner)
Is the distance from the Earth to the Sun changing? (Advanced)
Why do we not have eclipses every month? (Beginner)
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 far is each planet from Earth? (Intermediate)
When was the last time all of the planets were aligned? (Beginner)
Can artificial gravity be created in space? (Intermediate)
What is the difference between a "star" and a "sun"? (Beginner)
Why do the planets orbit the sun? (Beginner)
How do you measure the distance between Earth and the Sun? (Intermediate)
Why do airplanes take longer to fly West than East? (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)
What color is each planet? (Intermediate)
How far is each planet from Earth? (Intermediate)
When was the last time all of the planets were aligned? (Beginner)
Why are the Moon and Sun sometimes orange or red? (Beginner)
What is the difference between a "star" and a "sun"? (Beginner)
Can artificial gravity be created in space? (Intermediate)
At what speed does the Earth move around the Sun? (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'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)
How long does it take for the Sun's light to reach us? (Beginner)
When was the last time all of the planets were aligned? (Beginner)
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