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1500 questions
19
votes
6 answers
Why do small mirror imperfections matter with modern computers
Modern telescopes go to great lengths to have perfectly shaped parabolic mirrors. My question is, why go to the trouble of having a perfect mirror? Why not take a mirror roughly the right shape, and then correct for the distortion using computers?
DanielOfTaebl
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votes
3 answers
Why can space telescopes see through a planetary nebula?
I recently read the book "An Introduction to Planetary Nebulae" by Jason J. Nishiyama. Although I'm not an astronomy student, I could at least understand the written texts and less the physical formulas. So, I got a nice basis knowledge now -- or…
kiaat
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19
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4 answers
Can Newton's gravity equation explain why black holes are so strong?
I was just wondering why black hole's gravitational forces are so powerful. I know it's usually explained by Einstein's relativity which states that when an object becomes infinitely dense (a compact mass) it can exert such a force of gravity and…
AdiBak
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19
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2 answers
Why is the Moon receding from the Earth due to tides? Is this typical for other moons?
After reading the Q&A Is the moon moving further away from Earth and closer to the Sun? Why? about the tides transferring energy to the Moon and pushing it from Earth, I have a question:
How is that energy actually being transferred to the Moon? The…
Danubian Sailor
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19
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1 answer
Serious alternate form of the Drake Equation, or graffiti?
Where I live it is very common to see jackets and T-shirts with familiar yet casually garbled or modified content (example)
I recently spotted what looked a lot like the Drake equation on the back of a motorcycle, shown in the photo.
Here is the…
uhoh
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19
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1 answer
Exoplanet dip in transit light curve when the planet passes behind the star
In the animation below, I don't understand why the brightness slightly decreases when the planet is behind the star.
Where does this effect come from?
user16492
19
votes
4 answers
What are "non-Keplerian" orbits? What are some familiar examples in our solar system, and can some still be closed?
This excellent answer to Forms of stellar orbits around the galactic center invokes the following concepts:
non-Keplerian orbits
closed orbits
I have a fairly good idea what these mean and so might many of us, but our ideas may not overlap…
uhoh
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19
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2 answers
Can lightning occur in stars like the Sun?
In the Wikipedia article about lightining, the following explanation is given about the electrification process in clouds:
The details of the charging process are still being studied by
scientists, but there is general agreement on some of the…
ksousa
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19
votes
2 answers
Problem regarding the absorption lines of the Sun
Some of the wavelengths of light that are emitted from the Sun will be absorbed by atoms in the outer layer of the Sun and also the atmosphere of the Sun, and we see this as absorption lines in the spectrum. Now, this absorbed radiation will indeed…
User3141
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19
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3 answers
How can the 13.8 billion years old universe have a radius of 46 billion light years?
The universe is about 13.8 billion years old. Assume at the big-bang it starts from a small region and the maximum possible speed according Einstein is the speed of light how can the universe got a radius of 46 billion light years? According my…
Wernfried Domscheit
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19
votes
3 answers
During an eclipse, how big is the shadow of the moon on the earth?
This picture was taken from the ISS during a solar eclipse.
You can see the shadow of the Moon on the surface of the Earth. But how big is this shadow? How many kilometers is its diameter?
usernumber
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19
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3 answers
Why are asteroids with zero orbital inclination rare?
This is a plot of orbital inclination ($i_p$) vs. semi-major axis ($a_p$) of 96944 asteroids in the Main Belt, done by Piotr Deuar.
Some structure can be seen in this diagram; clumps are asteroidal families and vertical empty spaces are Kirkwood…
Swike
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19
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1 answer
Why isn't the asteroid belt affected by Jupiter's gravitational field?
Jupiter's mass is just about a 1000th of the sun's and the asteroid belt is slightly closer to Jupiter than it is to the sun.
If the heavier the object, the more curvy space is around it, why isn't the asteroid belt's movement more turbulent owing…
wireman
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19
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1 answer
Moon's unusual gravity
We know that the Moon's gravity is about one-sixth that of Earth. Then I recently read that the mass of the Moon is about one-eightieth the mass of Earth. Since gravity depends on the mass of the 2 objects, shouldn't the Moon's gravity be…
John Canon
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2 answers
How do we know Nemesis is not a black hole (or neutron star)?
Nemesis, the hypothetical "death star", is supposed to be a massive body that orbits the Sun at long distances and periodically sends comets from the Oort Cloud into the inner solar system. These comets impact the Earth and cause extinction events.…
Allure
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