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1500 questions
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How scientists find the direction of rotation of planets?
How do we know that Mercury, Earth, Mars, Jupiter, Saturn, and Neptune rotate counterclockwise and Venus, Uranus, and Pluto rotate clockwise? How do scientists determine the direction of rotation of planets?
apk
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How did astronomers get rid of microwave radiation from stars and galaxies in picures of the CMB?
Images of the CMB show no sign of stars or galaxies. If they did, shouldn't the Milky Way be a bright band dividing the CMB into hemispheres? Black body radiation in a given wavelength/frequency range gets more intense as the object in question gets…
zucculent
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What limits the usable focal length of telescopes currently?
What barriers - of technology, physics and possibly economy (things that would be possible technologically but are simply too expensive) sets the upper bound on quality of telescopes for observation of the sky in visible spectrum - observing surface…
SF.
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What are those stars that cross the galactic center?
I found this GIF by the European Southern Observatory (ESO) in the Wikipedia article on the galactic year, with the following description:
Visualisation of the orbit of the Sun (yellow dot and white curve) around the Galactic Centre (GC) in the…
d_e
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At what point in history was the idea of planets being spit out by the sun abandoned?
For context, at some point during the 20th century (and maybe earlier as well), the most popular planet formation theory and the one that was taught at (at least some) schools was the theory that the planets were somehow ‘spit out’ by the sun.
I am…
Justin T
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Depth of gravitational well within our local Virgo supercluster?
For simplicity we could imagine standing at the north pole so we do not have to care about how fast we are moving in relation to the gravitational field of the earth.
Now calculating how much faster our clock will tick if the earth suddenly…
Agerhell
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How exactly did JWST take a "selfie" of its own primary mirror, and what is the real purpose of this capability?
CNN's Webb telescope's first test images include an unexpected 'selfie' says only:
The mirror selfie was captured by a special lens inside NIRCam that can image the primary mirror rather than what Webb sees in space. The lens mainly exists for…
uhoh
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14,000 square degrees
The DESI Legacy Imaging Surveys says it produces a model of “the 14,000 square degrees of extragalactic sky visible from the northern hemisphere”. But I thought the whole celestial sphere (like any other sphere) had only $(180/\pi)^2 \approx 3282.8$…
Charles
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Are there a lot of collisions between stars in the core of the galaxy?
I'm reading on Wikipedia about Halo Stars that orbit the center of the galaxy at a high inclination away from the plane of the Milky Way. It seems that at some point, these stars must dive back into the core of our galaxy at very high relative…
Kevin Holmes
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Can you see the shadow of a spaceship on the Moon while looking towards the Earth?
It's a classic movie cliche. We see the surface of the Moon with the Earth in the distance and a dark shadow of an invading alien spaceship slowly covering the landscape.
We see this in the opening sequence of the 1996 movie Independence Day, and I…
Reactgular
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How exactly was Giovanni Cassini able to measure the distance to Mars?
Recently learned that Cassini was able to calculate the distance to Mars quite well using parallax in 1672. I was surprised, since even at opposition of Mars, the parallax (with respect to the Earth's Center) is about 30 sec arc. While I know that a…
d_e
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11
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How do rocky objects between 1cm and 1m accrete to form planetesimals?
I am having a hard time gaining an intuitive understanding of some of the middle stages of planetary formation from a protoplanetary accretion disk.
I understand that microscopic dust particles may accrete through something like electrostatic…
user438383
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Can earth grazers skip on the atmosphere more than once?
Earth grazing fireballs are asteroids that enter the atmosphere at a low angle, and skip off it, leaving to space again. Would it be possible that they skip more than once and still leave the atmosphere?
2080
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Will the James Webb Space Telescope be visible from earth?
Once the JWST is in orbit around L2, would it be possible to view it using any ground based telescopes? I’m mostly thinking of equipment available to amateurs, since I don’t have a 10m reflector. But would this be feasible for anything we have built…
user287095
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What's the meaning of virial in Astronomy, and in particular the expression "a virialized cluster of galaxies"?
The virial theorem relates the kinetic energy of a system to the total potential energy of the system:
$
\Delta K = -\frac{1}{2}\Delta V
$
so it has lots of uses in mechanics, thermodynamics and astrophysics.
My main question is what is the meaning…
Jim421616
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