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1500 questions
17
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1 answer
How can an amateur astronomer verify the position of near Earth objects?
Sometimes, hobby-astronomers use rather professional means to observe the big voids of space. Every now and then (think in months, not days) even I can locate an NEO (near Earth object).
Now, I'm assuming governments and institutions worldwide track…
e-sushi
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17
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4 answers
What is the shape of orbit assuming gravity does not depend on distance?
We know that the orbit of the earth is elliptical considering the force of gravity is inversely proportional to the square of the distance. But assume that, gravity does not depend on distance. Considering that situation, what will be the shape of…
Arafat
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17
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1 answer
Why do cosmologists assume that inflation began shortly after the Big Bang, rather than at the exact start?
Somehow, I have never come across an explanation of why cosmologists claim that the alleged inflation of the very early universe occurred not at the Big Bang, but very shortly afterwards (~10^-36 to 10^-32 seconds afterwards)....
Why? What…
Kurt Hikes
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17
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Where was the solar system born? Alternatively, how far back in time can we retrodict the location of the solar system?
I have two related questions:
Where in the Milky Way did the solar system form? Is there a particular nebula it can be traced to?
How far back in time can we track the location of the solar system within the Milky Way with reasonable…
Tim Campion
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17
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How do we know the moon is smaller than Earth?
The moon is smaller than the Earth, but how do we know that (without the use of modern technology)? To be more specific, how can we show that the moon is smaller than the Earth (smaller diameter) with technology before 1800s?
Obama2020
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2 answers
How do planetarium apps and software calculate positions?
In the most general terms (I'm not asking for the actual calculations), how do popular planetarium apps and software calculate the positions of celestial objects? Planets, for example. Do they use Keplerian formulas with their associated elements…
Peter
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How could low-gravity dust in the early solar system have formed hard stones?
I wonder how very low-gravity dust could make bind together and make hard and dense stones that later on will merge together and make some of the planets? I read some meteorites as hard as a hard stone are remnants of the early phase of solar…
Mehdi Abbassi
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17
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2 answers
On Mars, why are the seasons "strongly amplified" in the southern hemisphere and masked in the northern hemisphere?
In the Darian calendar entry on Wikipedia we read (emphasis mine):
The Martian year is treated as beginning near the equinox marking
spring in the northern hemisphere of the planet. Mars currently has an
axial inclination similar to that of the…
d_e
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17
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3 answers
If planets are ellipsoids why don't we have 3 diameters?
We know that each ellipsoid has 3 diameters named $2a$, $2b$, and $2c$.
The Earth and all planets, in general, are ellipsoids (Saturn is the best example because it's the most oblate planet in the solar system).
But all we have read and heard are…
Snack Exchange
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3 answers
Can the Earth be seen from the moon when we have a total lunar eclipse at the perigee?
We know that the Moon doesn't have an atmosphere; thus the sky is seen dark.
Also, from this question, the angular diameter of the Earth viewed from the Moon is a bit bigger than $2^\omicron$ at the perigee, meaning that it will block the Sun…
Snack Exchange
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17
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3 answers
Dimensions of a black hole
How big can a black hole become and how small can a black hole become?(minimum and maximum dimensions of a black hole)
M.Tarun
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17
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4 answers
If the Sun was replaced with a sun-mass black hole, would it be visually detectable?
Assuming it had no accretion disk, could we still detect e.g. distortions of the background star field?
2080
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Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?
When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us.
As I understand it, the consensus among cosmologists is that this observation is best explained by the expansion…
Brionius
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17
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2 answers
How do we know that the planets of our solar system began their formation at more or less the same time?
A long time ago, when I had to help my children with their homeworks, I often had the vexing question « how do we know ? ». It is true that reading a middle-school science textbook is like reading another Bible. Hardly do we have an explanation:…
Ng Ph
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17
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1 answer
Is stellar ignition all-or-nothing?
The boundary between brown dwarfs and stars is around 80 Jupiter masses. Only stars generate a self-sustaining hydrogen fusion, although brown dwarfs sometimes fuse lithium and deuterium.
Is hydrogen ignition all or nothing? If so, there should be a…
Kevin Kostlan
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