Most Popular
1500 questions
25
votes
4 answers
Are there any double stars that I can actually see orbit each other?
If I had a nice amateur telescope†, are there any multiple star systems that I could observe over a few years or a few decades and actually see the movement of one or both of them over time?
My short human lifespan and limited telescope put heavy…
uhoh
- 31,151
- 9
- 89
- 293
25
votes
1 answer
What's the reason that we have a different number of days each month?
It always was interesting for me to understand the answer for the question:
What's the reason that we have a different number of days each month?
If the month is fixed on the time that the moon circles the earth, then the time of the circling…
Reckless Glacier
- 737
- 8
- 15
25
votes
9 answers
Simple experimental evidence that Earth revolves around Sun
What are the simplest experiments or calculations that give evidence that the earth revolves around the sun? Can you please explain them and reference the history? Many simple explanations such as this cite observations such as that relative…
user7496
- 351
- 1
- 3
- 4
25
votes
2 answers
What exactly is the "paradox" in Olber's Paradox?
To the extent of my understanding, Olber’s paradox states that if the universe was static and homogeneous, we should see a star at every point in the night sky and therefore the night sky should be equally as bright as day.
However, since the night…
Sam
- 353
- 3
- 6
25
votes
2 answers
Why do we believe that the super massive black holes at the centers of two merging galaxies would themselves merge?
When listening to podcasts or watching youtube videos of astronomers discussing galaxy mergers, I often hear talk about how the super massive black holes at their centers will themselves merge during or shortly after the collision. Why do we believe…
asgallant
- 561
- 3
- 9
24
votes
4 answers
Is there a upper limit to the number of planets orbiting a star?
Our sun has 8 planets orbiting as well as a number of dwarf planets. Are there any calculations that hint as to whether this number is close to some theoretical maximum value or are we simply an average solar system in this particular way?
I could…
bogen
- 2,356
- 2
- 18
- 32
24
votes
8 answers
Why can't we see distant galaxies with the naked eye?
If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if this is a dumb question:)
Guit4eva
- 341
- 1
- 2
- 3
24
votes
4 answers
Is Jupiter made entirely out of gas?
I heard that Jupiter is made out of gas. But in school I learned that Jupiter has gravity which is 2.5 times that of Earth (Gravity that can tear apart a comet) and gravity is proportional to mass.
So if Jupiter is made out of gas alone, how does it…
Strikers
- 1,109
- 3
- 11
- 16
24
votes
2 answers
Can you see man-made lights on the dark side of the Earth from the surface of the moon with the naked eye?
This question is prompted from a comment on this answer:
Could a person on the surface of the moon see man-made lights on the dark side of the Earth with the naked eye? If not, how much magnification would be required to do see them?
The closest…
reirab
- 343
- 3
- 9
24
votes
6 answers
Can a natural satellite exist in a geostationary orbit?
While browsing through Physics SE, I noticed a question about satellites in geostationary orbit (unrelated to the one I'm asking here), and for a moment I interpreted it as referring to natural satellites (e.g. a moon). So I wondered: Could a…
HDE 226868
- 36,553
- 3
- 123
- 201
24
votes
3 answers
Did the Sun's light always peak in the green wavelengths?
So, I know the sun is getting brighter over it's lifespan and I'm wondering how that affects its emission spectrum. The reason I'm asking this is because I find it weird that plants reflect green light, when it's the most abundant wavelength. Was it…
Elhammo
- 1,107
- 5
- 13
24
votes
3 answers
Is the Big Bang a theory or a model?
I ask this because someone mentioned ‘it isn't a theory, it's a model’ in the comments in an old question of mine: Is the expansion of the universe proof of the big bang?
I guess defining terms is important. If there are different opinions about…
Kilise
- 435
- 3
- 9
24
votes
2 answers
How much larger will the "observable by us" universe be when JWST becomes operational?
Right now, using all our various current means of observing, we can "see" a sphere of X diameter around us. Webb will increase that to Y diameter. So our observable volume will increase by some percent (Volume Y - Volume X) / Volume X.
I'm not sure…
BradV
- 737
- 3
- 15
24
votes
2 answers
Why does the Moon stablize Earth's axis?
In an academic study titled 'The Moon and the Origin of Life on Earth' it is said that
'If the Moon did not exist, the orientation of the Earth’s axis would not be stable, and would be subject to large chaotic variations over the ages. The…
Kyriakos Kyritsis
- 529
- 2
- 5
24
votes
6 answers
What makes protoplanetary disks start rotating? (Initial energy needed to rotate)
Planets form from a protoplanetary disk that has been rotating around its star. The initial energy that makes them rotate really matters to me.
Why did the protoplanetary disk start rotating around the star?
Where did the initial energy to rotate…
Farid Rjb
- 343
- 2
- 7