175
votes
Accepted
How can there be 1,000 stellar ancestors before our Sun?
The Sun is actually a THIRD generation star. What I mean by this is that there are chemical elements in the Sun that were made inside another star, but that star itself can only have made those ...
- 152k
114
votes
Accepted
Would we have more than 8 minutes of light, if the Sun "went out"?
If nuclear fusion were to suddenly stop in the centre of the Sun, then the only clear signature we would have of this is the lack of detectable neutrinos received at Earth, starting about 8 minutes ...
- 152k
86
votes
Accepted
How did Astronomers deduce that the Sun was not a ball of fire?
I think it's maybe not the case that there was a moment when the astronomy community conclusively rejected the ball-of-fire hypothesis; astronomers simply accumulated more and more evidence against it....
- 36.6k
76
votes
Accepted
Is it dark inside the Sun?
No, it's not. The radiation field in the interior of the Sun is very close to a blackbody spectrum.
If you look in any particular direction the brightness (power per unit area) you see is $\sigma T^4$,...
- 152k
74
votes
Accepted
Why can't we see Saturn's phases from earth?
Phases are just different perceived illuminations of an object at different illumination and observing angles. If the observer is, with respect to the object, located in a similar direction as the ...
- 3,916
71
votes
Sun constantly converts mass into energy, will this cause its gravity to decrease?
If the sun is constantly converting the mass into energy, then will its gravitational field go on decreasing?
It's a very interesting question and the answer is yes!
The solar constant indicates the ...
- 31.1k
70
votes
What happens to the 99.9 % of the sun-rays that do not fall on any planets or any other celestial body?
The light from the Sun spreads, at least initially, in a roughly isotropic fashion into the universe.
As it gets further from the Sun, some of that light will interact with the interstellar medium (...
- 152k
68
votes
Accepted
When will the Sun end all human life on Earth?
The Sun is gradually getting larger and brighter. In fact, as called2voyage pointed out, its brightness is increasing by 1% every 100 million years. You can see how the Sun will change in the future ...
- 8,115
64
votes
Why is moon light not the same color as sunlight?
The light from the moon is light being reflected from the sun.
This is at least one reason you should not expect the Moon to have the same color. Sunlight hitting an e.g. blue object would appear ...
- 6,341
63
votes
How were sundials and moondials possible 800 years ago?
As @JohnHoltz points out in a comment, planting a stick in the ground or in a wall and watching where the shadow falls is something very easy; sundials have been known since prehistoric times.
I’m not ...
- 7,492
61
votes
Do our sun and moon have names?
What is a name?
A name is a word, that is reasonably unique, that is used to identify a person or thing. When a child is born there is no word that identifies it, and so its parents have to choose a &...
- 121k
60
votes
Accepted
Why isn't the asteroid belt affected by Jupiter's gravitational field?
The asteroid belt is affected by Jupiter's gravity.
There are stable orbits inside of Jupiter's orbit. Jupiter's Hill Sphere has a radius of 53 million km. If you are more than 53 million km from ...
- 121k
60
votes
Is there enough matter orbiting the sun to make a second sun?
The vast majority of the stuff in the solar system other than the Sun itself is contained in one body, Jupiter. The total mass of the solar system is estimated to be about 1.0014 solar masses, or ...
- 34k
57
votes
Why can't we see Saturn's phases from earth?
All the other answers here are complete, and more in-depth than anything I would write. However, if you prefer to look at things visually, here is a terrible not-to-scale 2 minute paint drawing.
No ...
- 671
56
votes
Accepted
Why does the Sun have different day lengths, but not the gas giants?
It's a matter of how "day" is defined.
Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:
The equations for ...
- 3,393
52
votes
Accepted
Is the sun's volume shrinking currently?
Is the sun shrinking currently?
It's the other way around: The Sun is slowly growing hotter and thus is slowly expanding. The Sun accumulates ever more helium in its core as it ages. This growing ...
- 34k
52
votes
Accepted
How much of the surface of other planets is lit by the sun?
OK, let start with some assumptions: spherical objects and no atmospheric effects.
Here's the relevant geometry with the object on the left representing a planet and the object on the right ...
- 2,339
50
votes
Accepted
Is the Solar core hard?
The solar core can be considered soft in a relative sense (compared to other materials at the same density), but hard and incompressible in an absolute sense. The material behaves almost exactly like ...
- 152k
48
votes
When will the Sun end all human life on Earth?
At what point will the sun make earth uninhabitable for humans?
It nearly happened on May 23, 1967.
According to this history paper released yesterday, summarized nicely here on Space.com, at the ...
- 597
47
votes
Accepted
Does the sun cross other spiral arms in its movement around the galaxy's center?
What is a spiral arm?
The reason that the Sun, in principle (but see below), may cross spiral arms is that galactic spiral arms are not rigid entities consisting of some particular stars; rather they ...
- 38.2k
47
votes
Accepted
Why is the summer solstice night shorter than the winter solstice day?
Why is the summer solstice night shorter than the winter solstice day?
Aside: If you use your sunrise / sunset calculator you will see that day and night are not equal at the equinoxes. The reason ...
- 34k
46
votes
Why is the Sun's density less than the inner planets?
The sun isn't the same density all the way through.
According to MSFC's solar interior page, the core density at the centre of the sun is a whopping 150,000 kg/m$^3$. Surrounding it the radiative ...
- 2,467
46
votes
Can a lunar eclipse happen at night and be followed by a solar eclipse the next day?
No.
A lunar eclipse occurs when the moon is on the opposite side of the Earth as the sun.
A solar eclipse occurs when the moon is on the same side of the Earth as the sun. And it takes the moon 14 ...
- 121k
45
votes
Accepted
Do we know a star that is similar to the Sun when it would be a red giant?
Models for the future behaviour of the Sun do vary, mainly as a result of uncertainty of mass loss during the red giant (H shell burning) and asymptotic red giant (H+He shell burning) phases.
A ...
- 152k
45
votes
How were sundials and moondials possible 800 years ago?
Those 2 wheels work like a perfect sundial.
No they don't. They're flat. The timespan from one hour to the next on a flat sundial varies from season to season. At the same time that that temple was ...
- 34k
44
votes
Sun constantly converts mass into energy, will this cause its gravity to decrease?
I wanted to expand a bit on a point @uhoh made. (I would have made this a comment, but lack the reputation). The Sun is not converting mass to energy. The Sun is converting matter (not mass) into ...
- 541
43
votes
Why is moon light not the same color as sunlight?
Reflected moonlight is actually slightly reddened compared with the incident solar spectrum (Ciocca & Wang 2013). That same light is then transmitted through out atmosphere in exactly the same way ...
- 152k
41
votes
Simple experimental evidence that Earth revolves around Sun
The answer is ironic: Without good instruments, there is no evidence. The people who thought that the Sun went around the Earth were perfectly correct as far as the actual evidence went until the ...
- 7,650
Only top scored, non community-wiki answers of a minimum length are eligible