95
votes
Accepted
Could the dinosaurs have seen the asteroid that killed them?
The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could be a bit longer than this if the body was larger ...
- 115k
81
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....
- 33.8k
55
votes
Accepted
How did Eratosthenes know that the sun is far away?
The sun and the moon go around the observer once a day, Eratosthenes knew that the apparent size of moon doesn't change. This must mean that Alexandria is near the centre of the moon's orbit. But ...
- 88.7k
43
votes
Accepted
Are there any old/ancient star maps that we can compare to today’s and see drastic differences?
In practice, you're probably not going to get anything useful from ancient star maps, for several reasons:
Very few of them actually survive from more than a few hundred years ago.
Maps (and visual ...
- 14.7k
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 ...
- 7,390
33
votes
Accepted
How did Ole Christensen Romer measure the speed of light?
Ole Rømer did not measure a change in the frequency of light. He measured an apparent change in the orbital period of Io, one of Jupiter's moons.
The orbit of Io can be measured very accurately by ...
- 88.7k
33
votes
Accepted
When was it worked out/discovered that our sun can't go supernova?
I think the definitive work is that of Hoyle & Fowler (1960).
They argued that supernovae were produced by two possible mechanisms - what they called an implosion/explosion or an explosion within ...
- 115k
32
votes
How did Kepler "guess" his third law from data?
Kepler's account of how the third law came to be is as follows (Caspar p.286; emphasis mine):
On the 8th of March of this year 1618, if exact information about the time is desired, it appeared in ...
- 7,674
32
votes
Accepted
How was the mass of Venus determined?
How was the mass of Venus measured for the first time?
In the mid 19th century, Urbain Le Verrier's predicted of the existence of a then unknown planet beyond the orbit of Uranus. He even predicted ...
- 28.1k
30
votes
Accepted
When did people first measure that the Earth was closest to the Sun during January?
Hipparchus, not Kepler
Kepler got the conic sections right, and Newton gave us the mechanics. But the question is about when people knew that the Earth was closer to Sol in one part of the year than ...
- 506
29
votes
How did Eratosthenes know that the sun is far away?
Exactly how Eratosthenes calculated the radius of the Earth has been lost. What is presently taught as his method is a simplified version described by Cleomedes.
It is unlikely that Eratosthenes ...
- 115k
28
votes
Accepted
What exactly is the "paradox" in Olber's Paradox?
Olber's Paradox was created at a time before the idea of a finite universe was accepted. (It was thought of in the 1600's). In order to resolve Olber's Paradox, you have to introduce the idea that ...
- 3,046
28
votes
Accepted
What's the reason that we have a different number of days each month?
You make a great point. The reason behind the discrepancy between the dates is due to a complicated history behind it.
The calendar is based on the calendar created by ancient Romans, which is based ...
- 1,630
28
votes
Accepted
Why was there a gap in the number of asteroid detections between 1807 and 1845?
Ceres, Pallas, Juno and Vesta were all discovered between 1801 and 1807. After that, astronomers looked in vain for 38 years until the 5th, Astraea was spotted on December 8, 1845 by German amateur ...
- 3,236
26
votes
Accepted
How did Kepler "guess" his third law from data?
Kepler's third law is trivial (in my opinion) compared to his first law. I am quite impressed that he was able to deduce that the orbits were ellipses. To get that, he had to go back and forth ...
- 634
26
votes
Accepted
How was the Earth-Sun distance originally calculated?
The book The Transits of Venus, by Sheehan and Westfall, describes how Aristarchus used Hipparchus' calculation of the Earth-Moon distance, who in turn used Eratosthenes' calculation of the Earth's ...
- 778
23
votes
Accepted
How did our ancestors discover the Solar System?
1. Ancient cultures observed the sky
Night skies are naturally dark and there was no light-pollution in ancient times. So if weather permits, you can easily see a lot of stars. No need to tell about ...
- 952
23
votes
Accepted
Has great eyesight been necessary for astronomers?
Johannes Kepler
Wikipedia:
"However, childhood smallpox left him with weak vision and crippled
hands, limiting his ability in the observational aspects of
astronomy."
He made great use of ...
23
votes
How did Astronomers deduce that the Sun was not a ball of fire?
Scientists figured that the sun couldn't be a ball of coal during the industrial age, because given the mass of the Sun, all the coal would have burned out before humans appeared on Earth. But we didn'...
- 16.8k
20
votes
Accepted
We know what a nova is, but how?
Following a reference to Darley et al., ApJ 746, 61 (2012) from your Wikipedia link gives a (very technical) discussion of nova progenitors, including distinctions between nova systems where the ...
- 971
20
votes
Simple experimental evidence that Earth revolves around Sun
You cannot prove that the Earth orbits the Sun rather than vice versa because this goes very much against the grain of all frames of reference being equally valid (but some make a lot more sense than ...
- 28.1k
20
votes
Accepted
How much does the sky change in a few thousand years?
Here's part of the sky in the year 1
It is part of the sky you may know well, Orion and the dogs. I've marked the current positions of Sirius, Procyon and Betelgeuse, with green markers so you can ...
- 88.7k
19
votes
Was lunar libration first observed or first predicted? In either case, who was the responsible party?
The variable speed of the Moon on the celestial sphere has been known since ancient times. The Babylonians made ~7 centuries of daily astronomical observations from around 700 BC. That data was the ...
- 9,379
18
votes
Has radio astronomy ever been done on objects that appear very close to the Moon? Is this avoided?
Yes, and lunar occultations have proved useful in several cases.
Hazard et al. 1963 used a lunar occultation to produce a high-resolution brightness profile of the now well-studied radio quasar 3C ...
- 33.8k
18
votes
How was the mass of Venus determined?
The mass of Venus was determined by weighing the Earth, or more precisely, by determining the ratio of the density of the Earth to the density of Schiehallion, and assuming Schiehallion to be typical ...
- 2,958
17
votes
Accepted
Metallicity of Celestial Objects: Why "Metal = Non-metal"?
To first order, the relative abundances of the heavier elements to iron (for instance) are constant. So the metal content of a star is shorthand for the content of any element heavier than He. (NB: we ...
- 115k
17
votes
Accepted
How did the authors of Surya Siddhanta find the diameters of other planets in the solar system?
The authors assume a geocentric universe (first thing that is wrong). They then assume that the planet Mars has the same apparent diameter as a globe 30 yojana in diameter (about 150 miles) in the ...
- 88.7k
16
votes
Accepted
When did scientists discover that the Sun has a life cycle and that it is going to die?
Although various astronomers have speculated that the Sun was a star (some were imprisoned or even burnt alive for such heresy), this was not known definitively until 1838 when Friedrich Bessel used ...
- 28.1k
15
votes
Accepted
When was the martian dichotomy first observed?
It looks like the Mariner 9 era.
Based on a review paper by Watters et al. ("Hemispheres Apart: The Crustal Dichotomy on Mars"): "The north-south asymmetry ... was clear from the first ...
- 1,843
15
votes
At what point in history was the idea of planets being spit out by the sun abandoned?
That specific idea doesn't seem familiar to me, and I work in that field. Particularly this idea would only be called 'theory' when making testable predictions.
The only thing that comes to mind here ...
- 9,069
Only top scored, non community-wiki answers of a minimum length are eligible