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101 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 ...
ProfRob's user avatar
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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....
HDE 226868's user avatar
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67 votes

Why did it take so long to invent telescopes given glass was used 4000 years ago in Mesopotamia?

Ancient glass was opaque or at most translucent. It was also often full of bubbles. Glass was not even suitable for windows until the first century AD, and even then it was as a means of letting ...
James K's user avatar
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58 votes
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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 ...
James K's user avatar
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47 votes
Accepted

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

This is not so hard to do. All you really need is a bit of care, a few sticks and a convenient place to observe the sunrise or sunset. So note that there is a cycle of the year and you want to know ...
James K's user avatar
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43 votes
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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 ...
Peter Erwin's user avatar
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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 ...
Mark Olson's user avatar
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37 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 ...
ProfRob's user avatar
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34 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 ...
David Hammen's user avatar
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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 ...
James K's user avatar
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31 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 ...
ProfRob's user avatar
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30 votes
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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 ...
Phiteros's user avatar
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30 votes
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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 ...
Max0815's user avatar
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30 votes
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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 ...
JdeBP's user avatar
  • 506
30 votes
Accepted

How did the ancient Greeks measure celestial angles?

In his Mathematical Syntaxis (better known as the Almagest), Ptolemy details the construction of three instruments: the plinth, the parallactic instrument, and another which he calls “astrolabe” but ...
Pierre Paquette's user avatar
29 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 ...
Nilay Ghosh's user avatar
  • 4,462
29 votes

Was Galileo expecting to see so many stars?

tl;dr: Probably yeah, Galileo was a smart guy and probably reasoned that if he could get a better view, he could see more stuff (like stars) Consider what a night sky looks like with absolutely no ...
Justin T's user avatar
  • 3,404
29 votes
Accepted

Why did the dust between the planets disappear during the birth of the solar system?

Dust happens in two ways. "Primordial dust" just condenses out of the protostellar material in the disc providing it gets cool enough and dense enough. "Second generation" dust is ...
ProfRob's user avatar
  • 153k
26 votes
Accepted

What's the issue with Olbers' paradox?

Olber's paradox is - as you state - the phenomenon, that the night sky is dark, but would have to be bright as the sun if the universe was infinite and infinitely old. The unspoken assumption here is ...
planetmaker's user avatar
  • 19.5k
25 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

It's easier than you think to notice the fraction... simply because the rounding error compounds over the years! After a good amount of years, you notice that solstices are drifting from their ...
Offirmo's user avatar
  • 351
24 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 ...
Vladimir F Героям слава's user avatar
24 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'...
usernumber's user avatar
  • 17.5k
21 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 ...
Mark's user avatar
  • 3,393
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 ...
rob's user avatar
  • 1,021
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 ...
David Hammen's user avatar
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20 votes
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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 ...
James K's user avatar
  • 123k
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 ...
PM 2Ring's user avatar
  • 14.8k
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 ...
HDE 226868's user avatar
  • 36.6k
18 votes
Accepted

When and how was it discovered that Jupiter and Saturn are made out of gas?

I'm unsure of the "history of science" aspect of this, but an actual deduction that these are gas giants would require Kepler's laws and Newton's law of gravity combined with a modest ...
ProfRob's user avatar
  • 153k
18 votes

What telescope is Polish astronomer Kazimierz Kordylewski holding in this April 1964 photo at the Jagiellonian University Observatory in Krakow?

I believe this is a 20 cm Grubb refractor with a focal length of 248 cm. This page mentions some of the telescopes at the Jagiellonian Observatory in 1964: In 1964, a jubilee 600 years of ...
Peter Erwin's user avatar
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