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95 votes
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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 ...
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81 votes
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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....
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55 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 ...
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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 ...
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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 ...
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33 votes
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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 ...
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33 votes
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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 ...
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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 ...
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32 votes
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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 ...
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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 ...
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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 ...
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28 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 ...
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28 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 ...
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28 votes
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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 ...
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26 votes
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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 ...
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26 votes
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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 ...
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23 votes
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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 ...
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23 votes
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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 ...
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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'...
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20 votes
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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 ...
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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 ...
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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 ...
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  • 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 ...
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  • 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 ...
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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 ...
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17 votes
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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 ...
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17 votes
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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 ...
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16 votes
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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 ...
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15 votes
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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 ...
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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 ...
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