Questions tagged [astronomy]

The study of celestial objects and phenomena outside of the Earth's atmosphere.

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Why do we call Tycho Brahe by his first name?

Why do we use the fist name in Tychonic system or Tycho's comet of 1577, instead of using the last name of Tycho Brahe? For comparison, we have the Ptolemaic system and the Copernican system. I am ...
timur's user avatar
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What attracted Einstein to the anomalous precession of Mercury?

The story is usually told starting with Einstein's 1915 paper Explanation of the Perihelion Motion of Mercury from General Relativity Theory, or at least its drafts from 1913-14. It was the first ...
Conifold's user avatar
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26 votes
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Is there an astronomical reason behind the order for the names of days of the week?

The seven days of the week seems to be commonly named after celestial bodies. What I find curious is that all seven days apparently share the same names in both West and East. Sunday is, of course, ...
Semaphore's user avatar
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When did it become possible to predict the time and place of solar eclipses?

That is, when did astronomy figure out how to predict when and where a solar eclipse will be visible? It seems people noticed fairly early on that the Sun, Moon and Earth return to the same ...
Semaphore's user avatar
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5 answers
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Did Galileo Galilei believe in astrology?

The Wikipedia page on Gallileo Galilei mentions, among other things: His multiple interests included the study of astrology, which at the time was a discipline tied to the studies of mathematics and ...
Kostya's user avatar
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How did Kepler "guess" his third law from data?

It is amazing that Kepler determined his three laws by looking at data, without a calculator and using only pen and paper. It is conceivable how he proved his laws described the data after he had ...
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21 votes
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Who first measured the distance to the Moon? How was it done?

Who first measured the distance to the Moon? How was it done? I think it had to happen after Newton, but I am not sure.
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When & how was it known that our Sun is the same thing as the night time stars?

Who was the first person to conjecture that our Sun is just another star? Relatedly, what was the first evidence that this was true?
BMS's user avatar
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When was it realized that the giant planets do not have solid surfaces?

When was it realized that the gas giant planets Jupiter and Saturn, and the ice giant planets Uranus and Neptune, do not have solid surfaces? When was that idea first proposed and when was it accepted ...
M.A. Golding's user avatar
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Before 1964, did scientists generally believe there was life on Mars?

Mariner 4 was the first spacecraft to return photographs of Mars from near the planet, making its flyby of Mars in 1964. Those photographs showed what appeared to be a barren, desert surface. ...
Joe's user avatar
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How did Ptolemy know that days were unequal lengths?

Apparently Ptolemy was aware of the fact that the duration of time from noon to noon varied by many seconds throughout the course of a year. In modern times this fluctuation in length of day leads to ...
Jagerber48's user avatar
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What data did Kepler work out his laws from?

It's well known that Kepler worked out his laws by fitting curves to Tycho Brahe's data on the trajectories of planets through the sky. What was this data? How does one record the trajectory of a ...
Jack M's user avatar
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Did Archimedes use epicycles in his planetarium?

Archimedes constructed a planetarium where as described by Cicero "he had thought out a way to represent accurately by a single device for turning the globe those various and divergent movements with ...
Conifold's user avatar
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How did Babylonians figure out that the evening star is the morning star?

Hesperus (Roman Vesper) is the name ancient Greeks gave to the evening star that appears in the sky for an hour after the Sun sets. Phosphorus (Roman Lucifer, sic!), was the name of the morning star ...
Conifold's user avatar
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Who was the first to postulate that space was a vacuum?

The fact that space is a vacuum and that the Earth's atmosphere only extends a short way above the surface is accepted as obvious. However, there is nothing a priori obvious about it: you first have ...
Emilio Pisanty's user avatar
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Hidden agenda of the Galileo trial?

Redondi argued that Galileo's trial on heliocentrism was merely a show trial concealing the real objection against Galileo among the catholic establishment, which was his atomism thought to be at ...
Mikhail Katz's user avatar
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15 votes
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Why did 18th century writers think that Mars had 2 satellites?

At least two 18th century writers wrote that Mars has two satellites: Swift in Gulliver's travels (1726) and Voltaire in Micromégas (1752). How did they guess this? Was Voltaire repeating Swift's ...
Alexandre Eremenko's user avatar
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6 answers
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Has science fiction ever caused scientists to do real research?

Has science fiction ever caused scientists to do real research? Science fiction here means fiction that tries to explain things in the world rather than speculate about the future or unexplorable ...
rus9384's user avatar
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3 answers
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When did humans realize that there is no air on the Moon?

What is the easiest evidence that there is no air on the Moon? Frankly speaking, I myself have no idea how to prove it.
wdlang's user avatar
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2 answers
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Why was China slow to recognise the sphericity of Earth?

Wikipedia notes that, while knowledge Earth is approximately spherical was obtained in ancient Greece, and became standard among educated people in Europe and the Middle East long before 1300 AD, ...
J.G.'s user avatar
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13 votes
3 answers
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What happened in astronomy between Hipparchus and Ptolemy?

Hipparchus applied Apollonius's epicycle/eccenter construction to the motion of the Sun and the Moon, but not to the planets. There are speculations about epicyclic gears for planets in the ...
Conifold's user avatar
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Why didn't Aristarchus' theory of Heliocentrism stick?

This might be more a question for historians, but it's a question I've given some thought to. By using what was essentially Euclidean geometry, Aristarchus was able to calculate, with some measure ...
userLTK's user avatar
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2 answers
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How did ancient Greeks explain moon phases without reflection of sunlight?

Did the ancient Greeks understand that the moon shines by reflection of sunlight, and that this was the explanation of its phases? Did this allow them to conclude that the moon was a sphere? From what ...
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12 votes
2 answers
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Did the ancient Chinese know the earth is a sphere?

The ancient Greeks knew this fact. How about the chinese? If not, when did they realize that the earth is a sphere? By themselves or from other people?
S. Kohn's user avatar
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3 answers
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Who first distinguished planets from the stars?

This is a pretty straightforward question, when the first observations of the night sky were being made, who was the first person to suggest that a planet, say Mars, was not a star, in the sense that ...
L.R.'s user avatar
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1 answer
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Division of the circle and compass constructions

It is well known that every construction that can be performed by a compass and a ruler can be also performed by a compass only. This is a good (and difficult) exercise in elementary geometry. My ...
Alexandre Eremenko's user avatar
11 votes
3 answers
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How did Eratosthenes determine that Alexandria and Syene were on the same meridian?

As discussed over here, Eratosthenes measured the earth’s circumference by comparing shadows cast at apparent noon at two locations separated by a known distance. Although accounts of the event (like ...
Chaim's user avatar
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1 answer
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When did we first learn that Jupiter was a gas giant?

The term "gas giant" was invented in the 1950s, but I think the concept has been known longer than that. When did we first learn that Jupiter was a gas giant, not a terrestrial-type planet?
Joe's user avatar
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10 votes
3 answers
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What is the historical basis for the length of a year?

It is currently accepted that a year is equal to the time it takes for the earth to revolve around the sun. However around Roman times, Ptolemy's geocentric model was the widely accepted view of ...
cspirou's user avatar
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10 votes
3 answers
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Why should February have 28 days?

According to the Gregorian calendar the second month i.e. February have 28 days and in a leap year 29 days. I am not sure what calculations(science) it takes to decide the total number of days in ...
Amit Tyagi's user avatar
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Did Indian astronomers realize the sphericity of the earth independently of the Greeks?

Reading Wikipedia's articles on the flat earth, spherical earth, and history of geodesy makes it clear that virtually every society recognizing the spheroidal shape of the earth today owes the ...
Mr. Bultitude's user avatar
9 votes
2 answers
242 views

Was science the driving force behind the Apollo program?

Was science really the driving force behind the Apollo program? Or was the "race to the moon" the primary reason and the science objectives were put together as a secondary step?
Cedric H.'s user avatar
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9 votes
1 answer
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When did we learn that our galaxy was merely one amongst many billions?

This Kurzgesagt YouTube video claims that Without [the Hubble Space Telescope], we would never have known that our galaxy is one of billions in an enormous universe. But, the actual human, Mr. ...
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8 votes
2 answers
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First to realize that seasons were reversed above and below the equator?

I assume this conclusion was hard to make empirically in the days of slow travel -- one could not as we can today fly from above the equator to below it and observe the difference in weather and even ...
releseabe's user avatar
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8 votes
4 answers
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Name of Polaris before it became a pole star?

It seems that all stars as bright or brighter than Polaris have names dating to ancient times, including many stars dimmer than Polaris. So what was Polaris called, in any language, before it became ...
dotancohen's user avatar
8 votes
3 answers
1k views

Has anyone explored Ptolemy's epicycles as an early form of Fourier analysis?

Whilst researching science in the ancient world, I came across an observation, which unfortunately I did not make a note of, and so cannot credit, that Ptolemy's epicycles were an early form of ...
Mozibur Ullah's user avatar
8 votes
2 answers
542 views

Did Bruns establish that the 3 body problem has no non-trivial conservation laws?

I'm reading Colin Pask's book Magnificent Principia and in 16.7.2 he states that the difficulty of the 3 body problem is in part tied to the lack of additional conservation laws at our disposal. In ...
L.P.'s user avatar
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8 votes
2 answers
317 views

How did Kepler infer three-dimensional positions from Tycho Brahe's data?

This has bugged me for some time. Tycho Brahe's data on planetary observations, presumably, consisted of the direction in which a planet was observed at a given date and time, but not the distance to ...
Emilio Pisanty's user avatar
7 votes
1 answer
1k views

Did Bacon analogize planets to holes in the head to explain why their number was (believed to be) seven?

I'm looking for a source (of which I've only ever read a quote) discussing the then seven known planets. In particular, I'm looking for the part where the author explains why that number seven makes ...
tkp's user avatar
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2 answers
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How scientifically valid were Galileo's heliocentric arguments?

As far as I know, while Galileo's hypothesis about the tides was wrong, his discovery of the phases of Venus while passing the sun should have been sufficient to leave the geocentric crystal spheres ...
elias_d's user avatar
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7 votes
2 answers
622 views

When was the issue of time zones at different longitudes first described?

What are the earliest recorded acknowledgements of the concept that motivates time zones - that the sun and other celestial objects appear in different parts of the sky to people at different ...
Isaac Moses's user avatar
7 votes
2 answers
705 views

Who first reported the Crab pulsar's pulsing but was dismissed by an astronomer?

This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example ...
uhoh's user avatar
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7 votes
1 answer
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What was the "libration of Pallas" that Gauss studied, when Pallas is not a moon of Jupiter?

This question is a request for general explanation of an astronomical phenomenon known as "Pallas libration", and isn't much about the details of Gauss's mathematical model of this ...
user2554's user avatar
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7 votes
2 answers
388 views

Did Archimedes know about Callipus?

Various sources, such as Cicero's Republic state that Archimedes had made a machine consisting of glass spheres that represented the Eudoxian system of the world. Considering that Callipus died over ...
Michal Paszkiewicz's user avatar
7 votes
1 answer
656 views

Did Ibn Al-Haytham believe that the Moon reflects sunlight or that it is self-luminous?

There are at least two articles about Ibn Al-Haytham in Encyclopedia First and Second Both these articles have one major difference that is according to the First article: The Light of the Stars (III ...
Abhishek Yadav's user avatar
7 votes
1 answer
210 views

Who created the energy conditions?

The earliest text I've been able to find that explain the GR energy conditions is "The large scale structure of space-time" (1973) by Hawking and Ellis. However in Barcelo and Visser's paper "...
Rammus's user avatar
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1 answer
691 views

Entry 97 in Gauss's diary and the status of "lunar parallax" in the late 18th century

Pp. 539-542 of volume 10-1 of Gauss's werke include entry 97 in Gauss's diary: I have found new exact formulas for the parallax of the Moon. as well as the formulas themselves (which were rather ...
user2554's user avatar
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7 votes
1 answer
325 views

Calculation of Gauss leading to 18:7 resonance between orbits of Jupiter and Pallas

After Gauss helped relocate Ceres, he studied the orbit of the asteroid Pallas and discovered (1812) that Jupiter and Pallas have an orbital resonance that is nearly equal to 18:7. For instance, using ...
KCd's user avatar
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7 votes
1 answer
183 views

When did the idea of naming asteroids after humans come about?

There are some trends to naming celestial objects: Planets and moons in the solar system may be named after ancient Greek and Roman gods Comets may be named after their discoverer Asteroids may be ...
HDE 226868's user avatar
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6 votes
3 answers
772 views

Did Kepler arrive at his planetary laws based on Mars's orbit alone?

Kepler apparently arrived at his first two laws based on the Tycho's data for Mars. But Mars has the largest eccentricity except for Mercury, so it is easier to tell the difference between a circle ...
wdlang's user avatar
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