Questions tagged [astronomy]

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

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332 views

When was the airless void above the earth discovered?

For a very long time, people had no reason to believe that an airless void could exist in nature at all, whether above the earth or anywhere else. According to Descartes, in his 1633 work The World, ...
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Do astronomers still use decimal time?

Wikipedia states that decimal time - where the time of the day is expressed as a decimal part of the day - "have been used by astronomers ever since [Laplace introduced them]". An example by Herschel ...
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Hevelius-Hooke dispute

Johannes Hevelius of Danzig (1611-1687) was the most famous astronomer of his time, and also the last famous astronomer who did not use telescope. Most books on the history of astronomy (and even the ...
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Kepler's position with respect to Tycho Brahe's world system?

When Kepler was an assistant of Tycho Brahe, did Kepler in public declare his support for Copernicus' system or Brahe's system (the earth at rest, but the planets orbiting the sun) or was he undecided?...
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Were epicycloids from astronomy acceptable curves in Greek geometry?

My simplified historical understanding is as follows. Euclidean geometry accepted a limited number of geometrical objects (straight-edge and compass constructions, conics). Descartes' Géométrie ...
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Who was the first person to use physics to suggest that both the Sun and the Earth move?

I imagine it to be Isaac Newton, who brought the discussion of "force" rather than "center" into the modeling of orbits. I imagine that prior to Newton's forces, one had to be either a geocentrist or ...
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174 views

Did Schiaparelli comment on the martian canals debate?

It s well known that in 1888, Italian Giovanni Schiaparelli announced finding a network of narrow lines on Mars, which he described as "canali," which a lot of English speakers including American ...
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366 views

When did the estimates of planetary distances made between Ptolemy and Copernicus produce the pattern suggesting heliocentrism?

Two patterns in the structure of the Ptolemaic model make the transformation of coordinates to the Copernican model seem "natural" to modern eyes: the alignment of the radii of the (second) ...
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762 views

Who discovered the "Comet" as a celestial object?

Who first discovered that comets were physical objects with a Keplerian orbit? Was this accidentally discovered or was it discovered as part of an intentional effort by astronomers after they ...
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260 views

Was an expanding universe proposed before Edwin Hubble's observations?

General relativity (1915), as I've heard it explained, describes a universe that is either shrinking or expanding. By adding a cosmological constant it can describe a universe in eternal steady state, ...
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181 views

Was Captain Cook’s voyage to observe the transit of Venus going to enable better ship navigation at the time?

On a recent visit to the Royal Observatory at Greenwich I was struck by its proximity to the Naval Academy next door. The theme of the history of clocks and development of astronomy was driven by the ...
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807 views

How important was the prediction of Neptune in 1846 for the Oxford evolution debate?

The short story is that based on Kepler's and Newton's physics, in 1846 Le Verrier mathematically predicted the existence and current location of Neptune within a single angular degree, and it was ...
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How large were the differences in the orbit of Uranus which led to the calculation of the existence of Neptune?

After Uranus was discovered and its orbit calculated, its future orbit was calculated, and its future positions as seen from Earth were calculated. And observers of Uranus began to notice that Uranus ...
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How long did it take to prove that the Earth revolves around the Sun?

I get that Galileo Galilei was a major contributor in proving the helio-centric theory, and same goes to Sir Isaac Newton. The battle for the theory to become law took centuries to prove. People ...
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372 views

Did Ptolemy and other Greek scientists actually measure the distance to the Sun?

According to Subhash C. Kak: Early Theories on the Distance to the Sun: “Pancavimsa Brahmana states that the heavens are 1000 earth diameters, de, away from the earth. The sun was also taken to be ...
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When was the mechanism behind seasons on Earth discovered

When was the mechanism behind seasons on Earth discovered? I'm talking about the angle between the Earth's rotational axis and its orbital axis. I read on Wikipedia here that Earth's obliquity ...
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144 views

Who coined the term "degenerate star"?

I'm trying to find a good source for the definition of degenerate matter to differentiate it from Fermi gases. For my research a good section on history would be nice. This question is more ...
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465 views

When William Herschel discovered Uranus, who else at the time had a comparable telescope?

William Herschel built a big telescope and observed Uranus in 1781. I'm trying to figure out who else had a comparable telescope at the time, who could verify these observations? Apparently Johan ...
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254 views

Why did Greek Olympic games take place every fourth year?

I was wondering why Greeks chose to have Olympic games every four years. Now, since we usually every fourth year is a leap one, it makes sense; but the reform of the calendar which stated this is due ...
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475 views

When was the first true Gregorian telescope built?

I know that James Gregory came up with the idea of using a parabolic mirror to eliminate spherical aberration in 1663. The theory behind it had actually been around since classical antiquity I think....
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How did Hertzsprung-Russell diagrams end up so confusing?

HR diagrams show in which of several sequences individual stars fall, each respecting the rough principle that hotter stars are of higher luminosity. (Sequences other than the main sequence may bend ...
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Notable theories on the far side of the moon pre 1959

On October 7th 1959, the soviet Luna 3 probe took the first picture of the far side of the moon. It has been known since ancient times that the moon was a sphere. It would have doubtless been ...
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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 ...
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Why did the ancients believe celestial matter was of a different type than terrestrial matter?

Why did the ancients believe celestial matter is of a totally different type than terrestrial matter? From a footnote in Christopher A. Decaen's The Thomist 68 (2004): 375-429 article "Aristotle's ...
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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 ...
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When and how was water first detected outside of Earth?

When and how was water (in ice or any other state) first observed outside of Earth? What is the high-level chronology of this discovery, and how did the scientific community first reach reasonable ...
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Martian dust as ferric oxide and Rupert Wildt

Samuel Glasstone, in The Book of Mars (NASA, 1968, p. 109), wrote "In 1934, the German-born astronomer Rupert Wildt suggested that the bright areas on Mars were composed 'of strongly oxidized ...
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2k views

Who determined the temperature of the Sun first?

It is commonplace that it is about 6000 Kelvin. But who came to this value first? And with what method? Based on the black body radiation theory?
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How has the estimate of the number of stars in the universe changed over time?

Current estimates for the number of stars in the universe are about 10^22. However, that number has changed several times as new observations have come forth. How has the estimate of the number of ...
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Historical knowledge of Distance of Earth from Sun

I asked the following question on the Physics stackexchange, only to be notified that it was more suitable for this forum. The link to original post can be found at: https://physics.stackexchange.com/...
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How accurate are Mayan astronomical "ephemerides"?

Because of recent hype surrounding the "end" of the Mayan calendar it is nearly impossible to find an objective quantitative assessment of the accuracy and sophistication of Mayan astronomy. ...
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Sphericity of Earth from lunar eclipses - is Aristotle's argument valid?

Aristotle is often credited with proving the sphericity of Earth from the fact that the shadow of the Earth on the moon during lunar eclipses is always an arc of a round circle (as opposed to arcs of ...
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Could 17th century astronomers in the Netherlands predict solar eclipses a few months in advance?

In the 17th century Netherlands, could the astronomers, or sailors trained in stellar navigation, predict either total or partial (at least 40% obscured) solar eclipses over the the town of Aardenburg ...
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Why was Charles Hutton's estimate of the density of Mercury so far off?

In the Schiehallion experiment (original paper), Charles Hutton computed the density of the Earth, and from there estimated the densities of the major bodies of the Solar System. His numbers for most ...
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590 views

What were the applications of conic sections before Kepler?

When recently asked for a practical application of parabolas, I responded by talking about objects in free-fall. Afterwards as I was re-thinking this conversation it occurred to me that an object in ...
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512 views

Was "Kepler's third law" deduced from the Galilean moons, or from planetary motion?

I have read that Galileo was able to start observing the four large satellites of Jupiter in 1610. Did he ever attempt to estimate the relative sizes of the four orbits, and their periods? I made a ...
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372 views

Was Newton's successful calculation of precession of equinoxes a fluke?

I have looked at several sources, and Newton was right about the fact that the Earth is not a perfect sphere, but an ellipsoid caused the precession of equinoxes, as the Moon's gravitational ...
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How was stellar parallax tested by Tycho Brahe?

Explanations of stellar parallax that I have found involve examining the apparent motion of a nearer star relative to a background of more distant stars, as the Earth moves around the sun or as the ...
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209 views

When did astronomy first discover that the stars are bigger than the moon?

We take it for granted these days that the stars are unimaginably bigger than the planets and the moons. But when you look at the sky, it does not appear this way. The moon looks bigger and brighter ...
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335 views

How did Kepler make his discovery?

It is often said that he used Tycho's data. But the apparent motion of a planet is chaotic, right? The reason is simply that we are living on and observing from the earth, but not the sun. So, how ...
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109 views

How was longitude determined in the 1700s?

I'm going through the journals of Alexander Mackenzie (ca 1790) and I came across this passage: I gather that he's determining his latitude and longitude but I'm not clear on what units he's using, ...
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190 views

Why did it take so long to discover the shape of the Milky Way?

It was not before the early fifties of the last century that the shape of the Milky Way was figured out. Uptill then only other galaxies were known to have certain shapes It's always easier to find ...
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What was Galileo's opinion of Kepler's work?

They were contemporaries. Kepler lived from 1571 to 1630, and Galileo lived from 1564 to 1642. The former's life span was contained in that of the latter. So, did Galileo hear of Kepler's work and ...
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In Newton's cannon image, where do the shapes drawn into the sphere come from?

I find quite interesting the choice for the shapes drawn into the sphere that resembles continents. Was this choice arbitrary or do we know if there is some justification behind it?
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How did Khayyam calculate the year so accurately?

Regarding the Islamic mathematician and astronomer Omar Khayyam, known (among other things) for his accurate calculation of the year, quoted from https://www.famousscientists.org/omar-khayyam/ ...
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289 views

What role did meteors and comets play in early astronomy?

Apart from the location, brightness and color of the stars themselves, astronomy obviously originated from an interest in transient phenomena against the fixed but rotating star sky. The rise and set ...
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398 views

Why does JPL at NASA give two different values in astronomical units for planetary distances?

Why is it that JPL (Jet Propulsion Lab) at NASA gives astronomical unit values for the planets for two different time periods, namely 3000 B.C. to 3000 A.D., and 1850 to 2050?
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Planets/stars as more than points of light

Who was/were first one(s) to recognize that what we see in the night sky are not just points of lights but full blown lands(in case of moon and some planets) and so on? I am guessing it would not have ...
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471 views

Did the Mayan's really predict the solar eclipse?

The Mayan's astronomical observations were outstanding given the tools they had, and investigations of the Dresden codex published by Harvey and Victoria Bricker in 1983 predicted the July 11th, 1991 ...
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Why does the start of the calendar year not correspond to a natural event?

Why is Jan. 1, the start of a new year, several days after the Winter Solstice, instead of coinciding with a solstice or equinox or other natural annual event? Note: The question does not ask why ...