All Questions
9 questions
3
votes
1
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121
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What were the estimated distances of planets from the Earth in the geocentric model?
The geocentric model was used before the 16th century, and was standardized by Ptolemy in the 2nd century. What were the estimated distances of each planet from the Earth, and what are the same ...
- 133
7
votes
4
answers
214
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Ancient Astronomy, Distances, and Parallax measurements
Andrew Michael Chuggs in his recent book The Pharos Lighthouse in Alexandria (Routledge 2024) goes into an excursus on the ancient astronomy of Eratosthenes. The author is a published historian whose ...
user54772
1
vote
1
answer
160
views
How did scientists decide the boundary of the Milky Way at Edwin Hubble times?
I know Edwin Hubble used Cepheid variables to prove the Andromeda Galaxy is not part of the Milky Way. But how did scientists at that time decide the boundary of the Milky Way?
And how did they find ...
- 127
11
votes
1
answer
2k
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How exactly was Giovanni Cassini able to measure the distance to Mars?
Recently learned that Cassini was able to calculate the distance to Mars quite well using parallax in 1672. I was surprised, since even at opposition of Mars, the parallax (with respect to the Earth's ...
- 1,707
2
votes
2
answers
737
views
How were the distances to stars measure before parallax?
A comment under When was the distance to a star measured for the first time without using parallax? mentions that the distance to stars was measured before parallax was possible. How was this done?
- 17.7k
4
votes
2
answers
481
views
When was the distance to a star measured for the first time without using parallax?
This is somewhat of a follow-up to When was the parallax of a star first measured? Once the distance to the nearest stars was determined, it was possible to discover physical properties of stars (such ...
- 17.7k
4
votes
2
answers
474
views
Before the 1761 transit, what was our best estimate of the distance to the Sun?
In 1761, many expeditions were launched to determine the distance to the Sun using parallax during the transit of Venus. Prior to the 1761 transit, what was the best estimate for the Earth-Sun ...
- 17.7k
31
votes
2
answers
9k
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How did Eratosthenes know that the sun is far away?
The famous measurements and calculations done by Eratosthenes around 300 BC are very widely known. He concluded correctly that the circumference of the Earth is about $252\,000$ times the length of an ...
- 495
14
votes
1
answer
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How was the Earth-Sun distance originally calculated?
AFAIK it was possible long before the first interplanetary probes.
Who did it?
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