# Questions tagged [johannes-kepler]

Questions about the German astronomer famous for his three laws of planetary motion. Do not use this tag for questions about the Kepler spacecraft.

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### Why do planets' orbital velocities drop off by less than a third when twice as distant from the sun, rather than three-quarters? If gravity is $1/4$?

Looking at the speeds of the planets in our solar system when traveling around the sun and their distances from it (or, using Kepler's third law,), it seems that when a planets distance is doubled, it'...
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1 vote
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### Is it safe to look at an annular eclipse during sunrise using a medium

will looking at annular eclipse reflection through a bowl of water damage your sight? i already tried viewing it reflection through a bowl of water.
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### How to derive Kepler's 1st Law?

I was going through the derivation of Kepler's 1st Law in the textbook "An Introduction to Modern Astrophysics" by Carroll and Ostlie. From there, I got stuck in a few places in their ...
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1 vote
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### How did Kepler come to the potencies in his Third Law?

How did Kepler come to the conclusion, that exactly the square of the period and the third potency of the great semi-axis of the ellipse is proportional? Why is only square divided by cubic = ...
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1 vote
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### Can Kepler's 3rd Law be applied in higher dimensions to describe orbits (quadric surfaces)?

Motivation for asking: The 2-D orbital path of a celestial body revolving around another celestial body due to the force of gravity can be described by a conic section; this is the curve formed by ...
1 vote
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### Given that Kepler's Third Law as stated on most websites doesn't include mass, how does it work for planets in other star systems? [duplicate]

Kepler's Third Law as stated on websites I found while searching for "how to convert between a planet's orbital period and semi major axis" is $P^2 = A^3$ where P is the orbital period in years and A ...
198 views

### How Long Will Earth's Year be When Our Sun Goes Red?

We live in a planet that orbits 93 million miles from a G-type main-sequence star, or "yellow dwarf". That is far enough for a revolution of 365 days. Such is the case of Kepler's Third Law of ...
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### In System KIC 9246715, How Far Does One Star Orbit the Other?

I was going to ask if it's physically possible for one red giant to orbit another, but fortunately, I have just found such a thing--a red giant binary system known only as KIC 9246715. In this ...
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### What are Kepler's laws (as he wrote them)?

There are of course many, many sources that quote Kepler's laws of planetary motion. This is preventing me from finding out what I really want to know: which is - what are Kepler's laws as he wrote ...
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### Kepler - Creating the Ellipse (Astronomia Nova)

In Chapter 58 in Astronomia Nova, Kepler made his final step to finally create the ellipse (for the orbit of planets) http://science.larouchepac.com/kepler/newastronomy/part4/58/index.html In the ...
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### Kepler's second law of motion

Planets sweeps out equal areas in equal times. Is the area being calculated here the area of a triangle? You draw a straight line from the center of the sun to the earth at point A. The Earth moves ...
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1 vote
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### What is the shape of the Sun's orbit around the Earth taking into account elliptical orbits?

Consider the non-inertial frame that is at rest with respect to the Earth's revolution around the Sun. (Ignore the Earth's rotation around its own axis.) My question is, what is the shape of the Sun'...
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### How well do planetary orbits fit with Johannes Kepler's in- & circumscribed Platonic solids?

In Mysterium Cosmographicum (1596) Johannes Kepler proposed that the relative distances between the orbits of the six ancient planets (six because heliocentrism had recently added Earth as one of the ...
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### What were the challenges for the ancients to observe the orbit of the Moon (instead of Mars)?

Astrophysics can be said to have been founded by Johannes Kepler around the year 1600. He based his break-through science on data of the position of Mars in the sky and disproved the ancient ideas ...
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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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### Are epicycles and mean Earth/Sun actually useful astrophysical concepts?

Copernicus put the Sun in the center of the Solar system. This turns the Moon's orbit into an epicycle around Earth orbit. And the Jovian moons (later discovered) have orbits which are epicycles ...
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