3 ms·

This, by the way, is why there is a thing called "sidereal time", with days that are slightly shorter than 24h. The commonly used 24h days are solar days, defi

by GuB-42 3y ago

This, by the way, is why there is a thing called "sidereal time", with days that are slightly shorter than 24h. The commonly used 24h days are solar days, defined relative to the sun, but since the earth goes around the sun too, that makes an extra rotation relative to the star background, which means a year has 366.25 sidereal days instead of the usual 365.25.

thunderbong 3y ago
That's incredible! I've never thought of it that way! Thanks a lot. I guess I'm one of today's lucky 10,000! https://xkcd.com/1053/ https://xkcd.com/1053/
- Natsu 3y ago
  It's funny, I usually only think about circles this way when trying to construct mutually tangent circular arcs, because if you have one circle inside (or outside) the other, their arcs are tangent at the point where they touch. I used circles a lot when doing CADs because they let you measure all the points a certain distance away from a given point, so intersecting two of them lets you do a lot of construction, like finding the two possibilities for the center of a circular arc that passes through two points of a given radius, assuming that they're not too far apart for that to exist.
_Microft 3y ago
Satellites in sun-synchronous orbits need to precess (their orbital plane must slowly rotate) because of this situation to actually stay sun-synchronous. https://en.wikipedia.org/wiki/Sun-synchronous_orbit https://en.wikipedia.org/wiki/Sun-synchronous_orbit
mannykannot 3y ago
the 24-hour day is a construct of mean solar time. Because the speed of the Earth varies through the year (fastest at perihelion - see Kepler I and II), the apparent or true solar day varies in duration throughout the year. https://en.wikipedia.org/wiki/Solar_time https://en.wikipedia.org/wiki/Solar_time This is one of the causes of the analemma. https://en.wikipedia.org/wiki/Analemma https://en.wikipedia.org/wiki/Analemma

by GuB-42 3y ago

thunderbong 3y ago

That's incredible! I've never thought of it that way! Thanks a lot. I guess I'm one of today's lucky 10,000! https://xkcd.com/1053/ https://xkcd.com/1053/

Natsu 3y ago
It's funny, I usually only think about circles this way when trying to construct mutually tangent circular arcs, because if you have one circle inside (or outside) the other, their arcs are tangent at the point where they touch. I used circles a lot when doing CADs because they let you measure all the points a certain distance away from a given point, so intersecting two of them lets you do a lot of construction, like finding the two possibilities for the center of a circular arc that passes through two points of a given radius, assuming that they're not too far apart for that to exist.

_Microft 3y ago

Satellites in sun-synchronous orbits need to precess (their orbital plane must slowly rotate) because of this situation to actually stay sun-synchronous. https://en.wikipedia.org/wiki/Sun-synchronous_orbit https://en.wikipedia.org/wiki/Sun-synchronous_orbit

mannykannot 3y ago

the 24-hour day is a construct of mean solar time. Because the speed of the Earth varies through the year (fastest at perihelion - see Kepler I and II), the apparent or true solar day varies in duration throughout the year. https://en.wikipedia.org/wiki/Solar_time https://en.wikipedia.org/wiki/Solar_time This is one of the causes of the analemma. https://en.wikipedia.org/wiki/Analemma https://en.wikipedia.org/wiki/Analemma