Timeline for What is the formal definition of a stellar day?
Current License: CC BY-SA 3.0
9 events
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| Nov 1, 2012 at 23:34 | comment | added | orome | @JoeH: Also more detail: isn't there no way that the stellar day could be "based upon any reference star" since the time to reach any reference point after a period of precession will depend on the new orientation of the earth's axis (and not on its "sidereal rotation period", which can be the only basis for a definition)? | |
| Nov 1, 2012 at 21:48 | comment | added | orome | My comment above isn't quite right. Even assuming an idealized constant stellar day, and an idealized constant rate of precession, it seems to be that the duration of the sidereal day must vary systematically. But that's totally different question. | |
| Nov 1, 2012 at 7:11 | comment | added | Eduardo Guerras Valera | Even through the eclyptic, the real Sun has no constant speed (thank Kepler for that), not to mention the variations in the orbital parameters of the Earth, a fraction being totally unpredictable... So, take only mean ideal speeds in the equator for definitions such as your stellar day. | |
| Nov 1, 2012 at 7:00 | comment | added | Eduardo Guerras Valera | That is similar to the question that leads the Solar Day to be defined by the Mean Sun (ideal point at constant speed in the celestial equator instead of the eclyptic), since the eclyptic plane is tilted with respect to the equator (defined as normal to the rotation axis). Only average ang speeds are used in these definitions. In the sidereal day too. | |
| Nov 1, 2012 at 2:50 | history | edited | Emilio Pisanty | CC BY-SA 3.0 |
Yes, "nutating" exists in english. Added the WP link.
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| Nov 1, 2012 at 1:23 | comment | added | orome | Another complication (at least if I'm visualizing this right): The process you describe above for making the correction between the length of a stellar and sidereal day in an average one, since, even though $\Delta\lambda$ varies only slightly, due to the eccentricity of the earth's orbit, and may be taken as constant, the corresponding $\Delta\alpha$, which determines the difference between stellar and sidereal day length, varies with the $\delta$ of the point being tracked along the ecliptic. | |
| Nov 1, 2012 at 1:17 | comment | added | orome | The term "stellar day" isn't one I'd come across before either. I first saw it on Wikipedia, actually, where it appears in several articles. It is also referred to here. | |
| Nov 1, 2012 at 0:16 | history | edited | Eduardo Guerras Valera | CC BY-SA 3.0 |
(added some information)
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| Oct 31, 2012 at 23:31 | history | answered | Eduardo Guerras Valera | CC BY-SA 3.0 |