Like latitudes and longitudes on earth, we have equivalents called Declination and Right Ascension. And there's a celestial equator (extension of earth's equator in the sky) and the Ecliptic (path of Sun's movement).
Imagine living a long life of say 10,000 years at one place on earth (say Mumbai). You are interested in observational astronomy. As you know the earth precesses in 26,000 years, you can imagine that in 10,000 years, one circle of equator or ecliptic will move w.r.t. the other. The question is: which one?
Another related question: 10,000 years later, would the coordinates of a star (defined by RA and Dec), be the same as of now?
Question by : Mayank Jha
* For those of you new to amateur astronomy look up
http://en.wikipedia.org/wiki/Altitude_(astronomy)
http://en.wikipedia.org/wiki/Precession_(astronomy)
3 comments:
the ecliptic remains the same as it can be defined uniquely by the revolutionary orbit of Earth which does not change due to precession. The celestial equator changes orientation (although it remains at 23.5 degrees to the ecliptic, its points of intersection with the ecliptic shift). The coordinates (RA and dec) of the star change as the reference circle (equator) for these coordinates has changed.
That's correct!
The ecliptic is the extension of the plane in which the earth revolves around the sun. Since that plant doesn't change due to precession, the ecliptic won't change.
The earth precesses in 26,000 years, hence, in a period of 26,000 years, the (celestial) equator will "slip" over the ecliptic. The point of intersection of equator and ecliptic, called the vernal equinox (actually there are two points when two circles intersect, the 2nd one being autumnal equinox) will move from its current position in pisces to aquarius, capricorn and further west and completes a whole circle in 26,000 years. So the term "Age of Aquarius", usually referred to the hippy culture of the 70s would acutally come after 2100 years from now! :P (en.wikipedia.org/wiki/Age_of_Aquarius)
Hence, the celestial equator, which currently includes constellations like Orion, Cetus, Pisces, Virgo etc will have a very different composition a few thousand years from now! And as you correctly pointed out, the celestial equation will still remain at the same location if you draw an imaginary line in the sky, the whole celestial dome will adjust relative to that (and hence, you would see different constellations on the equator, and new stars like Vega and Deneb as the pole stars).
The celestial coordinates are defined as Declination (parallels of latitude measured from celestial equator) and RA (meridians of longitude measured eastward of vernal equinox). Since BOTH celestial equator and vernal equinox shift, both the RA and declination of stars will change over the period, returning to the same coordinates in 26,000 years.
Hello,
I an the Coordinator of Astronomy events in the Annual technical festival of IIT Kanpur, Techkriti'12. Here is the link,
http://techkriti.org/#/competitions/cosmos/
If you have any queries regarding the event, feel free to contact us anytime.
regards
Akshat Singhal 9559754558
Post a Comment