PDA

View Full Version : Winter in July 13,000 years from now?



Marjorie
2004-Jun-04, 05:22 PM
I've just been reading that 13,000 years from now it will be possible to see winter constellations in July because of the gradual changes in the position of the stars over long periods of time. Does this mean that the seasons themselves will be at different times of the year, or does it only refer to the position of the stars?

aurora
2004-Jun-04, 05:53 PM
I've just been reading that 13,000 years from now it will be possible to see winter constellations in July because of the gradual changes in the position of the stars over long periods of time. Does this mean that the seasons themselves will be at different times of the year, or does it only refer to the position of the stars?

Refers to the position of the stars.

Try here:

Precession of the equinoxes (http://www.encyclopedia.com/html/p1/precequi.asp)

(corrected spelling mistake)

TravisM
2004-Jun-04, 07:16 PM
Earth is also 'slowing' its rate of rotation down by 0.001 seconds per year. That's a whole 13 seconds in 13,000 years, so I guess my point is moot. :-?
[edit]
Ah, the direction of the orbital tilt changes in relation to the earth's orbit. How long until it points somewhere other than than Polaris?

Spaceman Spiff
2004-Jun-04, 07:38 PM
I've just been reading that 13,000 years from now it will be possible to see winter constellations in July because of the gradual changes in the position of the stars over long periods of time. Does this mean that the seasons themselves will be at different times of the year, or does it only refer to the position of the stars?

This just refers to the winter constellations being visible in July. This effect is due to the precession of Earth's rotation axis. We tie our calendar year to Earth's "Tropical year" which (along with the leap year corrections) fix Earth's seasons within our calendar.

tracer
2004-Jun-04, 09:48 PM
I've just been reading that 13,000 years from now it will be possible to see winter constellations in July
You can see the winter constellations in July this year, if you're in the southern hemisphere. ;)

milli360
2004-Jun-04, 09:53 PM
Earth is also 'slowing' its rate of rotation down by 0.001 seconds per year.
You must be referring to the tidal braking, but that is 0.001 seconds each rotation per hundred years, and it's actually sped up quite a bit recently, esentially undoing the effects of the last hundred years.

aurora
2004-Jun-04, 10:32 PM
Ah, the direction of the orbital tilt changes in relation to the earth's orbit. How long until it points somewhere other than than Polaris?

Today. :P

IIRC, Polaris is currently about 45 arcminutes from celestial north in the sky.

But that isn't what you meant.

Since there isn't much that is bright and near Polaris, as Polaris moves off celestial north, it will be awhile until it gets a bright replacement.

5,000 years from now, Alderamin will be the pole star. But there isn't much between Polaris and Alderamin, especially with light pollution.

Marjorie
2004-Jun-05, 05:14 PM
Thanks for the link, Aurora. It is an excellent description of how precession works. Our descendants in the future should have a really great view of the winter stars when they see them in the summer when the weather is good.

milli360
2004-Jun-05, 05:29 PM
You can get a good view of winter stars in the summer, if you get up early. :)