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Gary W
2003-Sep-23, 06:59 PM
Great site. I wish I'd found it earlier.

Anyway, in "Bad Astronomy" the book, on page 55 there is a statement I am having problems with. It says "Right now the Earth's north axis points toward the Sun in June. But due to precession, 13,000 years from now - half a precession cycle- the Earth's north pole will point AWAY from the Sun in June and TOWARD it in December. The seasons will be reversed realative to our present calendar."

With the Gregorian calendar, the year is based on the Tropical year which includes a correction for precession. For this reason, the Vernax equinox (when you can stand an egg on it's end (hehe)) will remain in March on or around the 21st. The Earth's north pole will continue to point toward the Sun in June. What will change is where June (and all the other months) will occur with respect to the Earth's orbit. The constellations that we see in the summer now (such as Scorpio) will become winter constellations and the present winter sky (Orion for instance) will be seen in the summer.

I really want to be sure I have this right. I don't want to go around spreading any Bad Astronomy. I could start an epidemic!

Gary
gwas@optonline.net

kilopi
2003-Sep-23, 07:14 PM
really want to be sure I have this right.
Welcome to the BABB, Gary W. jimbenet (http://www.badastronomy.com/phpBB/viewtopic.php?p=138022#138022) and myself (http://www.badastronomy.com/phpBB/viewtopic.php?t=710) agree with you. It's probably too late (http://www.badastronomy.com/phpBB/viewtopic.php?p=139966#139966).

Gary W
2003-Sep-25, 02:28 AM
Hi Kiopi,

Thanks for the support. This was a question an astronomy exam I am taking, and I answered saying that the tropical calendar takes precession into account such that the seasons stay in their proper months, but that the constellation seen during those months change. At the same time, I was reading the book, which contradicted my answer. I thought about it a while and I couldn't see a reason that would make my answer wrong. So I posted here. I then saw your and jimbenet's posts saying the same thing (too bad I didn't see them BEFORE I posted).

I wonder what my astronomy professor will say when the test gets graded.

Gary

The Bad Astronomer
2003-Sep-25, 03:21 AM
From what I have read, yes, the tropical year accounts for precession. Hopefully, your prof knows that. If not, send him here! Where are you, by the way? I might know your prof!

Gary W
2003-Sep-25, 03:47 AM
Well, I live in the New York area on Long Island. The course I'm taking though is online with Swinburne University in Australia. I love the computer age!

The Professor for this class is Kurt Liffman.

Also taking a second class with Brad Gibson.

Loved the book. Did you ever address the slowing speed of light brought up by the Young Earth Society?

Gary

Eroica
2003-Sep-25, 03:36 PM
With the Gregorian calendar, the year is based on the Tropical year which includes a correction for precession. For this reason, the Vernal equinox will remain in March on or around the 21st.

Is this accurate? The Gregorian calendar is 365.2425 days long, while the tropical year is about 365.24219 days long. That's a difference of 0.00031 days or about 27 seconds. This error will accrue to one day in 3200 years, so by the time Vega is the North Celestial Pole, the calendar will be three days out. The Vernal Equinox would take place on March 18 rather than March 21.

Presumably Pope Gregory assumed that some future boffins would take care of the problem long before then!

Gary W
2003-Sep-25, 05:30 PM
What you said is true, but this doesn't take into account the decrease in the Earth's rotation. Between now and 13,000 years from now, I agree, a small correction is going to be needed. However, the question I was asked in the first place was in WHAT MONTH winter will be in 13,000 years. This will still be June in the Southern hemisphere and December in the Northern Hemisphere.

Gary

milli360
2004-Feb-01, 07:48 PM
With the Gregorian calendar, the year is based on the Tropical year which includes a correction for precession. For this reason, the Vernal equinox will remain in March on or around the 21st.

Is this accurate? The Gregorian calendar is 365.2425 days long, while the tropical year is about 365.24219 days long. That's a difference of 0.00031 days or about 27 seconds. This error will accrue to one day in 3200 years, so by the time Vega is the North Celestial Pole, the calendar will be three days out. The Vernal Equinox would take place on March 18 rather than March 21.

Presumably Pope Gregory assumed that some future boffins would take care of the problem long before then!
And, for purposes of the OP, March 18 is "on or around the 21st." :)

Eroica
2004-Feb-01, 08:19 PM
And, for purposes of the OP, March 18 is "on or around the 21st." :)
What took you so long? :D

milli360
2004-Feb-02, 09:51 AM
I actually posted that four months ago, but I forgot which month I was in. :)