 |
 |
Earth Sidereal Year and NEO
Name: Tom
Status: educator
Grade: other
Location: CA
Country: USA
Date: N/A
Question:
I'm compiling a list of NEOs for my kids and I to track.
I have all their orbital parameters calculated from JPL
(http://neo.jpl.nasa.gov/ca/).
Most of their orbits I have been
able to model if they are within a year away. But for example,
Apophis which is scheduled to swing by in 2029 and 2036, I can only
get it to be as close as .3AU, and not within our Moon's orbit. I
have just had some trouble in determining what the precise variable
is for Earth's year, (period-yr). I have 365.256363004 days as the
most precise sidereal year that I can find.
(http://hpiers.obspm.fr/eop-pc/models/constants.html) Is there a
more precise number for the number of days that make up Earth's
Sidereal Year?
Replies:
Dear Tom,
Our sidereal year, according to Wikipedia, is
365.256363004 days.
It is the amount of time it takes Earth to revolve about the Sun once
with respect to "fixed" stars.
Sincerely,
David H. Levy
The precision with which the Sidereal Year is known is greater than the
accuracy, due to small but measurable variations. These variations result
from the location of other planets, the moon and changes in the Earth's
gravitation. You will also notice in the website you site
http://hpiers.obspm.fr/eop-pc/models/constants.html that some "constants"
are "exact" that is they are taken as "fixed" and other related "constants"
are adjusted to keep those parameters "exact".
Vince Calder
Click here to return to the Astronomy Archives
| |
Update: June 2012
|
|
