1
$\begingroup$

Is 0 degrees in the J2000 Epoch 'right ascension' is a line from Earth to the sun on January 1, 2000? Or is 0 degrees the direction towards the ascending node 'equinox'? Which is NOT towards the Sun on January first...

$\endgroup$
3
$\begingroup$

Or is 0 degrees the direction towards the ascending node 'equinox'? Which is NOT towards the Sun on January first...

The answer is yes, more or less. From JPL's HORIZONS, the location of the Sun at Noon Terrestrial Time on 1 Jan 2000 is, ignoring atmospheric effects, a right ascension of 18 hours, 45 minutes, and 9.36 seconds. This is nowhere close to a right ascension of zero hours (or 24 hours, same thing).

The right ascension of the Sun with respect to the center of the Earth is zero at the March equinox.

$\endgroup$
2
  • $\begingroup$ Where is that point on Earth, by the way? 0 degrees right ascension.... What country or ocean? What longitude? $\endgroup$
    – Kurt Hikes
    Jul 30 '20 at 8:13
  • 1
    $\begingroup$ @KurtHikes The Earth rotates, nutates, and precesses. You appear to be asking how to convert between Earth-Centered Inertial and Earth-Centered Earth-Fixed coordinates. $\endgroup$ Jul 30 '20 at 10:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.