Celestia Forums

While I was discussing the equatorial frame of reference in another thread, I ran across something that makes me think that I have incorrectly identified certain directions in the Celx Visual Guide and elsewhere.

I had always assumed that if you were looking towards RA 0 / Dec 0 that you were looking towards the vernal equinox. I could swear that I have heard and read it expressed this way before. However I ran across this diagram at Wikipedia:
http://en.wikipedia.org/wiki/First_Point_of_Aries

The diagram there makes me think now that my terminology is wrong. If you are looking towards RA 0 / Dec 0 you are looking towards the "vernal equinox point". The "vernal equinox" is an event, not a direction.

Am I making a faux pas in academia? Are Fridger and Selden snickering at me behind my back? Or is this just a tiny transgression? Or perhaps I'm just up too late.

Clive,

I'm not a professional astronomer, and I often mix up the terminology just as you do.

Clive,

The Explanatory Supplement to the Astronomical Almanac from the U.S. Naval Observatory defines vernal equinox as "the ascending node of the ecliptic on the celestial equator; also the time at which the apparent longitude of the Sun is 0?°". So according to the USNO (they would know), it's both a direction and an event.

- Hank

hank wrote:Clive,

The Explanatory Supplement to the Astronomical Almanac from the U.S. Naval Observatory defines vernal equinox as "the ascending node of the ecliptic on the celestial equator; also the time at which the apparent longitude of the Sun is 0?°". So according to the USNO (they would know), it's both a direction and an event.

- Hank

Thank you. That seems to clinch it.

When used as a reference to direction, both the Wikipedia explanation and the USNO agree that it is towards the first point of Aries.

My confusion was that the diagram at Wikipedia seems to imply that, from the vantage point of the Sun, to look towards the Vernal Equinox would mean looking at where the Earth is shown - 180 degrees from the First Point of Aries.

Now that I've had some sleep - and some help - I can see that the diagram is showing the position of Earth during the event called the Vernal Equinox and is not implying that the direction lies that way.

P.S. How did man ever figure out anything before the discovery of coffee?
It took us 20,000 years to go around the globe before coffee, and only 300 to get to the moon after coffee - coincidence? I think not.
B.C. - Before Coffee. A.D. After Decaffination - coincidence? I think not.