A question about the Equinox for the astronomically literate

[A HERETIC I AM]

I'm here in SW Florida and at the moment (11:38 PM) the full moon is not quite straight above me. I understand that this is the day that the tilt of the earth has shifted so the equator is pointed directly at the sun and the day and night equal 12 hours each.

So here is the question;

To an observer at the equator, is the moon directly overhead at precisely midnight? Was the sunset at exactly 6:00 PM this evening and is the sunrise going to be at 6:00 AM tomorrow? If not, is this the case at the Tropic of Capricorn or the Tropic of Cancer?

I'm sure I should have grasped all this minutia at my age, but it still confuses me a bit.

Since many religious holidays are coupled with celestial events (most, actually) I thank you for any help in a deeper understanding of what is a rather dramatic cultural occasion.

edited for spelling

[stevedeshazer]

1. The equinox has nothing to do with the Moon.

It is about the Earth's tilt (or lack of) in its orbit of the Sun.

[A HERETIC I AM]

3. I completely understand that...

I know that the equinox has to do with the equality of the length of night and day.

So maybe I need to ask more questions in order to understand what I am curious about.

Since this is the "Harvest Moon" tonight and since the Harvest moon always occurs on or near the day of the equinox, I am just trying to understand the mechanics of the travels of the moon across the night sky during this event.

Is that clear? Or am I not asking my question properly?

In the 1970's I lived in Alice Springs, Australia, 13 miles south of the Tropic of Capricorn. On December 23rd, the shortest day in the Northern Hemisphere, it was the longest day there and the sun was exactly overheard at 12:00 noon. So I am just trying to understand if there is a similar correlation with the moon with this celestial event.

[Canuckistanian]

2. The moon's orbit is on a completely different cylcle

It's position in the sky has nothing to do with our orbit around the sun.

[A HERETIC I AM]

5. Got that too.....

but is it correct to say that occasionally the two "sync up"?

I guess what I mean is, is it not the case that every so often the harvest moon is precisely overhead to an observer at a specific point on the globe at midnight on the day of the equinox?

[Canuckistanian]

8. "midnight" is our own invention

Based on our arbitrary division of years into 365 days and days into 24 hours.

The moon follows no such schedule. If you notice the chart on Wiki, the equinox does not follow our calendar and clock times exactly.
http://en.wikipedia.org/wiki/Equinox

It may be close, but it's not exactly "in synch".

[ProdigalJunkMail]

18. just a matter of semantics...

but years and days are not arbitrary...the words may be, but the period of those events is not...

sP

[Blues Heron]

4. when the moon is full it is directly opposite the sun

since this happened on the equinox, it is directly overhead on the equator, as is the sun (midnight and noon respectively) this day. the 6:00 and 6;00 rising and setting is for the most part correct but will be offset by time zone issues, eccentricty of the earth's orbit issues, and other minor effects...

basically whatever the sun is doing, the full moon is doing the opposite, hence the bright, high full moons of the northern hemisphere winter.

[Silent3]

6. First of all, Daylight Saving Time...

...can throw things off an hour (although the closer you are the the equator, the less likely it is that you observe DST). Exactly where you within your time zone also makes a difference -- only at exact multiples of 15 degrees of longitude does clock time and local mean time correspond.

Mean solar time and true solar time vary because of the ellipticity of the Earth's orbit.

Further, a full moon is only exactly full for one precise moment during the day of a full moon, and will drift as much as around 50 minutes' worth solar movement over the course of a day. The technical definition of "full" is opposition in celestial longitude, celestial latitude not being taken into account. Since the moon's orbit has about a 5-degree tilt, a full moon isn't necessarily directly opposite the from the sun in the sky. (If every full moon were exactly opposite from the sun, every full moon would turn into a total lunar eclipse.)

At any rate, you are onto the right basic idea: the sun being (close to) directly overhead at noon on the day of an equinox at the equator, the full moon being (roughly) opposite the sun, the moon therefore being (roughly) in the same position as noon's overhead sun twelve hours later at midnight.

The devil is in the details, however, so the actuality of these events doesn't come out as neatly as one might hope.

[A HERETIC I AM]

9. Thank you. Perfect answer!

Very lucid and descriptive.

Your mention of "The devil is in the details" underscores the answer I seek.

I appreciate your response.

Thanks.

[Silent3]

21. I've written astronomy software...

...that draws pictures of the sky, computes rise and set times of the sun, moon, and planets, even shows graphically how the moon crosses the face of the sun during a solar eclipse, how the shadow of the moon moves over the surface of the Earth, how the shadow of the Earth moves over the face of the moon during a lunar eclipse, etc.

I've had to get way, WAY into the "details".

My avatar, by the way, comes from a picture of the June 2001 solar eclipse that I took while visiting Zambia -- an eclipse that just happened to take place on the same day as the summer solstice. You might guess that I get into this stuff a little. :)

[Motown_Johnny]

10. the moon can be at any phase during an equinox, solar and lunar cycles have nothing to do

with each other


I suppose that every 28 or 29 years you will have a full moon on an autumnal equinox and then what you said might be true, but it doesn't happen every year.

[Silent3]

20. I don't think the OP was implying...

...that there's a full moon every autumnal equinox, he was simply asking IF there's a full moon on the AE what that means for the position of the moon at midnight that day.

He had the right basic idea too, it's just that when you take a bunch of complicating factors into account the idea is only roughly true, not exactly true.

[Motown_Johnny]

7. summer and winter solstice are the longest and shortest days of the year

vernal and autumnal equinox are the days where day and night are equal in length


time zones and lunar cycle don't have anything to do with any of it.


also the sun rise and sun set vary within time zones. I am on the western side of American's eastern time zone, Detroit. The sun does not rise for me at exactly the same time that it does for New York City which is on the eastern side of the eastern time zone, or for Buffalo New York which is in the middle of the two.



http://en.wikipedia.org/wiki/Equinox


^snip^

An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator. The term equinox can also be used in a broader sense, meaning the date when such a passage happens. The name "equinox" is derived from the Latin aequus (equal) and nox (night), because around the equinox, the night and day are approximately equally long. It may be better understood to mean that latitudes +L and -L north and south of the Equator experience nights of equal length.

At an equinox, the Sun is at one of two opposite points on the celestial sphere where the celestial equator (i.e. declination 0) and ecliptic intersect. These points of intersection are called equinoctial points: classically, the vernal point and the autumnal point.

[A HERETIC I AM]

11. I'm with you on all you've said and I lived in Detroit through the 1990's...

so I get what you are saying.

I know I might seem a bit of a dolt asking this, but I'm really not, trust me.

Tonight, BTW is a perfectly clear, cloudless night here in SW Florida and the moon is as brilliant as I've seen (or noticed, anyway) for years. I remember one evening when I lived in The Detroit area, a perfectly clear, full moon evening after a snowfall had occurred that day. The sky and just the ambient light was so bright at midnight because of the snowcover and the full moon, it was almost like walking outside on a cloudy day. You know what I mean?

It was gorgeous.

[BlueJazz]

12. I'm traveling to Australia next month. (I was born there) I can't wait to see..

...the Southern skies. When I left, my knowledge of Astronomy was limited. (I was 5) :)

[A HERETIC I AM]

13. Where are you going and where were you born?

As I mentioned upthread, I lived in Alice Springs in the 1970's but got the chance to go back downunder, to Surfers Paradise, Queensland a few times in the 1990's when I worked in Indycar Racing.

Some day I'll go back and either retire there or spend a few months traveling the continent.

[BlueJazz]

14. I'm going to Sydney (was born in Parramatta). Going to drive down to...

..Canberra...stop and see my Aunt...then on to Melbourne to see my Cousin. (I've never met any of them..only E Mail) ...rather nervous about the whole thing...Don't know why.
I am a little concerned about driving on the left but I got through the Class A CDL test here so I suppose I'll be OK.
(Why is that truck coming straight at me?) :)

[A HERETIC I AM]

15. LOL on the driving concerns....

The first time I went to Queensland for the Gold Coast Indy was the first year it took place, in 1991. I arrived a day before the rest of my team to set up our tech center. I was charged with renting a car from Coolangatta Airport and had to drive up to Surfers Paradise. I've had a CDL since they came into existence and started driving heavy trucks in 1978, but I wasn't prepared for driving on the other side of the road, by any stretch! I kept finding myself drifting over to the left because of my being used to sighting down the left portion of the lane I was driving in. I wanted my body to be over to the left! I almost hit the left curb several times, but soon got the hang of concentrating on the center line instead and was able to keep the car where it was supposed to be.

Don't worry, you'll be OK after few miles.

Take the chance to get away from city lights and check out the southern sky on a moonless night. It is something that you won't forget.

Bon Voyage!

[ProdigalJunkMail]

19. I agree you will be fine after a few minutes of

fighting your driving 'instincts'...my caution is this...be MORE careful when you get home. After driving for a month or so in a 'wrong sided' country...I find it harder to drive when I get home...

sP

[canetoad]

17. Let's work out a way

to send a message when your in Melbourne. We could have a beer, or three....

[BlueJazz]

22. Sure...Sounds good to me. I'm leaving Oct 20. I'll keep you informed.

:) :)

[Kringle]

16. the moon's orbit takes it, north and south, of earth's equator

the moon is over the equator,
twice a month

,so most pf the time,
the answer would be no.