how often

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james_

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does a full moon happen on New Years Eve? i thought i read somewhere that it happens around every 19 years, but now i cant find the article i read it in.

thanks for the help
 
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Gravity_Ray

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A full Moon happens about every 30 days. So its about 15 days for a new Moon, and about another 15 days for a full Moon. Your thinking of a "Blue Moon" and that depends on your defenition of a Blue Moon.

http://ask.yahoo.com/20010302.html

This link should explain it.

If there is a thread about it on these boards I am sure MW will inform us with his sage advice (if he isnt grumpy).
 
M

MeteorWayne

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It's actually pretty complicated (And I ain't GRUMPY!! :) )

A year is about 365.25 days. A lunar cycle is about 29.53 days. Both vary a tiny bit because of the calendar we use (which for most of a century is 3 years of 365 days, followed by a 366 day year) and the lunar cycle is not exact, since the exact timing varies because of the elliptical lunar orbit. Then you throw in the fact that New Year's Eve is 24 hours long, and it get's too ugly to really compute with any precision.

It would take hours to come up with a true answer, so the best thing to do is hopefully find an accurate google search result, which I would not assume is correct without knowing the source. Unless the name associate is Jean Meeus, I woudn't trust it.
 
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moreandless

Guest
MW, is there a better orbit diagram site for the lay person than the NEO program; for instance
they show 3200 phaethon at a close approach in Dec 2017. whereas your sources show it'll be
a long long time.
 
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MeteorWayne

Guest
Well, it's really all in how close it has to be to be called a close approach. the 2017 CA is at about 0.069 AU, or 35 times the distance to the moon.

The orbit diagram at the JPL site is only an approximation anyway, it is just a projection of the current orbit. The orbit of any object in the solar system constantly changes as it is influenced by the gravity of the Sun, (which actually orbits the center of the mass of the solar system) planets, and the larger asteroids.

For example, the 3200 Phaethon page:

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3 ... ;cad=1#cad

Note the disclaimer on the orbit diagram:

"The applet was implemented using 2-body methods, and hence should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances. For accurate long-term ephemerides, please instead use our Horizons system."

In addition, the angle that you are viewing the solar system can create the illusion of close encounters when none actually occurs. If you grab the handle on the right side of the diagram, you can change the angle all the way from a direct overhead view, to one along the plane of the solar system. If you see what looks like a close approach, look at it from different perspectives.

The Horizons Ephemeris generator (link toward the bottom) on the other hand constantly recalculates the orbit using the gravitational influences of the Sun, planets, and the 3 largest objects in the main asteroid belt, which contain about half the mass of the whole belt.

The close approach table at the bottom takes all those future orbital perterbations into account, so it's far more accurate than the diagram. Again as an exmple, the orbit diagram show 0.066 AU, while the actual CA will more like 0.069 AU. Not much of a difference, but it shows that the diagram is an approximation, rather than a precise calculation.

Hope that helps.

Wayne
 
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michaelmozina

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MeteorWayne":3dffp7za said:
It's actually pretty complicated (And I ain't GRUMPY!! :) )

A year is about 365.25 days. A lunar cycle is about 29.53 days.
Of course there is a "cheap and dirty" answer (close enough for government work. :) ) based on pure probability. The odds are 1 in 29.53+- that the moon will be full on any given day, including new years eve. :)
 
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MeteorWayne

Guest
That's a great resource, thanx yale_s and welcome to Space.com! I added it to my astronomy links.

Wayne
 
G

Gravity_Ray

Guest
MeteorWayne":29m81y6x said:
That's a great resource, thanx yale_s and welcome to Space.com! I added it to my astronomy links.

Wayne
The Year: 3702
The place: Space.com Forums
Newbie poster: When is the first full Moon?
MW: BAM!! Jan 27 2:02
MW: muhahahaha
:twisted:
 
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