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About Tom Whiting
Expertise
Astronomy has been my hobby/pasttime for over 50 years. Currently own 3 telescopes, the largest of which is a 30 inch Newtonian truss Dob that is portable.I taught Astronomy/Meteorology at the University Level for 13 years before retiring in 1995. Being retired and home most of the time, I am able to answer all questions relatively quickly, unless it's a new moon weekend with good observing conditions. No astrology questions please, or questions about alleged UFO picture identifications.

Experience
Experience: Astronomy has been my hobby and study for over 50 years. We currently now own a 30 inch portable telescope (Updated - Pennsylvania`s largest portable telescope). It can be seen on our website at:http://www.velocity.net/~bwhiting and also attend several regional starparties during the year, and have been on 5 total solar eclipse expeditions.

Organizations: President, Erie County Mobile Observers Group for over 15 years.

Publications: Wrote the "Over Erie Skies" newspaper article in our local newspaper for 11 years (1975-86).

Education: Masters Degree- Taught at the University level for 13 years. Retired 20 years -USAF Pilot - KC-135 with 180 combat missions; Also Eagle Scout, Philmont staff 2 Yrs, Order of Arrow Lodge Chief, Ham Radio (inactive).

Awards: two discoveries: The mini-coathanger asterism in Ursa Minor (the little dipper) And the mini-ladle- another asterism in the bowl of Ursa Minor. Clients: Currently President of the ECMOG as mentioned above.

Education/Credentials
BS Metallurgical Engineering Grove City College, PAMaster's Degree, Gannon University, Erie, PA Also retired USAF pilot, 20 years.

You are here: Experts > Science > Space and Astronomy for Kids > Astronomy > measuring the moon

Astronomy - measuring the moon

Expert: Tom Whiting - 11/5/2009

Question
I need help figuring some things out about the moon with some data I have gathered. I have observed the moon throughout the course of the past month, and have gotten a good 8-9 measurements on its phase and approximate position in the sky from night to night. I measured its position relative to several bright stars, then used star charts to estimate the moon's approximate declination. How can I calculate the deviation of the moon from the ecliptic at the time of each observation? I'm a little confused as to how I figure that out.
Also, where is the moon in its orbit when it crosses the ecliptic plane, and where it is in its orbit when it reaches its farthest above and below the ecliptic plane?

Answer
Hi Lindsey,
If you are really interested in where the moon is located in the night sky from night to
night (and this just isn't another 'homework' question)...get yourself a copy of Guy
Ottewell's Astronomical Calendar 2009...although since it's near the end of the year, I'd wait
and get the 2010 calendar since they cost around $30. But you get the entire sky every night
and what's going on from a daily basis, of everything, not just the moon. (Thus the high cost
for that particular calendar). Order through www.universalworkshop.com or Sky and Telescope
magazine.

The moon's motion in the sky is the most complicated of all the heavenly bodies from a mathematical standpoint...even our navigator aboard my KC-135, circa 1969, never used the moon in celestial navigation, preferring bright stars and the sun for celestial fixes in the sextant...he didn't even use the bright planets as it involved too many calculations to pre-comp. (In the old days before GPS, navigators would pre-compute [pre-comp] their celestial
sightings before the flight occurs to get most of their heavy work already completed).

As you probably already know, the moon's orbit is tilted 5 degrees to the ecliptic, and it
precesses, so the ecliptic crossings are always moving backward during the complete Saros
Cycle of 18.61 years, so none of those dates and positions you request are fixed on a monthly
basis. One question is easy...as we know on eclipse dates the moon has to be crossing the
ecliptic. These Greenwich dates for 2009 were (are) Feb 9, July 7, August 6, and December 31.
Notice the backward precession dates of 9, 7, 6, and 31....so every month is different as
the nodes (where the moon's orbit intercepts and crosses the ecliptic)...are different.
And as a general rule, 7 days before eclipse and 7 days after, the moon was (is) at it's maximum
deviation from the ecliptic, and these dates will migrate monthly too...about one day every
1.64 months. (How did I get this? 18.6 years is 223.2 months, and that number divided into
a complete 365 days of travel = 1.64 days of travel around the ecliptic, per calendar month...
on average.) And even this is not a constant number as the moon's orbit is elliptical, not
circular. So see, the mathematics, even for the easy stuff, can become very cumbersome and
bewiltering.

Actually from an observational astronomy standpoint, we astronomers don't even care about all
this...since we hate the moon because when it's up it ruins our dark night sky, all we care
about is when the moon is bright and visible in the night sky, because we don't go out
observing the deep sky objects when it's up and bright. So basically from just after first
quarter until last quarter, all deep sky telescopes (including the 10 meter Keck's on Hawaii)
are out of business for about 2 weeks per month. So to us, the more important time is the
moon's setting time so it gets out of the way from our observing schedule. And we can just
look that time up on our computer star chart programs.

But to your question, rather than go through reams and reams of calculations if you want
the actual dates of maximum deviation for the moon, simply look it up in Guy Ottewell's
Astronomical Calendar, and it will save you an awful lot of un-necessary work and time...time better spent on actually observing the night sky, rather than sitting at a desk doing all those calculations. We are observational astronomers, not mathematicians. Plus, computers have already
done all those calculations for us...there is no need for all that manual type work today.
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA

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