Saturday, March 21, 2009

Patterns in Titan transits & shadow passes!

I don't know why, but I've always been fascinated by patterns. Titan's orbital period is approximately equal to 2 weeks + 2 days - 1 hour. So we have 3 patterns superimposed here:

- You can see the time of day for the events slowly march backwards in approximately one hour increments from 4:52 AM to 3:16 PM.

- You can see the lack of transit transition through "barely" a transit to full transit to perfect ringplane transit to full transit to "barely" transit to no transit.

- You can see the altitude at shadow pass start times decrease, then increase. I'm not sure why Mar 28 has 18*43' and not 21*, but I'm just going by what Starry Night Pro indicated. I tried to eliminate as a source of error how far advanced the shadow was when I stopped the software and read off the numbers. The time is when the whole shadow is first visible. I also made a point of recording the minutes of arc as well. Still the March event is lower in the sky than the April 13 event. I'm stumped. The only thing I can think of is the curvature of Saturn's surface is playing a role here.

This pattern is to be expected as the ecliptic is doing its usual "Summer = Sun high, planets low / Winter = Sun low, planets high" pattern. The April 13 event has the highest altitude we're going to see for Saturn this year.

- There's a 4th pattern that I didn't really allude to very much, except with the "Rings flipped" reference. The shadow of Titan starts off to the left of Titan, and thus trailing behind Titan (which is moving left to right in front of Saturn), then it transitions after passing behind the Sun to the state of having the shadow of Titan leading it. You can see that the Aug 2 event has the transit starting in daylight, but the shadow pass starts at 9:25 PM, after sunset. Thus we start with a "Transit first, shadow after" pattern, then go to "Shadow first, transit after" situation.

I didn't continue into 2010, there probably are more there, but the inexorable "time of day for the events marching backwards" pattern will put the transits in full daylight. Not much for photography...

Titan shadow pass start times:
Mar 28 - 4:52 AM - 18*43' alt - No transit.
Apr 13 - 3:40 AM - 19*1' alt
Apr 29 - 2:45 AM - 18*17' alt
May 15 - 1:43 AM - 17*20' alt
May 31 - 12:46 AM - 16*1' alt
Jun 15 - 11:56 PM - 14*20' alt
Jul 01 - 11:04 PM - 12*38' alt - No transit.
Jul 17 - 10:12 PM - 11*6' alt - Titan barely transits, ends at sundown, 8:13PM.
Aug 02 - 9:24 PM - 8*55' alt - Transit starts during daylight, till 10:47PM (but sets at 10).
Aug 18 - 8:37 PM - 6*38' alt - Nice transit, but is setting & close to the Sun.
Sep 03 - 7:52 PM - 4*1' alt - Lost in Sun. Rings exactly edge on. Titan centered on ring plane.
Sep 19 - 7:08 PM - 1*15' alt - Lost in Sun. Rings flipped. Shadow precedes Titan.
Oct 05 - 6:23 PM - 1*18' below horizon.
Oct 21 - 5:42 PM - 4*42' below horizon. Titan just barely transits at 10:23 PM.
Nov 06 - 5:01 PM - 8*8' below horizon. No transit.
Nov 22 - 4:24 PM - 12*25' below horizon. No transit.
Dec 08 - 3:49 PM - 17*13' below horizon. No transit.
Dec 24 - 3:20 PM - 23*11' below horizon. No transit.
I just love patterns and astronomy is chockablock with them!


NiteSkyGirl said...

Really interesting Richard !
I love it when people write about their interpretation of how they see the cosmos. I'll be out there studying this new way of seeing planetary transits now that Saturn is out now, later Jupiter will be back . Both for the summer . Two planets this year yay! Had a blast observing Jupiter and it's moon movements . My new 12 inch skyquest will be so fun to view everything this year.

Such a fascinating post i'm passing the link onto my readers.

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