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Purbach Cross (Lunar X) - Sunset Viewing Project

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#1 Carol L

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Posted 07 December 2012 - 06:17 PM

(Just a note - although i call this particular light phenomenon 'The Purbach Cross', i'll call it 'the X' here for brevity's sake.)

We know that the X is easy to see at night, during lunar sunrise (waxing phases) - but what about in daylight hours, during lunar sunset (waning phases)? I was curious about this a number of years ago, and decided to find out.

The first favorable date was August 15th 2006. Luna had risen at 11:00PM the previous night, transited at 7:00AM that morning, and would set at 2:00PM that afternoon. I wasn't able to get out till 11:00AM though, and she was already sliding down toward the western horizon. But thankfully there was enough time to get what i needed before she slipped into the turbulent 30° airmass. It would have been ideal to do this when she was high in the sky with the X directly on her terminator, but we lunatics have to take what we can get, and be happy with it. :smirk:

Here's an image from that day, placed below another image of mine (not the same one that was on LPOD, though) - the images are comparably sized in order to make identification easier. Although the daylight image is poor at best, the shadowplay appears to suggest that the X is sloping slightly towards the east limb (right side in the images), and the X's appearance might very well disintegrate as the terminator got closer. I never found out, but it was a fun observation anyway.

Oddly enough, i never went back to look at the X during the daytime again and it made me wonder if anyone here in the LunieBin might be interested in making it an ongoing project - i think it would be a lot of fun to take things to the next level. If there's any interest, someone could (thanks in advance! :bow:) post a list of available dates below. It'll give us something to start with, and as time passes we could bump the thread up as needed in order to keep everything in one discussion.

How about it? :grin:

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#2 RobDob

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Posted 07 December 2012 - 10:38 PM

Count me in!

I was able to get a few afocals of last September's 'X' which at it's best was in daylight for me...

This pic was taken 9/22/12 6:15 PDT about 1 1/2 hr. before sunset.

Rob

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#3 RobDob

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Posted 07 December 2012 - 10:51 PM

OOooops, I get it now. Waning phases :foreheadslap:. So, the X illuminated from the other side? Edit: A reverse 'X' ehh?

I'm still in...

#4 edosaurusrex

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Posted 08 December 2012 - 11:12 AM

Predictions for Long 1.1E, 25.4S Sun Alt 1.0deg

WERNER X REVERSE PREDICTIONS FOR 2013
MMM DD HHMM (UT)

JAN 04 1107
FEB 03 0124
MAR 04 1536
APR 03 0519
MAY 02 1818
JUN 01 0630
JUN 30 1803
JUL 30 0515
AUG 28 1626
SEP 27 0358
OCT 26 1610
NOV 25 0513
DEC 24 1906

#5 Carol L

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Posted 08 December 2012 - 04:41 PM

Thanks so much, Ed! :bow: :bow: :bow: I'll add them to my calendar.

Thanks for joining in Rob - and yes, it'll be a 'reverse X' - cool !!! :grin:
Know what? I just checked the first date Ed gave us, and the event will occur early in the morning when it's still dark out. Having done my one and only observation of the reverse X in August, i'd mistakenly thought the events would take place in full daylight. Well, like they say... you learn something new every day (at least i do, anyway :lol:). Here's hoping it'll be a calm, clear morning with a user-friendly temperature.

#6 Dave Chapman

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Posted 09 December 2012 - 04:59 PM

Know what? I just checked the first date Ed gave us, and the event will occur early in the morning when it's still dark out.


I'll try as well, it is before Earth sunrise here (east of you, I reckon). Some folks here say they have seen the (Moon) sunset X, but I have not!

#7 edosaurusrex

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Posted 10 December 2012 - 01:40 PM

Getting out ahead of the predicted time (1/2deg of Sun elevation per hour) is strongly recommended. I pulled the 1 deg Sun elevation out of the air for the table. It's a very "Sixth Sense" thing to post about an event then have an ideal opportunity present itself for the poster the next time it occurs. That's what I call being "In Tune with the Moon!".

Ed

#8 Dave Chapman

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Posted 10 December 2012 - 01:55 PM

Getting out ahead of the predicted time (1/2deg of Sun elevation per hour) is strongly recommended. I pulled the 1 deg Sun elevation out of the air for the table. It's a very "Sixth Sense" thing to post about an event then have an ideal opportunity occur for the poster the next opportunity. That's what I call being "In Tune with the Moon!".

Ed


I heartily agree with that, especially as we do not really know what to expect.

Dave

#9 Tom and Beth

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Posted 10 December 2012 - 11:04 PM

Predictions for Long 1.1E, 25.4S Sun Alt 1.0deg

WERNER X REVERSE PREDICTIONS FOR 2013
MMM DD HHMM (UT)

JAN 04 1107
FEB 03 0124
MAR 04 1536
APR 03 0519
MAY 02 1818
JUN 01 0630
JUN 30 1803
JUL 30 0515
AUG 28 1626
SEP 27 0358
OCT 26 1610
NOV 25 0513
DEC 24 1906


Yippee! At the risk of being impertinent, might I be so bold as to request a list of Curtiss Cross events?

Thanks for these. I do save them and try to observe.

#10 edosaurusrex

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Posted 11 December 2012 - 01:23 AM

CURTISS CROSS PREDICTIONS FOR 2013
MMM DD HHMM (UT)

JAN 05 1846
FEB 04 0917
MAR 05 2322
APR 04 1237
MAY 04 0058
JUN 02 1229
JUL 01 2333
JUL 31 1033
AUG 29 2152
SEP 28 0952
OCT 27 2238
NOV 26 1227
DEC 26 0251

#11 Tom and Beth

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Posted 11 December 2012 - 03:28 AM

thank you!

#12 edosaurusrex

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Posted 22 December 2012 - 10:01 AM

And while you are waiting for the perfect Reverse X lighting conditions, check out the Walther crater ray predicted to occur at 1123UT the SAME DAY!!!!

WALTHER SUNSET RAY PREDICTIONS FOR 2013
MMM DD HHMM (UT)

JAN 04 1123
FEB 03 0133
MAR 04 1548
APR 03 0543
MAY 02 1858
JUN 01 0725
JUN 30 1911
JUL 30 0628
AUG 28 1736
SEP 27 0458
OCT 26 1654
NOV 25 0540
DEC 24 1920

Crater Position and Sun altitude for these predictions are from the Robinson Lunar Observatory. For Walther and many other ray predictions check out Rob's site at
http://www.lunar-occ...o/rays/rays.htm

#13 67champ

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Posted 24 December 2012 - 12:10 PM

Ed, Thanks for the Ray info.

That is something that I learned from you years ago and it is really interesting. Unfortunately the 'reverse X' isn't visually what many might hope for. :bawling:

Nothing against this, Just saying.............. It is however, a neat area to observe in general at any phase. :waytogo:


dana t

#14 Tom and Beth

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Posted 25 December 2012 - 03:19 PM

Thanks you, Ed and Dana, for both Crosses, Walther Ray and Pico 2013 timing predictions.

#15 edosaurusrex

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Posted 03 January 2013 - 08:22 PM

Bumping this up because of the first opportunity tomorrow morning (US).

#16 RobDob

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Posted 04 January 2013 - 12:38 AM

Errggh! I was looking up at the moon this morning thinking about this, I knew it was getting close. Of course tomorrow I will miss it because of work... Dang work gets in the way of my hobbies...

Rob

#17 Carol L

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Posted 04 January 2013 - 02:00 AM

(Thanks for the bump-up Ed, you beat me to it. :grin:)

It's clear out and is supposed to stay that way all night, so i'd planned on using the 16LB on the patio. But that plan got scrapped when i pulled my back out this morning moving some firewood. Thankfully, the 80ST i use for wildlife watching is always set up in the south window, so that's what i'll use. The window's a triple-pane and throws reflective ghosts, but it's better than nothing. Everything still depends on how my back feels when the alarm goes off in the morning, though - - fingers crossed.

#18 Dave Chapman

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Posted 04 January 2013 - 05:44 AM

OK it is clear and cold here in Nova Scotia, and I have been observing since about 10:10 UT. The X area is deep in the shadow cast by the eastern wall of Purbach, and I can see 3/4 of an X with a short detached linear feature off to the northeast. A small crater is at the cross of the T. I feel I should have been observing even earlier to see a full X. I am up now, so will continue to observe sporadically as the sun rises here and sets on the X.

Just south of the X, the Walther sunset ray is developing nicely. To the west, the Straight Wall has an illuminated face (contrary to the more familiar view after the sunrise terminator has passed the location, when the scarp face is in shadow).

I am observing with my TeleVue Ranger 70 mm f/6.8 with 7 mm Nagler for 68X.

Update at 11:30 UT: the northeast feature is gone, and the T looks more like a Greek lowercase lambda. There is pseudo-X just to the south, but its western flank and surroundings is illuminated by the setting Sun.

Dave

#19 Magellan

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Posted 04 January 2013 - 07:42 AM

This is a quick process of the Walther sunset Ray. Seeing was terrible and with the rising sun, didn't make it any easier. I have many more images I will process later:

Telescope: Orion 8" F4 Newt
Mount: CGEM
Camera: Astro Modified Full Spectrum Canon XSi
Filter: Astronomik CLS (was already inserted as a clipin)
Time: 0645AST
Location: Enfield
Captured with BackyardEOS
Frames: 800/1000

Posted Image
MOON_100iso_06h45m800frames by AstroJeff, on Flickr

#20 Dave Chapman

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Posted 04 January 2013 - 08:41 AM

This is a quick process of the Walther sunset Ray.


Good catch, Jeff. Your photo and my description make a pretty good pair, I'd say!

Dave

(Disclosure: Jeff and Dave are friends and live not far from each other, both members of the RASC Halifax Centre.)

#21 thewheel

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Posted 04 January 2013 - 02:16 PM

Hi Folks, I gave this a shot at 11:53AM UT on 1/5/2013.

I labeled some stuff , wonder if you could tell me IF I have it labeled correctly?

I had to resize it a bit to get the 225Kb limit here.

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#22 edosaurusrex

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Posted 04 January 2013 - 02:57 PM

Very good catch! Did you watch the ray until it completely collapsed?
Good report Dave, wish I could have seen it.
Ed

#23 Carol L

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Posted 04 January 2013 - 05:49 PM

(@ member 'thewheel': looks like you got everything labelled ok. :waytogo:)

Thanks for your detailed report, Dave - i viewed a bit earlier.
Not realizing how late it was when i posted last night (1:00 AM local, 07:00 UT), i decided to just stay up for a while longer and began viewing Luna through an eastern window at about 2:00 AM local (08:00 UT). The telescope used was an 80ST [400 fl; f/5] with a 9mm SWAN ep in a Klee 2.8 Barlow [123x]. The view was surprisingly decent despite the triple pane windows, and it didn't take more than a few moments to see that the X doesn't benefit from western illumination like it does during lunar sunrise.

It was still easy enough to see, but the high elevations of the Delaunay complex [NE of la Caille] were still illuminated and stole the X's thunder so to speak, by preventing the X from standing out like it does under opposing lightplay. The X's NE arm [between la Caille and Blanchinus] was already beginning to darken with shadow, and the NW arm [between la Caille and Purbach] was darker than the two southern arms - but brighter than the NE arm.

Jeff, Kudos on the great capture of the ray! :grin:
Dave, is the pseudo-X you mentioned in Jeff's image? The SW arm begins on the northern rim of Walter. (Yeah, yeah, i know - it's supposed to be 'Walther' but my copy of Rukl's says 'Walter' and i cut my lunar teeth on that atlas - old habits die hard. :lol:)

#24 Dave Chapman

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Posted 04 January 2013 - 08:23 PM

(@ member 'thewheel': looks like you got everything labelled ok. :waytogo:)


@thewheel: Great photo! Based on my observations, you have labelled what I call the pseudo-X as the Purbach Cross (Lunar X, etc.) In your photo, the classic X (what remains of it) is just north of that (see Magellan's photo).

Dave, is the pseudo-X you mentioned in Jeff's image? The SW arm begins on the northern rim of Walter. (Yeah, yeah, i know - it's supposed to be 'Walther' but my copy of Rukl's says 'Walter' and i cut my lunar teeth on that atlas - old habits die hard. :lol:)


Yes, Jeff has captured the X (what's left of it), the pseudo-X. and the Walther Ray. I only mentioned the pseudo-X as it could be mistaken for the X we were looking for. I call it "pseudo" as it is never completely surrounded by shadow, like the classic X.

The I.A.U. renamed Walter as Walther in 2000, as there exists another crater named Walter. That's good enough for me! http://the-moon.wikispaces.com/Walther

#25 edosaurusrex

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Posted 05 January 2013 - 01:53 AM

After reading Dave's report I have revised the Sun Angle so the Sun is at 1.5deg. The 1deg I reported for the first set of predictions was an error. The actual Sun angle in the program was 0.5deg (I'm so ashamed)

REVERSE WERNER X PREDICTIONS FOR 2013
MMM DD HHMM UT

FEB 02 2324
MAR 04 1337
APR 03 0320
MAY 02 1619
JUN 01 0431
JUN 30 1604
JUL 30 0316
AUG 28 1427
SEP 27 0200
OCT 26 1412
NOV 25 0314
DEC 24 1707






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