Gemma Frisius A Lunar Sunrise Light Ray

Observer: Tony Donnangelo
Date/time of observation: 2004/12/18  00:10 U.T. 
Site location: Hummelstown RD 3, PA, USA (40.26° N., 76.75° W.)
Site elevation: 479 feet (146 meters) 
Site classification: Suburban
Instrument: Takahashi FS-102 f/8  
Magnifications: 117x, 137x, 164x
Moon’s age: 5d 09:40 
Illumination: 36.6% Apparent Dia.: 31.58’ Distance: 378,392 Km.
Librations: 7.7° N/S 4.31° E/W 6.39° PA 304° 
Object: Gemma Frisius A
Lunar ray coordinates: 17.5° E, 35.25° S
Rükl chart #: 66

It was a cold night, with the temperature dropping into the low 20’s. A thin layer of high clouds resulted in poor transparency; however, seeing was steady, and the Moon appeared crisp. I wasn’t dressed warm and only stayed outdoors for approximately 5 minutes at a time. I was running in and out of the house trying to accomplish some preparations for Christmas. The sub-freezing weather could also be construed as a factor in my actions.

I began observing at 11:15 U.T. This was one hour and fifty-one minutes prior to the predicted time of the ray’s occurrence. It was initially reported that it might be visible at an earlier time. Gemma Frisius was well within the terminator and couldn’t possibly create a ray at the scheduled time. I concluded there must be a large error in the calculation. However, I failed to read David Ryle’s follow-up report beforehand. It proved to be a grievous error. This should always be done, and I’m a stickler to do it. However, this time, I’ll blame it on the holiday frazzle.

David reported seeing it two hours prior, and that it was actually in Gemma Frisius A. I first observed the ray at 00:10 U.T., fifty-four minutes early. This was very close to its inception. I immediately realized it wasn’t in the reported crater. I was confused on whether this was the same or an unreported ray. It was close to the predicted time and location, and the initial description characterized what I was seeing.

Craters A and B are superimposed. The beam of light emanated from a break in the wall between A and B and extended westward approximately 51 Km. (27.0”) onto the floor of A. The ray was slightly widened to the west. There were two perpendicular shadows segmenting the ray. The western shadow was caused by a craterlet, and the eastern one appeared to be the result of a raised area.

Crater B’s northern and southern floor area and the adjacent interior walls were only shadowed. The remaining two-thirds of the crater appeared as a very extremely wide cone-shaped swath of light.

Most of crater A was within the terminator. Its western interior wall was illuminated, revealing craterlets. Only the very eastern rim of Maurolycus was illuminated. There was no hint of Gemma Frisius or Goodacre. The sunlit crests of craters Barocius, B, and C were evident. They almost looked like Mickey Mouse’s head and ears (maybe the cold was getting to me – what do you think?).

By 01:30 U.T., the ray began to widen. Within fifty-five minutes, it became more cone shaped. It remained further unchanged as the Moon set behind a house at 03:28 U.T.

At this time, the U-shaped crest of Goodacre was visible, with the southern end open. The eastern half of Maurolycus’ rim was visible.

11/30/2003 1-5 UT
Wichita Falls, TX 33.824, -98.544 994 ft.
Clear skies, transparency good, seeing moderate to poor. Limit magnitude at zenith 5.
Wind southwest 8-10 mph. Temperature 40F. Barometric pressure 1,000 mb.
Moon 5day, 1 day prior to first quarter. In Aquarius.

The time was a little early (9 PM CDT, 3 UT) but I proceeded to find the scheduled Lunar sunrise ray in Gemma Frisius. This was due to happen around 11 PM CDT, but my calculations had the terminator revealing the ray around an hour earlier. The original June 2000 report from Brien Stratton stated the ray to possibly be visible earlier than his first sighting of 23 UT. As I looked it was obvious which crater was the target. A fine ray was seen in the interior of a crater north of Maurolycus. The crater was third in a series of three craters in a chain from east to west. The crater was defined nicely with contrasting rims and an obvious craterlet to the west end. This craterlet was most likely the source of confusion in the report by Brien. The classic “flashlight” beam of a ray was intersecting this craterlet from the joining segment at the preceeding eastern crater in the chain, and causing the perpendicular lines Brien noted. Upon further study and a couple of looks at page 66 of the Rukle’s Guide, I noticed the subject crater was not Gemma Frisius but rather Gemma Frisius A. This explained the apparent loss of a craterlet bisecting the floor of Gemma Frisius. I watched this sight in the 8” f/9 refractor at x203 until 4:45 UT. It stayed essentially unchanged as the outline of the eastern rim of Gemma Frisius became defined by the moving terminator.