Terminator surprise discovered by Phillip Koch of Las Vegas, Nevada. He writes:

"Several times I've observed an event on the Moon I'd like to share. As the morning terminator crosses the crater Hesiodus, the crater is bisected by a shaft of light coming through a cleft in the wall between it and the adjoining crater Pitatus. My drawing from the night of March 26, 1988, shows this phenomenon.

"The first time I viewed this, the bottom of the break in the wall was lit, and a beam of light shined through and split the crater in two. Since the rim of the crater  was also lit, it created a circle of light split precisely in half by a ray of light.

"How often does the Moon reach this precise orientation where the light breaks through the cleft when the terminator reaches this spot?"

"Figure 8 craters" Petatus & Hesiodus at right.  (Section 54)  Hesiodus A.  One of the rare examples of a crater with double concentric walls. The diameter of the outer wall of Hesiodus A is 15 km. A similar formation, in an adjacent area, is the crater Marth, 7 km in diameter, which is located in Palus Epidemiarum (Section 63).

Perspectives on the Hesiodus Ray
1996 Dec 18

Despite a cold and the prospect of having to get up early, I stayed up late enough on December 18-19 to watch the start of the Hesiodus ray apparition from my yard in Palo Alto, California. Seeing was pretty good -- diffraction rings around Polaris were continuously visible, but continuously in motion, in my "Baby Brandon" 63 mm f/5.6 refractor at 141x. I was using my Vixen Lanthanum 2.5 mm eyepiece for the first time with this instrument; it worked very well, and gave sharp images all the way across the field. The Brandon was doing a fine job as a "quick look" telescope.

At about 0655 UT 19 December (1055 PST on the 18th), Hesiodus lay with its bright-rimmed bowl almost completely filled with darkness, but the gap in its wall into Pitatus was clearly visible, as was the bright spot on the opposite wall of Hesiodus where sunlight was already streaming across the crater. Over the next 25 minutes the ray developed, starting at the west wall and growing back toward the gap at the east, narrow and fine, wider at the west than the east. By the time I went back inside at 0720 UT, it was at least 75 percent of the way across the crater, and a little south of center. The ray was not sharply defined; larger apertures may have seen more of it than I did, or sooner, or both.

I also had a nice view of the Straight Wall nearby.

--- Jay Freeman

I set up my Pronto at about 8pm PST. Nothing unusual was visible. By about 11pm I was able to see the beginnings of the ray. With a 4.8mm Nagler and a 2x Barlow I was up to 200x (and an almost literally microscopic exit pupil (.35mm)) and getting a pretty nice image albeit with a lot of motion from the crappy seeing (I'm in the middle of San Jose). I had been unsure exactly which crater was Pitatus but it was pretty clear by then.

So now convinced that this thing really was going to happen, I set up my 12" LX200. It is
surprisingly easy to set up actually; it took less then 10 minutes from the decision to the first view. The extra brightness of the image was not particularly useful and higher powers than I was using with the Pronto were not possible given the seeing but it was a lot easier on my eye at 250x with a 1.2mm exit pupil.

I watched the ray grow across the Hesiodus. I had to give up at 1pm as the Moon had gone behind the trees to my west. (I actually spent about 1/2 the time viewing thru the small upper branches; about the only ill effect was somewhat reduced contrast.) The ray had not quite reached the eastern wall. But I thought that the ray had rotated around toward the south a bit. I would not have said the ray was sharply defined. Had I not known about this phenomenon I would have though that I was seeing a linear hill sticking up into the sunlight.

It was an odd experience using averted vision on the Moon.

--- Bill Arnett

I looked for it with the 6" Cave at 10:15-10:30 at 180x, and with the 6" refractor at Foothill at about 10:50 and 11:20. Looks like I'm the only one who looked and didn't see it ... or maybe I did after all:

I was also unsure which crater was Pitatus, though I thought I had it narrowed down to two. On the dark side of the terminator in that area, I saw two bright areas which looked like tops of mountain ranges protruding into the sunrise. Perhaps one of them was the ray?

The Straight Wall was very nice, though (and, oddly, seemed more prominent in the Cave than in the Foothill refractor), as was the big crater with the two sharply illuminated craterlets inside, which in my selenographical inexperience I was unable to identify.

Between looks at the moon, I had a chance to whip over to Orion to show one of my housemates one of the best views of M42 I've ever seen from Foothill -- the fifth Trapezium star was obvious in both the 16" and 6", and the red color in the "wings" was as obvious (in the 16") as I've ever seen it from the Peak.

--- Akkana

Nuts! I got home late and didn't take my scope out. I'm glad the rest of you folks aren't so lazy. ;)

--- Rich Neuschaefer

Here's another article about The Sunrise Ray in Hesiodus from Robinson Lunar Observatory.
 Download map of area

Bill Arnett; last updated: 1997 Jan 4

Image of Pitatus

Lunar Orbiter image:

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