#83 Small Telescope Adventures: Part 6

The Olcott Project:  Adventures with a 2" Telescope--Night 7

Tonight's lunar observation (October 22nd) was aided by still air and mild temperatures.  Our 50 mm refractor is proving to be a wonderful instrument with which to study the lunar surface once again, something we haven't done much of in many years.  We observed our 25th object with Space Eye tonight, a minor milestone.  This marks our second lunar observation, with eight more allowed in our initial project of sixty objects.  We are hoping to eventually include several planets, too.

Object #25:  Sinus Iridum

We used Plate VII from the Field Guide, studying a very attractive and conspicuous area in and around Sinus Iridum, also called "Bay of Rainbows."  The Bay is 242 miles x 157 miles, and has a flat floor that sits about 2,000' lower than adjoining Mare Imbrium.  The curving mountain range ringing the north end are the Jura Mtns., rising to 18,200'.  They were spectacular tonight.  While some of the Bay was still in deep shadow, the mountain tops were brightly lit beyond and into the terminator.  We studied the area at 60x and 75x (without a filter), noting many other involved features (see sketch, below).  This area was lit spectacularly tonight, repaying careful study, and was easily the finest sight on the moon!  The moon was exactly ten days old.

Each curving end of the Juras has a name.  Cape Laplace, on the eastern end, rises to 7900', while Cape Heraclides, on the opposite side of the Bay, rises to 5500'.  The craters Bianchini, Helicon, and Leverrier all require a 2" glass to see clearly.  Their diameters are 23 miles, 15 miles, and 12 miles, respectively.  The adjoining Straight Range/ Montes Recti rises to 5500'.

 Deb's sketch of the Sinus Iridum area.  60x, 2" refractor.  10-day old moon.

Here is what Olcott says about the Sinus Iridum area:  "Capes Heraclides and La Place are at the eastern and western extremities respectively of the Sinus Iridum or "Bay of Rainbows."  They are 135 miles apart.  The former is 4,000' high [now 5500'], and its shadow forms the silhouette of the "moon maiden," best viewed when the moon is 11 days old."

 We also explored the Carpathian Mountains, a complex area near the terminator tonight, and just north of Copernicus.  The crater Tobias Mayer, at the eastern edge of the mountains, is 9300' deep and looked like a circular black pit!  This would also make a good area for detailed observations around the 10-day phase.

Mapman Mike