Date: Mon, 22 Apr 2002 19:54:47 -0700
From: Jane Houston Jones 
Subject: [SHALLOW] The Mercator Sunrise Ray

To the south of Kies, on the other side of rugged slope of Rupes Mercator are the craters Campanus and Mercator. A sunrise ray was forming right next to the tiny crater Mercator C filling the dark flooded floor of Mercator with a fat wedge of light. Opposite the ray, the tiny crater Mercator B perched on the rugged rim of the crater lip. Half of the nearby section of Palus Epidemiarum formed a black triangle wedge of shadow.

I sent a note off to my local observing pals to see if anyone else was still out observing so they could be the first to see my sunrise ray (it was now 11:00 p.m. PDT). Only Bill Arnett replied and by the time he looked, the crater floor was flooded with light. I sketched the area and added the sketch to my lunar sketching page.

The event took place on 04/21/02. In her lengthy report, she stated observing a transit of one of Jupiter's moons at 9:00pm PDT. She mentioned she sent an email off to Bill Arnett at 11:00pm PDT. The time I used was 10:00pm PDT for April 21st. 10:00pm PDT for April 21st would have been 6hrs UT on April 22nd. She gave site coordinates of 122.3W and 37.567N. By running predictions using site coordinates, date and time of the event, it was determined that the event could be seen when the sun was 2.006 degrees rising, with an average colongitude of 28.400 degrees. This data was used to compute the predictions, found on the prediction page.

Starting Date  = 2002 / 4 / 22  U.T.
Site Longitude =  122.30   Latitude =   37.57   Elevation =  122 meters
Feature = MERCATOR
Longitude = -26° 6'  Latitude  = -29°18'
Reproducing Lighting For:  2002 / 4 / 22  at  6 : 0  UT
Desired Solar altitude =   2.006° (Rising),  Azimuth =  90.190°
Average Co-longitude =  28.400
In the time column, D=daylight, T=twilight

                      ---- Moon's ----
                         Topocentric     -- Earth's --    ------- Sun's -------
   UT Date    Time     Alt°  Semi-diam"   long°   lat°    colong°   lat°   azim°
 2002/ 4/22   6: 0    57.41    986.89    -5.40   -6.00     27.76   -1.15   90.19

Mercator, -386,-488: A fine ringed plain about the same size as Campus and forming with it a good example of a pair of ringed formations very similar in many respects. The interior is 28 miles in diameter, while the surrounding walls rise, in places, to 5,000 feet, with a crater on the western crest from which a short crater chain runs south down the slope. Just within the crest of the rampart, on the east, are two craterlets. The outer walls are very broad, and three prominent rocky mountain masses project on to the Mare on the north. To the north of the most westerly of these promontories is a low ring which is connected with Konig by a discontinuous ridge

The south wall of Mercator is cut through by a cleft which curves out on to the floor, ending at a small depression nearly in the center. The are also some craterlets on the interior, which is rather dark in tint. The wall on the south-west expands into a large and broad mountain pass of considerable elevation, rising as much as 6,000 feet at one point and separated from another mountain, on the west, by a narrow ravine or valley. To the south of this mountain mass is a large depression; several hillocks also lie on the plain between Mercator and Capuanus. - Wilkins and Moore, The Moon, Faber and Faber, 1955