January 14th, 2005: Lunar observing log: A 4-day-old moon

Tonight I wanted to observe the 4-day-old Moon, but first I tried the capture the earthshine with the digital camera (sunlight reflected from earth onto the lunar surface) in the evening twilight. I got the equipment out in the late afternoon, and waited for the earthshine to become visible. As it grew darker, the earthshine could be seen with the naked eye, but it proved to be very difficult to capture this beautiful bluish glow with the camera. The image below is one out of fifty images shot with the Nikon Coolpix 4500. The earthshine image was shot through a Televue 32mm Plossl eyepiece and a 4-inch TAL refractor mounted on a Synta EQ6. If you look carefully you can identify a few light and dark features on the unilluminated part of the Moon due to the earthshine. A lot of practicing to be done!

For people interested in the camera settings of the earthshine-image, here are the details: Nikon Coolpix 4500 set at ISO 100, f /4.1, shutter speed 1 second, resolution 2272 x 1704.

Later that night I observed the 4.2-day-old Moon with my 4-inch refractor and 15x80 binoculars. The features marked on the image below (move mouse-pointer over image to identify features), where all visible with binoculars. The image of the 4-day-old Moon was shot with the same equipment as the "earthshine" image above. The orientation is the same as in the Rukl atlas of the Moon, North is up and East is to the right. The settings of the Coolpix for the image were: ISO 100, Res. 2272x1704, f/3.0, s1/60. The image was processed (unsharp masking).

On a 4-day-old moon Mare Crisium (Rukl 26,27,37,38) and Mare Fecunditatis (Rukl 37,48,49) are completely illuminated by the sun. The mountains at the border of Mare Crisium are beautifully lit. You can see lots of detail in these big stone "walls" surrounding the Crisium basin. Take your time for observing this great feature. South of Mare Crisium lies another, not so well known "sea", Mare Undarum, the "Sea of Waves" (Rukl 38). Mare Undarum is a relatively small and very irregular patch of dark Mare material. Strangely, this lunar feature is not labelled in the Clementine Atlas of the Moon, though it is listed in the gazetteer at the back of the atlas. (This is not the first time I found a misplaced label or a label missing in the Clementine)

There are three other "seas" or "Maria" visible near the limb of the Moon, Mare Humboldtianum (Rukl 7), Mare Marginis (Rukl 27/38) and Mare Smythii (Rukl 38/49). Mare Humboldtianum has a diameter of 160 km and lies on the northern half of the Moon, northeast of the walled crater Endymion. Mare Humboldtianum was named after the German explorer Alexander von Humboldt. The Mare lies at the centre of a 600 km wide impact basin with several concentric mountain ridges, though the ridges are not as well defined as in the Orientale basin. The Humboldtianum basin is situated between Endymion and the lunar limb, and extends onto the far side of the Moon. You can only see a small part of it during a favourable libration.

To the east of Mare Crisium lies Mare Marginis, or the "Border Sea". Mare Marginis is an elongated dark mare plain covering an area of 62,000 square kilometres. Mare Marginus is not a central part of any impact basin. South of Mare Marginis you will find Mare Smythii, named after William Henry Smyth, a British astronomer that lived from 1788 to 1865. Mare Smythii and Mare Humboldtianum are the only two Maria named after actual people. Mare Smythii is a dark, circular patch of Mare material, covering an area of 104,400 square kilometres.

North of Mare Crisium there are some big craters to be seen. Near the terminator lies Atlas (Rukl 15), a crater 87 km wide. Between Atlas and Mare Crisium lie, lined up from north to south, Messala (Rukl 16), Geminus (Rukl 16) and Cleomedes (Rukl 26). On the floor of Cleomedes (northeastern part) I can detect two small craters and a small peak. To the west of Mare Crisium lies Macrobius (Rukl 26), a well-defined crater about 64 km wide. I could not detect the central peak on the night I shot this image.

To the South of Mare Fecunditatis lie four big craters lined up from north to south, Langrenus (Rukl 49), Vendelinus (Rukl 60), Petavius (Rukl 59) and Furnerius (Rukl69). For a more detailed report on these 4 craters please follow this link. Way down to the south lie the big crater Janssen (Rukl 67) and the Rheita Valley (Rukl 68). The crater Janssen and the Rheita Valley will be discussed in a separate article.