Sunrise & Sunset over the Straight Wall

 

Hi all,

The weather here in Sydney has been rather miserable for astronomy.  So this post is something I’ve been wanting to do for some time, show how the angle of incoming sunlight can totally change the appearance of otherwise familiar features.

The straight wall is one of the most striking features outside of its innumerable craters.  Astonishingly long and straight, this 110km long Faultline escarpment is surprisingly only 300m tall at its highest.

By far the most frequently seen images of Rupes Recta is during sunrise over it when its dark shadow marks out is location on the eastern section of Mare Nubium.  The lunar landscape is very well known, although less well known are the two domes that sit on the northern end of the smaller Rima Birt, Birt 1 & Birt 2.  There is a twist to this familiar moonscape – viewing it during sunset.

The shadows on the plain are different, showing an unfamiliar perspective around what otherwise are familiar features of craters and rilles.  And the appearance of the Straight Wall is not a dark shadows but a brilliant white.

I was very surprised to see such a different set of shadows on the plain surrounding the Straight Wall.  Admittedly sunlight was at a shallower angle.  All the same, the distinct play of textures and landscape was unexpected.

Even the Straight Wall itself shows interesting shadows, giving insight to the different angles at which surrounding planes that form the fault are set at.

Both sketches were done using an 8" SCT.  Sunrise at 250X, Sunset at 200X.

Clear skies, cool cameras and sharp pencils,

Alex.

"Valentine Dome" - a giant hiding in plain sight

Hi all,

We have had a run of very clear, but very cold, nights here in Sydney.  A fantastic cold front swept in over the weekend dumping snow down to 800m in the mountains to Sydney’s west.  This has also meant that transparency has been excellent along with very good seeing conditions.

Last night while scanning the terminator (the area of the Moon where the light and dark meet, NOT a homicidal robot…) and came across a huge feature that I had never seen before – an enormous round blister of a dome smack on a seemingly featureless Mare!

Lunar domes are volcanic features.  Some of these are magma displacements that had pushed up from below the lunar surface but did not breach the surface.  Others are actual volcanos.  The “Valentine Dome” is a volcano.

It gets its nickname from being a little heart shaped.  I did not give it this nickname!  I found it while researching this feature after I sketched it.  Who says astronomers are not romantic?!

The Valentine dome is some 35km in diameter, but only 300 meters tall.  For this reason it requires the Sun to be at a very shallow angle for the low mound to be visible.  It is a very short volcano because lunar volcanoes are shield type volcanoes, just like the ones on Hawaii.

Its official lunar designation is Linne A 1.  The “1” refers to it being a volcanic feature, with volcanic features having numerals in the same way that lesser craters have letters.

Valentine Dome would also have been one of the last volcanic features to form on Mare Serenitatis, forming over the long cooled lava plains of Serenitatis.  But all volcanic features are very old.

Conversely, crater Linne is a relatively young feature.  Though small (3km), its collar of ejecta material is still very bright.  As time wears on, the solar wind will weather this bright material until it loses its brilliance and the bright collar fades to blend into the surrounding grey material.  There are other craters in this sketch that are larger than Linne.  Linne A, B & F are all larger than the principal (4km, 5km & 5km respectively).  But all of these have lost their bright ejecta collars, hence giving  clues to the relative ages of these features, volcanic and crater.

It was a thrill to chance upon this lunar feature.  It was also the first lunar volcano that I was able to show my wife as it was so distinct and free from other distracting features.  I hope you are able to find it for yourself one day.

Alex.

Object:  “Valentine dome” Linne A 1

Scope:  Santel 9” Maksutov Cassegrain

Gear:  10mm Vixen SSW eyepiece, 310X

Date:  25^th of August, 2020

Location:  Sydney, Australia

Materials:  White & grey soft pastel, charcoal and white gel ink on A4 size black paper (no blending stump used).