"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).

Planetary Nebulae - a sketching marathon of how many I could see from my home

Hi all,

These two works deal with DEATH.  The death of stars.

It also deals with looking to make the most of observing from under light polluted skies, pushing equipment and eyes.

Because I was not able to travel to my customary dark sky site, I was still itching to get some time under the stars with Deep Sky Objects.  Then the idea came to me of doing a Planetary Nebula marathon of how many I could see and sketch from my home in Sydney.

Inspiration for these two works came from two friends soon after the start of the Covid-19 lockdown that took place here in Sydney earlier this year.  One friend was testing some equipment using planetary nebulae, and the other friend had done a series of astro sketches who was also stuck at home at the time.  The idea then occurred to me that there actually are many planetary nebulae that are visible from under light polluted skies, and as a challenge to myself why not try to sketch as many of them as I could as these are relatively simple objects to sketch.

A planetary nebula is the last death throes of a star like our Sun! Our Sun is not large enough to explode in a supernova. Instead when it has exhausted its hydrogen fuel, the star/Sun will have series of "burps" where it will shed all its layers except for its core. The material that is released puffs out to form a sort of cosmic bubble that is called a planetary nebula. These are short lived bubbles, eventually expanding like a smoke ring into nothing, leaving behind the exposed core of the star/Sun that will slowly cool like a cinder, eventually after many billions of years just stop shining and be as black and cold as coal. No more star, no more Sun.

And there are hundreds of these cosmic bubbles all around us! The two sketches below are of the brighter ones I could spy out in one night from my home starting from 7pm through to 5am the next morning, over two successive nights. If I had been out bush to do this piece, I would have been able to spy out dozens more.

The different shapes that can be seen is due to various gravitational and magnetic influences on the expanding material from an invisible companion star (if the shape is not an even bubble), or if it is a smooth round bubble, then the star has no companion star (like our Sun). The shape of a planetary nebula can actually reveal A LOT about it!

So, if you are stuck at home, have a telescope but don't know what to look for, chasing dying stars (planetary nebulae) is something a little different and certainly possible from under light polluted skies. A few of these are surprisingly bight. Most are dim. Some are very dim and will really challenge your observing skills. And of course, they vary in size from large (only one or two like that in the sky), down to stellar-like and everything in between. Spotting the tiny stellar-like ones is its own challenge best done using a "blinking paddle" to hold an OIII filter, but this is beyond this post.

The position of the nebula in each individual sketch I tried to position so to make the composition a little more interesting by trying to accommodate as many stars as I could that surrounds each nebula within the field of view of the scope.

For what it is worth, I used a 9" Maksutov telescope, most at 258X with a 12mm Vixen SLV eyepiece, and an OIII filter.  Four individual nebulae I used different eyepieces as they needed different magnification of field of view to provide the best quality of image for that planetary nebula. The sketches were done on A3 sheet of black paper using white and blue soft pastels. Each individual sketch took approx 20 minutes to half an hour.

Alex.

 

Volcano Alley - Sunrise over Aristarchus and a myriad of lava rivers

Hi all,

A few nights ago I managed my first lunar sketch in a couple of months. Come to think of it, the last twelve months have been pretty lean of sketches from me - work, poor conditions, cloud, all conspiring against me. This particular night all my ducks finally all lined up - excellent seeing, work not in the way, and an itchy sketch pad 

The brilliant crater Aristarchus and the sinuous Vallis Schroteri all too often steal the show in this area of the Moon, an area that appears to harbour very little other detail or features. How wrong this thinking is! It is only a very shallow angle of sunlight that can reveal the wealth of detail that actually litters this area.

At sunrise over Aristarchus reveals a series a very fine, long lava rivers, and for several of these the head of each river can be traced to different volcanic domes. These lava rivers are not as pronounced as Vallis Schroteri, so when the Sun is higher up their shadows are lost. These volcanic features are visible for only a few short hours each month.

There are also a multitude of volcanic domes all around here too. Most of these would go unrecognised as such because they look like a mountain. But one tell-tail sign of their true nature comes from careful examination of the shape of these peaks - domes tend to be more rounded in shape, like a blister. When the angle of the incoming sunlight is as shallow as this, it can be difficult to make out this blister shape. But leave the timing too long after sunrise, and these domes disappear because they are not very tall, and their rounded shape does not allow for stark and sharp angles that true mountains have.

The shallow angle of sunlight also makes for very dramatic long dark shadows that extend out towards the terminator and beyond it. It never ceased to amaze me how quickly these long shadows actually recede as the sun rises.

Object: lava rivers and domes between Prinz & Aristarchus

Scope: 9" Santel Maksutov, MK91

Gear: 7mm Vixen SSW eyepiece, 443X

Date: 1st August, 2020

Location: Sydney, Australia.

Media: White & grey soft pastel, charcoal and white gel ink on A4 size black paper.

Alex.