Saturday, June 11, 2016

UPDATED: South polar cap not prominent


This is my first imaging of Mars this season, taking the opportunity of a good clear night. Previous observations for this apparition season included the sketching the Martian surface using different colour filters. Hopefully, I plan to upload these sketches once I complete the full observation of the Martian surface.

During last night's session I decided to use my trusty old philips webcam. Camera settings included a 60fps to acquire 10,000 coloured images using my 2x televue barlow.

Surface features on Mars

The RGB image shows a very interesting albedo composition. Syrtis major is seen as dark blue compared to the neighbouring Iapygia region, which has a reddish-brown hue. Hellas region is brighter but lacks the usual bluish hue. Perhaps this is due to oversampling of red signal by the webcam.

The complex structure of Syrtis major together with the small protuberance of Moeris Lacus are very conspicuous. The indentation pattern of Sinus Sabaeus is very prominent especially at Sinus Meridiani, and shows the good atmospheric conditions present at the time of image acquisition.

The isolated Alcyonius Nodus next to S. major tip is very prominent. On the opposite site of S. major is Utopia which is lighter than S. major region. Ismenius lacus is subtle but visible.

The desolate expanse of Arabia region is prominent, and has a lighter colour when compared to its slightly darker borders in areas adjacent to S. Sabaeus and S. Major. Here I am referring to the regions of Aeria and Edom in particular.

The south polar cap is not visible. 

Wednesday, April 27, 2016

Bullialdus crater and its central peak.

Bullialdus lunar crater. 17 July 2013, 22:00-22:28 LT
The relatively isolated impact lunar crater Bullialdus is found in the western portion of Mare Nubium. This crater has a high outer rim that is circular with the usual subtle polygonal appearance. The inner terraced walls for which this crater is famous for are hidden in darkness. On the other hand the outer ramparts are conspicuous, and highlight a radial pattern of low ridges and valleys.

The illuminated part of the floor of the crater is generally rough with many low rises. In the center of the crater is a formation of several peaks and rises that climb to over a kilometer in height. The sketch shows this prominent peak that comes out of the surrounding shadow simply because of its height.

Klima et al., (2013) showed how the central peak of Bullialdus Crater is significantly enhanced in hydroxyl relative to its surroundings. This is indicative that the peak originated from deep down below the crater as result of the immense impact pressure and heat.

Two smaller but notable craters lie just to the south of the main crater. Bullialdus A lies just to the south-west of Bullialdus, within its ramparts. To the south of Bullialdus A is the slightly smaller Bullialdus B.To the Southwest is the conspicuous but smaller lunar crater Konig. Its shadow suggests a tapering side wall towards the northwest.


R. Klima, J. Cahill, J. Hagerty, D. Lawrence (2013). Remote detection of magmatic water in Bullialdus Crater on the Moon. Nature Geoscience 6, 737–741 (2013) doi:10.1038/ngeo1909

Saturday, April 16, 2016

UPDATED: Extensive terracing and rille features in Arzachel crater

Arzachel crater sketched on 15 April 2016: 16:45-17:51 UT. f/11 10mm eyepiece, C14 SCT
Lunar crater Arzachel is another magnificent feature to sketch at the telescope eyepiece. It is clear in its hexagonal structure and a favourite telescopic subject for advanced amateur astronomers.  I spent a bit of time scanning the lunar surface before deciding to focus on this crater. To the north of this crater is the larger and more conspicuous Alphonsus.

Crater Arzachel is some 66 miles in diameter. The bright interior includes a large and rugged central mountain (which rises 1.5 kilometers above the floor), some smaller hills, a deep crater accompanied by smaller carters to its north and south, and a very interesting winding rille to the East of the central peak, which at the time of sketching was close to the shadow cast by the eastern terraced wall. This rille system, known as Rimae Arzachel, runs from the northern wall to the southeast rim. In my sketch I tried to capture the dramatic shadow patterns on the eastern high terraced wall.

The entire rim has a detailed interior which proved to be a challenge to sketch. Below is an image from my archive of the same crater dated 8th February 2014.

Arzachel. Photo taken on 8th February 2014 from Znith Observatory, Malta

Check out another interesting sketch of the same crater here.

Friday, April 1, 2016

Weather systems on Jupiter

The vivid colours seen in Jupiter's clouds are the result of subtle chemical reactions of the trace elements in its atmosphere. The colours correlate with the cloud's altitude: blue lowest, followed by browns and whites, with reds highest (including the GRS). The coloured zones are regions of upward moving convective currents triggered by Jupiter's hot interior. On the other hand, the darker belts are made of downward sinking material. Because of such fluid dynamics, these two are always found next to each other.

Interesting features can be observed on the above coloured image, including the blue barges and plumes in the Equatorial Zone (EZ). The South Equatorial Band (SEB) is very active with a prominent wakefield next to the GRS. It looks as if  the flow is breaking up into individual elements, known as eddies. Unfortunately, the average seeing during this observation was poor and zooming in on such detail is not possible.

The zones and belts are zonal jet streams with velocities up to 650 km/hr and where wind direction alternates between them. One expects therefore strong wind shear visible only under excellent observation conditions as distinctive brown-coloured features next to bands, especially the SEB and North Equatorial Band (NEB).

Upward moving gases in Jupiter's atmosphere bring white clouds of ammonia and water/ice from beneath. Downward moving gases are darker as they sink down.

Jupiter's atmosphere is filled with methane, a gas which is a strong absorber of sunlight at 890 nm and therefore its presence appears as dark bands as in the right image below. The bright clusters in this image consist of high-rising energetic plumes high up in the atmosphere, able to reflect sunlight before it enters the planet's methane-dark interior. Each of these bright areas consists of massive convection cells rising very high that are low in methane, equivalent to the orange-hue areas highlighted in the coloured image below to the left. The dark streaks in both the EZ and SEB are made up of a higher concentration of methane gas (as shown by the right image below) which is sinking down to deeper layers and therefore seen as dark filaments in the coloured image.

If we were to create an illusion of depth on the basis of methane-deficient, high level clouds, the resulting image would be something similar to the one shown on the left. Especially prominent are the equatorial zone (EZ) and the great red spot (GRS). The GRS is an exceptionally energetic weather process, twice the size of planet earth, which rises high up in the atmosphere of Jupiter.