Saturn Report - White Spots

white spots

equatorial storms

The most exciting events like large white spots in the Equatorial Zone are rare,but regularly, they seem to appear in a time period of about 30 years. The last big storms were visible in 1903 , 1933 , 1960 and 1990.This period corresponds interestingly with the orbital period of Saturn and the reheating of the northern hemisphere.Why it does not happen with the southern hemisphere reheating is unclear.As a visual observer, I experienced the 1990 storm with a 6cm(2.4inch) refractor.It was the best visible detail on the planet with this limited aparture.

white EZ / EB spots (plumes)

Beside the rare big storms in the EZ which start as a compact but very bright spot,visible with even small backyard telescopes, are every apparition some smaller EZ spots there.These are mostly white spots,rather plumes then white ovals.Jupiter shows similar spots in its EZ. Because the zone is considerably bright itself, the spots are generally not very contrasty but are relatively easy detectable in a normal contrast image.They are visible well at red wavelengths,which is an advantage considering the less influence of seeing in this area.Recent observations show that in some cases,when the white spot is located maximum low of latitude,it can form partially a 'bay' within the EB,and this can increase its visibility.

below: example of a spot located just at the edge of the EZ and the EB.The spot forms a bay within the Equatorial belt. Observation from February 2, 2006:

click here for an animation showing this spot together with the big STrZ storm on Febr 2, 2006.Note also the small SPR white oval:

http://img213.imageshack.us/img213/4435/s20060202ebezws4af3.gif

Clearly a chain of white EZ spots was found in red light images obtained on Nov 7, 2006,see below.Position is in the EZ-n, the northern part of the EZ which is just visible well with the current ring-position.The spots seem to form bays in the nothern edge of the EB also.The animation shows them moving with the rotation.

below right: normal contrast: 05:10 UTC CM 3 = 294

link below: the complete visible EZ-n seems structured,as seen in this negative featured animation from images taken Nov 7, 2006.Visible is a fixed pattern which moves clearly with the rotation:

http://img214.imageshack.us/img214/2995/sateznspots20061107brd7.gif

white spots in the SEB / NEB

The SEB is currently the most obvious belt on Saturn,already easy to see in the smallest telescope.It's in fact composed of different smaller belts,but darker and more concentrated at its northern edge currently,see page: technique. In moderate telescopes it's possible to see some structure sometimes,mostly caused by brighter spots disturbing the belt.Here is an observation of a typical low contrast SEB-zone white spot on Dec 14, 2004:

2 long existing obvious spots are visible in this image obtained through a red filter (610nm) on February 1, 2006:

They appear actually in the 'space' between the 2 darker north and south edges of the SEB (SEBn and SEBs).This region is called the SEB-zone (SEBz)The spots are relatively easy to photograph due to the high contrast and the fact that they are visible well in red light images which are generally less deteriorated by seeing.

Below: white SEB-zone spots captured in a one-shot color image on Febr 2, 2006:

Below: white SEB-zone spot early in the season,captured on Nov 7, 2006 in the very active region around CM 250-300 system 3.Red light R610nm images in fair seeing:

February 4, 2007; Area of a big white spot in the South Equatorial Belt,together with an interesting disturbance,which appears as a waving line from the southern SEB edge to the north side of the SEB.This is visible in both images taken 6 minutes apart,see red box.It's suspected that this is a further development of the moderate disturbance found in the November 7, 2006 images which has drifted to another longitude in the meantime(see chapter dark spots).Images taken in the red light at 610nm in a very short clear moment between clouds and mist.

March 28, 2007; a white spot in the SEB-zone is captured in these red light images at L3=340.It's probably the same spot,unchanged in appearance as the one captured on Febr 4 at L3= 355/357.This would mean the spot has drifted approximately 0.30 degr/day in the P(rotation) direction.(system 3).ATK-1HS/R 610nm images).

tropical storms / white ovals

Very interesting bright spots appear regularly within the STrZ (South tropical Zone)for example,recently in 2002 and early 2006.These are mostly white ovals.The STrZ (at about -35° latitude)is a very active region for the emerging of these oval spots.Some big storms seem to appear regularly and are possibly a rebirth of the same storm.Possibly,the storm is still there in the quiet periods,but too weak to see with normal equipment from the Earth.Although they can be visible well in red light images,it can be interesting to watch these spots at other wavelengths,and the appearance of the early 2006 STrZ-storm has learned that finding the right wavelength can even be necessary to observe the spot at all at certain stages.

Jan - April 2006: storm in the STrZ and STeB

A particular interesting spot appeared around January 23, 2006 at the edge of the STeB and STrZ. It was first detected by the Cassini-probe,orbiting Saturn,but at that time on its night-side.Cassini's Radio and Plasma Wave Science (RPWS) instrument detected radio-emisions from lightning flashes,and not much longer, Earth-bound observers found an obvious and compact STrZ-spot.It was the same area and in fact it was a very big lightning storm.This spot remained its compact stage until mid February approximately and then became rapidly fainter and elongated.The spot disapeared early April in most images.

After imaging the spot a few times, a drift rate was found and I used this information to find the right Central Meridian and thus the right time to image,to trace the spot again, even after the regular periods of cloudy weather sometimes for weeks.Unfortunately,most of the observations had be done in poor to very poor seeing conditions,but the spot remained visible in higher contrast images.

Interesting about this spot,which is actually one in the category of white oval spots (WOS) were the photophysical properties; although the spot was still visible well in a red light image just after its emerging,it wasn't in the later images.The spot had changed color,as it seemed to get good contrast only in green light images later.This 'color-change' is probably connected with its changing appearance.

click here for an animation showing the spot in a red filter (R610nm) image,also my first capture of the spot on Jan 29,just some days after emerging,but unfortunately taken in poor seeing:

http://www.kk-system.co.jp/Alpo/kk06/s060129d2.gif

Below: I had a first good opportunity to capture the storm on Febr 2, 2006; at the end of the session, the spot came just into view.

For an animation click: http://www.kk-system.co.jp/Alpo/kk06/s060202b2.gif

Such a long duration of more then 2 months is exceptional for a spot of this kind.It was an extraordinary occasion to study the effects on the spot which certainly occur due to the long existance,the rotation and other factors.Just as expected,the spot became more elongated through the months.It wasn't bright anymore after February,contrast with the surroundings became low and the poor seeing in this period made the observations not easier.

below: left; The storm was even captured in very poor seeing on March 2, 2006.This nicely illustrates how obvious it was.Right: negative observation on March 14 in also poor seeing.Despite this,the spot was live visible on screen.

Around mid-March the spot was pretty large fanned out and it appeared to disturb surrounding higher latitude belts and zones,especially the STeB, but even slightly the STeZ.

below: the STrZ-storm on March 15, taken in fair seeing conditions.Note the obvious disturbance by the spot of at least 2 other belts/zones, south from the STrZ.The 2 smaller windows show a special contrast processing.The moon directly below Saturn(north side) is Tethys.

Below: animation showing the spot moving together with moon Tethys:

Click here for an animation showing the spot just moving out of view (limb leftside) together with 4 moons: http://www.kk-system.co.jp/Alpo/kk06/s060312a3.gif

Below: interesting comparison of the STrZ-spot between early February,when the spot was in the early compact stage,with the situation during mid-March.This represents nicely the result of what happens to a spot when it exists for such a long time:

A selection of images showing an overview of the spot's morphology can be found here:

http://www.kk-system.co.jp/Alpo/kk06/s060405rp.jpg

animation:

http://www.kk-system.co.jp/Alpo/kk06/s060405rp.gif

Overview-animation of the transition of the storm made from images during the 2 -3 months of visibilty:

A definite white spot in the STrZ was found in images,obtained on Nov 30, 2006.The feature appears in high contrast red light images.Its appearance looks very much like the later stages of the STrZ-storm from early 2006.At the moment, it's not sure whether this is a rediscovery of this storm-remnant in the new apparition or a new feature.Longitude of the feature is at L3=240.Images: 05:40 UTC / 05:45 UTC. CM system 3= 240/243.(R 610nm).

Images obtained on March 15 in the red light, reveal a moderate disturbance within the STrZ, visible already in normal contrast images,and exellent visible in the high contrast images.It's apperance is a bit remarkable,and it seems connected to a white spot.(ATK-1HS images/R 610nm).

High latitude white spots

contact: ralf.vandebergh@home.nl