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Wednesday, 21 September 2011

[BAA-ebulletin 00612] Jupiter well placed for observing

BAA electronic bulletin

Jupiter well placed for observing this autumn

Jupiter is now rising before midnight for observers in north temperate latitudes, and climbing higher than it has done since 2003, now being north of the equator.  Moreover, it is close to perihelion, so at opposition on 2011 Oct.29 it will almost equal last year's once-in-a-lifetime proximity.  October oppositions of Jupiter are especially good for northern observers because of the combination of large disk diameter, high altitude, and a chance of reasonable weather.

The Jupiter Section welcomes both images and drawings; please see our web site (URL below) for guidelines.  Already we are receiving first-class images from British and other European observers, comparable to those from more southerly latitudes in recent years, showing that top-quality observations can indeed be made from Europe when the planet is high enough.

At present the planet is settling down after the SEB Revival of 2010 and the NEB expansion event of 2009.  Most regions are comparatively quiet, but of course there is still plenty of interest to see.
The NTB has largely faded away again, but we want to keep an eye on this almost-blank band, as a new outbreak of super-fast brilliant spots could erupt at any time.
The NEB carries the most impressive spots: three exceptionally large and dark ovals ('barges'; these are cyclonic circulations), which have developed as the NEB north edge receded. In the adjacent N.Tropical Zone there are several white ovals, the brightest being the long-lived White Spot Z.
The SEB is fully revived. White spots (convective storms) were still arising close to the position of  the source of the Revival: at up to L2 ~ 260 in June, and up to L2 ~ 250 in July.  In August they were more subdued and continued prograding towards the GRS without new outbreaks, though they were still present as usual following the GRS.
The S.Tropical Zone is largely occupied by a dark grey S.Tropical band, which emerged from dark material around the GRS as the Revival reached its conclusion.
The STB has two dark sectors, one just preceding the GRS, the other following oval BA.

Positions and drifts of major long-lived anticyclonic ovals, as of Sep.1, in System II longitude, are as follows:
       Oval BA L2 = 330;  DL2 = -15 to -17 deg/month (varying)*
       GRS             L2 = 168;  DL2 = +0.8 deg/month
       WS-Z            L2 = 11  ;  DL2 = -11 deg/month
       NN-LRS-1        L2 = 88;    DL2 = -9 deg/month (varying)*
*( Oval BA is slightly reddish at present; NN-LRS-1 has lost its colour in recent weeks.)

A map has been posted on our web site identifying these and other features presently visible:

John Rogers
2011 Sep.16

John H. Rogers, Ph.D.
Jupiter Section Director,
British Astronomical Association

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(c) 2011 British Astronomical Association

Good Clear Skies
Colin James Watling
Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
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