Astronomical Events

Phases of the Eclipse - David…

 

And on the 14th of December (well 5th to 22nd) is the Geminid meteor shower.

More details of where to look soon.

As promised, the details on the Geminid shower:

 

Geminids (GEM)

One of the finest, and probably the most reliable, of the major annual showers presently observable.

This year, the waxing crescent Moon will set by mid-evening across the globe on December 14 (the actual moonset timing is progressively later the further south you are), giving mostly dark skies for all observers, especially those in the northern hemisphere.

The Geminid radiant culminates around 2h local time, but well north of the equator it rises around sunset, and is at a usable elevation from the local evening hours onwards, while in the southern hemisphere, the radiant appears only around local midnight or so.

Even from more southerly sites, this is a splendid stream of often bright, medium-speed meteors, a rewarding sight for all watchers, whatever method they employ. The peak has shown slight signs of variability in its rates and timing in recent years, with the more reliably-observed maxima during the past two decades all having occurred within 2h20m of the time given above. The main predicted timing, coupled with moonset, favours places from central Asia eastwards across the Pacific Ocean to Alaska. An earlier or later timing would extend this best-visible zone some way eastwards or westwards respectively.

Some mass-sorting within the stream means the fainter telescopic meteors should be most abundant almost 1° of solar longitude (about one day) ahead of the visual maximum, with telescopic results indicating such meteors radiate from an elongated region, perhaps with three sub-centres. Further results on this topic would be useful.

Abbreviations and Tables

 

• α, δ: Coordinates for a shower's radiant position, usually at maximum. α is right ascension, δ is declination. Radiants drift across the sky each day due to the Earth's own orbital motion around the Sun, and this must be allowed for using the details in Table 6 (page [add page number]) for nights away from the listed shower maxima.
• r: The population index, a term computed from each shower's meteor magnitude distribution. r= 2.0 —2.5 is brighter than average, while r above 3.0 is fainter than average.
• λ: Solar longitude, a precise measure of the Earth's position on its orbit which is not dependent on the vagaries of the calendar. All λ are given for the equinox 2000.0.
• v_∞: Atmospheric or apparent meteoric velocity, given in km/s. Velocities range from about 11 km/s (very slow) to 72 km/s (very fast). 40 km/s is roughly medium speed.
• ZHR: Zenithal Hourly Rate, a calculated maximum number of meteors an ideal observer would see in perfectly clear skies with the shower radiant overhead. This figure is given in terms of meteors per hour. Where meteor activity persisted at a high level for less than an hour, or where observing circumstances were very poor, an estimated ZHR (EZHR) is used, which is less accurate than the normal ZHR.
• TFC and IFC: Suggested telescopic and still-imaging (including photographic) field centres respectively. β is the observer's latitude (“<” means “south of” and “>” means “north of”). Pairs of telescopic fields must be observed, alternating about every half hour, so that the positions of radiants can be defined. The exact choice of TFC or IFC depends on the observer's location and the elevation of the radiant. Note that the TFCs are also useful centres to use for video camera fields as well.

Lifted in whole from: www.imo.net/calendar/2007