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Wednesday, December 05, 2018


Geminid Meteor Shower 13-15 December 2018

The northern horizon at 4:00 am ACDST as seen from Adelaide on Saturday December 15. The Geminid radiant is marked with a starburst. Similar views will be seen elsewhere in Australia at  a similar latitude and the equivalent local time. (click to embiggen).The northern horizon at 3:00 am AEDST as seen from Sydney on Saturday December 15. The Geminid radiant is marked with a starburst. Similar views will be seen elsewhere in Australia at  a similar latitude and the equivalent local time. (click to embiggen).

The Geminids are unusual meteor shower in that their parent body is 3200 Phaethon, an asteroid, rather than a comet. It is speculated though that Phaeton is actually a "gassed out" comet, and so the debris that makes up the Geminids may still be cometary particles, but is more likely broke rock fragments from its close approach to the sun.

The Geminids are a fairly reliable meteor shower and this year moonlight will not significantly interfere. Some decent meteors rates should be seen.

Unlike the Leonids, where there is a very narrow peak of high activity, the Geminids have a broad peak and will show good activity well before and after the peak, and on the day before and after. The peak is December 14, 12h 30m UT. That is 23:30 pm AEDST December 14 in Australia.  This is just before the Moon set, and before the radiant is high enough for decent rates, but there will still be very goor rates from around 2-3 am AEDST (1-2 am AEST) on the morning of the 15th in Australia. As the radiant doesn't rise until just before midnight (daylight saving time) in most of Australia, so you will still have to disturb your sleep for this one.

Australians should see a meteor every two to three minutes under dark skies in the early morning of the 15th, between 1:00 am and 4:00 am local daylight saving time. You can find predictions for your local site at the meteor flux estimator (choose 4 Geminids and date 14-15 December, don't forget to change the date to 2018). I have also made a table for major citiess below.

Unfortunately, both Chrome and Firefox have changed their security settings to prevent plugins from running, and the flux estimator only runs under Internet Explorer now.
You can follow the progress of the shower at the IMO Geminids Live page.

At 1.00 am in the morning AEDST (midnight, AEST) Castor (alpha Geminorum) is about two hand-spans above the horizon and 10 hand-spans to the right of due north. Pollux, the other twin, is less than a hand-span to the right again. The radiant is just below Pollux.

When you get up, allow at least 5 minutes for your eyes to adjust and become dark adapted (even if you have stumbled out of bed in the dark, here's some hints on dark adaption of your eyes so you can see meteors better) and be patient, it may be several minutes before you are rewarded with you first meteor, then a couple will come along in quick succession (a meteor every three minutes is an average, they won't turn up like a ticking clock but more or less randomly).

Predicted meteor rates for selected towns

TownMorning December 13 Morning December 14Morning December 15
Adelaide8 meteors/hr17 meteors/hr22 meteors/hr
Brisbane10 meteors/hr21 meteors/hr31 meteors/hr
Darwin14 meteors/hr31 meteors/hr40 meteors/hr
Perth10 meteors/hr21 meteors/hr31 meteors/hr
Melbourne7 meteors/hr15 meteors/hr20 meteors/hr
Hobart5 meteors/hr12 meteors/hr16 meteors/hr

Choose a viewing spot where you can see a large swathe of sky without trees or buildings getting in the way, or with street lights getting in your eyes. The darker the spot the better (but do be sensible, don't choose a spot in an insalubrious park for example). While the radiant is where the meteors appear to originate from, most of the meteors will be seen away from the radiant, so don't fixate on the radiant, but keep your eye on a broad swath of sky roughly centred just above the radiant (as the radiant doesn't rise very high, looking exactly at the radiant will mean you miss some higher up).

A lawn chair or something similar will make your observing comfortable (or a picnic rug spread on the ground and a nice pillow), and having a Thermos of hot coffee, tea or chocolate to swig while watching will increase your comfort. Despite it being summer, make sure you have a jumper or something as the night can still get cold

Guides to taking meteor photos are here and here.

As well, Orion and the Hyades will be visible and bright Venus, rises an two and a half hours before sunrise. So it will be a quite nice morning for sky watching. Keep an eye out for satellites!

Cloud cover predictions can be found at SkippySky.  

Here is the near-real time satellite view of the clouds (day and night) http://satview.bom.gov.au/

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