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Monday, May 04, 2015


eta Aquariid Meteor Shower 7-9 May, 2015

Morning sky on Thursday May 7 looking east as seen from Adelaide at 4:00 am ACST.  The radiant of the eta Aquariid meteor shower is shown.   Similar views will be seen elsewhere in Australia at the equivalent local time. (click to embiggen).

The eta Aquariids meteor shower, the debris from Halleys comet, will peak on May 6 UT . However, the best (but weak) rates will be seen from Australia on the mornings of the 7th and 8th.

Unfortunately, the waning but nearly full Moon will significantly interfere with viewing meteors this year. People in the suburbs should see a meteor around once every 9 minutes, and in the country about once every 6 minutes. The radiant of the shower is about five hand-spans up from the eastern horizon, and three hand-spans to the left of due east at 4 am (see spotter chart at 4 am above).

The figure ZHR is zenithal hourly rate. This is the number of meteors that a single observer would see per hour if the shower's "point of origin", or radiant, were at the zenith and the sky were dark enough for 6.5-magnitude stars to be visible to the naked eye.

In practise, you will never see this many meteors as the radiant will be some distance below the zenith. Also, unless you are out deep in the countryside, the darkness will be less than ideal. How many are you likely to see in reality? I discuss this further down, lets talk about when to see them first.

Although the actual peak is on 6th at 17:00 AEST, for Australia the best time to see the eta-Aquarids is in the early morning of the 7th, 8th and 9th. This year the first quarter Moon sets long before the radiant rises, so you should have almost ideal observing conditions if the cloud stays away.

How many will be seen on the 7th is not clear, but very good rates were seen last year, and dark sky sites may possibly see one meteor every two minutes or so. There were many bright ones reported with persistent trains. People in the suburbs may be will see less, but at least one every 6 minutes should be possible.

People in the suburbs should see a meteor around once every 6 minutes, and in the country about once every 3 minutes on the 7th, a bit more on the 8th and around the same rates as the 7th on the 9th. The radiant of the shower is about five handspans up from the eastern horizon, and three handspans to the left of due east at 4 am (see above for a spotter chart at 5 am).

When looking, be sure to let your eyes adjust for at least 5 minutes so your eyes can be properly adapted to the dark. Don't look directly at the radiant site, because the meteors will often start their "burn" some distance from it, but around a handspan up or to the side. Be patient, although you should see an average of a meteor every six to three minutes, a whole stretch of time can go by without a meteor, then a whole bunch turn up one after the other.

Make yourself comfortable, choose an observing site that has little to obstruct the eastern horizon, have a comfortable chair to sit in (a banana lounger is best), or blankets and pillows. Rug up against the cold.  A hot Thermos of something to drink and plenty of mosquito protection will complete your observing preparations. As well as meteors, keep an eye out for satellites (see Heavens Above for predictions from your site).

Use the NASA  meteor shower flux estimator for an estimate of what the shower will be like from your location (you may need to enter your longitude and latitude, surprisingly, while Adelaide and Brisbane are hard wired in, Sydney and Melbourne are not). See the image to the left for typical output. The peak is rather sharp and not very high, due to the Moonlight.

You need to choose 31 Eta Aquariids and remember to set the date to 6-7, 7-8 or 8-9 May 2015. You can follow the progress of the shower at the IMO live Aquariid site.

Cloud cover predictions can be found at SkippySky.


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