Friday, December 13, 2013

Earth will NOT be hit by a "Wave of Killer ISON Debris"

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Chart showing the predicted position of ISON as seen from STEREO H1A on 1 December 00:09 UT (click to embiggen). The Pleaides is the cluster at centre left in both images.Image showing the actual position of ISON as seen from STEREO H1A on 1 December 00:09 UT (click to embiggen). The STEREO image has Earth and Mercury in the centre, these are not plotted on the star chart.

Now that Comet C/2012 S1 ISON has fallen apart into a sad pile of gravel and dust, the fear merchants are at it again. With headlines like "COMET ISON'S KILLER Debris Wave Heading for EARTH" (I'm not going to link to the various pages and give them the page views, but you can google it yourself if you want to kill a few brain cells) the fear merchants are trying to scare people into thinkg a massive strom of rocks is headed our way.

But it isn't.

The location of ISON on 1 December 00:09 UT, for STEREO (indicated by the red cross) to see ISON near the Pleiades (as in the predicted and actual images), ISON must be well above the plane of Earth's orbit.  (click to embiggen to see the location of Earth clearly.

ISON's predicted orbit takes it well away from us,  the nearest the pile of gravel formerly known as ISON comes to us is 0.43 AU (64,000,000 km), that's a bit under half the distance form Earth to the Sun, or the distance from Earth to Venus's Orbit.
 
i.e. Nowhere near us. I have previously checked ISON's orbit as it came out from its close approach to the Sun in the SOHO LASCO C3 images, it was right on track. I've done it again for ISON is the high resolution STEREO H1A imager images. This is more tricky as STEREO-A does not have the same field of view as Earth, so I needed to make a special ephemeris using JPL horizons based on the STEREO-A spacecraft's position.

They match to within 8 arc seconds. This means that ISON is on track in it's predicted orbit, and will come no closer to Earth than 0.43 AU. The rather compact debris trail will be high above Earth's orbit heading out to space. Oh yes, and the leftover material will not be "city sized". ISON itself was less than 1 Km in diameter (more like 600 meters), the biggest bits in the leftover gravel will be meter sized, at the outside as big as the Chelyabinsk meteor. If the debris cloud did come near us, we would get a pretty meteor display, but nothing more.

But of course, they will not come anywhere near us.


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Thursday, December 12, 2013

The Aurora Chasers Handbook Launches

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Tonight was the launch of the book The Aurora Chasers Handbook. Skilfully put together by aurora follower Margaret Sonnemann, this book has tips and tricks for watching and photographing aurora in Australia, and a section on aurora science written by someone that you just might recognise.

Oh yeah, and pictures, lots and lots of amazing aurora pictures by some outstandingly talented Australian auroraphiles from the Aurora Australis facebook group I am lucky to be a part of.. 

So if you want to lean about the Aurora Australis, find out how to see it, or just revel in the glorious imagery in the book, you could do worse than purchase a copy.
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Wednesday, December 11, 2013

Nova Centauri 2013 still Bright (12 December 2013)

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Nova Centauri 2013 captured with my Canon IXUS at  ASA 400, 10 second exposure. Click to embiggen.Nova Centauri 2013 captured with my Canon IXUS at 3x Zoom, ASA 400, 15 second exposure. Click to embiggen.

Finally got to see Nova Centauri 2013  with my own eyes, magnitude probably between 3.6 and 3.9
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Nova Centauri 2013 brightens again (11 December 2013)

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Nova Centauri 2013 imaged with iTelescope T9 on the morning of Wednesday 11 December at 4:05 am AEDST.



Nova Centauri faded from it's peak of around magnitude 3.5 to around 4.5, and now has bounced back again to magnitude 3.6-3.7 (see this magnitude plot from the AAVSO). I still have not seen it with my unaided eye, but I got another shot with iTelescope.

Exposure time was 10 seconds, and it is still overexposed. Compare this with my image from the 7th. No useful nearby reference stars to estimate the magnitude.
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Tuesday, December 10, 2013

Geminid Meteor Shower 13-14 December 2013

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The northern horizon at 3:00 am ACDST as seen from Southern Australia (northern Australia is similar but Gemini and the radiant is higher in the sky) on Saturday December 14. The Geminid radiant is marked with a cross.
(click to embiggen).

The Geminids are unusual 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.
 
The Geminids are a fairly reliable meteor shower and this year moonlight will not significantly  interfere. 


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 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 14th, between 2:00 am and 4:00 am local time. You can find predictions for your local site at the meteor flux estimator (choose 4 Geminids and date 13-14 December, don't forget to change the date to 2013).


The International Meteor Organisations Live Geminid report will be useful to follow the shower.

At 1.00 am in the morning AEDST (midnight, AEST) Castor (alpha Geminorum) is about two handspans above the horizon and 10 handspans to the left of due north. Pollux, the other twin, is less than a handspan to the left 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 two minutes is an average, they won't turn up like a ticking clock but more or less randomly).

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 non 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 Jupiter and Mars will be nearby. So it will be a quite nice morning for sky watching. Keep an eye out for satellites!

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The Sky This Week - Thursday December 12 to Thursday December 19

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The Full Moon is Tuesday December 17. Mars is  prominent in the early morning. Saturn rises higher in the morning sky. Venus is easily visible late into the night in the western evening sky above the Teapot. Jupiter is visible in the evening sky now, the Moon is close to Jupiter on the 19th. There is a bright Nova near Beta Centauri that is currently visible with the unaided eye. Geminid meteor shower on the  morning of the 14th.

The Full Moon is Tuesday December 17.


Evening sky looking west as seen from Adelaide at 21:00 pm ACDST  on Saturday December 14.  Venus is high in the evening sky above the Teapot asterism of Sagittarius.  The inset shows the telescopic view of Venus. Similar views will be seen elsewhere at the equivalent local times.  Click to embiggen.

Venus continues to fall back  in the evening twilight. However, it can easily be seen shortly after sunset (indeed, with a little effort you can see it before sunset) until late in the evening.

The brightest (spectacularly so) object above the western horizon it is still visible up to three hours or more after sunset (depending on how flat your western horizon is) when the sky is fully dark. Venus is beginning to sink to the horizon, but will be spectacular for many weeks hence.

Venus is in the Constellation of Sagittarius. It is a distinct crescent moon shape in even small telescopes. This week Venus is above the "Teapot" asterism of Sagittarius.

  
Evening sky on Thursday December 19 looking north as seen from Adelaide at 2s:00 pm ACDST in South Australia. The inset shows the view of Jupiter through a telescope at this time. The Moon is close to Jupiter. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).

Jupiter is in the constellation Gemini. Mars is is in the constellation of  Virgo. Saturn is in Libra.

Mars rises still higher in the morning twilight, and is visible well before twilight.  


Jupiter is now well above the northern horizon near the bright stars Castor and Pollux, the twins of Gemini. It is quite easy to see in the morning sky well into the twilight.  Jupiter's Moons are now readily visible in binoculars. Jupiter rises around 10:00 pm local daylight saving time, but is still best for telescopes in the early morning. Jupiter is close to the Moon on the 19th.


Morning sky on Sunday December 15 looking east as seen from Adelaide at 5:00 am ACDST in South Australia. Mars is high above the horizon, Saturn is low above the horizon. Both are roughly equidistant from the bright star Spica. Similar views will be seen elsewhere at the equivalent local time (click to embiggen).

 Saturn is visible low in the eastern horizon before dawn. It will be difficult to see unless you have a flat, level horizon.


Mercury  is lost in the twilight.

The northern horizon at 3:00 am ACDST as seen from Southern Australia (northern Australia is similar but Gemini and the radiant is higher in the sky) on Saturday December 14. The Geminid radiant is marked with a cross.

The Geminids are a fairly reliable meteor shower and this year moonlight will not significantly  interfere.

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 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 14th, between 1:00 am and 4:00 am local time. You can find predictions for your local site at the meteor flux estimator (choose 4 Geminids and date 13-14 December, don't forget to change the date to 2013).

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

As well, Orion and the Hyades will be visible and bright Mars will be nearby. So it will be a quite nice morning for sky watching. Keep an eye out for satellites!



Location of Nova Centaurus 2013 as seen looking north from Adelaide at 3:00 am ACDST local time.The location is marked with a square. Similar views will be seen at the equivalent local time in other Southern Hemisphere locations. Click to embiggen.

UPDATE: Nova Centauri has re-brightened.

A new nova has been reported  near beta Centauri. It is currently bright enough (magnitude 4.5-5 back up to 3.6-3.7) to be seen faintly with the unaided eye, and very easily in binoculars. Unfortunately, you have to wait until early morning for the nova to be heigh enough for a good look.

More detailed spotters charts and instructions are here.


There are lots of interesting things in the sky to view with a telescope. Especially with Venus so prominent in the sky.  If you don't have a telescope, now is a good time to visit one of your local astronomical societies open nights or the local planetariums.


Printable PDF maps of the Eastern sky at 10 pm AEDST, Western sky at 10 pmAEDST. For further details and more information on what's up in the sky, see Southern Skywatch.
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Monday, December 9, 2013

 
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