The Double Lunar Occultation of Feb 18, 2013

It was a bit of a mixed bag on Monday night with the moon passing in front of Jupiter.

I first went out for look while twilight was just kicking in. The moon was at its highest point in the sky, almost due north and not very high. Jupiter was barely visible to the east (right) of the moon. As the sky darkened Jupiter shone more brightly, becoming easily visible beside our nearest neighbour, slowly closing in.

I recalled studying the diagram in this post where I said Jupiter would disappear behind the lower right hand side of the moon. I assumed the terminator (day-night line) would be vertical. Jupiter seemed to be lined up almost exactly with the centre of the moon’s terminator. Chalk it up to a small and difficult to read section of the diagram. And me not quite knowing what I was doing!

Animation of Lunar Occultation of Jupiter 18 Feb 2013

Animation of Lunar Occultation of Jupiter 18 Feb 2013

As the hour of action drew closer I noticed Jupiter was dropping in the sky relative to the moon. But if anyone was using what I wrote last week as a guide to finding Jupiter they should have had no trouble. It was so bright you couldn’t miss it, even when it came close to the moon’s night side. I was snapping pics every few minutes with my DSLR and its standard 55 mm lens. Here’s an animation I put together of frames spanning the 35 minutes leading up to occultation, plus a bit more.

Each frame is roughly 3 minutes apart except the last few where the moon darkens. These were taken about 15 and 20 minutes after Jupiter disappeared. The darkening was caused by smoke from a grass fire north of Melbourne hanging on the western horizon, effectively occulting the moon just as Jupiter was scheduled to emerge from behind the moon 40 minutes after the beginning of occultation.

So a beautifully clear 35 degree day that promised perfect conditions for viewing the occultation, ended in disappointment for those of us in the east who, instead of seeing the end of occultation with the re-emerging Jupiter, witnessed a Lunar occultation of a different kind: that of the moon completely obscured by grass fire smoke.


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