Tag Archives: Adelaide

Meteors, Asteroids? Bah! Jupiter is About to Disappear…

It’s a big week in astronomy. You’ve no doubt heard about the meteor lighting up the Russian sky earlier today. And in a few hours time a 50 metre wide asteroid will be closer to us that some of our geostationary satellites. It will be 4:30 AM here. I won’t be watching it because I can’t find my binoculars and it’s too dim and fast-moving to be easy to find with the naked eye. Never mind.

Anyway, the original purpose of this post was to talk about a disappearance. In January I noticed the moon passing suspiciously close to Jupiter in the sky and wondered when was the last time I paid any attention to lunar occultations – when the moon passes in front of a planet or a star or something interesting other than the sun (because that’s known as a solar eclipse and is orders of magnitude more spectacular).

As it turns out from Melbourne, Australia on the Monday 18th of February the moon will in fact pass in front of Jupiter, briefly winking it out of view for about 40 minutes or so. Check out this confusing diagram (or click it to get the original at the Astronomy Almanac Online!):


Shadow diagram of Moon-Jupiter Occultation Feb 18 2013 (reproduced from The Astronomical Almanac Online and produced by the U.S. Naval Observatory and H.M. Nautical Almanac Office.)

The diagram shows the shadow of the moon cast by Jupiter on the Earth at ten minute intervals from start of occultation in the Indian Ocean (marked by the tiny red shadow) to the end, about 3 hours later in Tasmania at the other red shadow.

Now, assuming I interpret this diagram correctly, Melbourne will be near the top of the Lunar shadow, so from here Jupiter will be seen to disappear behind the night side near the north end of the first quarter moon. Look at the bottom right of the moon when gazing up towards the moon in the north western sky from Victoria . This will be the most dramatic part visible. It will be much easier to see the bright planet vanish behind the unlit half of the moon’s disc than trying to watch it reappear in the glare of the moon’ day side.

In fact the flat side of those half-oval shapes is the moon-set line across the Earth so Tasmanians will see the moon set just as Jupiter emerges from behind it, about 70 minutes after it disappeared.

When can you see this you may ask? Well, from the above diagram it’s difficult to get an accurate estimate but working backwards from the last shadow in Tasmania at 13:13 UT (00:13 19 Feb) The shadow will be over Melbourne between 12:23 UT (23:23 AEDT) and just after local midnight. But I don’t guarantee anything in case I read the diagram incorrectly. The moon will be on its way down in the west so it is recommended to have a clear view of the western and north western horizon.

Hope the skies are clear on the night and enjoy seeing our humble little moon obscure the mightiest planet in our solar system. Adelaide and Perth will see it too, just earlier in the evening than Victoria.

Take that 2012 DA 14!