16Feb2013

Jupiter-Moon Occultation February 18, 2013

The January 2013 occultation of Jupiter by the Moon as seen from South America. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).

The movement of the Moon makes a fascinating study of celestial mechanics. Despite the light pollution it brings to the nighttime sky, we’re fortunate as a species to have it where it is.

This weekend, we’ll get to follow that motion as the Moon crosses into the constellation Taurus for a near-pass of the planet Jupiter, and for a very few citizens of our fair world, occults it. In astronomy, the term “occultation” simply means that one astronomical body passes in front of another. It should be visible around 11.15pm-11.30pm (AEST). While the sight of Jupiter winking out behind the dark edge of the Moon will be spectacular to the unaided eye, this is far better seen in binoculars, or better in a small telescope.

The Moon versus Jupiter during the previous occultation of the planet last month. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).

The Moon versus Jupiter during the previous occultation of the planet last month. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).

The term has its hoary roots in astronomy’s ancient past; just like the modern day science of chemistry sprung from the pseudo-science of alchemy, astronomy was once intertwined with the arcane practice of astrology, although the two have long since parted ways. When I use the term “occultation” around my non-space geek friends, (I do have a few!) I never fail to get a funny look, as if I just confirmed every wacky suspicion that they ever had about us backyard astronomers…

But those of us who follow lunar occultations never miss a chance to observe one. You’ll actually get to see the motion of the Moon as it moves against the background planet or star, covering it up abruptly. The Moon actually moves about 12° degrees across the sky per 24 hour period.

The position of the Moon & Jupiter as seen from Tampa (Feb 18th, 7PM EST), Perth, (Feb 18th 11:30UT) & London  (Feb 18th at 19UT). Created by the author using Stellarium.

The position of the Moon & Jupiter as seen from Tampa (Feb 18th, 7PM EST), Perth, (Feb 18th 11:30UT) & London (Feb 18th at 19UT). Created by the author using Stellarium.

Details: On the evening of Monday, February 18th, around 11.30om (AEST) the 56% illuminated waxing gibbous Moon will occult Jupiter for Tasmania and southern Australia – that’s  around 12:00 Universal Time (UT). Folks along the same longitude as Australia (i.e., eastern Asia) will see a close pass of the pair. For North America, we’ll see the Moon approach Jupiter and Aldebaran of February 17th (the night of the Virtual Star Party) and the Moon appear past the pair after dusk on the 18th.

Orientation of Jupiter, the Moon & Vesta on the evening of February 18th for North America. (Created by the author in Starry Night).

Orientation of Jupiter, the Moon & Vesta on the evening of February 18th for North America. (Created by the author in Starry Night).

 But fret not; you may still be able to spot Jupiter near the Moon on the 18th… in the daytime. Daytime planet-spotting is a fun feat of visual athletics, and the daytime Moon always serves as a fine guide. Jupiter is juuuuuust bright enough to see near the Moon with the unaided eye if you know exactly where to look;

Jupiter captured during a close 2012 pass in the daytime! (Photo by author).

Jupiter captured during a close 2012 pass in the daytime! (Photo by author).

To see a planet in the daytime, you’ll need a clear, blue sky. One trick we’ve used is to take an empty paper towel tube and employ it as a “1x finder” to help find our target… binoculars may also help! To date, we’ve seen Venus, Jupiter, Sirius & Mars near favorable opposition all in the daylight… Mercury and Vega should also be possible under rare and favorable conditions.

This week’s occultation of Jupiter is the 3rd and final in a series that started in December of last year. The Moon won’t occult a planet again until an occultation of Venus on September 8th later this year, and won’t occult Jupiter again until July 9th, 2016. We’re also in the midst of a long series of occultations of the bright star Spica (Alpha Virginis) in 2013, as the Moon occults it once every lunation from somewhere in the world.

Four major stars brighter than +1st magnitude lie along the Moon’s path near the ecliptic; Spica, Aldebaran, Regulus, and Antares which we caught an occultation of in 2009. Source: Universe Today

 
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