January 26, 2015

Astro-Event: Scoping Out the Jovian Action.

Jupiter & moons + shadow transit.

(Photo by Author).

These next few weeks are a great time to keep an eye on the largest planet in our solar system. The planet is fresh off of opposition, which occurred on December 2nd of last year, and resumes direct motion eastward through Taurus towards quadrature on February 25th. In fact, Jupiter doesn’t even reach opposition this year, something that hasn’t happened since 2001 and won’t happen again until 2025. This is because Jupiter orbits the Sun once every 11.9 years and thus successive oppositions occur approximately every 400 days apart.

January finds Jupiter high in the sky at dusk for mid-northern latitudes, shining at magnitude -2.5 and showing a respectable 44” arc second disk. This is a great time for imaging, as Jupiter is very near the zenith post-dusk. Approaching quadrature, we begin to see the three large Jovian moons of Io, Europa, and Ganymede alternately cast shadows and pass into the shadow of the giant planet…

Ah, you ask; but what about Callisto? The most distant of the Jovian moons, Callisto takes 17 days to orbit the gas giant. Tilted slightly to our line of view, shadow transits of the moon do not always occur with each orbit. In fact, Callisto transits are set to resume this year on July 20th, 2013 and continue as we approach an orbital plane crossing of the Jovian moons on November 7th, 2014. Mutual phenomena of Callisto will continue until July 21st, 2016. Much like Saturnian ring plane crossings , these seasons occur twice every orbit of the planet Jupiter, spaced 4-5 years apart. Jupiter’s orbit is itself is tilted 1.3° relative to the ecliptic and its axial tilt is 3.13° relative to its orbit. Callisto’s orbit is tilted only 0.192° to the invariable plane; all 4 moons have less than 0.5° orbital tilts. Watch the shadows of the moons as well as they transit the Jovian cloud tops; careful observation will reveal differences due to the relative distances of the moons, from the tiny black dot of Callisto to the wide, diffuse spot of Io’s shadow.

Scott Degenhardt also has a fascinating campaign underway to observe the mutual transits and eclipses of the Jovian moons as they begin to pass in front each other later this year. This program seeks to model the local dust field and tenuous atmospheres of the moons as well as map the complex flux tube and dust torus that exists surrounding Jupiter and its energetic moon Io. This is a noble pursuit for those suitably equipped and a chance to do real science. This sort of data would also prove invaluable to such radiation sensitive spacecraft as Juno, set to go into orbit around Jupiter in 2016. Juno sports enormous solar panels, a concern as the spacecraft loops close to the radiation and dust-filled environs of Jupiter.

Finally, keep an eye out on Jupiter next week as it begins an exciting series of occultations by the Moon.

The footprint of the January 22 occultation of Jupiter by the Moon. (Note: solid lines denote regions in darkness).

(Graphics created by the author using Occult 4.0).

The next occultation of Jupiter by the Moon after 2013 won’t be until July 9th, 2016. Next week’s occultation is centered over South America on January 22nd ~03:03 UT and will be one of the best planetary occultations by the Moon in 2013. Fans of this space will recall last month’s occultation of Jupiter by the Moon; this month’s is the second in a series of 3, with the third and final occultation of Jupiter occurring in darkness for southern Australia on February 18th centered on ~11:36UT.

The footprint of the February 18th occultation of Jupiter by the Moon.

This month’s occultation sees the Moon at 83% waxing gibbous phase, February’s occultation occurs at 59% waxing gibbous. For the rest of us, this will be a fine chance to engage in the pursuit of daytime planet-spotting; the evening of January 21st presents one such opportunity before sunset;

Daytime orientation of the Moon and Jupiter ~5PM EST for the US East Coast.

(Created by the author in Starry Night).

Do keep an eye on the King of the Planets as it heads towards solar conjunction on June 19th. If you’ve got cloudy skies, stop by the Virtual Star Party every Sunday night from 9-10PM EST for some live-streaming action! Who knows, the next big Jovian impact MIGHT just be broadcast live…


  1. [...] 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 [...]

  2. [...] “Shadow transit seasons” for Callisto occur twice during Jupiter’s 11.8 year orbit, each spanning about 3 years. We just started the current season in July of this year, and shadow transits of Callisto will continue until July 2016. It’s also worth noting how different the shadows of each moon appear through a telescope. [...]

  3. [...] and the modification of a Logitech 3000 that I bought on rebate for 50$ later, and I was soon imaging planets that same [...]

  4. [...] that can ‘miss’ Jupiter’s disk from our line of sight. We’re lucky to be in an ongoing season of Callisto transits in 2015, a period that ends in July [...]

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