2016 February 14

Jupiter’s upcoming opposition, notable satellite phenomena, and an occultation

John Rogers

Jupiter will be at opposition on March 8, and thus above the horizon all night long.

One striking phenomenon for a day or so around opposition is that the galilean moons can transit directly in front of their shadows on Jupiter’s disk.  This year, on the night of March 7/8, there will be a very rare opportunity to see both Europa and Io doing this at the same time!  Europa and its shadow move onto the disk at 23:09-12 UT; Io and its shadow, at 00:28-29 UT, while Europa is in the centre of the disk; Europa and shadow leave at 01:57-58, and Io and shadow at 02:43.  This will be very well placed for observers all over Europe including the UK.

A second dual phenomenon occurs on March 9 at 18:54-58 UT:  Ganymede ends a transit just as Io and its shadow begin a transit.  Ganymede’s shadow remains on the disk till 19:10; Europa is hidden behind the planet.  This event will be visible from America, but will be very low in the sky for European observers.

You can see hi-res images of moons transiting in front of their shadows (one at a time), at the last 4 oppositions, on our web site at:

            http://www.britastro.org/jupiter/2014_15report04.htm

            http://www.britastro.org/jupiter/2013_14report05.htm

            http://www.britastro.org/jupiter/2012_13report08.htm

            http://www.britastro.org/jupiter/2011report02.htm

Jupiter’s moons have coupled orbits, so dual transits of Europa and Io will continue to occur at intervals of 3.5 days right up to mid-April, as well as dual transits of Ganymede and Io on March 16, 23/24, and 31.  Times are given in the BAA Handbook, and simulated views can be produced in WinJUPOS.

One more notable and rare event occurs on April 12: Jupiter will occult a 7^th-magnitude star.  Ingress is at approx. 14:45 UT, visible from the Far East and Australia.  Egress is at ~17:45 UT, visible from western Asia and south-eastern Europe.  Although the star will be rather faint relative to the planet, observers with large telescopes may be able to take videos of the event, which can involve irregular fading and multiple flashes as the star passes behind the planet’s atmosphere.  Details can be found in:

            A. A. Christou & E. Kardasis, ‘Stellar occultation by Jupiter and Ganymede’,

            http://www.hellas-astro.gr/articles/astromanos-2015-12-13-1615

For results from the last stellar occultation, on 2009 Aug.3/4, see the Journal of the BAA (2016 Feb), vol.126, p.37.