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June 2009: More Double Shadow Transits of Jupiter


Double Shadow TransitJune 2009 features three double shadow transits of the moons Io and Ganymede across the surface of Jupiter. Io is the innermost of Jupiter's four major Galilean moons, whereas Ganymede is the 3rd Galilean moon outward from Jupiter. These double shadow transits take place on June 2, June 9 and June 16, recurring in periods of 7 days and a few hours. The June 2nd double transit is rather short and sweet, lasting from 2:12 a.m. to 2:15 a.m. Eastern Daylight Time. On June 9, the double shadow transit occurs from 4:06 a.m. to 6:15 a.m. EDT, and on June 16, the double shadow transit lasts from 6:39 a.m. to 8:15 a.m. EDT.
Of course, you can always watch a single shadow transit before and after these double shadow transits. The tables below give you the transit times for the shadows and the moons themselves for these dates in Eastern Daylight Time.


Transit Times (Eastern Daylight Time)

June 2, 2009

Jupiter's moonShadow TransitMoon Transit
Ganymede10:38 p.m. (June 1) to 2:15 a.m.3:56 a.m. to 7:33 a.m.
Io2:11 a.m. to 4:28 a.m.3:29 a.m. to 5:45 a.m.

June 9, 2009

Jupiter's moonShadow TransitMoon Transit
Ganymede2:38 a.m. to 6:15 a.m.7:44 a.m. to 11:21 a.m.
Io4:05 a.m. to 6:21 a.m.5:20 a.m. to 7:36 a.m.

June 16, 2009

Jupiter's moonShadow TransitMoon Transit
Ganymede6:38 a.m. to 10:15 a.m.11:28 a.m. to 3:05 p.m.
Io5:58 a.m. to 8:15 a.m.7:10 a.m. to 9:27 a.m.


Lag Times between Shadow and Moon Transits

As seen from the above tables, the shadows of Jupiter's moons transit Jupiter before their respective moons do. However, the lag time between the shadow transits and their respective moon transits continually lessen from week to week until middle August 2009. This is to be expected, because Jupiter is getting closer and closer to its August 14th opposition date - the day on which Jupiter stands opposite the sun in Earth's sky. As seen from Earth, the shadows of Jupiter's moons come closer to pointing directly away Earth the closer Jupiter approaches opposition. The table below helps to illustrate.

Lag times between Shadow and Moon Transits

DateJupiter's MoonLag Time
June 2Ganymede5 hours 18 minutes
June 2Io1 hour 18 minutes
June 9Ganymede5 hours 6 minutes
June 9Io1 hour 15 minutes
June 16Ganymede4 hours 50 minutes
June 16Io1 hour 12 minutes

copyright 2009 by Bruce McClure

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May 2009 Feature * July 2009 Feature