Today, all four Galilean moons go through a perijove. This is a very rare event and I don't think should be overlooked. On top of that, the locations of these perijoves -- at least for three of the moons -- is rather interesting. Io, Europa, and Ganymede all have perijoves that more-or-less line up with the the Sun and the Earth! Are the perijove and apojove positions always in alignment with the Sun? I'll be watching this phenomenon for the next few months and probably write some code to allow me to look at this more closely.
JUPITER TODAY is a daily blog about the dynamic Jupiter system for the purpose of monitoring activity.
We start with the overall view of activity with the Jupiter system, showing the orbits of the four Galilean moons:
This is a view of the Jupiter system looking down on it. Following the blue line to the left is the line of sight to Earth, while following the gray line to the left is the line of sight to the Sun. The orbits of the four Galilean moons are shown. The large dots indicate the position of each moon at 0h, 6h, 12h, 18h, and 24h (0h the next day) UTC for this date. From this point of view, the moons revolve around Jupiter in a counter-clockwise motion. For more information about this graphic, see the post from 30 July 2015.
By 6h UTC, Io is firmly in quad 3 moving west and Europa is firmly in quad 2 heading west. At this time, all four moons are heading west.
At 12h UTC, Io is just past its western elongation and is now in quad 4 moving east.
By 18h UTC, Io is firmly in quad 4 still moving east. Europa and Ganymede are in quad 2 moving west about to transit Jupiter.
At 0h UTC tomorrow, Io has moved behind Jupiter, Europa and Ganymede have transited Jupiter, and Callisto continues in quad 3 moving west.
Perijove #1: At 14:42 UTC, Callisto is 1,869,056.1 km from Jupiter
Perijove #2: At 17:53 UTC, Ganymede is 1,069,182.8 km from Jupiter
Perijove #3: At 21:13 UTC, Io is 420,026.7 km from Jupiter
Perijove #4: At 21:16 UTC, Europa is 664,491.0 km from Jupiter
At 0h UTC, Jupiter is at an RA of 10h 10m 52.5s and a DEC of +12d 09m 41.3s. The phase angle is 1.811 degrees, which is 0.138 degrees less than yesterday. The angle between Jupiter and the Sun as seen from Earth is 9.669 degrees, which is 0.742 degrees less than yesterday. This distance between Jupiter and the Sun continues to grow. Today the distance is 805,578,382 km, which is 37,237 km greater than yesterday. Jupiter appears to be moving away from the Sun at a velocity of 1,551.542 km/h, which is 1.875 km/h faster than yesterday. The distance between Jupiter and Earth gets larger as we approach Superior Conjunction on 26 August. Today we are 954,585,810 km from Jupiter, which is 417,437 km greater than yesterday. This means we're moving away from Jupiter at a velocity of 17,393.208 km/h, which is 1,270.917 km/h slower than yesterday. Whew! We are Moving! Or are we???????
From 20:03 to 22:55, Europa transits Jupiter. From 20:03 to 23:41, Ganymede transits Jupiter. Yes, both Europa and Ganymede begins their transit of Jupiter at the same time! So of course we'd see them both in transit if Jupiter wasn't so close to the Sun! At 20:09, Io moves behind Jupiter. From 20:26 to 23:17, the shadow of Europa transits Jupiter. From 20:52 to 00:27 tomorrow, the shadow of Ganymede transits. Io reappears from behind Jupiter's shadow at 22:38 UTC.
Glorious Orbital Ribbons today:
Jupiter is so near Superior Conjunction (taking place at 22:00 UTC on 26 August 2015) that photography and other data collection isn't practical. We'll have to wait about a months after SC to start viewing the Jupiter system again.
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Please send me your feedback, comments, and questions to jupitertoday AT gmail DOT com or the comments section of this blog.
With my gratitude, the data used to create the orbit plots and ribbons was supplied by the JPL Horizons website. The graphics showing the location of the four moons as seen from Earth are via 'Jupiter Viewer 2.8'. Jupiter-Satellite and Satellite mutual events data is supplied from IMCEE.
Until tomorrow, I bid you Peace.
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