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Various astronomical "shadow events" occur throughout the Solar System!  This month's more interesting ones are featured here.

SHADOW WORKS

Here we highlight the most awe-inspiring eclipses taking place in our Solar System.  We also set them up so that all you need to do is click on their links.  Don't forget that you can generate lists of Earth's, Jupiter's, Saturn's, Uranus's, Neptune's and even Pluto's eclipses, using CELESTIA's own built-in "Eclipse Finder."  You'll find it in the program's menu under "Navigation".

Unless noted otherwise, the events identified below are displayed as if viewed from Earth, their magnifications shown in parentheses at the lower right of CELESTIA's window.  Events involving more than one moon are often cyclical, so usually only the first example is given, and then the period of the cycle.

Remember: you can press the   M   key to toggle Moon Labels on and off .

JUPITER

Jupiter is now in that part of its orbit where its equatorial plane, and the orbital planes of the four Galilean moons, are increasingly tilting with respect to the Sun.  While Io, Europa and Ganymede all produce solar eclipses each time they orbit Jupiter, this is not true of Callisto, whose increasingly tilting orbit has made it incapable of casting its shadow on Jupiter since last December.  It will not be able to cast its shadow on Jupiter again until 2013!

Like last month, because Io, Europa and Ganymede fail to "converge" between Jupiter and the Sun this month, no simultaneous solar eclipses (i.e. involving more than one major moon) occur in April.  Nonetheless, there are times when two or more Galileans are visible near Jupiter.  Here are highlights of the 30 solar eclipses that Io, Europa and Ganymede spawn in April, as Jupiter's movement behind the Sun early this month makes its shadow move from its east (left) to its west (right).

With the Galilean info below, it is easy to see why some events involving more than one moon repeat.  This info also lets you predict when events may recur.
Periods:
   Io:  1.769 days
   Europa:  3.551 days
   Ganymede:  7.155 days
   Callisto:  16.69 days
Resonances:
   Io & Europa: 2 to 1
   Io & Ganymede: 4 to 1
   Europa & Ganymede: 2 to 1

• Apr 1: Io passes Europa east (left) of Jupiter, and then follows Europa around; both casting their shadows, though several hours apart  (1.6.x)   (1.4.1)
• Apr 2: Io nears Ganymede and both move behind Jupiter; Europa follows hours later  (1.6.x)   (1.4.1)
• Apr 3: As Io changes its direction and passes Ganymede, slower Callisto appears and follows Io past Europa and in front of Jupiter; all 4 major moons are visible near Jupiter  (1.6.x)   (1.4.1)
• Apr 6: Io and Ganymede approach Jupiter from opposite directions; then Ganymede passes Europa  (1.6.x)   (1.4.1)
• Apr 7: Ganymede passes Europa, which then moves behind Jupiter while the mighty planet's shadow is near directly behind it  (1.6.x)   (1.4.1)
• Apr 12: Io and Europa approach Jupiter from the east, while Callisto approaches from the west  (1.6.x)   (1.4.1)
• Apr 20: Io emerges from behind Jupiter and passes Ganymede and Callisto as all are near Jupiter; Ganymede and Callisto then pass Europa on the west side of Jupiter  (1.6.x)   (1.4.1)
• Apr 24: it's easy to see that Jupiter's shadow now stretches westward when Io, then Ganymed and then Europa enter it   (1.6.x)   (1.4.1)
• Apr 29: Io passes behind Jupiter and into its shadow, as more distant Callisto moves "above" it  (1.6.x)   (1.4.1)
• Apr 30: Europa passes Io and Callisto east of Jupiter  (1.6.x)   (1.4.1)

SATURN

Like Jupiter, Saturn is now in that part of its orbit where its equatorial plane, as well as the orbital planes of its major equatorial moons, are all tilting more and more relative to the Sun.  So fewer and shorter eclipses will occur on the ringed planet for some time.  Rhea, Titan and Iapetus have not been able to cast shadows on Saturn since Oct 2010, Feb 2010 and Jun 2007 respectively.  They will not cast their shadows on Saturn again until Mar 2024, Oct 2024 and July 2022 respectively.

While CELESTIA 1.6.x shows the shadows of Titan, Rhea, Iapetus, Dione and Tethys, version 1.4.1 displays only the shadows of Titan, Rhea & Iapetus.  So, 1.6.x and 1.4.1 respectively show 25 and no solar eclipses on Saturn in April.  In addition, version 1.6.x reveals no double simultaneous solar eclipses this month.  But you'll notice that Dione is casting its shadow further and further south, and before long it will not be able to create a solar eclipse on Saturn for awhile.

To aid in your viewing, here are the periods of Saturn's major moons.  These do not exhibit the resonances that Jupiter's Galileans display.  Still, you can use this info to predict subsequent eclipses of a single moon.
   Tethys:  1.888 days
   Dione:  2.737 days
   Rhea:  4.518 days
   Titan:  15.95 days
   Iapetus:  79.33 days

• Apr 1: Tethys casts its shadow on Saturn, as it now does about every 2 days  (1.6.x only)
• Apr 2: Dione casts its shadow deep in Saturn's southern hemisphere, as it now does about every 2¾ days  (1.6.x only)
• Apr 19: Dione casts its shadow so far south on Saturn that it can barely be seen; Tethys casts its shadow a short time later  (1.6.x only)  Here's another view (Dione is near top)  (1.6.x only)
• Apr 26: this is the last time that Dione will cast its shadow on Saturn until 2023! You have to look VERY closely to see it  (1.6.x only)  Here's another view (Dione is near top)  (1.6.x only)

URANUS, NEPTUNE & Dwarf Planet PLUTO

Neither Uranus nor Neptune will experience eclipses for decades.  Dwarf planet Pluto will experience no eclipses by Charon for about a century!