2010:  Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec 

2011:  Jan  Feb  Mar  Apr  May  Jun 

 1.6.x & 1.4.1 LINKS

Throughout this website you will find pairs of links labeled "1.6.x" and "1.4.1".  Click here for a brief explanation.


CELESTIA's clock displays Coordinated Universal Time, UTC.  Click here for a brief explanation.


In the month of April, Mars follows Mercury and the Sun eastward out of Aquarius and into Pisces.  Before month's end, Pisces is "playing host" to the Sun and four planets!  What a gathering!

Note: in the 1.6.x and 1.4.1 links in this column below, planets east ("left") of the Sun are visible in your sky after sunset, while planets west ("right") of the Sun are visible before sunrise.

Run the links below as often as you like, and keep an eye on CELESTIA's clock near the top right corner of the program's window.  Don't forget that you can use your keyboard's   J  K   and   L   keys respectively to reverse, slow down and speed up time in CELESTIA.

MERCURY: 2011 Apr

Mercury "goes retrograde" for most of the month and passes north of Jupiter and just north of Mars  (1.6.x)   (1.4.1)

VENUS: 2011 Apr

Venus exits Aquarius in the middle of the month, chasing the Sun eastward.  It enters Pisces, then Cetus (briefly) and then Pisces again just before month's end  (1.6.x)   (1.4.1)

MARS: 2011 Apr

In Pisces at the beginning of April, Mars passes Uranus.  It then moves toward the "thick of things", passing close to Mercury and even closer (less than half a degree!) to Jupiter!  (1.6.x)   (1.4.1)


Continuing to distance itself from slower Uranus, Jupiter remains in eastern Pisces and is overtaken by the Sun in early April.  The largest planet is then passed by Mercury near mid-month, and approached by Mars at month's end  (1.6.x)   (1.4.1)

SATURN: 2011 Apr

Slow-moving Saturn remains in retrograde motion in Virgo for the whole month of April  (1.6.x)   (1.4.1)

NEPTUNE: 2011 Apr

Slow-moving Neptune lingers in Aquarius, as the Sun, Mars and Venus all leave the blue planet behind  (1.6.x)   (1.4.1)


The following will help you enjoy this page's many links that run events directly in CELESTIA.  If you're new to the program, these tips will also help you learn to use it.

You'll find more information about many of CELESTIA's controls on our  Learning Center  page.


"celestia4all" CHOSEN A RED ORBIT

"celestia4all" is delighted to have been selected a "RED HOT" SITE OF THE DAY by the Red Orbit technology site on  2011 April 15.  Their recognition is greatly appreciated.


Our brand new  Anatomy of the Milky Way poster  is now available, joining our  Our Corner of the Cosmos posterTime Zones poster  and  Earth's Tides poster, which are being enjoyed by customers from around the globe!  All are exclusively from SkyMarvels and will be welcome additions to any collection, classroom, library, office or dorm room!



Here are the Sun's positions along the Ecliptic at 00:00 UTC on the days shown.

The slightly curved lines above and below the Ecliptic show the extent of the Zodiac, which you may download from our  Bonuses  page and add to any version of CELESTIA.  Note that the curve in the Zodiac lines is the result of CELESTIA's rendering in perspective.

W A R N I N G !     It is never safe to look directly at the real Sun with the naked eye!  Moreover, looking at it through a telescope or binoculars—even for an instant—can cause permanent blindness!  NEVER DO IT!  Consult the professionals at your local planetarium or observatory to learn how you can safely "observe" the Sun and any SOLAR eclipse!

Of course, you can safely view CELESTIA's depiction of the Sun's apparent path in the sky in April.  Here are the links:  (1.6.x)   (1.4.1).  Note that versions 1.6.x and 1.4.1 differ in the way their "follow" and "lock" features work.  If you "follow" Earth and then "lock" the Sun to it, versions 1.6.x and 1.4.1 respectively maintain the "attitudes" of the Ecliptic and the the Celestial Equator.  This means that the Ecliptic remains "level" when you run the first link, but begins to tilt when you run the second!  Differences like this will be discussed on our  Help  page.


During your voyages in CELESTIA, would you like to be able to position yourself directly over the center of the half of Earth in sunlight or the half in darkness at any time this month?  On our  Tips  page, you'll find that it's quite easy to do so!  If you're any kind of sky watcher at all, you probably know just how helpful this can be!



In UTC per CELESTIA 1.6.x:
  New: Apr 3, 14:33.  1st Qtr: Apr 11, 12:06.
  Full: Apr 18, 2:44.  Last Qtr: Apr 25, 2:47.
(Celestia 1.4.1 usually indicates respective phase times within about one minute of those in version 1.6.x.)

NOTE: New, 1st Quarter, Full and Last Quarter Moons respectively are defined to occur when the Geocentric Ecliptic Longitudes of the Moon and the Sun differ by 0°, 90°, 180° and 270°.

To watch a short video demonstrating the Phases of the Moon,  click here.

The above diagram is produced with our "Moon Phases Calendar" script.  The numbers of the days of the month were added with an image-editing program.

To watch a short video of our Moon Phases Calendar in action,  click here.


Per CELESTIA 1.6.x:
    Apogee: Apr 2, 8:55 UTC; 406,657 km.
    Perigee: Apr 17, 5:49 UTC; 358,101 km.
    Apogee: Apr 29 17:46 UTC; 406,045 km.
(Celestia 1.4.1 usually indicates apogee and perigee times within about one minute of those in version 1.6.x.  Both versions of Celestia almost always indicate equal apogee distances and equal perigee distances.)

Note that this month's lunar perigee again occurs near the Full Moon, though not as close as last month.  The magnitude of the tides near mid-month should still be expected to be greater than usual.

Determined by our "Earth-Moon Distance" and "Moon's Apparent Path" scripts.  Note that distances given are those between Earth's and the Moon's centers. 


Here is the lunar analemma, generated by the Moon's positions relative to the mean lunar orbit and the Ecliptic at 0:00 UTC every day of April.

This phenomenon can be observed using our "Moon's Apparent Path" script.  The analemma's change of shape month after month begins to give us an idea of just how irregular the lunar orbit is.

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


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 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.
   Io:  1.769 days
   Europa:  3.551 days
   Ganymede:  7.155 days
   Callisto:  16.69 days
   Io & Europa: 2 to 1
   Io & Ganymede: 4 to 1
   Europa & Ganymede: 2 to 1


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


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

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News: 2011 April