HIGHLIGHT EVENT

JUPITER DOUBLE & MUTUAL SOLAR ECLIPSE 2010 March 31

To view this video in a larger size, click here.

THE SUN

APPARENT PATH OF THE SUN: 2010 Mar

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 March.  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.

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HALF OF EARTH IN SUNLIGHT & DARKNESS

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!

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VERNAL EQUINOX: 2010

The ancients recognized that day and night are most equal in length at two specific times of year.  They called these times "equinoxes", which means "equal night".  Equinoxes occur at the two times each year when the Sun—in its "apparent" motion in our skies—crosses the Celestial Equator.

In modern times, the term "equinoxes" has broadened to include at least two additional meanings—both denoting "locations" instead of times.  First, the term can also mean the "points" in the sky where the above-mentioned crossings appear to occur.  Second, it can mean the two "points" in the sky—at "any" instant—where the Ecliptic and the Celestial Equator intersect.  This last definition is what is meant when we speak of an "equinox of date."

In its meaning as a "time", the Vernal (or Spring) Equinox is important, as it is the moment the Sun's center appears to move north of the Celestial Equator.  This usually occurs on March 20 or 21 and marks the first instant of Spring.  As noted in the "Apparent Path of the Sun" image near the top of this page, the 2010 Vernal Equinox occurs on March 20 at 17:32 UTC.

The "point" (location) where the Sun's center appears to move north of the Celestial Equator, the Vernal Equinox "point", is very important to astronomers too.  It provides an "origin" or "starting point," on the background of stars, from which they can "map" the sky with a system similar to Longitude and Latitude.  Astronomers call the sky coordinates of this system "Right Ascension" and "Declination", and their respective values at the Vernal Equinox "point" are 0 hr, 0°.

Now, users should be aware that CELESTIA will not show the Sun crossing the program's Celestial Equator at the times generally published for equinoxes.  This is because it draws the Celestial Sphere for the J2000 epoch, not a constantly updated one for any "equinox of date."  We should therefore expect CELESTIA to most accurately show the time of the Sun's crossing of the Celestial Equator for the year 2000 CE, and less and less accurately the farther you get from that year.  And this is indeed the case.  Thus, in the following views of the 2000 Vernal Equinox, we see the Sun's center ascend through the Celestial Equator at very near the theoretically correct time of 7:35 UT  (1.6.x)  (1.4.1).  Conversely, the following views of 2010 show the Sun's center crossing the Celestial Equator considerably later than the predicted 17:32 UT  (1.6.x)  (1.4.1).  We stress that this is not a bug or an error.  It is rather a simplification or "streamlining" not unlike astronomers referring sky-object positions to the J2000 epoch.

Don't worry if you don't fully understand the previous few paragraphs.  Our "Unlocking CELESTIAL Secrets" feature will soon contain more detailed yet clear and understandable explanations of equinoxes, epochs, coordinate systems and much more.  Soon, you may be the one explaining these intriguing and useful concepts to your friends.

THE MOON

PHASES OF THE MOON: 2010 Mar

In UTC per CELESTIA 1.6.x (& 1.4.1):
  3rd Qtr: Mar 7, 15:43 (15:44). New: Mar 15, 21:02 (21:03).
  1st Qtr: Mar 23, 11:01 (11:02). Full: Mar 30, 2:26 (2:27).

NOTE: New, 1st Quarter, Full and 3rd 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°.

Produced with our "Moon Phase Calendar" script.  The numbers of the days of the month were added with an image-editing program.

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LUNAR PERIGEE & APOGEE: 2010 Mar

Per CELESTIA 1.6.x (and 1.4.1):
    Apogee: Mar 12 10:02 (10:03) UTC; 406,013 km.
    Perigee: Mar 28 4:52 (4:53) UTC; 361,871 km.
Determined by our "Earth-Moon Distance" and "Moon's Apparent Path" scripts.  Note that distances given are the distances between Earth's and the Moon's centers.

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LUNAR ANALEMMA: 2010 Mar

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 March.

This phenomenon can be observed using our "Moon's Apparent Path" script.  Compared to the previous two months, the lunar analemma now appears to be widening into a clockwise oval.  Its change of shape month after month begins to give us an idea of just how irregular the lunar orbit is.

ASTRONOMICAL SEASONS

In this month of the Vernal Equinox, it is appropriate to make the following points regarding the seasons.  Since their beginnings and ends are explicitly defined by the Sun's arrival at the equinoxes and the solstices, Earth's astronomical seasons have precise durations.  Moreover, though the equinoxes and solstices are equally spaced at 90-degree intervals around the Celestial Sphere, the astronomical seasons are not of equal length!  This is because Earth's changing velocity in its elliptical orbit makes the Sun appear to arrive a little early at parts of the Celestial Sphere, and a little late at others.

The lengths of the astronomical seasons are very close to the following: Spring: 92 3/4 days; Summer: 93 2/3 days; Autumn: 89 5/6 days and Winter: 89 days.  You can verify these durations quite easily in CELESTIA.  As the Sun makes its yearly journey around our sky, just take note of when its center crosses the following hours of Right Ascension: 0 hr (Vernal Equinox)  (1.6.x)   (1.4.1); 6 hr (Summer Solstice)  (1.6.x)   (1.4.1); 12 hr (Autumnal Equinox)  (1.6.x)   (1.4.1); 18 hr (Winter Solstice)  (1.6.x)   (1.4.1); and 0 hr (next Vernal Equinox)  (1.6.x)   (1.4.1).

We'll let you do the math for the time being, but very soon our free CELES-TIMER tool will make it easy for you.  You can also verify that any Winter and the very next Spring always begin at nearly the same time of day.

Since Earth travels a quarter of the way around the sky during each season, and since it does so in the shortest time in Winter, this also must be when it is traveling its fastest in its orbit.  In fact, Earth's velocity is nearly 3,600 km/h higher in early January (at its maximum) than in early July (at its minimum.)  No doubt, many of you have already deduced the connection here, that the lengths of the astronomical seasons turn out to be a confirmation of Kepler's Laws!  Why?  Kepler's Laws tell us that Earth travels fastest when it is closest to the Sun.  And, as we saw in our News page for January, that is the month when Earth is indeed at  perihelion!

One final note: we often make the mistake of thinking that the seasons are unchanging.  But, like nearly everything else in astronomy, the seasons too constantly (though gradually) vary.  This is due to the many cycles of Earth's inclination, rotation and orbit.  For example, during the dynasty of the Great Pyramid, Autumn was the shortest "astronomical" season, while Spring was the longest!

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