THE SOUTHWORTH PLANETARIUM
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43.6667° N                   70.2667° W
Altitude:  10 feet below sea level
Founded January 1970
Julian Date:  2459310.18
2020-2021: CVII


THE DAILY ASTRONOMER
Monday, April 5, 2021
April 2021 Night Sky Calendar Part II

We wish we could bring you everything the sky has to offer.
Instead, we have decided to present a night sky calendar in three separate
parts.  By doing so, we can at least devote more words and graphics to each
event that we could were we to condense it into one article.

We hope this calendar helps you in finding your way through the night sky!



*SUNDAY, APRIL 11:  MOON NEAR MERCURY*
One could almost describe this one as an "academic event," meaning one
that, while noteworthy, is difficult to observe.   This morning one will
probably not see the waning crescent moon (1% illuminated) close to the
planet Mercury.    Both celestial bodies will be within 8 degrees of the
Sun in the early morning eastern sky.


*                 [image: skychart.png]*

*MONDAY, APRIL 12:  NEW MOON*
The beginning of lunation cycle 1216.       Pisces the Fish is the new
moon's host constellation.   One will be able to see the thin waxing
crescent moon by early Wednesday evening.

*TUESDAY, APRIL 13:  CASSIOPEIA  IS STILL WITH US*
Our mid latitude sky contains six circumpolar constellations, defined as
those that do not set:

   - Camelopardalis the Giraffe
   - Cassiopeia  the Queen
   - Cepheus  the King
   - Draco the Dragon
   - Ursa Major the Great Bear
   - Ursa Minor the Little Bear


                   [image: Cassiopeia.gif]

Although circumpolar constellations do not set, they might not always be
easy to find as they will sometimes be located low on the northern
horizon.   Cassiopeia, the w-shaped constellation representing an ancient
Ethiopian queen, begins the night low in the northwestern sky.   Around
midnight, Cassiopeia rests almost directly on the horizon line.    At this
time, one might find it difficult to find Cassiopeia due to land
obstructions such as buildings, houses and trees.   However. Cassiopeia
ascends after midnight into the northeastern sky.  By 4 .m. the ancient
queen will be poised high in the east.

*WEDNESDAY, APRIL 14, 2021: MOON AT APOGEE*
What does one call the moon when it is new around the time of apogee, its
greatest distance from Earth? Well, nothing really.   It just happens to be
a new moon that, if visible, would appear slightly smaller than other new
moons.  Of course, as they aren't visible, apogee new moons don't command
our attention, except during a solar eclipse.    If a solar eclipse occurs
when the moon is at or near apogee, the moon will appear smaller than the
Sun, resulting in an annular solar eclipse:

                         [image: 1_36ZkU_1iq9OKQ4cUd29FGg.jpeg]

At totality, the sun resembles a ring of fire, hence the term annular
eclipse, taken from the word "annulus," meaning "ring."

*THURSDAY, APRIL 15:   MOON NEAR THE PLEIADES*
The Pleiades Star Cluster is known as the "winter sky herald."  As it is
the westernmost of the winter stars, it is the first to appear in the early
morning sky in the summer (around mid June) and the first of the winter
stars to set with the Sun (around late April.)   Just before the Pleiades
vanishes into the dusk, one will find it close to the waxing crescent moon
(11% illuminated).

                  [image: pleiades-Ernie-Rossi-Florida-e1540922814442.jpg]
A galactic star cluster approximately 444 light years from Earth, the
Pleiades (or "Seven Sisters") is the first of the "winter sky" stars to
rise in the early morning summer sky.     Tonight, one will see this
cluster "close" to the waxing crescent moon low in the western evening sky.

*THURSDAY, APRIL 15:  MOON NEAR ALDEBARAN*
Remember that the moon can appear to move near four bright stars:
Aldebaran, Antares, Regulus and Spica.   Tonight, the waxing crescent moon
(11% illuminated) will seem to pass close to Aldebaran, the brightest star
in Taurus the Bull.


                  [image: skychart (1).png]
The above image shows the moon's position relative to Aldebaran, the
brightest star in Taurus the Bull.   The nearly horizontal line extending
between both sides of the image is the* ecliptic*, the Sun's apparent
annual path through the sky.

*SATURDAY, APRIL 17: MOON NEAR MARS*
The waxing crescent moon (25% illuminated) ventures "close" to Mars
tonight.  Whenever we mention these lunar appulses, we put the word close
in quotation marks.  We know that the moon won't actually be close to any
of these other celestial objects.    For instance, the moon will be about
249,000 miles from Earth tonight.  Mars' distance will equal approximately
176 million miles!

*MONDAY, APRIL 19:   MERCURY AT SUPERIOR CONJUNCTION*
Don't bother looking for Mercury toward the middle or end of April.  It
will appear too close to the Sun to be seen.   Today, Mercury moves into
superior solar conjunction, which places it on the far side of the Sun
relative to Earth.

Two  important definitions:


   - *Inferior conjunction: *when a planet passes between the Sun and Earth
   - *Superior conjunction: *when a planet moves to the far side of the Sun
   relative to Earth


See graphic below:
                         [image: opposition_and_conjunction.jpg]


Only the two inferior planets Mercury and Vemus can be at either inferior
or superior conjunction.  The superior planets, defined as those farther
from the Sun than Earth, can only ever be in superior conjunction.  The
graphic above shows why a superior planet can never be at inferior
conjunction.

Mercury will move into the western evening sky next month.

*TUESDAY, APRIL 20:   FIRST QUARTER MOON*




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