THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
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.
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
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:
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).
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.
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.
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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:
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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