THE SOUTHWORTH PLANETARIUM
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70 Falmouth Street   Portland, Maine 04103
43.6667° N                   70.2667° W
Altitude:  10 feet below sea level
Founded January 1970
Julian Date:  2459279.18
2020-2021:  XCVIII


THE DAILY ASTRONOMER
Monday, March 8, 2021
March 2021 Night Sky Calendar Part III

____________________________________
PLANETARIUM REOPENS ON MAY 3!
Details to come!
_____________________________________

Our apologies.  We encountered a few disruptions last week.   Now, we begin
this week with Part III of the March 2021 Night Sky Calendar.   We
anticipate no further disruptions in the foreseeable future.


*SATURDAY, MARCH 20:  VERNAL EQUINOX (GOLD EVENT!!!)*
In the northern hemisphere, astronomical spring begins precisely at 5:37
a.m. Eastern time.  At the same moment, autumn begins in the southern
hemisphere.
Today is one of the two days of the year -the autumnal equinox being the
other one- when the Sun crosses the celestial equator, the projection of
Earth's equator onto the sky.  One could say that from our northern
hemisphere perspective, the Sun has reached the ascending node and will be
moving above the celestial equator.     As the  beginning of spring is such
an important astronomical event, we decided to include a few questions and
answers pertaining to it.


*Why is the vernal equinox called the "First Point of Aries" when the Sun
is actually in Pisces on this date?*

The Sun used to be "in" the constellation Aries on the first day of Spring,
otherwise known as the vernal equinox.   We should explain that as Earth
revolves around the Sun, the latter will appear to travel through thirteen
constellations comprising the "zodiac."  Greek astronomer Hipparchus of
Nicea (190-120 BCE) introduced the term "First Point of Aries" (or "Cusp of
Aries.") when he observed that the Sun was within the constellation Aries
during the vernal equinox.     However, the Sun's
apparent vernal equinox position has continuously shifted along the
ecliptic by about 1 degree every 73 years due to precessional wobbling.
The wobbling, caused primarily by interactions with the Sun and Moon,
causes our planet's pole to describe a 47 degree circle through the sky
every 26,000 years.   Consequently, the thirteen zodiac constellations will
all "host" the vernal equinox point during this 26,000 year cycle.
   According to astronomer Jean Meeus, the vernal equinox point crossed the
Aries-Pisces border in 68 BCE.  Ironically, this shift occurred less than a
century after Hipparchus' death. The vernal equinox point has been moving
westward through Pisces ever since.  In AD 2597, the vernal equinox will
move into Aquarius the Water Bearer.  Or, to be more specific, it will
cross into the rectilinear region that the International Astronomical Union
has designated as the Aqarius "region." Perhaps even then, astronomers will
continue to refer to the vernal equinox as the "First Point of Aries."



*Why isn't the day length on the first day of spring exactly 12 hours?*

Simply because we're not living on a perfectly spherical, uniformly dense
sphere devoid of an atmosphere.  First, Earth is an oblate spheroid, an
object that looks spherical, but contains a "bulge" around its middle due
both to its rotational motion and tidal stresses. Secondly,  land is not
divided evenly between the Northern and Southern Hemispheres.   The
Northern Hemisphere currently contains 68% of Earth's land mass.  The
Southern Hemisphere contains thirty two percent.  This uneven land
distribution has caused Earth to develop a slight "pear shape."
Consequently, sunlight falls unevenly on Earth.   Third, the atmosphere
refracts light, which "pushes" the image of the Sun above the horizon, even
when it is actually just under the horizon!



Interestingly (well, at least to us), the actual date when one experiences
twelve hours of daylight and twelve hours of night varies with the
latitude.    At Portland's latitude (43 degrees),  the parity between day
and night occurs around March 17th and September 25th.    Observers at 60
degrees North experience this parity around March 18th and September 26th,
while those at 20 degrees North have precisely twelve hours of daylight
around March 14th and September 28th.



Even though the word "equinox" is derived from the Latin term
"aequinoctium," meaning "equal night," the length of daylight and night is
not actually equal on the equinox.



*The March Equinox marks the first day of spring in the Northern Hemisphere
and the first day of autumn in the Southern Hemisphere.  What season will
it be on the Equator?*

The Equator is a line of no thickness and therefore doesn't qualify as an
actual location.  Let's assume that you're standing on the Equator on
the equinox. Or, more correctly, you're straddling the equator so that one
foot is to the north of it and the other is to the south of it.    At the
moment of the equinox, your northern foot would be in spring and your
southern foot would be in autumn.



*Is it  true that you can balance eggs on the equinox?*

Yes, you can balance eggs on their ends on the equinox.

Of course, provided you have enough patience, you can balance eggs on their
ends any day of the year. You'll have better luck if the egg ends are
slightly flat, but the equinox, itself, has no effect.

The notion that one can balance an egg on its end only on the equinox stems
from the mistaken belief that Earth's tilt varies throughout the year: that
it veers from an extreme (23.5 degrees) at either solstice to being upright
(0 degree tilt) on each equinox. When perfectly vertical, Earth can keep
everything on its surface in balance, even those objects such as eggs that
would fall over on any other day.

Of course, Earth's tilt doesn't vary throughout the year.* It stays the
same. What changes is the orientation of the poles relative to the Sun. On
the summer (June) solstice, the north pole is aligned toward the Sun,
whereas the south pole is directed away from it. Six months late, the north
pole is oriented away from the Sun, but the south pole points toward it.
The actual planet tilt remains constant. Imagine for a moment that you have
a pen tilted over by a certain amount. Have it revolve around a stationary
object, such as a ball. Notice that at one location, the top of the pen is
pointing toward the central object, but the bottom is pointing away from
it. At the opposite point, the top is pointing away, but the bottom is
pointing toward the ball.

Today, one can attempt to balance an egg on its end. One might well
succeed, provided one that one is patient enough. As I said, having a
slightly flattened egg end is helpful. I hope this answer was helpful, as
well.

*SUNDAY, MARCH 21: FIRST QUARTER MOON*

*WEDNESDAY, MARCH 24:  MOON NEAR PRAESEPE (THE BEEHIVE STAR CLUSTER)*

                  [image: skychart.png]

Observe the waxing gibbous moon (82% illuminated) close to the Praesepe
(Beehive) Star Cluster tonight.   Praesepe marks the center of Cancer the
Crab and is its only prominent feature.     The lunar light interference
will likely obscure the star cluster from somewhat.

*FRIDAY, MARCH 26:  VENUS IN SUPERIOR CONJUNCTION*
               [image: 5868256dcd8d3.image.jpg]

If we could look down onto the solar system today, we would see Venus and
Earth on either side of the immensely large Sun.      Nobody on Earth will
be able to see Venus and, if anybody lived on Venus, he/she/it would not be
able to see Earth.      Throughout the winter Venus had been visible in the
eastern pre-dawn sky.    Later this spring, it will reappear in the western
evening sky.


*SUNDAY, MARCH 28:  FULL MOON*The end of March brings us the full "worm"
moon, an allusion to the worms that will emerge from the thawing soil.
The March full moon is also known as the sap moon, in reference to the
increased flow of sap through the trees.  Other March full moon names
include the "Crow Moon," and the "Sugar Moon."


*PLANET WATCH*

*MERCURY  *
The best time to seek Mercury is early in the month, when the first planet
will be visible in the eastern pre-dawn sky.       After Mercury reaches
its greatest western elongation on March 6th, the planet will quickly
descend back toward the Sun.   Verdict:   We advise you to search for
Mercury during the first two weeks of March.

*VENUS*
Although Venus might be visible during the first week of March, it will
still be difficult to observe.   VERDICT:  Don't bother searching for Venus
this month.  Our sister planet will return to the late spring western
evening sky.

*MARS  * (Host constellation:  Taurus)  PICK PLANET!
Well, of course Mars is our pick planet this month.  It is the only visible
planet in the evening sky.    Mars begins the night high in the eastern sky
and will set just after midnight at month's beginning and just before
midnight at month's end.  VERDICT:  Easy peasy!  Venture out after dark and
see the red planet

*JUPITER *(Host constellation: Capricornus)
The largest planet returns to the pre-dawn eastern sky.     At month's
beginning, Jupiter will rise at 5:25 a.m. At month's end, the planet
appears around quarter to five.    VERDICT:   While one can see Jupiter
throughout March, it will be easier to find toward the end of the month.
Also, Jupiter will continue to rise earlier throughout the spring and
summer, when it will become a prominent evening sky object.

*SATURN  *(Host constellation: Capricornus)
Like Jupiter, Saturn is now visible in the eastern pre-dawn sky.   The
ringed world rises before Jupiter.  At the beginning of March, Saturn
emerges above the horizon around 5:00 a.m.    Saturn rises around 4:15 at
month's end.   VERDICT: As is true with Jupiter, Saturn is easier to find
at the end of March than at the beginning.  Also, Saturn will become a
prominent planet this summer.



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