THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
43.6667° N 70.2667° W
Founded January 1970
Julian date: 2457768.16
"A Stonehenge tunnel sounds completely fantastic to us!"
*THE DAILY ASTRONOMER*
*Monday, January 16, 2017*
*Week 20 Night Sky Calendar*
Imagine winter as a long tunnel burrowed through ice. Each year we
trudge through this conduit and occasionally glance upward through the
sheaths of arctic blue ice in desperate search for the remote Sun. We
console ourselves with an assurance that every step we take through the
tunnel conveys us all the closer to its exit. Today, as we pass
January's mid point, we glimpse a hopeful future. For instance, let's
contrast the solstice sun set time and the sun set time today. (This is
only for Portland, Maine, so the times will be slightly different if you
live in Boston, Caribou or Antananarivo, Madagascar.) On December
21st, Sol slumbered at 4:07 p.m. Civil twilight -the well-lit period
immediately following sunset, often known simply as "dusk"- ended at 4:40
p.m.. On January 16, the Sun sets at 4:31 p.m. Civil twilight ends at 5:03
p.m. Now, on the summer solstice, the sun will set at 8:26 p.m and civil
twilight will end at 9:02 p.m. We're certainly not at this point, yet,
but with the Sun setting about 1 - 2 minutes later each day, we're moving
in the right direction.
Our Winter Hexagon tour continues this week. Our next stop is Rigel in
Orion. However, CJ, the Orion piece is a bit long winded, so I put it at
the end of the Night Sky Calendar.
Most of this week's astronomical events this week are all clustered on
Thursday! If the night sky would just allow humans to do the scheduling,
astronomy would be so much improved.
THURSDAY, JANUARY 19 JUPITER 3 DEGREES SOUTH OF THE MOON
We should recall last week's sky watching tip. Jupiter will appear to
be three degrees south of the moon around midnight. By the time Jupiter
and the moon rise later in the evening, their separation distance will have
increased to about 5 - 6 degrees. As they travel through the sky tonight,
the separation distance will widen by about half a degree each hour. The
last quarter moon, being fifty percent illuminated, is still bright, but
won't obscure the brilliant planet Jupiter.
THURSDAY, JANUARY 19: MERCURY AT GREATEST ELONGATION (W 24 DEGREES)
Last week, Venus was at greatest eastern elongation, meaning it was visible
in the western evening sky. This week, Mercury is at greatest western
elongation, so it is visible in the eastern pre-dawn sky. Whereas Venus
can stray as far as 47 degrees from the Sun, Mercury's greatest possible
elongation cannot be more than 28 degrees. Today, it falls slightly short
of its maximum, but it is still easier to observe now than it will be for
the rest of this apparition
THURSDAY, JANUARY 19: LAST QUARTER MOON
SATURDAY, JANUARY 22: MOON AT APOGEE
It's simple.
Perigee - when the moon is closest to Earth
Apogee - when the moon is farthest from Earth
The moon's distance from Earth changes continually because its orbit isn't
perfectly circular. Instead, its orbit is elliptical. We measure an
ellipse's departure from circularity with eccentricity. An ellipse with an
eccentricity of zero is a perfect circle. If its eccentricity is 1, it
becomes a parabola. The moon's eccentricity is 0.054: almost a circle.
The moon's mean distance is about 239,000 miles. Its average perigee
distance is 239,000(1 - 0.054) or 226,094 miles, while its average apogee
distance would be 239,000(1 + 0.054) =251906 miles. These values vary
somewhat due to the influences of other bodies, principally that of the
Sun. Its apogee distance this time is 251,046 miles.
*ECCENTRICITIES. This diagram, compliments of NASA.gov, shows how an
ellipse's departure from circularity increases with increasing
eccentricity. Whereas an ellipse with zero eccentricity is a perfect
circle, an ellipse with an eccentricity of 0.9 is much more of a flattened
oval. No planetary orbit in our solar system is nearly this elongated.
Mercury's eccentricity is 0.206 and Pluto's is 0.248. No planetary
orbit is perfectly circular, either. Venus's orbit is the least
elongated, with an eccentricity of 0.007. Image: NASA.gov*
PLANET WATCH
MERCURY: A beautiful morning planet this month, Mercury rises earlier each
morning until late January. The little planet reaches its greatest
western elongation on the 19th, when it will be 24 degrees west of the Sun.
VERDICT: Mercury is never an easy planet to observe, but it is
slightly easier this month if you venture out before sunrise and look to
the east.
VENUS: (PICK PLANET!) Yes, we knew that you knew that we'd choose Venus
as the pick planet again. How could we not? Our sister planet is not
only at its greatest brilliance, but reached its greatest eastern
elongation on January 12th. VERDICT: Unless you hate astronomy,
you will want to see Venus this month. And, if you do hate astronomy, um,
well, we hope you enjoy the DA, anyway.
MARS: Venus' evening sky companion, Mars is more than a hundred times
dimmer, but still brighter than all but fifteen night sky stars. If one
can find Venus, one need only look a bit to the west to find Mars.
VERDICT: It doesn't dazzle, but Mars is still moderately bright and
therefore not to difficult to observe.
JUPITER: A morning sky object this month. The giant planet rises well
after midnight, but will be high in the pre-dawn eastern sky. Jupiter
is that bright "star" one sees in the morning just before sunrise.
VERDICT: A beautiful planet that one can even see as the morning twilight
brightens.
SATURN: Yet another morning planet. However, Saturn remains low in the
eastern pre-dawn sky throughout the month. It rises about four minutes
earlier each day. As winter progresses, Saturn will move into greater
morning sky prominence. We can look forward to seeing Saturn in the
evening sky when the spring and summer warmth returns. VERDICT: You can
find it if you absolutely have to. However, Saturn will be on stage almost
all year and will be easier to find as we move into spring.
And, now, for Orion.
Being a bit of an Orion freak, I have written about this constellation many
times before. To save time, I have re-posted a previous article about this
grand and mighty hunter. (And, yes, I know it is just a collection of
stars and that Orion is merely a figment produced by our collective
tendency to impose human characteristics on celestial objects so as to
elevate ourselves above ourselves, but, to be honest, being high above
yourself is a beautiful state as the view is stunning and the endorphin
flow never abates.)
Oh, and a brief piece about Rigel is tacked on at the end.
ORION
*ORION THE HUNTER**: Front and center around 9:00 p.m. in mid January,
this giant hunter dominates the winter evening sky. Notice the four star
rectangle enclosing Orion's belt. Rigel, one of the Winter Hexagon
stars, occupies the lower right corner of this rectangle. Image by
Matthew Spinelli*
Orion has now appeared in our eastern early evening sky. His return
doesn't occasion him the same ecstasy that so profoundly affects the rest
of us. After all, Orion has been milling about the sky for more than a
century of centuries: he loomed high in the firmament when the Stonehenge
builders convened their first meetings on the English plain; looked upon
the flames and revelry of Rome's Saturnalia festivals; was largely ignored
by the Bayeux tapestry weavers; revered by Doctor Faustus; studied by
Thomas Jefferson and observed by Harry Potter. And, he lingered about
thousands of years before Stonehenge was even just a blue print just as he
will be traipsing through the heavens centuries after Harry becomes a
figure of ancient literature. To Orion, this most recent return is just the
latest go around in an interminable circuit through Earth's skies. (As Orion's
stars are quite distant, he is likely poised high above many nearby alien
planet scapes, as well.)
Tonight, Orion will have completely risen by 6:00 p.m. One can find the
grand hunter on its side, as though in repose, just above the eastern early
evening horizon.
A large rectangle enclosing a diagonal three star belt comprises his main
pattern. Two star lines curling out from his northeastern rectangle star,
Betelgeuse, form a bronze club. A semi circle of stars surrounding the
northwestern rectangle star, Bellatrix, represents a lion skin shield. A
faint sword dangles from his belt. A solitary star marks his head.
Mythologically, Orion has assumed various identities: the Egyptian Death
God Osiris; the grand Hebrew hunter Nimrod; the Sioux warrior Long Sash;
and in some traditions was Feryja, a Nordic Goddess. One will find other
Orion incarnations in various African, Asian and other cultural folklore
around the world. Since the celestial equator -the projection of Earth's
equator onto the sky- passes just above the belt, Orion is wholly visible
to more than 99% of the world's population. (Only the chest and shoulder
section appear around the North Pole; whereas a South Pole observer sees
only the belt and legs.) His widespread visibility. his stark
resemblance to a standing human, and his collection of brilliant stars have
assured Orion a global fame surpassing that of any other single star
pattern.
Of all his other identities, he is now principally known as Orion,
considered the greatest hunter in Greco-Roman mythology, superior even to
Artemis, Goddess of the hunt and the Moon. One tale portrays Orion as
reckless and boastful. So proud was he of his hunting prowess that he
openly proclaimed himself capable of slaying any beast, no matter how
formidable. Appalled by Orion's impertinent attitude -such irrational
arrogance was only deemed proper in Olympus- Artemis deployed Scorpius the
Scorpion onto Earth. The Scorpion promptly found Orion and nipped his
ankle, killing him instantly. Curiously, Artemis then foisted Orion's
spirit into the sky and bejeweled him with bright stars as a tribute to his
superb hunting skills. He was perhaps also set into the stars as a warning
to other gifted mortals that it is best for one to remain quiet about one's
exceptional abilities.
And there he remains on full display as he has for such a long time. We
should point out that even Orion is ultimately mortal. His component
stars all move through the galaxy in various directions and after tens of
thousands of years, the pattern will become noticeably distorted and
ultimately unrecognizable. For us mortals, Orion's life is interminable.
However, by galactic time periods, Orionis a fleeting configuration: just
one of the myriad star patterns through the galaxy that form and dissolve
in deep time.
*RIGEL An artistic impression of the blue supergiant star marking Orion's
western knee. This hot star is nearly half a million times larger (in
volume) and 40,000 times brighter than the Sun. *
Even though Betelgeuse is Orion's most famous star, Rigel is the
constellation's brightest. Representing the western knee, Rigel is a blue
supergiant nearly 500,000 times larger than the Sun in terms of volume.
With an effective temperature of more than 12,000 degrees C, Rigel produces
more than 40,000 times the amount of energy the Sun releases. Rigel
is ultra-energetic, as it is not only hot, but highly massive: more than 23
times more massive than the Sun. Being only about eight million years
old, it is also young. Despite its youth, Rigel has exhausted its core
hydrogen reserves and has expanded to the supergiant stage in the process.
Eventually -in a few million years- Rigel will finally reach the
end-stage and explode as a supernova. When this cataclysmic explosion
occurs, Rigel will become the brightest object in our night sky apart from
the moon. Currently, it is a highly massive and furiously energetic
star that burns blue-hot in our winter night sky
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