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: 2457633.16
"Welcome back!!"
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More information. More graphics. More of everything.
That is our aim for the new Daily Astronomer.
One significant change: we are going to post weekly sky calendars,
instead of monthly calendars. A subscriber suggested that we might want to
divide the sky calendars into more digestible fragments now that we
are going to delve into far more detail. At the subscriber's request, we
will not name him/her publicly.*
Today's weekly sky calendar covers Sept 1 - 11, inclusive. Starting on
September 12th, we'll post a weekly sky calendar every Monday.
We hope this change proves more pleasant than perturbing.
Input always welcome!
-E.G.
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*THE DAILY ASTRONOMER*
*Thursday, September 1, 2016*
*Week 1 Night Sky Calendar*
September 1 - 11, 2016
September already?!
Foliage splashes blotting otherwise healthy trees through which whispers
the first hints of winter chill. Yes, of course, and add all those other
pseudo Frost-esque images that attempt to sweeten the sudden demise of what
should have been a perpetually oppressive summer. Of course it couldn't
last. After all, we are gravity-trapped passengers onboard a star
orbiting planet careening inexorably toward both the receiving autumn and
enveloping winter lurking wraith-like in the fogs beyond. We'll still
cleave vainly to September's lingering heat like forlorn lovers, wondering
how something so beautiful could possibly have ever gone awry, only to
awaken to the iron-hard reality that it wasn't meant to be.
Then again, there are so many bright sides to this tragedy that we could
fashion an iridescent dodecahedron out of them. First -and, of course,
foremost- the DA has returned after its long and lamented absence. (And,
that vacation really worked wonders for our narcissitic personality
disorder.). Secondly, the autumn star patterns are ascending into the
evening sky, led majestically by the winged Pegasus. And, following this
procession will be that brilliant spectacle of winter constellations
destined to soon loom large over our crystalline ice forests. Not least
amongst these stellar characters are the mountain-high Orion and his
retinue of enricling creatures. (You can find them all now, provided you
venture outside well after midnight.) The luminiscent Milky Way arcs high
overhead: providing a panoramic vista into the star rich reaches of our
home galaxy. Phoebe's orb remains ever changeable and churns through
its monthly cycle of crescents, quarters, conjunctions and oppositions.
Venus slowly brightens, while Jupiter quickly sinks.
And, if all these wonders cannot assuage the anguish of your grief, realize
that summer isn't quite over yet, at least not astronomically. Moreover,
life remains irritatingly over-exciting. No matter how quiet a moment, or
sedate day it might appear to be, the dynamic cosmos remains ever restless:
from cellular mitosis to star cluster dissipation to ebbing tides,
prodigious star birth, and the ceaseless bustle of life in soils, seas,
subways and, if some astrobiologists are to be believed, growing and
evolving on millions, if not billions of worlds scattered throughout the
Universe.
What with all this, how could even the imminent death of a perfectly
innocent summer dampen the spirits? Why are we waiting? Let's stumble
clumsily into the infinite…
*THURSDAY, SEPTEMBER 1: EQUATION OF TIME IS ZERO*
Ha ha ha! After all that innane bluster, we begin the new school year
with an event that will likely land with a muffled thud onto an indifferent
populace. The Equation of Time might seem too esoteric a topic for
polite company, but, to us, it is quite an interesting concept because it
demonstrates that one will find complexity even in the simplest places.
We know that the Sun apppears to rise somewhere over the eastern horizon
and sets somewhere along the western horizon. This apparent motion is
illusory, because the only thing moving is our own planet. Earth's
rotation merely makes the Sun seem as though it soars across the sky, an
illusion so convincing that even astronomy types still employ Ptolemaic
words such as "sunrise" and "sunset." Once a day, the Sun will reach its
highest point above the southern horizon during a moment called "upper
culimination." The Sun is at this culmination when it crosses the
meridian, the imaginary arc connecting due south and due north.
Although many believe the Sun reaches the meridian at noon, most of the
time it doesn't. It either lags behind or is slightly ahead of the
meridian at noon. The "equation of time" indicates the time difference
between civil noon and upper culmination, otherwise known as "true noon."
Today, the Sun crosses the meridian precisely at noon time. The graph
below shows the approximate equation of time throughout the year.
[image: cid:image002.jpg@01D1EFDE.8C95F0F0]
*Equation of time graph:** The red curve indicates the 'equation of
time' throughout the year. When the red line is below the mid-line
(0.00), the Sun has not yet reached the meridian at noon. When the red
line is above the mid-line (0.00), the Sun reached the meridian
before noon. When the red line is on the mid-line, the equation of time is
0. For instance, on Feb 11, the equation of time is at a local minimum of
approximately 14 minutes. Atnoon on Feb 11, the Sun was east of the
merdidian. Upper culmination actually occurs at 12:14 p.m.
On September 1, the equation of time is 0. *
*Now that we've lost our audience….*
*THURSDAY, SEPTEMBER 1: NEW MOON (ANNULAR ECLIPSE OF THE SUN….THOUGH NOT
HERE.)*
The proper term for new moon is "conjunction." The moon passes between the
Sun and Earth today and, in so doing, initiatives lunation cycle 1159.
The real news, however, is that today some skywatchers will behold an
annular solar eclipse. A solar eclipse occurs when the moon moves directly
between Earth and the Sun. These eclipses can be partial, when only part
of the moon blocks the Sun, or total, when the moon entirely blocks the
Sun. Another type is "annular," which happens when the moon is at or
near apogee, its point of greatest distance, at the same time as
conjunction. (This month, the moon is at apogee on Sept 6). At this
time, the moon does not appear as large as the Sun in our sky and therefore
the former doesn't completely block the latter. The word "annular"
derives from the Greek term "annulus," meaning "ring.' During totality
-when the entire moon is seen in front of the Sun- a ring of light remains
visible around the dark moon.
[image: cid:image005.png@01D1EFDE.8C95F0F0]
*Annular Eclipse.** During an annular solar eclipse, a 'ring of fire'
remains visible around the moon during totality as seen in this photograph
by Jay Pasachoff.*
Unlike lunar eclipses that are visible wherever the moon is above the
horizon, total and annular eclipses are visible only along a small strip
dubbed the "totality path." This path traverses the Atlantic Ocean,
sub-saharan Africa, Madagascar and the South Pacific. Any observer
within this path will see the annular solar eclipse. The greatest
eclipse occurs in southern Tanzania (and, wonderfully, some intrepid
tourists are participating in a annular eclipse safari in that country:
http://www.betchartexpeditions.com/pdf_files/tanzania_wildli
fe_safari_2016a.pdf ). Observers within regions north and south of this
totality path will observe a partial solar eclipse, the magnitude of which
decreases with increasing distance from the path. See map below.
[image: cid:image009.jpg@01D1EFDE.8C95F0F0]
*Eclipse map.** This map shows the totality path for the September 2016
annular solar eclipse. Observers within the totality path, here marked by
the deep red path, will see the annular solar eclipse. This path crosses
through a few African countriesm, including Gabon, the Democratic Republic
of the Congo, Tanzania (which contains the point of maximum eclipse),
Mozambique and Madagascar. Observers outside this totality path, but
within the grid region, will observe a partial solar eclipse. The
magnitude of the eclipse (the amount of the Sun blocked) decreases with
increasing distance from the totality path. [Note: the "sub-solar"
point, located in Northern Ethiopia close the Somali border, indicates the
position on Earth where the Sun occupies the zenith at the moment of
greatest eclipse.]*
If you're dissapointed that we won't see the annular eclipse, take solace
from knowing that we will observe a partial solar eclipse onAugust 21,
2017. (This event has already been billed as the "Great American Eclipse,"
so we will definitely hear much more about it.) And, wow…now we've gone
through one entire day!
*FRIDAY, SEPTEMBER 2, 2016: NEPTUNE AT OPPOSITION*
What is "opposition?" Simply, the configuration in which a planet appears
to be in the opposite part of the sky relative to the Sun. Opposition
occurs when Earth passes between that planet and the Sun. The only planets
that can ever be in opposition are the superior planets, those at a greater
distance from the Sun than Earth. (Mars, Jupiter, Saturn, Uranus, Neptune
and Pluto.) A planet is generally at its brightest when at opposition as
it will also be at its least distance from Earth during, or just before or
after, opposition. Neptune is at its brightest of the year, but, at a
magnitude of 7.8, it will be five times fainter than the dimmest naked eye
stars. Even skywatchers gifted with keen eyesight won't be able to
observe Neptune at its maximum brightness.
*FRIDAY, SEPTEMBER 2, 2016: MOON 5.7 DEGREES NNE OF MERCURY*
The waxing crescent moon and the small planet are both only about 17
degrees from the Sun in the western evening sky. Mercury will soon vanish
into the dusk, but tonight one can find it "below" the crescent moon. Be
sure to venture outside soon after sunset to find this thin sliver moon and
planet. Don't be distraught if you can't find them, as they'll be quite
close to the setting Sun.
*FRIDAY, SEPTEMBER 2, 2016: MOON 0.36 DEGREES NNE OF JUPITER (BRONZE
EVENT!)*
We might just barely see the moon and Jupiter close together in the western
evening sky. This event will be an occultation, meaning that from some
perspectives -mainly, the Pacific coast of the US and through parts of
Mexico, the moon will appear to move directly in fron the Jupiter. This
occultation will occur during the day, but since Jupiter is so bright, some
observers will be able to see this occultation, anyway.
*SATURDAY, SEPTEMBER 3, 2016: MOON 1.1 DEGREES OF VENUS (SILVER EVENT!!)*
The moon will be easier to see today than it was yesterday, as it will be
5% illuminated. See this waxing crescent moon close to the brightest
planet in the western evening sky. This evening will provide us with a
splendid opportunity to see the night sky's two brightest objects close
together.
*TUESDAY, SEPTEMBER 6, 2016: MOON AT APOGEE (DISTANCE 63.51 EARTH RADII)*
As is true with all the planets, the moon's orbit is elliptical. As the
moon travels around Earth, its distance from the planet is always
changing. (If the moon's orbit were perfectly circular, its distance
would be constant.) Each lunar orbit contains a point of greatest
distance, called "apogee," and a point of least distance, called
"perigee." It is true that when the moon is at apogee it appears
smaller than it does at perigee, but the difference isn't significant
because the moon's perigee distance is approximately 89% of the apogee
distance. (This value varies somewhat as the apogee and perigee distances
are also variable.
[image: cid:image005.jpg@01D1F001.C3263670]
*Apogee and Perigee:* *This image shows a full moon at apogee (to the
left) and another full moon at perigee (to the right). We can clearly see
that the size difference is readily apparent, but not great. The perigee
full moon will be about 14% larger and 30% brighter than the apogee full
moon. However, it would be difficult to notice much of a difference in
the real sky because we cannot see an apogee full moon and perigee full
moon simultaneously. (Images by www.moonconnection.com
<http://www.moonconnection.com/>)*
Astronomers use the term "Earth Radii" to measure the moon's distance from
Earth. One Earth radius equals 6,371 km (3,959 miles). The moon is
approximately 404,622 km (251,436 miles) away at the precise moment of
aphelion.
As the moon is at apogee just prior to reaching first quardrature (the
first quarter point), one won't notice much of a difference at all.
However, September 1st's solar eclipse was annular because the moon was
approaching apogee on this date. (See September 1st.)
*THURSDAY, SEPTEMBER 8, 2016: MOON 3.8 DEGREES NORTH OF SATURN*
The moon will be 42% illuminated on this date and will appear to loom high
above Saturn. One will observe both worlds together in the southwestern
evening sky. Both the moon and Saturn will set before midnight. We
often cite these degree measurements, but rarely ever discuss how one can
gauge these angular distances. One can use hands and fingers to
approximate such distances, as we can see from the graphic below.
[image: cid:image009.jpg@01D1F001.C3263670]
*Degree measurement:** One can approximate angular separation with just
one's hand. In all the five examples shown above, the arm is full extended
outward. The distance separating the pinky and thumb when stretched apart
to their greatest extent is about 25 degrees (# 1). When drawn in so as
to be nearly parallel, the pinky and index finger cover about 15 degrees (#
2). A closed fist equals about ten degrees (# 3). Three fingers held
together and upright covers about 5 degrees (# 4) and a pinky tip is 1.5
degrees (# 5). Image courtesy of the York County Astronomical Society.
[Note: York County, PA, not Maine.]*
*FRIDAY, SEPTEMBER 9, 2016: FIRST QUARTER MOON*
*FRIDAY, SEPTEMBER 9, 2016: MOON 7.9 DEGREES NORTH OF MARS*
One can almost shove a fist between the moon and Mars tonight. As the
moon is at first quarter (50% illuminated), it will certainly not obscure
the crimson world poised well below it. The moon and Mars appear as
though they're within arm's reach because the night sky does not reveal
depth. In fact, Mars is about 470 times farther from Earth than the moon.
If the moon were an inch away, Mars would be 39 feet from us!
*Stephen Hawking