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:  2457665.16

              "!yad sdrawkcab yppaH"

First full week of October: the month that ends the year for some and begins the holiday season for others. October is the month during which the summer-lovers who are mired in the denial's enveloping depths are wrested back into reality's chilled breezes.     We proceed despite the sudden onset of reality.   This week's night sky calendar turns out to be wholly moon based, as we watch the waxing crescent moon swing by some planets in the western evening sky.    Of course, we'll include the planet watch section and  we'll also visit the catacombs of infinite knowledge.      

Note: a few subscriber's asked us to give out medals again, as we  did when we posted the monthly sky calendars.  For those who are now scratching their heads, we once assigned medals -Bronze, Silver, Gold and on rare occasions Platinum- to the events we deemed the most important.  We conferred the gold (or occasionally platinum) onto the event we considered the true highlight.   The second most important received silver, the third most important, bronze.     We abandoned this scheme in September, but will now re-introduce it in October.   That announcement brings us neatly to this week's first event:

MONDAY, OCTOBER 3:   MOON 4.9 DEGREES NNE OF VENUS   (SILVER EVENT!!)

The thin crescent moon lingers close to Venus in the western evening sky.   This coupling is always one of the most beautiful night sky sights.    We see a brilliant planet next to a crescent moon.  Venus is a crescent, too, even though we can't see the crescent with just the unaided eye.  (See "From the Catacombs of Infinite Knowledge.")       The moon will be 7% illuminated tonight and will set just before 8:00 p.m.

Tonight, we'll see the larger crescent moon just north of Saturn, the sixth planet from the Sun.   The moon will be 27% illuminated and will set before 10:00 p.m.       One might wonder why the moon tends to veer close to planets as it moves through the sky.    The reason is simple.  The planets and the moon both travel within a band centered on the "ecliptic," the Sun's apparent annual path through the sky.     These worlds are restricted to this region because the solar system is disc-shaped and will remain very close to its "invariable plane."    A planet can move below or above the ecliptic by a certain number of degrees determined by its inclination relative to the ecliptic.  (For instance,  Saturn's inclination is approximately 2.5 degrees, so it can be as much as 2.5 degrees south or 2.5 degrees north of the ecliptic.)  The moon has a slightly greater degree of freedom, as its inclination is approximately 5 degrees.  

The Ecliptic Band.  The planets and moon travel along a band centered on the ecliptic, the Sun's apparent annual path through the sky.     The moon's inclination relative to the ecliptic is about 5 degrees, so it doesn’t' stray far from it.  The planets also travel close to the ecliptic because the solar system is disc shaped and the planets move close to the solar system's "plane."  Image by Astrobob  [IMPORTANT: this chart does not show the current configuration of planets!]

The third lunar-planet encounter of the week brings the moon close to Mars.    One can easily mistake tonight's crescent moon for the quarter moon, as it will be 45% illuminated.    This week the moon will prove a helpful guide to finding Mars and Saturn, which are almost equally bright and much dimmer than Venus!

SUNDAY, OCTOBER 9:  FIRST QUARTER MOON

PLANET WATCH

MERCURY  (Host constellation:  Virgo)

Mercury is only visible early in October and then vanishes for the rest of the month.  Even when visible, Mercury is low in the pre-dawn eastern sky.     Mercury passes into superior solar conjunction on October 27th and won't return to the evening sky until late November.   VERDICT:  Even by Mercury's standards, it is not an easy planet to find this month.  If you must try, do so at the very beginning of October.   Otherwise, wait until around Thanksgiving.  Yes, it will be that long of a wait.

VENUS   (Host constellation: Libra/Scorpius)  PICK PLANET!

Venus gets the crown again because it is so bright, even if it doesn't remain in the western evening sky for long.      Venus brightens only slightly throughout the month, but, as always, is brighter than any night sky star.  VERDICT:  It will be easy to find Venus provided you venture outside in the early evening.  Look to the west and see the brilliant Venus.   Best day to look this week will be October 3, when Venus will be close to the moon

MARS (Host constellation:   Sagittarius)

Though it is not as bright as Venus, Mars is easy to find in the western evening sky.  Interesting note:  Mars will be setting around 9:30 p.m. each night throughout the month.  This equivalence occurs because of the way Earth and Mars are moving relative to each other at the moment.   VERDICT:   Seek out the red world in the evening this month.    It will remain above the horizon for a couple hours after sunset.

JUPITER (Host constellation:  Virgo)

After a month-long hiatus, Jupiter retrurns to the early morning eastern sky.   Consider this to be a perfect "changing of the guard."  As Mercury vanishes in the pre-dawn twilight, Jupiter emerges.     Though not as bright as Venus, Jupiter shines brighter than any night sky star. VERDICT:  If you've dearly missed Jupiter, just venture outside to find it starting mid-month.  Jupiter will brighten throughout the rest of 2016 as it rises earlier each morning.

SATURN  (Host constellation:  Libra)

We'll lose Saturn next month.      In October, Saturn lurks low in the southwestern evening sky.   It is still a moderately bright planet and will be easy to find, at least early in October.   VERDICT:   Seek out Saturn at month's beginning just after dark.     Still a beautiful world, particularly through a telescope.   Although we lose Saturn in November, we'll regain it in late December. 

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FROM THE CATACOMBS OF INFINITE KNOWLEDGE

"Phases of Venus"

Have you ever observed Venus through a telescope?   If not, it might be surprising to know that when viewed telescopically, Venus will most likely appear as a crescent or, on occasion, as a quarter.    Venus exhibits a phase cycle, just as the moon does.  However, we'll never see a "full Venus," because the planet can never be farther from the Sun than Earth.

Phases of Venus:   Venus exhibits a phase cycle similar

to that of the moon.    However, we'll never see a "Full Venus"

because it will never be farther from the Sun than Earth.

Image:  T. Lombry

Venus and Mercury both have a phase cycle because they are both inferior planets, or closer to the Sun than Earth.     Unlike Venus, Mercury will never appear as quarter, but will always be a crescent as it can never be farther than 28 degrees from the Sun in our sky.

Galileo's observation of the crescent Venus lend credence to his belief that the Sun, not Earth, occupied the center of the solar system.      Were Venus to have revolved around Earth, it would have appeared full every so often.     It never did. 

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From a hidden chest within the catacombs of infinite knowledge

The term for a quarter Venus is the very catchy

Theoretical Dichotomy

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