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: 2457687.16
"Cubs in the series?!?
*THE DAILY ASTRONOMER*
* Monday, October 24, 2016 Week 8 Night Sky Calendar October 23 - 29, 2016*
We have a lot of ground to cover and a lot of sky to see, so this week
we'll dispense with our usual gratuitous preface and proceed headlong into
our weekly night sky calendar!
*TUESDAY, OCTOBER 25: MOON 1.5 DEGREES SSW OF REGULUS *Regulus is the
brightest star in Leo the Lion. This "little king" star represents the
lion's heart and marks the southern point on its "sickle" asterism.
Tonight, one will find the waning crescent moon hovering just to the
south of Regulus. The moon rises at 2:00 a.m. tonight and will be 22%
illuminated. As the moon is not particularly bright at this illumination,
one will easily be able to observe the moon and this bright star.
*Leo the Lion. **A late winter/early spring constellation, Leo the
Lion rises after midnight this time of year and remains in the eastern sky
until dawn. The image above -courtesy of space.com- shows an outline of
the lion. Regulus marks the southern tip of the lion's The waning
crescent moon will appear to pass just south of Regulus on October 25th.*
*WEDNESDAY, OCTOBER 26: VENUS 3.1o N of ANTARES *Even though Antares is
the brightest star in Scorpius the Scorpion, Venus will be 100 times
brighter than Antares during this apparent close approach. (For more
information about calculating this brightness difference, please refer to
"From the Catacombs of Infinite Knowledge.") This planet and star are
low in the southwestern sky and will set by 7:00 p.m.
*THURSDAY, OCTOBER 27: MERCURY AT SUPERIOR CONJUNCTION *We bandy about the
term "conjunction" almost as often as we plague the world with the term
"light year." Of course, we make matters worse by dividing conjunction
into both "inferior conjunction" and "superior conjunction." Today, we
decided to discuss these conjunctions in greater detail. A planet is at
"superior" conjunction when it is on the far side of the Sun relative to
Earth. Both inferior planets (Mercury and Venus) and superior planets
(those farther away from the Sun than Earth) can be in superior
conjunction. Refer to the image below.
A planet is at "inferior" conjunction when it is between Earth and the
Sun. Only the two inferior planets can ever be at inferior conjunction.
*A solar system configuration diagram. ** A planet is passing through
"superior conjunction" when it passes on the other side of the Sun relative
to Earth. A planet passes through "inferior conjunction" when it moves
between Earth and the Sun. While both inferior and superior planets can be
in "superior conjunction, only inferior planets can be in inferior
conjunction. Image by Planetfacts.org*
*FRIDAY, OCTOBER 28: MOON 1.4 DEGREES NNE OF JUPITER *The moon and
Jupiter will be low in the eastern pre-dawn sky tonight. The waning
crescent moon will only be 4% illuminated and will rise by 5:00 a.m, which
is slightly more than two hours before sunrise and an hour and a half
before the onset of civil twilight. If you haven't yet had the chance to
find Jupiter after its return, this morning you'll have no trouble finding
it as it will appear so close to the crescent moon.
*SATURDAY, OCTOBER 29: MARS AT PERIHELION *Planetary orbits are not
perfect circles. Instead, they are ellipses, or more like ovals.
Consequently, a planet's distance from the Sun changes constantly as it
revolves around it. The minimum distance separating a planet and the Sun
is called "perihelion." The greatest distance is known as "aphelion."
Today, Mars reaches perihelion and will be 114.9 million miles from
the Sun. When at aphelion, Mars will be about 154 million miles from
the Sun. This 40 million mile difference between perihelion and aphelion
is far greater than Earth, the heliocentric distance of which veers from a
perihelion value of 91.5 million miles to an aphelion value of 94.5 million
miles. Mars' distance varies so much more because its orbit is more
elongated than Earth's.
*SATURDAY, OCTOBER 29: VENUS 3.0o S of SATURN (GOLD EVENT!!!) *The
brightest naked eye planet (Venus) appears close to the dimmest naked eye
planet (Saturn). Distinguishing between these two worlds therefore won't
prove difficult, as Venus will be 69 times brighter than Saturn. (Refer to
"From the Catacombs of Infinite Knowledge" if you want to know how we
arrived at this outrageous value.) Both planets will set by 7:00 p.m.
PLANET WATCH
MERCURY (Host constellation: Virgo) . *Mercury is now gone!*
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 Saturday, October 29, when
Venus will appear close to Saturn.
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. Best day to find Saturn will be October
29th, when it will appear close to Venus in the southwestern early evening
sky.
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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
*"Calculating the brightness difference between two celestial objects"*
Astronomers use the magnitude scale to measure the brightness of any given
celestial object. Devised by Hipparchus of Nicaea (190-120 BCE), this
system assigns a number to a given object based on its brightness. The
brighter the object, the lower the number, which seems a bit
counterintuitive. For instance, a star of magnitude 1.0 is about 2.5
times brighter than a star of magnitude 2. A star of magnitude 1.0 is
2.5 x 2.5 = 6.25 times brighter than a star of magnitude 3.0.
Calculating the brightness difference between stars of whole number
magnitude is relatively straightforward. For instance, on Wednesday,
Oct 26, Venus will be at magnitude -4.0 and Antares is at magnitude
1.0. Venus is therefore 5.0 magnitudes brighter than Antares, or 100
times brighter!
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REMEMBER THAT DIMLY LIT WALL ETCHING?
The actual factor between magnitudes is closer to 2.512, which is a fifth
root of 100.
Therefore, a star -or planet- that is five magnitudes brighter than another
star or planet will be precisely 100 times brighter!
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However, how would one calculate the brightness difference between
celestial objects if the magnitudes are not neat whole numbers? For
instance, on Saturday, Oct 29, Venus will appear close to Saturn. Venus
will still be at magnitude -4.0. but Saturn's magnitude is 0.6. What
is the brightness difference?
We use the following formula
and we'll work through the Venus-Saturn example.
Venus' magnitude is -4.0.
Saturn's magnitude is 0.6
The absolute difference between these two values is 4.6.
We raise 2.5118…(the fifth root of 100) to 4.6 and yield 69.1 or 69.
Venus will be 69 times brighter than Saturn during their appulse on
Saturday, October 29.
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