SkyShot - Volume 1, Issue 1: Autumn 2020

SkyShot Autumn 2020
Astronomical
Sightseeing in
2020
Abby Kinney
Mars at its Best
This autumn has been a great time to view Mars. On October
13th, the planet reached opposition, meaning it appeared opposite
the Sun in the sky, reaching its highest point in the sky at
midnight.
However, Mars was a spectacular sight earlier this season as
well. Mars dramatically increased brightness, eventually surpassing
Jupiter’s brightness on September 24th, and reached a magnitude
of -2.6 at opposition. Additionally, the apparent size of
Mars’ disk was approximately 22 arcseconds [2].
Perhaps you’re reading this in disappointment remembering
the last Mars opposition in 2018 when Mars reached a magnitude
of -2.8 and disk size of about 24 arcseconds [1].
But for Northern Hemisphere observers this 2020 opposition
had something else going for it: Mars’s altitude in the sky was
much higher. In 2018, Mars appeared in the constellation of Capricornus.
But this year, Mars appeared in Pisces, which is further
North in the sky [2].
Whether you were viewing the red planet with your eyes, binoculars,
or telescopes, it fulfilled its promise of being a breathtaking
fall sight.
Source: EarthSky Community Photos.
Citations
[1] Dickinson, David. “Enter the Red Planet: Our Guide to
Mars Opposition 2018.” Universe Today, 18 July 2018, www.universetoday.com/139420/enter-the-red-planet-our-guide-to-marsopposition-2018/.
[2] Lawrence, Pete. “Mars Opposition 2020: Get Ready to Observe
the Red Planet.” Skyatnightmagazine, 24 Aug. 2020, www.
skyatnightmagazine.com/advice/skills/how-to-observe-mars/.
[3] Pasachoff, Jay M. Stars and Planets. Houghton Mifflin, 2000.
Halloween’s Blue Moon
Everyone’s heard the phrase “once in a blue moon,” but
this Halloween, we had a chance to see such a moon. However,
the term “blue moon” is actually quite misleading.
First, blue moons are not necessarily blue. Rather than indicating
a color, a “blue” moon usually refers to the second
full moon of a calendar month [1].
But this now-common definition was actually a mistake
created by the misinterpretation of the Maine Farmer’s Almanac
in a 1946 Sky and Telescope article titled “Once in a
Blue Moon.” The mistake was then popularized by a reading
of this article on the radio program StarDate. Eventually,
this new definition even found its way into the popular
game Trivial Pursuit [2].
The Maine Farmer’s Almanac defined a “blue moon” as
the third full moon of a season with four full moons. This
may seem like a distinction without a difference, but if we
look at this Halloween blue moon, it was actually the second
full moon of Autumn. Thus, by the almanac’s definition,
it would not be a full moon. In fact, the next seasonal
blue moon is in August of 2021, despite that month having
only one full moon.
In addition to lacking their eponymous blue hue, blue
moons are not as uncommon as the ubiquitous phrase
would suggest. Because most calendar months are longer
than the moon’s approximately 29.5 day synodic period
(the period of its phases), a blue moon can occur if the first
full moon was sufficiently early in the month. Thus, a blue
moon typically happens every two to three years and will always
occur on either the 30th or 31st [1]. While blue moons
in general are fairly common, a blue moon on Halloween is
more special: the last blue moon to fall on October 31st was
in 1974, and it won’t happen again until 2039 [4].
In light of the surprising frequency of blue moons, you
may be wondering how the common refrain “once in a blue
moon” came to indicate something rarely occurring; however,
the refrain actually predates our modern usage. It was
used to indicate something that was as absurd as the Moon
turning blue. Over time, the phrase came to mean something
similar to never or very rarely [2].
But the moon can actually appear bluish. While the light
from the moon is reflected from the Sun and, therefore,
virtually identical to daylight, atmospheric conditions can
change the appearance of the moon [3]. For instance, after
the eruption of the volcano Krakatoa in 1883, volcanic ash
in the air was the perfect size to scatter the redder colors of
the moonlight, giving the moon a bluer tint [1].
So whether you were handing out candy or trick-ortreating
yourself this year, that not-so-blue blue moon was
definitely worth looking at.
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