Shine on, Harvest Moon

By Matthew Johnson

“October” comes from “octo,” the Latin word for eight. It was the eighth month in the first, 10-month Roman calendar, but the name stuck after the calendar expanded to 12 months. On Sept. 22, Earth reached the point in its orbit designated as the autumnal equinox. We transitioned from summer to fall, with our days shortening as the nights lengthen. This trend will continue until December when we experience the longest night of the year: the winter solstice. The lengthening nights and cooler temperatures of fall are advantageous for observing the skies.

During midsummer, the sun sets around 8:30 p.m. and the observer must wait until 9 p.m. for the fully dark skies that are best for discerning faint objects in the heavens, meaning that observing sessions start late and continue into the early hours of the next day. It can be challenging. October is an ideal month for observing. The skies darken around 6:30 p.m., providing an earlier start and the chance to sleep before sunrise. Skies are freer of humidity since cooler temperatures condense much of the atmosphere’s water vapor, enabling crisper images of stars and planets. Even better, October’s nights hold some warmth for the observer but are cool enough so the evenings are mostly insect-free—one’s ankles, wrists and necks are no longer targets for mosquitos and midges.

Planets
Mercury is always close to the sun. It is briefly visible in the southwest just after sunset from Oct.18-28. Look for Venus gleaming in the predawn skies around 6:15 a.m. as the planet rises in the east. Venus will steadily become lower as the month progresses. Mars can only be viewed for 30 minutes or so after the sun sets and is very faint. Jupiter can be found in constellation Gemini rising in the east after midnight and will become higher in the sky during October. Saturn in Aquarius is visible throughout the night, setting in the west before the sun rises around 5:30 a.m.

Uranus can be located with a spotting scope, but Neptune demands a moderate sized telescope. Both can be seen in the east before sunrise. Uranus stands out against the background stars as a light blue-green, appearing as a small circle. Neptune is a darker blue-green, visible as a star-like point.

Meteor Showers
The Draconid meteor shower peaks around Oct. 8 with an estimated four to eight meteors per hour. This will be a difficult shower to see because the brilliance of the almost-full moon will obscure meteor streaks. The object responsible for the particles that we see as the Draconid meteor shower is the periodic comet 21P/Giocobini-Zinner. It circles around the sun before it ventures back, just past Jupiter’s orbit, and returns every 6.6 years. Since the particles are not distributed in a uniform orbit, with much of the particles clustered near the comet itself, it can produce spectacular showers known as “meteor storms” during which hundreds to thousands of meteors can be viewed per hour. This occurred in 1933 and 1946. In 2011, European observers viewed more than 600 meteors per hour.
October’s Orionid meteor shower peaks the night of Oct. 21 with an estimated 10 to 12 meteors per hour, the “zenithal hourly rate.” The new moon (no visible moon) occurs that night, ensuring a dark night to observe meteor trails. The meteors will appear to originate from the constellation Orion, thus the term Orionids. The meteors are the result of the earth’s orbit crossing the regular 76-year path of tiny fragments, most the size of a grain of sand, left behind by Halley’s Comet.

Sun
The sun is expected to continue a high level of activity, with 120 to 150 sunspots predicted for the month. Solar activity is monitored by several satellites with flares and ejections classified as “space weather.” So far, we have been fortunate to have experienced minimal damage to our communications infrastructure and nation’s grid with this high number of possible solar flares and coronal mass ejections. It is possible we will see auroras shimmering and brightening our night sky with pinks and greens generated by ionized oxygen and hydrogen.

Moon Phases
Oct. 6: Full moon, known as the Harvest Moon. Most difficult time to observe the heavens because the moon’s glare obscures details.

Oct. 18: Last quarter (left half illuminated)

Oct. 21: New moon (no visible moon) The few days before and after the new moon are the best time to observe meteor showers and faint objects such as distant galaxies and star clusters.

Oct. 29: First quarter (right half illuminated)

The Harvest Moon has its name because it is the full moon closest to the fall equinox. Traditionally, this moon is said to have provided light well into the night, allowing farmers to harvest crops. This Harvest Moon also marks the start of a three “supermoon” series. Supermoons appear a bit larger and brighter because the full phase occurs when the moon’s orbit comes closest to the earth or a full moon at perigee. This Harvest Moon will rise as the sun sets.