by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:14 a.m. CDT; Sunset, 7:28 p.m. CDT. Check local sources for sunrise and sunset times. Times are calculated by the US Naval Observatory’s MICA computer program.
The five-planet morning parade continues with Venus, Jupiter, and Saturn easily visible. Uranus is easy to locate through a binocular between Jupiter and the Pleiades star cluster. The challenging view, even through a binocular, is locating Neptune in a dim Pisces starfield, over 20° to the upper left of Saturn. For sky watchers interested in seeing the two more distant planets, see the directions in the August 27th article.
This evening, the moon reaches the Full moon phase at 8:36 p.m. CDT. This is the second Full moon during this calendar month, commonly named a “Blue” moon. Over time, each seasonal Full moon has been given descriptive names. July’s moon was the Buck moon. August 1st’s moon was the Sturgeon moon. The Harvest Moon occurs closest to the autumnal equinox. The Hunter’s moon follows during October. When the month has a second Full moon, there is no name for it and recently has been named “Blue.”
Usually, an astronomical season (solstice to equinox or equinox to solstice) has three full moons. During some years, a season has four Full moons. Following the traditions of naming a full moon after nature’s events in a season, there was no name for the extra Full moon. It was named “Bue.” An article in Sky & Telescope magazine traced the origins of the term to the Maine Farmers Almanac in the 1930s. The Blue moon name has been expanded over time to indicate the second full moon in a calendar month, a mistake by Sky & Telescope, when the color term was applied to the second Full moon in a month. The error has caught on in popular culture.
This year, the summer season has three Full moons (July 3, August 1, and tonight), but this third Full moon has no seasonal name. Autumn has three Full moons (September 29, October 28, and November 27).
Tonight’s Full moon occurs when the lunar orb is closest to Earth, perigee. This near point is about 14% closer to Earth than average, appearing slightly larger and brighter. This occurs about three times each year. This perigean moon has been named “supermoon” in the popular lingo. Newscasts and smartphones news feeds are filled with images of an unusually large full moon rising behind some wonderous landmark.
We applaud the news media’s interest in astronomical events, but likely the casual observer sees nothing larger or brighter than a typical Full moon. The next Blue moon occurs May 31, 2026.
One other note to consider, with February’s truncated length, every nineteen years it does not have a Full moon. This occurs during 2037. That’s one rare event that could be described as “once in a blue moon.”
Step outside this evening to spot the bright full moon – likely termed a “Blue Super Moon” or “Super Blue Moon” – near Saturn.
Here is today’s planet forecast:
Brilliant Venus careens into the morning sky after inferior conjunction that occurred before mid-month. This morning an hour before daybreak, the Morning Star is nearly 10° above the eastern horizon. It rises six to seven minutes earlier each morning compared to sunrise.
Through a telescope, Venus shows a crescent that is 10% illuminated. The cusps or horns point away from the sun, like a waning crescent moon, but the planet’s phase is known as a morning crescent.
Notice Sirius, slightly higher than Venus, above the southeast horizon. The Dog Star is far from the ecliptic – the plane of the solar system where the moon and planets move – so there is no conjunction. Beginning about September 10th and through early October, the night’s brightest star and brightest planet are about the same altitude – height above the horizon – in the eastern sky.
The star Procyon is higher in the eastern sky, above an imaginary line from Venus to Sirius.
Bright Jupiter, nearly 90° to the upper right of Venus, is high in the southern sky, slightly west of the south cardinal point. Each morning the planet is slightly lower and farther westward at this time interval.
The Jovian Giant is moving eastward in front of Aries, 13.5° to the lower left of Hamal, the constellation’s brightest star, and nearly 16° to the lower right of the Pleiades star cluster, part of Taurus.
Jupiter begins the illusion of retrograde next month. It then appears to move westward compared to the distant stars. This is from Earth overtaking Jupiter.
For late nighters, Jupiter’s Great Red Spot is at the center of the planet in the southern hemisphere through a telescope at 12:47 a.m. CDT.
Saturn is low in the west-southwest, over 157° from Venus and over 70° to the lower right (west) of Jupiter. The Ringed Wonder is retrograding in front of Aquarius, 8.5° to the lower right of Skat and 8.4° to the lower right of Lambda Aquarii (λ Aqr on the chart). Together the trio nearly makes an equilateral triangle.
For some sky watchers the moon is below Saturn, immediately above the horizon, depending on the obstructions in that direction.
Mercury and Mars are not easily visible. Mercury is nearing inferior conjunction, between Earth and the sun, next month, setting less than five minutes after the sun this evening.
Mars is dimmer than might be expected and it is awash in evening twilight, setting about an hour after sundown.
An hour after sundown, that Blue Supermoon is low in the east-southeast, 5.1° to the lower left of Saturn. Watch them move westward during the night.
Jupiter rises nearly three hours after sundown. As the calendar day ends, find it in the eastern sky.
- 2023, October 20: Jupiter’s Double Shadows, Mercury at Superior ConjunctionOctober 20: After midnight, Jupiter’s moons’ shadows dance across the cloud tops. Mercury is at superior conjunction.
- 2023, October 19: Poured Moon, See Planet UranusOctober 19: Sagittarius seems to pour the moon into the sky this evening. Find Uranus with a binocular.
- 2023, October 18: Moon-Antares Conjunction, Bright PlanetsOctober 18, 2023: The moon is near Antares after sunset. Venus, Jupiter, and Saturn are in the sky during the nighttime hours.
- 2023, October 17: Scorpion MoonOctober 17, 2023: The crescent moon is with Scorpius during evening twilight. Venus and Jupiter gleam from the predawn sky.
- 2023, October 16: Venus in Starry ConjunctionOctober 16, 2023: Venus passes a star in Leo before sunrise. A crescent moon is low in the western sky during evening twilight.