August 17-21, 2024: The bright blue Sturgeon moon, August’s Full moon, shows the track of September’s Harvest Moon.
by Jeffrey L. Hunt
Sturgeon Moon
During mid-August the bright moon appears farther eastward each night. It reaches the Full moon phase on August 19th at 1:26 p.m. Central Time, also known as the Sturgeon moon.
This bright moon is a rare blue moon. Usually, three Full moons occur during each season. This year the season has four: June 21, Strawberry; July 21, Buck; August 19, Sturgeon; and September 17, Harvest. Four Full moons during the summer season, but each as a seasonal name, tabulated by the Farmer’s Almanac.
In many cases the third moon, in a four Full moon season sequence, is the second bright moon in a calendar month. For example, during August 2023, two Full moons occurred, on the 1st – the second bright moon of the season – and then again on the 31st – the third moon. The seasonal Sturgeon name was assigned to the first bright moon and no name was available for the second one during August. September’s Harvest moon occurred on the 29th, after the equinox to begin astronomical autumn. The closest Full moon to the autumnal equinox is defined to be the Harvest moon, so this limitation left no seasonal name for the moon on August 31st.
Blue Moon
An article in Sky & Telescope magazine traced the origins of the blue moon name 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. The error has caught on in popular culture.
Confused? So, while this does not fit today’s notion of the second bright moon in the month, it fits the 1930s definition of the third seasonal moon, but this one has a name – Sturgeon – a Blue Sturgeon moon.
Next month’s Harvest moon occurs closest to the autumnal equinox. Traditionally, it provided extra light during the harvest season for lengthy work in the fields. The extra light is from the bright moon, but it is prolonged because of the angle the ecliptic – the solar system’s plane – makes with the eastern horizon.
While the moon moves about 13° eastward compared to the background stars, its height above the horizon, known as the altitude changes only a few degrees each evening. The moon is farther eastward compared to the horizon, but it is not much lower.
Note the moon’s altitude as it moves eastward through the Full moon phase. This month’s eastward-hopping moon is a preview of next month’s classic Harvest moon and harvest moon effect.
During the week, it passes Saturn as the Ringed Wonder appears higher in the sky earlier each evening.
Lunar Events
Here’s what to look for two hours after sunset.
- August 17: In front of Capricornus, the moon, 96% illuminated, is about 20° above the south-southeast horizon.
- August 18: Over 15° above the southeast horizon, the lunar orb, 99% illuminated, is 6.5° to the lower right of Deneb Algedi, Capricornus’ tail. In this moonlight, use a binocular to see the star.
- August 19: The moon is Full at 1:26 p.m. Central Time, when it is below the horizon in the Americas. It rises about 10 minutes before sunset. At two hours after nightfall, the Blue Sturgeon moon is less than 15° above the southeast horizon. It is about one-third of the way from Deneb Algedi to Saturn. Tonight, the Ringed Wonder rises 50 minutes after sunset.
- August 20: The bright moon, 97% illuminated, is near Saturn. It is 0.6° below the Ringed Wonder. From Europe, northern Africa, and northern South America, the moon occults or eclipses Saturn.
- August 21: The moon, 92% illuminated, is over 5° above the eastern horizon. Look for the moon tomorrow morning.
Regardless of the name of this month’s bright moon, step outside during the early evening to see it preview the harvest moon effect.
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