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Waxing toward full Hunter’s Moon

Image above: Jacob Baker of Fall River, Massachusetts calls this image the “Path of the Hunter Moon.” It’s a 16-shot composite of 2016’s Hunter’s Moon, made of photos taken in 10-minute intervals over 2 1/2 hours.

Tonight – October 23, 2018 – the moon is waxing for all of us, around the globe. If you’re in the Northern Hemisphere, it’s waxing toward a full Hunter’s Moon and the second full moon of autumn. If you’re in the Southern Hemisphere, the moon is waxing toward your second full moon of springtime.

The full Hunter’s Moon is the full moon immediately coming after the full Harvest Moon – the closest full moon to the autumn equinox. This year’s full Harvest Moon fell on the night of September 24-25, 2018, a touch more than two days after the September equinox.

For all of us, full moon will come on October 24 at 16:45 (4:45 p.m.) UTC; translate to your time zone. At United States time zones, that places the time of full moon on October 24, 2018, at 12:45 p.m. EDT, 11:45 a.m. CDT, 10:45 a.m. MDT, 9:45 a.m. PDT, 8:45 a.m. AKDT (Alaskan Daylight Time) and 6:45 a.m. HST (Hawaiian Standard Time).

The times don’t really matter. No matter where you live worldwide, look for a full-looking moon in the east as the sun goes down over the next several days. This full or full-looking moon will cross our skies throughout the night, as seen from around the globe.

For us in the Northern Hemisphere, this Hunter’s Moon will be displaying its unique features, characteristic of this time of year. That is, the inclination of our moon’s orbital plane to the celestial equator will cause the moon to rise further north along the eastern horizon for nearly all of the upcoming week. For northerly latitudes in the Northern Hemisphere, these more northerly moonrises reduce the lag time between successive moonrises, which is the legacy of the Hunter’s Moon.

Meanwhile, in the Southern Hemisphere, the opposite is taking place. The more northerly moonrises along the horizon mean a longer-than-average time between successive moonrises, from night to night, over the coming nights.

Tonight’s moon shines fairly close to the planet Uranus on the sky’s dome. That means this faint world will be lost in the glare of the almost-full moon.

On October 23, 2018, the moon is near Uranus on the sky’s dome.

Even on a dark moonless night, Uranus appears – at best – as a faint speck of light to the eye alone. You need exceptional vision to see this distant world without an optical aid, even under the best conditions. Here’s a good sky chart, if you want to see Uranus.

Just be aware Uranus is up there, near this nearly full moon. And think about the fact that Uranus is a real oddity in that it goes around the sun “sideways,” with its rotational axis almost lining up with its orbital plane. In contrast, the rotational axis of our planet Earth is inclined about 23.5o out of perpendicular to our orbital plane.

The orbital planes of Uranus’ major moons pretty much coincide with the planet’s equatorial plane. That’s in spite of the fact that Uranus’ equatorial plane is nearly perpendicular to the plane of its orbit around the sun.

As a general rule, the major moons in our solar system orbit their parent planets above their respective planets’ equators. There are a few exceptions: Saturn’s moon Iapetus, Neptune’s moon Triton – and, perhaps most significantly to us earthlings: Earth’s moon.

Our moon doesn’t orbit the Earth above our planet’s equator (0o latitude). Rather the moon’s orbital plane is inclined to the Earth’s equatorial plane. The moon’s orbital path took the moon from its maximum declination of 20.9o south of the celestial equator on October 15, and then the moon will swing to its maximum declination of 21.3o north of the celestial equator on October 30.

If the moon’s orbital plane – like that of Uranus’ moons – coincided with our planet’s equatorial plane, our moon would always rise due east and set due west – meaning no Hunter’s Moon in autumn. The Hunter’s Moon will come on the night of November 3-4, as the moon is going eastward as well as northward in its orbit.

Uranus and moons

Near-infrared image of the ice giant Uranus , its rings and some of its moons. Image credit: European Southern Observatory

Bottom line: To the eye, the moon will appear nearly full as the sun sets on October 23. Watch for it in the east as soon as the sun goes down. In fact, it has a bit more to go, and full moon is October 24.

Bruce McClure