Astro Bob: A Strawberry Aurora Moon?
Tuesday night's full moon reminds us it's strawberry season. There's also a chance for auroras the next few nights.
It was a month ago we watched the moon fade to an orange husk as it passed into Earth's shadow in eclipse. June's Strawberry Moon dips south of the shadow tonight (June 14) and escapes eclipse. Instead, we'll enjoy the sight of a classic, brilliant full moon, one that reminds us to start checking the woods and fields for wild strawberries.
The moon performs this cosmic limbo dance because its orbit is tipped 5.1° relative to Earth's. Twice a month its path intersects our planet's path — like two people on different trails meeting at an intersection. If the moon happens to be full at that time it will proceed into Earth's shadow, which falls directly behind the planet in the plane of its orbit (see above).
At most full moons, the moon lies above or below the shadow and in the clear. That makes eclipses a bit uncommon, with typically 2-3 per year. The next one takes place during the early morning hours of Nov. 8 and will be widely visible across the Americas.
The moment of full moon happened at 6:51 a.m. CDT Tuesday morning. When it returns tonight, the moon will be more than 14 hours past full, so instead of rising close to sunset, it will spill over the horizon during evening twilight. That's a good thing because a later-rising full or nearly full moon appears brighter and more dramatic in a darker sky.
Full moon is hardly the best time to watch the northern lights, but I feel duty-bound to tell you that a recent flare from a quickly growing sunspot group named AR 3032 blasted out an M3 (moderately powerful) flare early on June 13. The explosion propelled a cloud of protons and electrons from the sun bundled with a magnetic field in our direction. It's expected to arrive overnight June 14-15 and kick off a minor (G1) geomagnetic storm around midnight CDT.
Bright moonlight will greatly compromise the view. You might detect a glow low in the northern sky, but more than likely what you're seeing will be caused by the moon. Denser air near the horizon scatters the moon's light, creating a brighter, whiter "edge" to the sky around the horizon. A camera is usually the best way to detect aurora in moonlight. I'll set mine up on a tripod and make a few exposures to see if any green glow shows.
There's a smaller chance for a moderate (G2) storm. If that happens, sky watchers in the northern states may well see something. Effects from the flare as well as other sun-related causes will rattle Earth's magnetic field for the next few days. With dark, moon-free skies returning as early as Thursday night (June 16), we may well have the chance to see aurora sans moonlight soon.
"Astro" Bob King is a freelance writer for the Duluth News Tribune.