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Rare celestial display as full moon, northern lights both visible in night sky

  • A view from the Mount Washington Observatory shows the green of the northern lights alongside a full moon on Sunday evening. Ryan Knapp / Mount Washington Observatory



Monitor staff
Wednesday, August 29, 2018

Seeing unusual sights is pretty routine on top of Mount Washington, but the sight on Sunday was particularly rare: The northern lights at the same time as a full moon.

It’s unusual for the aurora borealis, the scientific name for the northern lights, to be visible as far south as New Hampshire. What made this sighting rare was the fact that light of a full moon usually overwhelms just about everything else in the night sky.

To have the green of the Northern Lights visible even past the lunar glow was so unusual that observer Ryan Knapp reported on the Mount Washington Observatory’s Instagram feed that he has seen it only once before in more than a decade of nighttime observations around the region.

The northern lights are caused when charged particles from the sun interact with molecules in the upper atmosphere. Green is the most common color, occurring when they interact with oxygen, but the lights can be red, blue or even white if conditions are correct.

They happen around the planet’s two poles – there are also southern lights – because the planet’s magnetic field channels the charged particles to our northern and southern extremities, similar to the way iron filings are attracted to the two ends of a bar magnet.

There’s no data kept about how often the northern lights are visible in New Hampshire, but they are likely to become rare in the new few years because the sun is entering the quiet phase of a roughly 11-year solar cycle, during which the amount of particle and radiation that it emits fluctuates greatly.