Northern Lights and the Moon: Dark-Sky Windows for 2026-2027

A bright Moon will not stop a big storm, but it can hide the faint glow that most aurora nights in the northern US actually bring. Here are the nights this season when the Moon is out of the way, worked out for three US latitudes.

Why the Moon matters for faint aurora

The aurora does not get dimmer when the Moon is up. The sky around it gets brighter, and your eyes judge the aurora against that background. A soft green arc that looks obvious under a black sky can fade into gray haze once moonlight fills the air.

Auroral scientists rate brightness on the International Brightness Coefficient (IBC) scale, in use since the 1950s. It is a handy way to see the problem:

• IBC I: about as bright as the Milky Way.
• IBC II: like thin cirrus clouds lit by moonlight.
• IBC III: like cumulus clouds lit by moonlight.
• IBC IV: bright enough to light the ground like a full Moon.

Under a full Moon the Milky Way disappears, and so does IBC I aurora. That is the level most displays reach when you watch from Minnesota, Michigan or Washington, near the southern edge of the auroral oval. Classes III and IV still show through moonlight without trouble.

How much a full Moon hides

Measurements of the night sky at observatories, summed up in the moonlight model of Krisciunas and Schaefer (1991), show that a full Moon raises the brightness of the sky by about 3 magnitudes away from the Moon itself. That is roughly 10 to 20 times brighter than a moonless rural sky, depending on where you look and how high the Moon is. Close to the Moon the glare is worse still.

The phase matters more than it seems. A quarter Moon looks half lit, yet it sends us only about one-tenth of the light of a full Moon, because a fully lit Moon reflects light straight back toward us. A thin crescent near the horizon barely counts.

In practice it works out like this:

• Strong storm, Kp 2 or more above what your place needs: the Moon hardly matters. During the May 10, 2024 storm people across the US saw color with a crescent Moon in the evening sky, and the October 10, 2024 storm was seen far south with a first-quarter Moon up in the evening.
• At your threshold: moonlight decides whether you see a faint arc or nothing. This is where dark nights pay off.
• Phone cameras: night mode still picks up aurora under a bright Moon, but the sky turns blue-gray and the green looks washed out.

Dark-sky windows for the 2026-2027 season

We ran every night from September 1, 2026 to April 30, 2027 through Astronomy Engine, the same code behind the forecasts on this site, for three places: 45°N (Minneapolis), 48°N (Minot, North Dakota) and 61°N (Anchorage). The table lists the runs of nights when the Moon stays below the horizon for the whole of 10 pm to 2 am local time, the hours when aurora is most often active. Each row is one lunar month, named by its new Moon (US Eastern date).

Two things stand out. First, latitude barely moves the dates: Minneapolis and Minot share the same windows give or take a night, and Anchorage shifts by a day or two, usually earlier. Second, the windows are generous. At 45°N, 103 of the season's 242 nights have the Moon down from 10 pm to 2 am, and the Moon is below the horizon for 53% of all dark hours.

Full Moon nights are the opposite. On every full Moon of the season, at all three latitudes, the Moon is up for the whole night: zero moon-free dark hours.

The darkest nights, month by month

If you want the Moon down for practically the whole night, not just the core hours, the list gets shorter. These are the nights when the Moon is below the horizon for at least 90% of the dark hours, which means about a week centered on each new Moon:

The length of the night matters too. We count a sky as dark enough for aurora once the Sun is more than 12° below the horizon, the same rule our forecasts use. Here is how many dark hours an average night gives at each latitude:

Anchorage gets the longest dark nights in December and January, more than 14 hours, but by April only about 5 hours remain. For Alaska trips, the September and March windows trade long nights for milder weather; the April window at 61°N is short and late.

One note for March 2027: the equinox on March 20 falls two days before the full Moon of March 22. Activity often rises around the equinoxes, so the dark windows on either side, Feb 27 to Mar 10 and Mar 27 to Apr 7, are the ones to watch.

Half-moon nights: evening and morning windows

Outside the new Moon weeks you still get dark hours, just not all night. The Moon rises about 50 minutes later each night, so the dark part of the night moves:

• Waxing Moon (after new, before full): the Moon is up in the evening and sets later each night. Around first quarter it sets near midnight, leaving the hours after midnight dark. In Minneapolis on November 18, 2026, for example, the Moon sets at 12:10 AM; by November 20 it sets at 2:28 AM.
• Waning Moon (after full, before new): the evening is dark and the Moon rises later each night. In Minneapolis it rises at 7:48 PM on November 27, 2026, about two hours after full darkness, and at 10:29 PM on November 29, close to last quarter.

For a single night at your own place, the moonrise and moonset tool gives the times, and the full Moon calendar shows which dates to avoid if you only care about faint displays.

Pairing the dark window with the Kp forecast

The Moon tells you when the sky will be dark. The Kp index tells you whether there will be anything to see. Use both:

1. Weeks ahead: the 27-day forecast repeats activity from the last solar rotation. If an active stretch lines up with a window in the table above, mark those nights.
2. Days ahead: the 3-day forecast gives the expected Kp in 3-hour blocks. Compare it with what your place needs: about Kp 5 for Minneapolis, Kp 4 for Minot and Kp 2 for Anchorage.
3. On the night: each state page, such as Minnesota, North Dakota or Alaska, shows tonight hour by hour with the Kp, the clouds and a Moon column that reads "down" when it is below the horizon. Watch the live Kp as the night goes on.

A simple rule of thumb: if the forecast only just reaches your threshold, go out on a moon-free night or during the moon-free hours. If it beats your threshold by 2 or more, go regardless of the Moon, put it behind you, and use trees or a building to block the glare.

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