Astro Bob's Astronomy for Everyone

Astro Bob's Astronomy for Everyone For the latest on "what's up in the night sky" please go to duluthnewstribune.com/lifestyle/astro-bob

Moonlight as paint brush Look at how deftly the moon painted the clouds Sunday night (May 31). I was looking somewhere e...
06/01/2026

Moonlight as paint brush

Look at how deftly the moon painted the clouds Sunday night (May 31). I was looking somewhere else, when I turned around to the deeply orange Blue Moon at work.

Attack of the Vegans No, not those vegans. I'm talking about the inhabitants of Vega, one of the brightest stars in the ...
06/01/2026

Attack of the Vegans

No, not those vegans. I'm talking about the inhabitants of Vega, one of the brightest stars in the spring and summer sky. A dense cirrus cloud lit by the moon stationed itself over the bright star for many minutes on Sunday night. The sight reminded me a scene from "War of the Worlds".

Have a Blue Moon weekend! This weekend we'll see our second full moon of the month, popularly known as a Blue Moon. It t...
05/30/2026

Have a Blue Moon weekend!

This weekend we'll see our second full moon of the month, popularly known as a Blue Moon. It takes 29.5 days for moon phases to repeat. Since the last full moon occurred on May 1, there was enough time to squeeze in a second one before month's end. We get a Blue Moon every 2-3 years.

The moment of maximum "fullness" happens Sunday morning, May 31 at 3:45 a.m. Central Daylight Time, so the moon will look full to the eye both Saturday and Sunday nights, May 30 and 31.

It will shine very low in the southern sky in Sagittarius and look golden the entire night especially for observers in the northern U.S., where the moon takes a lower path across the sky. The lower the path, the more air we look through and the more colors are scattered away by air molecules. The cooler hues are preferentially scattered, the reason the moon looks orange.

At moonrise, denser air near the horizon acts like a prism and bends (refracts) the moon's light upward. The densest air hovers just above Earth's surface at the horizon, where the bottom of the moon is. Refraction is so strong here it "pushes" or folds the bottom half into the top, squishing the moon's circular outline into a cigar like you see in the photo. If you could wave a wand and remove the atmosphere the moon would instantly pop back into a circle.

To see these effects, watch the moon rise from a location with an unobstructed horizon. Find your local moonrise time at https://www.timeanddate.com/moon/phases/ In Duluth, Minn. the moon comes up at 8:56 p.m. Saturday night.

Celestial Rorschach testJupiter (left) and Venus and their reflections last night, May 28. The two were 11.5 degrees apa...
05/29/2026

Celestial Rorschach test

Jupiter (left) and Venus and their reflections last night, May 28. The two were 11.5 degrees apart, a little more than a balled fist held at arm's length. Conjunction happens on June 9 when they'll be almost 8 times closer.

Goosing around waiting for aurora Last night the moon was so bright and sky so clear I couldn't resist going outside. Af...
05/28/2026

Goosing around waiting for aurora

Last night the moon was so bright and sky so clear I couldn't resist going outside. After a relaxing moon-walk I drove a few miles to a nearby lake in hopes of seeing the aurora.

Loons called, and two perfectly white swans — tundra or trumpeter, hard to tell — were radiant in the moonlight as they paddled near the shore. Most of my late-night avian companions were geese. They clucked, growled and softly honked a couple hundred feet offshore.

Aurora did arrive, but it was all-of-a-sudden and brief, lasting only about 15 minutes. The camera picked up colors and forms barely visible to my eye. I wondered if the geese and swans were having better luck.

Milky Way's clouds of stars boggle the brain Those billowy clouds in the photo are made of stars, billions of them. Silh...
05/26/2026

Milky Way's clouds of stars boggle the brain

Those billowy clouds in the photo are made of stars, billions of them. Silhouetted against the bright star clouds are dark nebulae composed of silicates, ice, organic compounds and hydrogen. Like clouds blocking sunlight, dust in dark nebulae absorbs the light of more distant stars, creating dark pockets and filaments along the length of the Milky Way.

The bright star clouds are windows where the dust is thin or missing, allowing us a glimpse of the galaxy's stellar riches. I've spent the past few mornings exploring and photographing them before the moon returns. Details: 50mm lens at f/2.8, ISO 800, 2.5-minute time-exposure on a tracking mount).

Jupiter meets the Twinkling Comet Cluster If you have a 6-inch or larger telescope, Jupiter will be your tour guide Mond...
05/25/2026

Jupiter meets the Twinkling Comet Cluster

If you have a 6-inch or larger telescope, Jupiter will be your tour guide Monday and Tuesday nights, May 25 and 26. Find the gas giant, enjoy the sight of its four bright moons — including a tight pairing of Io and Ganymede on May 26 — then look two-thirds of a moon diameter south of the planet. You'll see a small, dense patch of faint stars with a hazy look. That's the star cluster NGC 2420, one of my longtime favorites.

Also known as the Twinkling Comet Cluster, this clutch of suns lies 10,000 light-years away. A moderate-size telescope will reveal dozens of stars here, but the total population is estimated at around 1,000! Both Jupiter and Mr. Twinkles will fit in the same field of view at low magnification. They'll still be close neighbors tomorrow night in case you have clouds tonight.

Notice that Jupiter moves up and to the left (east) each night. You're seeing it orbit the sun!

Public observing Sunday night, May 24 in Duluth's Canal Park Want to see the moon and its magnificent craters up close? ...
05/24/2026

Public observing Sunday night, May 24 in Duluth's Canal Park

Want to see the moon and its magnificent craters up close? Or Jupiter and its moons? You can! Join members of the Arrowhead Astronomical Society TONIGHT in Duluth's Canal Park starting around 8 p.m. — weather permitting. Look for us and our telescopes in the parking lot next to the Lakewalk.

Yet another proof the Earth is round As if you needed any more evidence. This one you can see in the stars. The position...
05/23/2026

Yet another proof the Earth is round

As if you needed any more evidence. This one you can see in the stars. The positions of the constellations are affected by your latitude on the globe. If you live in the southern U.S., constellations that are low in the southern sky are higher up and more easily visible compared to the view from the northern states. For instance, Sagittarius scrapes along my southern horizon, but from Mississippi it's up in your face.

Likewise, northern sky constellations like Cassiopeia and Ursa Major are lower when seen from the southern states than from Minnesota. The reason is because we live on a globe.

As you travel south, stars in the northern sky (at your back) slowly drop closer to the northern horizon and disappear from view behind the curvature of the Earth — just like the accompanying Cassiopeia illustration. Meanwhile, stars that were once hidden below the southern horizon by Earth's curvature rise into view.

If Earth were flat without its curved bulk getting in the way, you would see both northern and southern constellations simultaneously anywhere on the planet.

You could look up from Minneapolis and see both the Big Dipper and Southern Cross because there would be no horizon to block the view. Similarly, someone in Sydney, Australia could look up and see the Big Dipper.

Both these things can't and don't happen because the planet's curvature creates a horizon. You can't see below that horizon unless you travel around the curved globe to see what lies beyond it.

Hold a basketball up to your eye and walk your fingers across the top until they reach the ball's "horizon". If you keep on going, you can walk your fingers BELOW the horizon. If your fingers had eyes, they could walk far enough along the basketball's curve to see the floor — the southern hemisphere stars. Substitute the Earth for the basketball, and there you go!

Unusual auroras haunt the dead of nightWhenever I'm out observing with my telescope in the small hours before dawn, I in...
05/22/2026

Unusual auroras haunt the dead of night

Whenever I'm out observing with my telescope in the small hours before dawn, I invariably see something out of the ordinary. That's why I always bring a camera. Those sights might include side-by-side pairs of orbiting satellites, dense airglow displays or unexpected aurora.

Two mornings ago, we had a minor aurora, the kind that's mostly red and low down to the northern horizon. But while looking for a small nebula in the Milky Way a short band of aurora low in the north caught my eye. When it disappeared a moment later then surged back into view I stopped what I was doing and watched.

I was seeing a form of proton aurora — northern lights sparked by the actions of protons, not the usual bright, lively auroras we get from electrons — called Sub Auroral Morning Proton Spots or SAMPS. Storms arriving from the sun carry a mix of both types of particles.

I know it's a mouthful, but scientists like to distinguish one form from another using carefully crafted terminology, the better to communicate with precision.

Like an irregular heartbeat, the short arc slowly pulsed on and off and gradually extended to the east over the next hour. Then it disappeared. All the while, very low to the horizon, a dim, distant, red aurora simmered away. Complemented by the sounds and rhythms of the frogs, toads and the occasional thunk of a beaver's tail on the nearby stream, the night was a hushed symphony of light and sound.

Photos — the SAMPS with red aurora; low, red aurora earlier in the evening and SAMPS animation.

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