New photos taken by the Messenger spaceprobe after its swingby of the planet Mercury yesterday are starting to trickle in. Here are the few posted by NASA this morning. Let your eyes do the walking.

Mercury from 16,700 miles away. The top of the thick crescent is a region of the planet never before photographed. All photos credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

A mixture of craters and smooth volcanic plains stretches away to Mercury’s northern horizon. This photo was taken at a distance of 10,000 miles.

A new, double-ringed basin (large crater) dominates the landscape in this photo made from 9,750 miles away. The outer ring is about 160 miles across. The floor of the basin has a series of curious troughs formed by extension and cracking of the surface.

At center is a pit crater, a rimless and irregular-shaped hole or trough. Pit craters may have formed when subsurface magma drained elsewhere and left a roof area unsupported, leading to collapse and the formation of the pit. This one has multiple floors, suggesting that volcanic activity was widespread in the geologic evolution of Mercury’s crust. 

This photo of the 3030 mile diameter planet was taken yesterday when the spacecraft was 337,000 miles away. Looks much like the moon except it’s missing the dark spots or seas. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The Messenger flyby of Mercury this afternoon was a success. Data, including photos, will start beaming its way to Earth just after 10:30 p.m. Central time this evening. More images will be released tomorrow morning around 9. See you then!

A portion of a rainbow stands up over Duluth’s downtown yesterday evening shortly before sundown. Photo: Bob King

I’m not sure why I turned to look out the window while at work last night. Maybe a barely perceptible hint of yellow had crept into the fluorescent-lit room. When I turned and saw the ragged clouds set aflame by the low sun and tearing through the sky like Judgement Day it was a moment to savor. Over the next 10 minutes the colors changed from yellow to pink to purple. I ran outside, camera in hand, and watched this rainbow stump take shape in a matter of seconds before my eyes. It was a big, fat, short thing with an exaggerated red top from the setting sun. Call it rapture on 4th Avenue West and First Street, the scene was a delight.

Mercury photographed during the previous Messenger flyby last year. Mercury is the smallest planet and is pocked with craters like the moon. Many of them shown in this photo are surrounded by bright rays of secondary craters that peppered the surface after the initial impacts. Credit: NASA

The Messenger spacecraft will make its final flyby of Mercury today, using that planet’s gravity to slow itself down for eventual entry into Mercury orbit in March 2011. Messenger will be traveling at 12,000 mph and at closest approach will fly just 142 miles above the planet’s surface. Like a tourist on a hurried schedule, the spacecraft will take in the sights and snap photos as fast as it can. Some 1,500 images are planned, and when they begin to arrive, I’ll grab a few and post them here.

Messenger (at right) will not only examine craters and landforms but also sniff out atoms of calcium and sodium baked off Mercury’s surface and pushed back into a comet-like tail behind the planet by the solar wind. To achieve orbit around the planet, scientists have had to send it once past Earth, twice past Venus and now three times past Mercury. Each time the craft whips by a planet, its orbit and speed are changed slightly by that planet’s gravity, allowing it to spiral in toward its target while slowing down to a safe speed to enter orbit. It’s rather like a game of pool, where after multiple rebounds off the rails, the ball finally rolls into the desired pocket. For more on Messenger, check out NASA’s website.

You can watch the apple of Messenger’s eye beginning this week. Mercury is visible very low in the eastern sky about 45 minutes before sunrise. Use Venus as your guide, a planet that’s bright enough to be unmistakable in twilight To see Mercury best, first find Venus and then point your binoculars about one fist below that planet using the map below. Mercury will look like a little star against the brightening sky. Once found in binoculars, see if you can spot it with your naked eye. And don’t forget, the waxing gibbous moon will be very near Jupiter tonight.

This map shows the sky tomorrow morning during twilight. Mercury is about one fist (10 degrees) below Venus. Be sure you’re watching from a place where you can see close down to the horizon. Created with Stellarium.

The winds are blowing and the temperature is still in the low 50s this morning. Our sweet September summer looks to be ending soon. Although snow isn’t in the forecast yet, temperatures will be near freezing by tomorrow night. I like the bluster and feeling of change in the air. Fall refreshes the senses with a briskness that summer lacks.

The star Deneb is almost directly overhead (at the zenith) for skywatchers in the northern U.S. around 9 p.m. in late September and early October. Altair and Vega form the Summer Triangle asterism with Deneb. Maps created with Stellarium.

Back in August, brilliant Vega, luminary of the constellation Lyra the Harp, lorded over the sky from its perch near the zenith, an imaginary point that’s directly overhead. Lay on your back and you’ll stare squarely at it. You may have noticed that astronomy involves all kinds of imaginary lines and circles: the celestial equator, the ecliptic (path the sun and planets travel through the zodiac) and the meridian to name a few. Then there’s the horizon. At least you can see that one. Anything on its edge has an elevation in the sky of zero degrees. Look halfway between the horizon and the zenith and you’re at an elevation of 45 degrees high (4 1/2 outstretched fists). The zenith itself is 90 degrees high. Since one degree is equal to two full moons side by side, you can squeeze 180 moons between the southern horizon and zenith. And although it sounds improbable, 10 full moons would fit between the five degrees separating the two stars at the end of the Bowl of the Big Dipper.

By late September, Vega is no longer the dominant star at the zenith during the early evening hours. It’s drifted westward to be replaced by Deneb, the brightest star in the Northern Cross. This ceaseless westward drift of the stars is caused by the Earth’s movement around the sun. As we travel in our orbit, we peer out into different sectors of the sky as the weeks and months pass. Think of sitting on one of those merry-go-round horses and looking out into the carnival crowd. As the merry-go-round begins to turn, we look out at a different part of the fairground as we move in a circle round and round. The view repeats every turn so we briefly face the same direction again as when we started. Substitute the Earth for the horse and our orbit for the merry-go-round and you’ve got the picture. Our view of the night sky repeats once a year, so if you look up tonight at 9 p.m. and see Deneb near the zenith, you’ll see it there again at the exact same time next year.

Here you can see the Cygnus is a swan flying south along the Milky Way. Vega is the brightest star in Lyra the Harp and Altair the brightest in Aquila the Eagle.

The Northern Cross is an easy shape to recognize even in moonlight. The constellation name Cygnus actually refers to a swan, which is just as easy to recognize though we don’t often look at it that way. Picture Deneb as the tail of the bird, the cross beams as outspread wings and the bottom of the cross as the swan’s head. See what I mean? In Greek mythology, Cygnus was the god Zeus disguised as a bird flying along the Milky Way on his way to yet another love affair. 

Last week we talked about the curve of the Earth’s surface and how, as you traveled south, new stars would eventually rise up from below the southern horizon. Likewise, as you travel north, stars would pop up from beneath the northern horizon. While Deneb is nearly overhead for the northern U.S., it’s not if you live in Florida or southern California. Miami is 22 degrees of latitude south of Duluth, which means that Deneb is pushed 22 degrees further up and into the northern sky as seen by Miamians (take off sunglasses first, please). The zenith point for southern Florida is midway between Deneb and Altair. Keep going south and Altair would be at the zenith in Caracas, Venezuela. As you travel, so does the sky.

On this map of the Earth, the horizontal lines represent latitude or degrees north and south of the equator. The vertical lines (arcs) are lines of longitude, measured east and west of the prime meridian in England. You can locate any place on Earth if you know its latitude and longitude. Ditto for the sky if you know a star’s celestial coordinates called declination and right ascension.

You can find your personal "zenith stars" by looking up a star’s celestial coordinates called right ascension and declination. The numbers are similar to latitude and longitude on Earth. Declination (latitude) is given in degrees and subdivisions of degrees called minutes. Right ascension (similar to longitude) is given in hours and minutes. For our discussion, we’re just interested in declination. Stars that have a declination the same or close to your latitude will pass through the zenith sometime during the day. Deneb’s declination is +45 degrees so it’s directly on the zenith if you live in say, Central Wisconsin. To find your latitude and longitude, click on either this website or this one and type in your city’s name.

Many of you have heard of Carl Sagan or seen parts of his famous "Cosmos" TV series. He was a professor of astronomy, planetary researcher and eloquent spokesman for astronomy back in the 1980s and 90s. His name typically comes up when people use the expression "billions and billions" even though he never actually said those words (they were spoken by late night talk show host Johnny Carson when he parodied Sagan). Carl had a gift for explaining difficult concepts in simple, understandable ways and putting things in a cosmic perspective.

I came across this video compiled from brief clips from "Cosmos" that I thought you’d enjoy. The creator has altered Sagan’s voice to fit a melody and even added a bit of Stephen Hawking. It sounds odd at first but it really works. Seeing Carl smile while looking up at the sky makes me feel good inside.

The moon’s phase swells as it moves about one outstretched fist eastward each night this week across the dim constellation of Capricornus the Sea Goat. It’ll make a nice pass at Jupiter on Tuesday the 29th. Created with Stellarium.

The moon moves beyond first quarter phase toward gibbous this week. Full Harvest moon will occur next weekend. If you live in the Duluth area and want to celebrate the Harvest moon, head on down to the 5th annual Harvest Moon and Sunset Watch next Sunday the 4th at the breakwater at Agate Bay in Two Harbors, which is a 30-minute drive north of Duluth. Ellen Moore Anderson will be there to greet you plus special guests will provide piano music and telescope observing. To top things off, the famous Betty’s Pies will be dishing out tasty desserts and beverages. Be there by 6 p.m. so you can be sure to catch the 6:25 p.m. moonrise. For more information, call 218-834-3370.

A fresh 20-foot crater taken on two different dates by the camera on the Mars Reconnaissance Orbiter (MRO). The bright material in the photo at left is ice. Three months later most of the ice had vaporized in the thin Martian atmosphere; fresh dust has also settled on the crater over time. Credit: NASA

In other news, scientists have discovered ice in five fresh meteor craters on the planet Mars. The MRO discovered the craters while re-photographing areas photographed earlier. The craters are only 1.5-8 feet deep and all located in mid-latitudes far from the poles. The bright ice darkened over a period of weeks as it vaporized in the thin air. The shallowness of the ice suggests that the Viking 2 lander, which used a robotic arm to dig into Mars way back in 1976, might have discovered ice if it had dug just four inches deeper. For more on Mars’ ice, you can read the full article here.

Two weeks ago I went to the Boundary Waters Canoe Area Wilderness (BWCAW) with my friend Glenn Langhorst, former director of the University of Minnesota-Duluth planetarium and now a teacher at Fond du Lac College in Cloquet, to study the pictographs on North Hegman Lake. Native people created these ancient rock paintings that are found scattered across the wilderness area. Glenn and I shared a previous adventure in Arequipa, Peru more than 20 years ago when we chased Halley’s Comet during its return in 1986. There we befriended a group of folk musicians, drank numerous large beers and saw the comet and the southern stars from the Atacama Desert.

A lasting memory from that time was when the car broke down in the desert on our return from the Toro Muerto archaeological site, famous for a different variety of ancient art. There one can see some 3000 petroglyphs of llamas, snakes and human forms carved into boulders by the native people over a thousand years ago. While a friend hitchhiked back for help, we hovered near our VW bug on a desolate plain of broken rock and lifeless soil. I’d never seen such an utterly deserted desert before. Suddenly it occurred to us we’d be great targets for kidnapping (or worse) by the then notorious Shining Path, a Maoist guerilla group with a hankering for trouble. Glenn and I looked at each other and decided that the most important thing we could do was to hide all of film we’d taken of the petroglyphs and comet. We looked around and found a little compartment somewhere under the car’s front hood. Once that was done, we were ready for the worst. Nice to know we had our priorities straight.

This photo shows a portion of the main pictograph panel at North Hegman Lake so you can appreciate the masterful work on the moose. One of the three canoes is at right. See below for wider views. Photos: Bob King

The trip to the pictographs (rock paintings) on North Hegman Lake was a considerably more relaxed affair. Great weather, easy portages and the only shining path we encountered was sunlight on water. You paddle up from South Hegman Lake to North Hegman and right near the north end as the lake narrows, a spectacular wall of granite cliffs rises perhaps 100 feet above the water. They’re zebra-striped from mineral staining and partially covered in scratchy lichens but wait, there in the middle, neatly-framed by the chaos of nature, your eyes are drawn to something utterly human. Painted in brick red-orange is a artful depiction of a human figure with upraised arms, a remarkably detailed moose, a cougar (or is it a wolf, fox, dog?), seven horizontal markings (Glenn sees the faint trace of an 8th), and three canoes carrying five occupants.

No one knows how old this set of pictographs are — estimates range from a hundred years to many hundreds — but they are among the best preserved in the Boundary Waters. Another Native artist of long ago may have even gone back to carefully repaint them so they’d stand the test of time. Our interest in the pictographs was in their possible connection with constellations of the night sky.

The winter sky (left) featuring Orion and the neighboring constellations of Eridanus the River, Taurus the Bull, Gemini the Twins and Canis Major the Greater Dog. At right is a view of the entire main pictograph panel and shows not only the three canoes but also a large red "X" that likely represents a star. Do you see similarities between the two? Maps: Stellarium, photo by Bob King

One recent interpretation of the enigmatic figures comes from Carl Gawboy, a member of the Bois Forte Reservation, who for many years taught American Indian studies at the College of St. Scholastica and University of Minnesota-Duluth. He contends the drawings represent Ojibwe Indian constellations — the human figure could be the Winter-maker, our Orion the Hunter, while the three canoes represent paddlers plying the Path of Souls or what we call the Milky Way. Kevin Callahan of the Department of Anthropology at the University of Minnesota agrees with Gawboy and suspects the dog and moose are star patterns below Orion, the dog being the equivalent of our Canis Major and the moose composed of stars in Eridanus the River and parts of other constellations. The paddlers in the leftmost canoe would represent the two bright stars in Gemini the Twins, the other pair might be Capella and its neighbor Beta Aurigae, while the third canoe has just one passenger –  the star Aldebaran in Taurus the Bull. The horizontal markings may have been used for counting or tracking the passage of time.

I’m standing on the lower ledge to take this picture of the rock face while Glenn paddles along the wall looking for additional pictographs. The main panel is at upper right. Photo: Bob King

Glenn and I climbed up on the first ledge — a tricky maneuver from a canoe — to get in close and take photos. We banged on the huge, dislodged rock below the panel and heard it echo right in front of us as well as across the lake. Matter of fact, if you ever go there, give a shout near the wall. You get a great echo off the lower set of cliffs on the opposite shore. Perhaps that echo gave this place even more significance.

We spent the remainder of the trip puzzling over just what those carefully painted figures meant: was the human a medicine man invoking the supernatural for good fortune in an endeavor? Might the lines represent the seven stars in the Seven Sisters star cluster also known as the Pleiades? Is the scene a hunting party in canoes setting out to hunt moose and cougars? Are the moose and cougar/wolf symbols of cunning and strength? Is it possible the big "X" represents the explosion of the supernova in the year 1054 A.D. which was bright enough to be seen in daylight? It’s large size would imply brightness or an important position in the sky.

Additional pictographs at Hegman are located below and to the left of the main panel. A = six horizontal bars, B= three small x marks, C= a crescent atop a squarish figure and D= four vertical streaks. There may have been two or three other possible pictographs just above the water line, too. Photo: Bob King

Glenn and I figured that if we could have asked the artist in real time, the answer would have been obvious. "Oh yeah, of course they’re for that. We should have guessed!" The spot is fairly well protected from the elements and the rock face steep and smooth; obviously this was a great surface on which to paint. The artist must have squatted on the upper ledge with his mixture of red ochre (mineral pigment derived from clay) mixed with animal fat or sturgeon glue (derived from the fish’s spine) and dabbed it across the granite surface. The day was likely sunny and pleasant which would have allowed the pigment to dry without running. Ravens croaked and white pines sifted the breeze while the artist’s eyes focused intently on his work.

Something like this scene must have played itself out above the deep waters of Hegman Lake in the distant past. The painter is long gone but the vision he left between the black rock and lichens created a lasting portal in time.

For more on the Hegman Lake pictographs, please stop by here and here. You can also check out Michael Furtman’s book Magic on the Rocks, a guide to pictographs of the canoe country.

This map shows the location of supernova that blew up in Taurus in 1054 A.D. Native Americans would have been in the Boundary Waters at the time and witnessed the event. Could it possibly be represented in the pictograph?

Can you see the pale wedge of light extending over the house in this photo? That’s the zodiacal (zo-DYE-uh-cull) light. It’s quite broad, especially near the horizon, where it’s easily two outstretched fists wide. The light extends all the way from bright Venus (at bottom) through Leo, Cancer and into Gemini — a full five fists above the eastern horizon. Details: 16mm lens at f/2.8, ISO 1600 with a 40-second time exposure. Photo: Bob King

Two mornings ago I was out comet hunting when I saw a familiar tongue of light sticking up from the eastern horizon. This soft, diffuse glow goes by the name of the zodiacal light and it’s well-placed for viewing at the very start of dawn every fall for skywatchers in the northern hemisphere. Now through October 2 is the best time to see it before the moon brightens the sky. Moonless skies return again after October 15.

You just need to get up early –  1 1/2 to two hours before sunrise is perfect — and find a place with a dark sky and open view to the east. Rural or fringe-of-city locations are best; don’t expect to see this ethereal light from heavily light polluted areas. Around northern Minnesota, you can spot it at 5 a.m. but it’s brightest and highest around 5:30 just as twilight’s beginning. Look for a smooth glow similar in appearance and brightness to the Milky Way. It’s BIG and clearly at an angle to the horizon. I often tell my friends to do a slow sweep with their eyes across the entire eastern sky to pick it up. Once spotted, you’ll be surprised at how bright the lower portion of the light is near the horizon. From there you can follow the cone as high as your dark sky will allow.

Remember Comet Hale-Bopp from 1997? It showed two tails and was a bright, naked eye comet during the spring that year. Photo copyright: Philipp Salzgeber

It was very appropriate I saw it while comet hunting because the zodiacal light is actually comet dust in the plane of the solar system illuminated by sunlight. That’s why it’s called zodiacal — the cone is centered on the zodiac, the path the sun, moon and planets take through the familiar 12 constellations of the zodiac. As icy comets’ orbits take them into the cozy inner solar system, the sun’s heat causes dust and ice on a comet’s surface to vaporize and form a cocoon of glowing material called a "coma". Pressure from the sunlight itself spreads the coma dust into a tail. As the comet departs the inner solar system, dust from the tail is left behind and glows faintly in the sunlight as the zodiacal light. Think of the Peanuts character Pigpen and you get the idea.

Of course it takes more than one comet to create such an enormous tower of light. Thousands of comet passes have created and continue to maintain the zodiacal light. There may even be a little asteroid dust from ancient collisions mixed in for good measure. Sizewise, the light is one of the largest structures in the solar system visible to the naked eye. If you succeed in catching some Z-rays, your gaze will span the space from Mercury’s orbit all the way out to the asteroid belt between Mars and Jupiter. Grand way to start a day, eh?

(At right is a closeup photo of Halley’s Comet taken by the Giotto space probe in 1986.The actual comet — called the comet nucleus — is a mixture of ice and dust only nine miles long by five miles wide. The cloud of dust and vapor boiled away by the sun forms a coma that can measure hundreds of thousands of miles across. Tails are much longer. Halley will return for viewing once again in the year 2061 on my 108th birthday. It’ll be a BYOOC (bring your own oxygen cart) party and you’re all invited. Credit: ESA)

Two sunspot groups have recently appeared on the sun. They’re not crackling (yet) with flares but they do give solar observers and aurora watchers hope for an upswing in activity. Details: 1480mm at f/14, ISO 60 at 1/6400" with solar filter on 9/23. Photo: Bob King

Can it be true? Are sunspots back? We’ve had so many blank days this year I hardly look anymore, yet our drought was broken just a day or two ago by not one, but two modest-sized spot groups. They two contain three Earth-sized sunspots and a few smaller ones. Spot group 1027 is in the sun’s northern latitudes while #1026 is in the south. We’ll just have to wait and see — looks like I’m back on solar detail

A pool of water in a creek in Crosby Manitou State Park reflects autumn color from treetops overhead. Photo: Bob King

Yesterday on a walk the obvious occurred to me: all the little stuff going on around us is as much a feature of the universe as black holes and spots on Jupiter. The falling maple leaves, rocky cliffs, small creeks tumbling through the forest, touch of skin … everything. While this blog primarily focuses on what’s overhead, we walk through the universe every day.

It’s time again for the weekly planet updater. Not too much has changed since last. Both Saturn and Mercury are now in the morning sky but still too low to see. Mercury’s on its way toward a fine appearance in morning twilight next month. Saturn will eventually climb into dark sky but it’s in no hurry. I’m almost tempted to include Uranus in the lineup because it’s officially a naked eye planet. Under an exceptionally clear sky last night, I pinned it down without much difficulty. If you’d like to give the 7th planet another try before the moon gets too bright, here’s the link to help get you there. At least for the Upper Midwest, we’ve finally shed the veil of summer haze that’s made our clear skies less than ideal.

This photo of Saturn was taken by the orbiting Cassini spacecraft last month. Because sunlight just grazes the edge of the rings at Saturnian equinox, it hardly lights them up at all. Most of the light on Saturn’s rings is from sunlight reflected off the planet (left side). You could say the rings are lit by "Saturnshine".The right side is illuminated only by the sun and very dark in comparison. Credit: All photos by NASA/JPL/Space Science Institute

Wow, every new set of Saturn photos sent by the Cassini spacecraft are more amazing than the last. The photo above, a composite of 75 images, was taken last month at Saturnian equinox (just like our equinox) when the sun lit both northern and southern hemispheres equally while shining along the edge of the rings. The rings lie above Saturn’s equator and look dark because sun’s angle to the ring plane is so low. To really appreciate the grandeur of this image, please do yourself a favor and click here to see the high resolution version. It’s an orbital experience!

Ring material is levitated by the gravity of the tiny moon Daphnis (not visible) into a wall towering 2.5 miles high, high enough to catch sunlight and cast a shadow on Saturn’s A ring 350 miles long.

Cassini is also changing our ideas on just how thick the rings are. The main rings, which are composed of ice chunks, are some 170,000 miles from end to end but typically only about 30 feet thick. Let’s just say that that number is now just an average — new photos taken around the equinox show vertical relief in the A ring up to 2.5 miles!

Check out these cool shadows taken near the equinox.Shadows from this series of vertically-extended clumps of ring material are 170 miles long. The clumps, lifted by the gravitational influence of the moon Daphnis, are 2000 feet high. Hi-res image here.

Or how about this photo of an impact cloud floating above the ring plane. Scientists estimate that an object about three feet across struck ice in the rings a day or two before and created a debris cloud. Rotation of the rings sheared out and elongated the cloud into a streak over 3000 miles long. Material rains down on Saturn and its rings just like meteorites rain down on our planet. They contribute to the ongoing erosion and creation of ring material. For more on Cassini’s recent photos, take a look at this website.

A cloud of debris created by the impact of a 3 ft. long meteorite onto Saturn’s icy ring chunks looks like a thin streak. Impact clouds are more easily visible around the time of equinox because the rings are barely lit by the sun. The cloud is higher and catches the sun’s rays.

The thick crescent moon will be just to the right (west) of the Scorpion’s brightest star Antares this evening (Tuesday). Watch for it during twilight in the southwestern sky about 30 minutes to an hour after sunset. Created with Stellarium.

A shard of summer sun shines through an insect-gnawed hole in a basswood leaf Monday afternoon. Photo: Bob King

Autumn begins this afternoon at 4:19 p.m. Central time when the sun crosses the celestial equator on its southward journey through the sky. The celestial equator is simply an extension of the Earth’s equator up into the sky — an imaginary circle drawn on the starry sphere above. For people living on the equator, the sun will be directly overhead at local noon today. For them and the rest of us, the sun will rise due east and set due west. It does this only at the equinoxes.

Earth’s tip is responsible for the four seasons. If our axis were straight up and down, there’d only be one season all year. In summer, the northern hemisphere’s tilted toward the sun while in winter it’s tilted away. On the first days of spring and fall the sun shines equally on both northern and southern hemispheres. Notice that our axis doesn’t flip back and forth from season to season. It always points in the same direction. Illustration: Tao’olunga

The first day of fall is also referred to as the autumnal equinox — autumnal for obvious reasons and equinox because day and night are nearly equally long. Earth’s axis is tilted 23.5 degrees. For half the year starting on the first day of spring (vernal equinox), the northern hemisphere is tilted toward the sun. The length of daylight and the intensity of sunlight increases as the sun moves higher in the sky. After the first day of summer, the sun begins its slow southern descent and the days begin to shorten. On the first day of fall, the sun is midway between its highest point in the sky (summer) and lowest (winter) and continues to move southward. By the winter solstice, the northern hemisphere is tipped fully away from the sun. Days are very short and sunlight less intense as the sun takes a low path across the southern sky. After the first day of winter, the sun once again climbs north to the spring equinox in March.

Fall touches sugar maples at Hawk Ridge Monday in Duluth. Photo: Bob King

Notice I said that day and night will be approximately equal on the fall equinox. The equinox is a specific point in time when the sun is at a specific point in the sky. Since sunrise and sunset times vary greatly across the planet depending on location, true equality of day and night — called the equilux (EE-qwill-lux) — occurs on slightly different dates depending on where you live. Equilux for Duluth, Minn. is on September 25 when the sun rises at 7 a.m. and sets at 7 p.m. To find your equilux date, go to the U.S. Naval Observatory website and type in your location to get the day’s sunrise/sunset information. Are there exactly twelve hours separating them? If not, then go back, change the date a couple days ahead (or back) and look again. You may have to do this a couple times to find out when they’re equal.

Jupiter and moons shortly before Io eclipses Europa tonight. They’re shown as you’d view them in a typical reflecting telescope. The south direction is up and east is to the right. Created with Stellarium.

One last item for telescopic observers tonight (Tuesday) — Jupiter’s moon Io will partially cover Europa from 10:01-10:08 p.m. Central time. You can go out a little earlier and watch them approach one another until they nearly merge. Then between 11:41-11:47 p.m. Io’s shadow will almost totally eclipse Europa. You’ll be able to watch Europa fade to a very faint point of light during mid-eclipse at 11:44 before it begins to brighten back up.

Fall also means equal time for all the colors otherwise hidden by the green of chlorophyll. As chlorophyll breaks down, other pigments in leaves that have always been there finally show through. Photo: Bob King