Monthly Archives: March 2011

Saturn’s rings surge in brightness this week

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Philippine amateur astronomer Christopher Go's photos clearly show the dramatic brightening of Saturn's rings around the time of opposition caused by the Seeliger Effect. Compare their brightness on the two dates. Credit: Christopher Go

On Sunday Saturn reaches opposition, when it will be closest to the Earth for the year. The closer something is to us, the brighter it appears in the sky. Not only will the planet be brighter than compared to months ago and months hence, but around opposition a curious phenomenon known as the Seeliger Effect is at play to briefly make Saturn appear even more luminous.

When the Earth is lined up on the same side of the sun as Saturn, our two worlds are closest for the year. That happens on April 3. Illustration: Bob King

At opposition Saturn is directly opposite the sun in the sky, meaning it rises in the east at sunset and sets in the west at sunrise. Earth is briefly lined up in the middle between the sun and Saturn as shown in the diagram at right.

This is the same arrangement we see during full moon, when the moon is opposite the sun in the sky, rising at sunset. A few days ago I mentioned that at full phase, the moon’s brightness kicks up a notch. Something is making the moon brighter beyond just the increase in the area lit up by the sun compared to say a half moon.

Apollo 17 astronaut Gene Cernan photographs his shadow on the moon surrounded by a bright halo caused by the "opposition effect". Objects like the grains of lunar soil are especially bright directly opposite the sun because their shadows are hidden. Credit: NASA

Several factors contribute to the brightening, but one of the key ones is called the opposition effect. When we face opposite the sun – with sunlight coming from directly behind us – objects in front of us are squarely in sunshine. Any shadows cast by rocks, bumps or irregularities are hidden directly behind the objects. Without shadows to ‘darken’ the scene, the view directly in front of us peaks in light intensity.

Something similar happens when we look at Saturn’s rings during the days leading up to and after opposition. The sun shines directly at the rings, shadows hide behind the icy chunks that compose them, and we witness a surge in their brightness.

Astronomer Hugo von Seeliger

This brightness enhancement  was first studied by German astronomer Hugo von Seeliger, who lived from 1849 to 1924. Seeliger thought the loss of shadows from the particles in the rings was the cause for their rapid brightening and saw it as confirmation that the rings were made of particles rather than being solid.

While that may be part of the explanation, another phenomenon called coherent backscattering is also at play and may be even more important in the case of Saturn’s rings. It’s like this. When you shine a beam of light at a material made of lots of separate particles or pieces like the rings, it’s reflected back with greater intensity from the direction directly opposite the beam. In other words, a brighter reflection comes straight back at you. Backscattering also plays a role in the bright halo effect in the moon photo above.

Now the big question is, can you see really see this through a telescope? Yes! It’s subtle but visible. If you pay attention and notice how Saturn’s rings look now and then go back and re-observe them in several weeks, you should be able to see the difference. Compare them to the planet’s globe or consider rating them on an intensity scale with 1 for pure white and 10 for dull gray. Assign a number to their brightness each time you observe the planet and then compare your results. We’d love to hear what you find out.

Life’s nice with liquid, gas and ice

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A series of remarkable bell-shaped icicles line the underside of an ice shelf over the Brule River this weekend. They were created by a combination of water dripping from the shelf and river water flow. Photo: Bob King

Mud turned to ice under our feet last night as the temperature dropped to 20 F. I spoke before a group of naturalists at the Boulder Lake Environmental Learning Center north of Duluth. After the talk we walked outside and set up a telescope in a parking lot for a tour the spring sky. Our shoes sank in the soft ground at first, but by session’s end, the puddles had solidified into icy patches. We soon were sliding to the telescope as each took their turn at the eyepiece.

Water vapor is carried around the globe by weather systems. This satellite image shows the distribution of water vapor over Africa and the Atlantic Ocean. White areas have high concentrations of water vapor, while dark regions are relatively dry. Credit and copyright: Eumetsat

In only an hour’s time, water went from fluid to solid literally beneath our feet. And don’t forget the vapor. Though invisible, it permeated the air around us.

Water is the most important chemical to life and can be found in all three of its states – solid, liquid and gas – simultaneously on Earth. Since life depends on water, ours is the most suitable world we know of where it can thrive.

Our group had a joyful time looking at Saturn, always a rave-getter, double stars, galaxies and little bit of everything in the universe.

I kept thinking about that water, though. How many planets around the thousands of stars we saw might be fortunate enough to have the H2O so necessary for life? With the number of known extrasolar planets now at 539 and counting, I’m confident we’ll find one like Earth within our lifetimes, another blue planet in the Goldilocks zone , where liquid water can set up shop, flow where it may and serve as a medium for an extraterrestrial evolution of life.

This image is the first ever obtained from a spacecraft in orbit about Mercury. The dominant rayed crater in at top is Debussy, named after the 20th century French composer. Mercury's south polar region is near the bottom. Credit: NASA/Johns Hopkins U. A. P. L./Carnegie Institution of Washington

Today the first images taken by the MESSENGER spacecraft in orbit around Mercury are being released. The approximately one-year mission will focus on a creating a detailed map of the entire planet in addition to studying its topography, crustal minerals, magnetic field and more.

Claude Debussy circa 1908

It gives me a little thrill that the first image sent back by the probe included the striking crater Debussy, named after Claude Debussy, one of my favorite composers. His atmospheric and impressionistic music stands in stark contrast to the rough-edged, cratered landscape of the solar system’s innermost planet.

According to the International Astronomical Union (IAU) Working Group for Planetary System Nomenclature, craters on Mercury are named after deceased artists, musicians and authors who have been significant figures for more than 50 years. Mountains are named for the word “hot” in various languages and valleys for radio telescope facilities. To learn how other features of the moons and planets of the solar system get their names, click on over the Group’s planetary names page.

The crater near the bottom of the left hand image is a beautiful example of a relatively small, simple, fresh impact feature on Mercury. The image at right is striped by rays of material from another crater outside the frame. Credit: NASA/Johns Hopkins U. A. P. L./Carnegie Institution of Washington

Above are two additional images taken by MESSENGER from orbit released this afternoon. To see more, please click HERE.

Crescent moon by way of nova

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This illustration shows gas pulled from a companion star into a disk around by a white dwarf star, where it's funneled down to the dwarf's surface. Credit: NASA/CXC/M. Weiss

Waking up to a crescent moon was nice enough this morning. I went out to spy a possible new nova in the summer constellation of Sagittarius. Novas occur in very close double star systems where stars like our sun or larger red giants are paired up with very dense, very tiny stars called white dwarfs.

The two orbit so closely that the intense gravity of the dwarf pulls matter (mostly hydrogen gas) from an envelope around the sun-like star down onto its surface. There the gas accumulates and heats up until it ignites in an enormous thermonuclear explosion.

Back here on Earth, we see evidence of the explosion as the sudden brightening of the system. Where no one even noticed a star before, a “new star” appears. Of course it’s not a new star, just an explosive brightening.

A nova in the constellation Eridanus in 2009 looks just like a bright telescopic star. Credit: Kevin Heider

The possible nova appeared as a dim 13th magnitude star, the limit for a typical 4-6 inch telescope. Why so faint? It’s very possible that because it’s located in the direction of our galaxy’s center, light years and light years of intervening dust have reddened and dimmed its light. Sometimes a nova can be as bright as the brightest naked eye stars if it’s relatively close and little dust gets in the way. It’s been a while since we’ve had a visit from one like that.

The brightest recent nova was in the Northern Cross in August 1975. That one climbed to magnitude 1.7, nearly as bright as Deneb, the constellation’s brightest star. If you happened to look up at the sky back then, you would have noticed that the outline of the Cross had suddenly changed thanks to the interloper.

Tomorrow and Thursday mornings the moon and Venus will vie for your attention in the southeastern sky 40 minutes before sunrise. Created with Stellarium

Anyway, I started out talking about the moon, and how fine it looked this morning as twilight began. I love it when dawn brings in a crescent to start the day.

You can watch the moon get whittled down to an ever thinner crescent during the next two mornings. Look low in the southeastern sky about 30-45 minutes before sunrise. Venus will provide an added bonus if you’ve got a clear shot to the horizon.

See the Spring Triangle and Saturn tonight

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The Spring Triangle stretches across the eastern sky around 10 p.m. last night. It's formed by the star Arcturus (upper left), Saturn (top right) and Spica (below Saturn). Photo: Bob King

I’m not the first to call it the ‘Spring Triangle’ but the name sure fits. We’re talking about Arcturus, Saturn and Spica and what a fine figure they cut in the eastern sky from 10 o’clock onward. I suppose it was inevitable given our fondness for triangles of bright stars that one should pop up in spring. You’re probably already familiar with the Summer Triangle and the Winter version, so why not one for spring?

Unlike the Summer and Winter standbys, this one’s only good for a year. That’s because one its members, Saturn, like the other planets, never stays put in one place. Next year the planet will have slid eastward and lie to the left of Spica. No triangle there. However, in 2013 it will be positioned below Spica and form a new, wider triangle with its starry pals.

The current triangle is huge, bright and really catches the eye. You can squeeze three fists held at arm’s length between Saturn and Arcturus. Spica and the planet are just a fist apart. Start your spring with this fun, connect-the-dots exercise tonight.

Cassini spacecraft chronicles the change of seasons as it captures clouds concentrated near the equator of Saturn's largest moon, Titan. This picture consists of an average of three images taken using a filter sensitive to near-infrared light, which 'see' through Titan's haze to its surface and lower atmosphere, plus an image in visible light. Credit: NASA/JPL/SSI

Speaking of Saturn and spring, we’ve already seen rain a few times here in Duluth, a welcome sign that the season is underway despite stubborn single-digit nighttime temperatures. Saturn’s largest moon Titan also experiences seasons, with changes in cloud cover depending on the season. Back in 2004, during late southern summer, the Cassini spacecraft photographed extensive clouds in Titan’s south polar regions.

The photo above was taken in October 2010, about a year into Titan’s southern fall, and shows a few clouds in the south, but most are now concentrated in a bright belt around the moon’s equator. The clouds may look familiar, but they’re composed of methane, the principle ingredient in the natural gas we use to heat our homes back here on Earth. Because Titan and Saturn are nearly a billion miles from the sun, it’s much colder there, allowing methane to exist as ice, liquid and cloud.

A huge arrow-shaped storm, measuring 930 by 750 miles, blows across the equatorial region of Titan last September. This storm darkened large areas of the moon, likely from methane rain. Credit: NASA/JPL/SSI

Scientists believe that methane evaporating from lakes on Titan’s surface rises to form clouds, which then release methane ‘rain’ during rainstorms, refilling lakes and creating new ones.

“It’s amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite,” said Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Md.

Spring has been underway since 2009 in Titan’s northern hemisphere. Storm clouds in the photos above have swept over the moon’s equatorial regions and left what appear to be dark, methane rain-soaked ground and replenished lakes in their wake.

Clouds move above the large methane lakes and seas near the north pole of Saturn's moon Titan. The outlines and color of the lakes have been enhanced for clarity. Credit:Â NASA/JPL/SSI

Those lakes are even colder than those in my part of the world. Temperatures on the surface of the moon hover at -290 F. Titan has hundreds of lakes brimming with methane and ethane. Largest is the 150,000 square mile Kraken Sea, nearly five times bigger than Lake Superior! The moon may be an alien world, but it’s the first place beyond Earth where we’ve seen stable bodies of surface liquid.

Saturn and Titan tonight. The view shows directions reversed with south at top and east to the right, the way you'd see it in most telescopes. Created with Stellarium

You can see this wintry world for yourself in even a small telescope. Tonight Titan is at greatest elongation (maximum distance) east of Saturn. 25x and up will show it as a small ‘star’ four ring lengths due east of the planet. If you’re using an 8-inch or larger scope, you’ll even be able to see Titan’s orange color.

Those willing to invest a little more time can watch Titan move closer to Saturn over the coming nights. The moon completes an orbit around the ringed planet in 16 days.

Curious glows of the night plus the sun gets cookin’

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The sun photographed this morning by the Solar Dynamics Observatory. Sunspot group 1176 is large and complex, the perfect breeding ground for flares that could spark northern lights displays. Credit: SDO/HMI

The sun is starting to heat up again. OK, it’s already hot, but do you remember the big sunspot group (1166) that jump-started the northern lights earlier this month with a succession of medium to large flares? After rotating around the backside of the sun, it’s returned. Joining it is another sunspot group, region 1176, that’s big and magnetically messy enough to spawn additional flares.

According to the NOAA Space Weather Prediction Center, 1176 is likely to be busy this week with a good chance for M and possibly X class flares. Yeah, it’s time again to face north before heading off to bed in case we get a return visit from the aurora. The forecasters say that there’s a possibility of minor aurora tomorrow night , March 28, due to an explosive coronal mass ejection that happened on the 24th. With clear weather predicted for nearly the entire week for the region, we’re looking pretty.

The zodiacal light (right) extended up to and beyond the Seven Sisters or Pleiades star cluster (clump near center) last night. The best time to look for it is 1 1/2 to 2 hours after sunset in the west. Can you spot Orion's Belt at left? Details: 16mm lens at f/2.8, ISO 3200 and 30-second exposure. Photo: Bob King

Last night was one of those perfectly calm, clear nights that recall the ease of summer sky gazing but without the bugs. Early on, the winter constellations of Orion, Taurus, Canis Major, and Auriga held sway in the south and west. They were joined by the strangely luminous zodiacal light, a misty, cone-shaped glow in the west seen near the end of spring twilight when the moon’s not in the sky.

The next couple weeks are an ideal time to go out to the country to see this vast cloud of dusty cometary debris that spreads across the plane of the solar system out to Jupiter’s neighborhood. Sunlight sets all those minute dust particles to glow with a brightness equal or brighter than the Milky Way.

Further to the left or west of the zodiacal light, Orion and other wintertime constellations still put on a good show during the early evening. The Milky Way arches across the top of the frame. Compare to the Stellarium chart below. Photo: Bob King

I drove far north of town for the darkest sky I’ve seen yet this year. It was dark enough to trace the zodiacal light beyond the Seven Sisters into Orion and beyond, where it narrowed into the zodiacal band, crossing through Cancer, Leo and all the way east to Virgo.

A fish-eye view of the zodiacal band. The slightly brighter oval is the gegenschein or counterglow. Credit: ESO

In Virgo in the vicinity of the planet Saturn, the dim arch swelled in brightness and size to form the gegenschein (GAY-gen-shine) or counterglow, an enhancement in the band caused by sunlight shining squarely on the dust particles that are exactly opposite it in the sky. The gegenschein is brighter for the same reason the full moon is extra bright compared to other phases. At full, sunlight shines directly at the moon rather than from the side, lighting up each rock and dust speck 100% square on. The result: a spike in brightness.

The gegenschein, being dust rather than a solid body, doesn’t exactly knock your socks off. Look for an oval-shaped, slightly more luminous patch about a fist wide. Since it’s directly opposite the sun, the counterglow is best placed for viewing due south at local midnight standard time (1 a.m. daylight saving time). Use averted vision as you search for a very faint glow one outstretched fist to the upper right of Saturn in Virgo. Dark skies are required! I usually start to see it around 10:30-11 p.m.

Even if you don’t have the darkest skies and have to deal with light pollution like most of us, have a look at winter’s best stars before they’re gobbled up by the western horizon.

A labeled view of the sky as you face west-southwest at nightfall in late March. Orion and friends are on the decline. Above them arches the winter Milky Way. The zodiacal light reaches up to the Milky Way from the west. Created with Stellarium

Mercurial light warms up tonight’s Earth Hour

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Wow, it’s been a busy day. So much so I nearly forgot about Earth Hour, an annual ‘turn off the electricity’ event celebrated around the world at 8:30 p.m. local time. It began in 2007 in Australia over concerns about global climate change. A few years later, it’s become a global event with people turning lights off everywhere. Here in Duluth, Minn., the lights illuminating the city’s landmark Aerial Lift Bridge will be shut off for an hour, transforming it into a silhouette against the downtown skyline.

Find Mercury 10 degrees high (about one fist at arm's length) in the west some 45 minutes after sunset this evening. Look for it above the spot where the sun set. Created with Stellarium

Not only would I encourage you to turn off unnecessary lights, especially the outside ones that can contribute to light pollution and poor skies, but use the time to enjoy outdoor twilight and the sight of the planet Mercury in the western sky.

Yep, Mercury is still there, so if you haven’t seen it yet, it’s time.

After your eyes get used to the gathering darkness, you can head back inside, pull some plugs and flip a few switches and relax in the coming night.

Of frost and space station watching

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Montreal, Canada at night as seen from the International Space Station late December 2010. The countryside is faintly lit by moonlit snow, while blurry areas at the top and bottom are caused by cloud cover. The station was located over the New York-Pennsylvania border some 360 from the city when the photo was taken. Credit NASA

Space station watchers are back in business again starting tomorrow morning with a 6:34 a.m. pass in the southern sky as seen from the Duluth region. This several-week-long ‘season’ of visibility features grazes of the moon and bright star Vega and a sudden appearance of the station at the zenith as it exits Earth’s shadow.

I’ve listed times for the Duluth region below, but you can always to to Heavens Above or Spaceweather’s Flyby page for precise times for your town. Although you’ll see the International Space Station alternately in the southern or northern sky, it always travels from west to east and appears as a very bright, unblinking star with a slight yellowish tint.

Times are Central Daylight:

* Tomorrow morning starting at 6:34 a.m. in the south-southeastern sky. Slices right atop the moon’s edge two minutes later.
* Sunday March 27 at 5:52 a.m. across the south-southeastern sky
* Tuesday March 29 at 6:18 a.m. A high, bright pass in the south. The station will pass directly
in front of the bright star Vega just after 6:21.
* Wednesday March 30 at 5:12 a.m. across the south-southeast
* Thursday March 31 at 5:37 a.m. Brilliant pass across the top the of the sky.
* Friday April 1 at 6:03 a.m. Bright pass across the northern sky. Zips
directly under Polaris just before 6:06.
* Saturday April 2 at 5:37 a.m. The ISS will “appear out of nowhere”
directly overhead at that time as it exits from Earth’s shadow and moves
eastward.

Frosty flakes line a wooden post this morning after a clear, cold night. Photo: Bob King

We’ve had a couple of very clear, calm nights here this week. They’ve made for great skywatching and photography but also for daylight surprises like this morning’s frost. Huge, fan-like ice crystals covered every exposed surface and added a special sparkle to the start of the day.

New aurora video a masterpiece

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A frame showing a rayed arc in action from Ole Salomonsen's northern lights video. Credit: Ole Salomonsen

After more than six months of picture-taking on dozens of cold nights, photographer Ole Salomonsen of Tromsø, Norway has combined some 50,000 still images into a spectacular 4-minute video of the northern lights. Key among his goals was to show the aurora as closely as possible in real time. We see graceful movements, sudden surprises and changing colors unfold in all their subtlety in Ole’s beautifully composed presentation.

The movie combines high resolution imagery and natural scenery set to music by Tromsø musician Per Wollen. It’s a masterpiece. Click HERE to watch.

A small orrery showing the Earth, moon and inner planets. Credit: Kaptain Kobold

Ever heard of an orrery? An orrery (OR-er-ree) is a mechanical device still found at some planetariums that illustrates the positions and motions of the planets around the sun. It’s typically driven by powered gears, but some are movable by hand. Orreries are great hands-on tools to get acquainted with the solar system’s layout and motions. At the planetarium here in Duluth we have a simple manual orrery. You can tell it’s been around for a while, because one of the planets is loose and keeps falling off.

The instrument was invented in 1713 by George Graham and made by instrument-maker J. Rowley. He presented a copy to his patron, English nobleman Robert Boyle, the 4th Earl of Orrery, for whom it was named.

A portrait of the 4th Earl of Orrery by Charles Jervas

Most of us don’t have access to a physical orrery, but this being the 21st century, there’s a online flash version that is one of the coolest tools I’ve seen in a long time.

Watch the planets go around the sun and moons go around the planets. Even the asteroids are included – something lacking in the Earl’s version. You can set the date, speed and even view an older, alternative view of the solar system proposed back in the day by 16th century Danish astronomer Tycho Brahe.

Tycho placed the Earth at the center of the solar system orbited by the sun, which was in turn orbited by Mercury and Venus. The outer planets moved along their own separate orbits. Complicated and ultimately incorrect, it was Tycho’s best shot at explaining the motions of the planets at the time.

Whether constructed of brass or source code, orreries will always have their place in helping us visualize how our solar system works. Check it out.

Astronomers discover star no hotter than your sauna

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This photo of the brown dwarf double star CFBDSIR 1458+10 was taken with the Keck II Telescope in Hawaii. It's the coolest pair of brown dwarfs found so far—the colder and dimmer of the two is a candidate for the brown dwarf with the lowest temperature ever found of 212 degrees. Credit: Michael Liu, University of Hawaii

I boil water for tea twice a day. And while boiling water burns like heck if it spills on your hand, it’s not usually what we think of when it comes to star temperatures. Those typically range from the low thousands to more than 70,000 degrees Fahrenheit. Many of the coolest stars, called brown dwarfs, can be under a thousand, but that’s still hotter than anything in my kitchen.

Today the European Southern Observatory reported that astronomers there, in coordination with Michael Liu of the University of Hawaii’s Institute for Astronomy,  were able to determine the temperature of the coldest star yet known. Called CFBDSIR 1458+10B, it’s a brown dwarf in a binary star system of two brown dwarfs 75 light years from Earth.

CFBDSIR 1458+10B is steaming away at the relatively pleasant temperature of 212 degrees Fahrenheit or the boiling point of water. That’s warm enough to support clouds of hot steam in its atmosphere. In comparison, the surface of the sun sizzles at 11,000 degrees.

The sun, a modest star, is large compared to the wee stars in the galaxy - the red and brown dwarfs

Although astronomers don’t yet know how large the dwarf is, typical brown dwarfs are similar to Jupiter in size but 15 to 75 times as massive. Those on the low end of the scale probably never burn hydrogen like real stars do, because they’re neither dense not hot enough in their cores to initiate the hydrogen fusion process responsible for a star’s light and heat.

Dwarfs on the higher end fuse a form of hydrogen at least early in their lives before cooling down and going dark like an old bulb. What’s remarkable about the new find is that it straddles the line between star and the hundreds of giant exoplanets that astronomers have discovered since 1995.

Used to be things were in neat categories like stars, planets and moons, but the more we dig around, the more connections and fine gradations we see between objects once thought to be separate and unique.

Take Pluto, which was recently re-designated a dwarf planet thanks to finding lots more objects like it in the outer solar system. As humans, we like to see things placed in nifty bins, but nature is more like a continuum, with room for just about anything, even oddball stars the temperature of your sauna.

The moon scoots up to Antares in Scorpius tomorrow morning. The two are best visible at the start of dawn in the southern sky. Created with Stellarium

Just a final observer’s note. If you’re up tomorrow at dawn, face south and look a few degrees to the lower left of the moon to find Antares, the brightest star in Scorpius the Scorpion. The moon pays regular visits to Antares, since the star lies so close to its monthly path through the sky.

A little tilt is all it takes

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I hope the first couple days of spring have lived up to seasonal expectations where you live. They have here, but now a howling snowstorm is on its way, threatening to repave all the lovely, exposed ground with a foot of wet, white concrete.

The sun is shown at noon on the first day of spring (left) and 10 days later. The arrow shows the direction it's moving. Notice that the sun's path, called the ecliptic, intersects the imaginary arc of the celestial equator on the first day of spring. By the 30th, the sun has moved noticeably north of the equator and is higher in the sky. Created with Stellarium

In Sunday’s blog we discussed that the reason for the seasons has to do with the tip or inclination of Earth’s axis, rather than our planet’s distance from the sun. The tip causes first one hemisphere and then the other to alternatively face toward and away from the sun. This makes the sun’s apparent path across the sun swing from low to high to low in the year-long cycle of four seasons. Spring began when the sun crossed the imaginary projection of Earth’s equator – called the celestial equator – on its march northward.

This diagram shows the various tilts of the planets and dwarf planet Pluto. Credit: Image courtesy of Courtney Seligman / cseligman.com

What about the other planets in the solar system? Do they have seasons too? Well, to have seasons, you need to be tipped on your side. You can see that Mercury, Venus and Jupiter have little to no axial tip, so it follows they don’t experience the seasons. The sun follows the same path across the sky, neither dipping low nor ascending to the heights, the entire year round on these planets.

On Earth, and sometimes in Duluth, liquid water returns as winter transitions to spring. Photo: Bob King

Venus is a bit of an oddball. It’s tipped so far over – 177 degrees – that its north pole is where the south pole should be. This extreme tip means Venus is actually rotating backwards or clockwise as seen from above the plane of the solar system. From the same perspective, most of the other planets rotate counterclockwise.

Because Earth, Mars, Saturn and Neptune have similar inclinations, they all experience similar seasons. For instance, right now it’s late spring in Mars’ northern hemisphere and early spring in Saturn’s northern hemisphere.

Keep in mind that seasons on these outer planets last longer than those on Earth, because they take longer to orbit the sun. A typical season on Mars last twice as long as the equivalent on Earth. Neptune takes takes 165 years to journey once around the sun, making spring a tedious 41 years in length. Well, maybe you like spring more than I do.

Pluto and Uranus also have seasons, but surprising things happen when you’re rolling around the sun on your side.

The Hubble Space Telescope photographed Uranus and its rings between 2003 and 2007. The rings, which lie above the planet's equator, went from open presentation in 2003 to edge-on in 2007. Credit: NASA/ESA/M. Showalter

Uranus orbits the sun every 84 years. As the north polar regions face the sun for 21 years, the sun hugs the horizon at the equator and the south pole is in complete darkness. During the next 21 years, the equator faces the sun and all parts of the planet experience sunlight. The poles see sunlight too, but just barely, as the sun circles the horizon for years on end. This is followed by 21 years of sunlight at the south pole and an equally long night at the north pole. The Uranian year wraps up with the equator once again facing the sun with sunlight across the whole planet. Just weird.

Seasons on Earth keep life interesting, but when you add in the rest of the planets, you really get a feel for how much variation is possible from a simple little thing like tilt.