Shhh! Don’t wake the sun

Contrast these views of the nearly spotless sun on July 16-17, 2014 with a picture taken about two weeks earlier (below). Credit: Giorgio Rizzarelli

Who doesn’t enjoy a nap on a lazy summer afternoon? That’s what the sun’s been up to past few days. Instead of a steady parade of sunspots, it put its pencils away and went to sleep. For a time on July 17 not a singe magnetic blemish marred the entire Earth-facing hemisphere. The last time that happened was nearly 3 years ago on Aug. 14, 2011.

Ten groups including three visible with the naked eye dot the sun on July 8, 2014. Credit: NASA

The solar blank stare lasted but a day; by the 18th two small groups emerged. Today three little spot clusters have emerged but again, they’re on the small side.

I think the reason the sun looks so stark is that only two weeks ago nearly a dozen sunspot regions freckled the disk including three visible with the naked eye with a safe solar filter.

These ups and downs aren’t unusual unless this downturn continues for weeks. Expect more bubbles of magnetic energy to rise from beneath the glaring surface of the sun called the photosphere and spawn fresh groups soon. Because we now have eyes on the farside of the sun courtesy of the dual STEREO solar probes, we know the complete story. There are at least seven spotted regions in hiding there today.

Sunspot numbers are plotted for the last three solar cycles through the present. The double peak of the current cycle is shown. Credit: NASA

Sunspots and flares peak approximately every 11 years. We’re still riding the roller coaster near the top of the arc after the most recent solar maximum in late 2013. Some maxima are strong, others weak. The current max – Cycle 24 – is the weakest since Cycle 14 in February of 1906 and one of the wimpiest on record. Occasionally a cycle will have two peaks like the current one. The first peak occurred in Feb. 2012 and the second just this past June. What makes Cycle 24 even more unusual is that the second peak is higher than the first – the first time this has ever been recorded. Like people, every maximum has a personality of its own.

Doug Bieseker of the NOAA Space Weather Prediction Center has analyzed historical records of solar activity and he finds that most large events such as strong flares and significant geomagnetic storms typically occur in the declining phase of solar cycles—even weak ones, so don’t give up hope for some great auroral displays ahead.

A coronal mass ejection blew off on the farside of the sun early this morning July 20. It appears to envelop Jupiter, but the planet is 490 million miles in the background. SOHO uses an occulting disk to block the brilliant sun. Credit: NASA/ESA

The sun’s got a buddy this week – Jupiter! We can’t see the planet from the ground because it’s swamped by solar glare, but the Solar and Heliospheric Observatory (SOHO) has a great view from space. Watch the sun approach from the right and pass the planet over the next few days. After the 24th, Jupiter will move into the morning sky.

Farewell Jupiter, hello moon!

The 2-day-old lunar crescent will shine low in the west-northwest tonight June 29, 2014. This view shows the moon about 30 minutes after sunset. Not far away – hidden by the tree – Jupiter makes its last stand. See below. Source: Stellarium

Tonight’s returning crescent moon will help us bid adieu to a planet that brought us through winter and spring to the doorstep of summer.

Jupiter’s put on a great show in Gemini this year. We’ve watched the nightly ballet of its four bright moons, pondered the shrinking of the Great Red Spot (how small it will get nobody knows) and witnessed the planet in many fine conjunctions with the crescent, quarter, gibbous and full moons.

That’s a lot of visual delight, but being one of the brightest planets, Jupiter rarely fails to please. Tonight you might see it for the last time this season using the moon as your guide. Face west-northwest about a half-hour after sunset. With binoculars, sweep the sky about 12 degrees to the right and below the crescent moon. Can you see it with your naked eye?

With a clear view to the west-northwest tonight, the moon will help you find Jupiter one last time. The map shows the sky 30 minutes after sunset from the central U.S. Jupiter lies about 12 degrees – a little more than a horizontally-held fist at arm’s length – to the right and below the moon. Use binoculars first and then see if you can spot it without optical aid. Source: Stellarium

No planet escapes the glare of the sun. The apparent movement of the sun across the sky caused by Earth’s revolution around it means that sooner or later our driven star catches up with the slower-orbiting planets that lie beyond the Earth. Indeed, the sun’s been gaining ground on Jupiter ever since January 5. On that date, the planet was at opposition, rising at sunset and remaining visible until the next morning’s sunrise. The very next day the sun gained 4 minutes on it and hasn’t stopped since.

Jupiter’s now (almost) hopelessly lost in bright evening twilight. It will still roast in the BBQ glow of the sunset until July 24 when it passes just a fraction of a degree north of the sun in conjunction. For several days before and after that date we’ll get to see it in SOHO’s coronagraph, an instrument that blocks out the sun to reveal the solar corona, background stars and occasional comet and planet crossings.

Wow! On Aug. 18, days after Jupiter returns to view in the morning sky, it will pass only 0.2 degrees (1/3 the diameter of the full moon) from Venus in the constellation Cancer. Source: Stellarium

As the sun passes and leaves Jupiter behind, the planet re-emerges in the east in morning twilight in early August. And what a grand entry it will be! On August 18 Jupiter passes just 0.2 degrees from Venus in one of the year’s most spectacular conjunctions.

If you recall, Jupiter spent most of this year in the constellation Gemini beneath the bright ‘twin stars’ Castor and Pollux. On its return in August you’ll be struck by how far the planet has moved east along the zodiac. Ceaselessly orbiting the sun, Jupiter will have abandoned Gemini for the faint constellation Cancer the Crab. And so it goes, round and round and round.

Lunar crescent returns – Mercury and Jupiter follow mother sun into twilight

The crescent moon will be near Mercury tonight (May 30) and below Jupiter tomorrow night. The map shows the sky facing northwest about 40 minutes after sunset. Stellarium

Nice to see to moon back in the evening sky just in time for the weekend. The 2-day-old slender slip of a thing makes an appearance about 40 minutes after sunset about 7 degrees (not quite one outstretched fist) to the lower left of Mercury.

Keen-eyed observers with haze-free skies may spot the planet without optical aid, but I’m guessing it will take a pair of binoculars. Mercury has faded in the past few weeks and will soon disappear in the sunset glow not to return again for northern hemisphere skywatchers until mid-July before dawn.

You’ve probably noticed that Jupiter’s been dropping lower and lower in the west and now sets near the end of evening twilight. The hefty planet and skinny moon will line up for one last easily visible conjunction tomorrow evening. By next lunar crescent (June 29), Jupiter will be difficult to pick out from the twilight glow.

In this map I’ve removed the atmosphere and added the ecliptic, the path taken by the sun, moon and planets across the sky. The sun’s day-by-day travel to the east is a reflection of Earth’s revolution around the sun. Its movement outpaces that of the outer planets, so it gradually catches up and then passes them one after another. When near the sun, a planet can’t be seen, but when the sun has left it behind, the planet reappears to the right or west of the sun in the morning sky to start the cycle all over again. Stellarium

Because sun, planets and moon all follow the same general path across the sky called the ecliptic, they inevitably pass near the sun for at least a few weeks every year (more often for the inner planets Mercury, Venus and the moon). Solar glare renders them invisible for a time until they pop back into view in the morning sky at dawn and begin the next cycle of visibility.

Jupiter’s Red Spot shrinks to smallest size ever – how long will it last?

In this comparison image the photo at the top was taken by the Hubble Space Telescope in 1995 and shows the spot at a diameter of just under 13,050 miles (21,000 km); the second down shows a 2009 photo of the spot at a diameter of just under 11,180 miles (18,000 km); and the lowest shows the newest image from taken in 2014 with the spot at its smallest yet, with diameter of just 9,940 miles (16,000 km). Credit: NASA/ESA

The Great Red Spot is arguably Jupiter’s most iconic feature. Mention the giant planet and most of us conjure up an image of striped gas ball with a big red beauty mark.

While the spot has been observed since the infancy of the telescope, we’ve come to accept it as a permanent part of the Jovian planet’s persona. Now it’s time to admit the truth. The Great Red Spot has been downsizing since the 1930s with particularly swift changes happening in just the last couple decades.

Ask any long-time amateur astronomer. Back in the 1960s the spot extended over a greater area and was more elongated or stretched out. In the past few years, its not only contracted thousands of miles but become more circular. Most of us have blamed the spot’s pale, watered-down color in recent years as the reason it’s become more difficult to see.

At left, photo of Jupiter’s enormous Great Red Spot in 1879 from Agnes Clerk’s Book ” A History of Astronomy in the 19th Century”. At right, Jupiter on Jan. 10, 2014. Credit: Damian Peach

But that’s only part of the problem. Since 1995 it’s downsized by over 3,000 miles. That’s nearly half an Earth diameter in 20 years! Since 2012 it’s been losing girth at the rate of 580 miles a year. 130 years ago the spot spanned about 25,000 miles (40,000 km) and looked like a giant blimp riding Jupiter’s cloud belts. Even in the small 2-3 inch refracting telescopes popular at the time it would have hard to miss. Now you need at least a 6-inch telescope to see it clearly.

“In our new observations it is apparent very small eddies are feeding into the storm,” said Simon. “We hypothesized these may be responsible for the accelerated change by altering the internal dynamics and energy of the Great Red Spot,” said Amy Simon of NASA’s Goddard Space Flight Center.

Reprocessed view by Bjorn Jonsson of the Great Red Spot made by Voyager 1 in 1979 reveals an incredible wealth of detail. The Spot is a vast, long-lived. hurricane-like storm located between opposing jet streams in Jupiter’s southern hemisphere. Click to enlarge. Credit: NASA

The not-so Great Red Spot (GRS) is a hurricane-like storm that rotates anticlockwise in Jupiter’s southern hemisphere immediately south of the prominent South Equatorial Belt. It takes its swirly appearance from winds blowing at several hundred miles an hour with the spot’s cloudtops reaching 5 miles (8 km) above Jupiter’s cloud deck.

Animation showing the rotation of the Great Red Spot made with images taken by NASA’s Voyager 1 spacecraft . Credit: NASA

The spot used to rotate once every 6 days, but smaller eddies or vortices feeding into the spot that may be responsible for its changing appearance have shortened that to about 4 days.

Red Spot Jr. on Feb. 1, 2014. It’s the first significant new red spot ever observed on Jupiter and located at longitude 332 degrees (Sys. II) The spot about half the width of the more familiar Great Red Spot. Credit: Christopher Go

What will become of the spot is anyone’s guess. It may continue to wither and disappear altogether. It is does go bye-bye, Red Spot Jr. waits in the wings. This new but considerably smaller red-tinted spot formed from the merger of three smaller oval vortices between 1998 and 2000. Or we could be completely surprised and see it revivified by the Jovian jet streams. Such is weather, whether here or on Jupiter, there will always be an element of unpredictability.

NASA’s Juno spacecraft is hurtling toward Jupiter now, due to reach the giant planet in July 2016.  Up close examination by the probe will hopefully fill in holes in our knowledge of the planet’s turbulent and fascinating atmosphere.

Saturn disappears, Mercury appears during ‘night of the planets’

Saturn covered and uncovered by the moon earlier today by Dave Herald, Murrumbateman, Australia

Enjoy the video. Dave Herald did a great job recording this morning’s Saturn occultation. The images are very sharp. I always find it remarkable how atmosphere-less the moon is. There’s not a hint of softness in the planet as it’s devoured by the lunar limb. If there were substantial air, the planet would gradually soften and fade.

For a moon or planet to be completely without air is next to impossible. The solar wind knocks atoms from minerals on the lunar surface and sends them reeling into the virtual vacuum above the surface. Studies have found potassium, sodium, helium and argon in the moon’s exosphere, the name given to the lunar atmosphere. Bombardment of the moon’s surface rocks by micrometeorites and the solar wind release potassium and sodium; helium and argon probably bubble up from radioactive decay of those same rocks. Helium may also arrive via the sun’s wind.

Glow from sodium in the lunar atmosphere. The light from the moon has been blocked by the telescope, but the size, position and phase of the Moon are shown by the superimposed image in the center. Rayleighs are a measure of brightness. Credit: NASA

At sea level on Earth, we breathe in an atmosphere where each cubic centimeter contains 10,000,000,000,000,000,000 (10 quintillion) molecules; by comparison, the lunar atmosphere has less than a million molecules in the same volume.

Comets and meteoroids striking the surface temporarily enhance the amounts of other atoms and molecules. But the sum total of all the sputtering and interacting is an atmosphere equal to the amount of air you’ll find 250 miles high where the space station plies it orbit. Not much.

Mercury stands all by itself low in the northwest in this photo taken about 50 minutes after sunset last night. Credit: Bob King

At my house, we saw no occultation of Saturn, but the two did stand together in the southeastern sky at dusk. On the opposite end of the heavens, Mercury made a fine naked eye appearance in the northwestern sky.

Jupiter glows over Amity Creek last night. Both the creek and the sky were lit by the light of the full moon. Credit: Bob King

I first caught it around 9:15 p.m. some 40 minutes after sunset and watched it for at least a half hour. Capella and Jupiter – both higher up in a darker sky – made for great sight lines to the planet.See yesterday’s map for details.

Jupiter in Gemini remains the most brilliant object in the western sky at dusk during early evening hours. I watched it from a nearby creek that rushed with water from snow melt and recent rains.

Mars stood between Jupiter and Saturn. This week the ‘boring’ hemisphere – the one with fewest dark markings – is turned toward western hemisphere observers.

The Moon, Mars (upper right), Saturn (lower left), Spica (immediate right of moon) and Arcturus (top) as seen from Dayton, Ohio on May 12. Credit: John Chumack
Dayton, Ohio

But there’s still much to see – enough to easily stay up past your bedtime. The north polar cap on Mars remains visible despite the seasonal summer ‘heat’, and white clouds topping the planet’s major volcanoes are visible along the planet’s western edge. Check it out.

Mercury returns, planets align, life is good

Mercury is just entering the picture tonight but by May 10 it will be easy to see, along with three other evening planets, 45 minutes after sunset in the northwestern sky. The pink arc is the ecliptic, the apparent path the sun takes during its yearly travels. It’s also followed closely by the planets and moon. Click to enlarge. Created with Stellarium

Planets are popping up everywhere. We’ve touched on Jupiter and Mars many times the past few months, but recently Saturn and now Mercury have entered the scene. Maybe you’ve noticed Saturn now in the southeastern sky at nightfall. From the northern U.S. and southern Canada, it’s bright but low at nightfall. Saturn reaches opposition a week from now when it will be at its closest and brightest for 2014. Each night that passes, the ringed rises higher and becomes better placed for viewing.

Mars, brilliant and fiery orange-red, now dominates the southern sky before midnight, standing above fainter Spica in the constellation Virgo. Only a month past opposition, we’re smack in the middle of the best time to observe the Red Planet through a telescope. I try to catch a look every clear or partly cloudy night but nearly missed the chance last night.

Two different hemispheres of Mars. The left image from May 2 shows a shrinking north polar cap and clouds blanketing the base of several volcanoes (dark dots) along the left edge of the planet. Right view taken on April 14 shows the hemisphere currently facing U.S. observers at nightfall. Credit: Christopher Go (left) and Anthony Wesley

The sky suddenly cleared after almost a week of overcast. I figured I’d walk my dog first and then set up the telescope, but 15 minutes later, clouds reappeared in the west. I turned around and footed it back home as quickly as I could, catching just five minutes of Mars light before a blanket of clouds suffocated the starry sky. Yeah, it was worth it.

Jupiter on May 2 displays its two most prominent belts visible in small telescopes, the North and South Equatorial Belts. Credit: Christopher Go

You might think it’s crazy to look at a planet night after night. Amateur astronomers do this for several reasons. First, most nights the air is too turbulent for a clear, sharp view. Looking often maximizes your chances of seeing the planet crisply in stable air. Almost nothing in observational astronomy beats viewing Mars or Jupiter or Saturn without air currents gooing things up. At these special times the dross falls away and the planet looks absolutely real. No exaggeration, you feel like you’re right there.

Planets also rotate. One hemisphere faces us one night, another on a different night or different time of night. Repeated observation gives you a certain familiarity with the “landscape” and alerts your eye to any changes happening. Remember, on most planets, weather plays a role in their appearance. Unexpected changes like a newly-spawned dust storm on Mars or the disappearance of a cloud belt on Jupiter lend an air of anticipation to the night’s viewing.

The sky from the central U.S. facing west-northwest this evening May 3 about 25 minutes after sunset. Mercury will be very low (about 3-4 degrees) but bright. The crescent moon passes just north of the star Eta in the constellation Gemini. Stellarium

Let’s talk about Mercury a minute. Skywatchers blessed with a clear view down to the west-northwest horizon can find the little planet as soon as this evening. Face the sunset direction about 20 minutes after sunset and sweep a few degrees above the horizon with your eyes or a pair of binoculars. The planet now shines at magnitude -1.4 or nearly as bright as it can, an equal to Sirius, the brightest star.

If you don’t succeed, try again in a week on the 10th. After the late January show, the period from May 10-23 will be the best time this year to see the planet at dusk.

Venus hides a star for 7 minutes

Venus occults or covers the star Lambda Aquarii April 17, 2014 

A planet covering a naked eye star is rarer by far than a total eclipse of the moon, and yet Venus did just that yesterday afternoon (U.S. time) from Australia, New Zealand and Micronesia. No one in the northern hemisphere witnessed the event; Venus passed south of the star from our perspective.

Jonathan Bradshaw of Australia captured this exceptional alignment well in his video despite the shaky atmosphere. Lambda Aquarii, a 4th magnitude star in Aquarius, was wiped from the sky for all of seven minutes.

It’s believed that the last bright star Venus or any major planet covered up was 2nd magnitude Nunki in Sagittarius for observers in eastern Africa in November 1981. Venus next occults Pi Sagittarii in 2035 and bright Regulus on Oct. 1, 2044. Mercury will cover up Theta Ophiuchi on Dec. 4, 2015.

Mars will pass in front of Jupiter in an extremely rare planet-over-planet occultation on Dec. 2, 2223. Stellarium

Very rarely, planets pass in front of each other. Over the 300 year span from 1800 to 2100 only 7 “mutual occultations” of this sort have or will occur. Venus crossed in front of Jupiter in 1818 – that was the last observable one. The next will happen when Mars passes in front of Jupiter on Dec. 2, 2223. Clearly, you and I and even our kids won’t be around for that event, but maybe some of our kids’ kids will.

Nature shows that once again even the most unlikely things can happen as long as one key ingredient is available – oodles of time.

See the space station this week / Jupiter and moon a sparkling sight tonight

One of the Expedition 39 crew members aboard the International Space Station photographed a curtain of aurora hovering over blue twilight over northeastern Kazakhstan recently. Click to enlarge. Credit: NASA

The International Space Station (ISS) returns this week to highlight the evening sky. Outside of Venus and the moon, the ISS is the brightest, star-like object in the nighttime sky. It orbits from west to east, the same direction the Earth rotates, and crosses the sky in about five minutes. At an altitude of about 250 miles, the station orbits above most of the auroras we see which is why astronauts get such cool photos of the northern and southern lights from orbit.

Expedition 38 photo of the Kavir Desert in Iran taken with a 200mm lens looks more like swirly water than rock formations. The lack of soil and vegetation allows the geological structure of the rocks to stand out. According to geologists, the patterns result from the gentle folding of numerous, thin, light and dark layers of rock. Later erosion by wind and water cut a flat surface across the folds exposing their internal structure. Click to enlarge. Credit: NASA

The new evening observing season begins for many locations across the northern hemisphere with passes happening once or twice a night. To watch the space station, go out a couple minutes before it’s expected to appear and look for a pale yellow “star” brighter than any other moving from west to east across the sky.

You might be able to also see the Progress 54 cargo craft in the coming week after it undocks with the ISS tomorrow morning and before its destructive re-entry over the Pacific Ocean on April 18. I’ll have viewing tips and times when they’re available. The departure makes way for the arrival of Progress 55 on April 9, which will deliver almost 3 tons of food, fuel and supplies.

Flight Engineer Oleg Artemyev looks at the Earth through the windows of the International Space Station’s cupola this past week. The Expedition 39 crew has been busy with biomedical research this past week focusing on how the immune system responds to living in space. Click to learn more. Credit: NASA-TV

Click HERE or HERE to find times and directions to look for your town. I’ve included a list of times when the ISS will be visible for skywatchers in the Duluth, Minn. U.S. region at the end of this article.

The half moon will be in conjunction with the brilliant planet Jupiter this evening. The map shows the sky facing southwest around 9 p.m. local time. Stellarium

While you’re waiting for the six-man crew of the station to fly over your house or apartment, don’t forget to look up at the first quarter moon in the constellation Gemini tonight. Just “three fingers” or 5 degrees above it shines Jupiter. They’ll make an eye-catching pair for sure.

The moon tonight as seen from North America. How many dark seas or lunar maria (MAH-ree-uh) can you see? Credit: Christian Legrande, Patrick Chevalley / Virtual Moon Atlas

For another easy observing project, try spotting all five of the lunar “seas” visible tonight. These largish, dark spots that form the face of the man in the moon are plains of now-solidified basaltic lavas that erupted 3-3.5 billion years ago in the basins of what were then enormous impact craters. They’re rich in iron and slightly younger than the lighter, older lunar highlands (white regions) which makes them appear darker.

Funny, isn’t it, that all that lunar tranquillity and sweetness should be marred by “crisis”, but I guess this half of the moon serves as a metaphor for life.

Space station viewing times for Duluth, Minn. region:

* Tonight Sun. April 6 starting at 8:29 p.m. Low pass across the south-southeastern sky. Max. elevation: 18 degrees (10 degrees equal one fist held at arm’s length against the sky)
* Mon. April 7 at 9:15 p.m. high across the southern sky. Brilliant pass with max. elevation of 66 degrees
* Tues. April 8 at 8:26 p.m. (high in the south at 42 degrees) and again at 10:03 p.m. across the northwestern sky. Max. elevation: 48 degrees.
* Weds. April 9 at 9:14 p.m. high in the northern sky. Max. elevation: 63 degrees

Mickey Mouse meets Jupiter

Amateur astronomers have been keeping watch over the “Mickey Mouse” ovals this observing season. The ovals are smaller-scale storms – the ‘nose’ rotates clockwise similar to a low pressure system in our planet’s southern hemisphere; the ears are high pressure center rotating counterclockwise. South is up. Credit: Damian Peach

This observing season, three of Jupiter’s many storms – called white ovals – happen to resemble the face of the famous Disney character Mickey Mouse. Two ears and a big nose. Just like Mickey, they might be up to mischief.

Jupiter has lots of these white ovals and brown ones, too. They’re hurricane-like storms in the planet’s atmosphere similar to but smaller than the behemoth Great Red Spot. Most don’t have names unless they’re around a long time or expand and merge with other ovals.

Like four little piggies in a row, four nameless white ovals appear near the Great Red Spot in this photo taken Dec. 29, 2013. South is up. Credit: Damian Peach

The white variety are swirling vortices of cold ammonia ice clouds high in the upper atmosphere. Astronomers find them at many locations tucked within the planet’s cloud belts. Brown ovals are holes in Jupiter’s cloud deck that let us peer deeper into the warmer atmosphere below. They typically only appear within a few degrees of the 20 degree north latitude zone.

The Hubble Space Telescope recorded the merger of three separate ovals in the mid-1990s into Oval BA a.k.a. Red Spot Jr. Notice a similar Micky Mouse shape prior to the merger. Credit: NASA/ESA

Back in the late 1930s, a bright white band of clouds appeared along Jupiter’s 30 degree south latitude zone and eventually coalesced into three separate counterclockwise spinning ovals named FA, DE and BC.

Red Spot Jr. rides Jupiter’s South Temperate Belt on March 7, 2014. South is down. Credit: Christopher Go

In the late 1990s the trio gradually met up merged into a single larger oval named ‘BA’ about as wide as the Earth around 2000. Five years later it developed a reddish-orange color, inspiring amateur astronomers to nickname it Red Spot Jr. The feature, now more circular than oval, still cycles around the planet to this day. Its color, like that of the Great Red Spot, is believed to come from the mixing of sulfur, carbon and phosphorus compounds sucked up from the lower atmosphere.

Zones, belts and vortices on Jupiter. The two most prominent dark stripes are the North and South Equatorial Belts. You can also see the Great Red Spot and many small white ovals. This 14-frame animation spans 24 Jovian days, or about 10 Earth days. The passage of time is accelerated by a factor of 600,000. Credit: NASA

The Great Red Spot (GRS) is one of the biggest storms in the solar system with wind speeds up to 400 mph (650 km/hr). Currently about 1.5 Earths wide,  it’s persisted for several centuries. For all we know it too resulted from a long-ago merger.

Coincidentally, you can see it late tonight across the Americas. The Spot sits squarely on the planet’s centerline around 12:30 a.m. CDT March 29 (1:30 a.m. Eastern, 10:30 p.m. Pacific). If that’s too late, you can start looking about 1-1/2 hours before these times when it will be to the east of centerline. Click HERE to find the best times for viewing the storm from your city.

A large brown oval is known was imaged by Voyager 1 on 2 March 1979. It’s 6,200 miles (10,000 km) across. Amateur astronomers often refer to large brown ovals as “barges”. Click to enlarge. Credit: NASA

Jupiter’s all weather all the time. Ovals change shape, push each other around and even merge. While you might strain to see white ovals or even Red Jr. in the telescope, make no mistake, these are big storms by earthly standards. Mickey Mouse’s ears are about one-third the width of the GRS or approximately half as big as our planet. I wouldn’t want to get close to that hurricane!

Rare treat: Catch Callisto’s shadow on Jupiter’s cloud tops tonight

Callisto’s shadow will follow along Jupiter’s south-south temperate belt from 9:09 p.m. to 12:54 a.m. tonight Feb. 22-23, 2014. A smaller telescope magnifying around 60x or higher will show it. Credit: Meridian software

If you have a 4-inch or larger telescope, tonight you’ll have the opportunity to see a rare shadow transit of the Jupiter’s bright moon Callisto. All four of Jupiter’s easily visible Galilean satellites, so-called because they were first seen by Galileo in the early 1600s, routinely pass in front of the planet and cast shadows on Jupiter’s cloud tops.

Europa is the smallest of the four with a diameter of 3,122 miles and casts the smallest shadow. Io’s shadow is larger and easier to spot, while Ganymede and Callisto – the largest of the quartet – cast the biggest shadows.

Jupiter’s four bright moons and their orbits. Io orbits closest. Each casts a shadow into space, which, when intercepted by Jupiter, appears as a black dot on the planet’s clouds. Credit: Ethan Siegel

Because Io and Europa orbit closest to Jupiter they make more frequent transits across the planet. Ganymede, being further from Jupiter, lines up less often.

Currently we see about five shadow castings per month for Ganymede with only about two for more distant Callisto. When you consider that some Callisto transits occur during daylight hours when Jupiter is unobservable, you can see how infrequent they truly are.

The last time Callisto “dotted” Jupiter was Feb. 6 between 3 a.m. and sunrise. Given the early hour, I suspect very few skywatchers across the Americas witnessed that event. Tonight’s transit occurs during convenient viewing hours starting at 9:09 p.m. CST (7:09 p.m. Pacific, 10:09 p.m. Eastern) and wrapping up about 3 1/2 hours later at 12:54 a.m. CST Feb. 23.

Shadow transits, particularly of Callisto, are leisurely affairs. That’s because it’s the most distant of the four moons and orbits slowest. Io, the closest, puts on a show lasting a little more than half as long or about 2 hours 10 minutes.

Callisto’s next shadow transit occurs on March 12 between 4:11-8:03 p.m. CST. With sunset at around 7 p.m on that date, the transit ends only an hour after sunset in the central U.S. After that we’ll have to wait until April for the next one.

I hope you’re skies are clear tonight so you can check it out.