Tag Archives: Jupiter

3 bright planets slow jam at dusk this week

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Jupiter, Venus and Mercury last night 35 minutes after sunset low in the northwestern sky. Details: 150mm lens at f/2.8, 1/30″, ISO 400. Photo: Bob King

Last night we finally cleared off after four solid days and nights of gray and rain. Sparkling low in the northwestern sky was a most welcome sight – Venus, Jupiter and Mercury. This week they will undergo to a series of remarkable gatherings in the early evening sky.

Venus leaped out immediately as the brightest of the trio. It stood 6 degrees above the horizon; that’s three fingers held horizontally at arm’s length. Jupiter jumped out next some 5 degrees to the upper left of Venus. Mercury, the dimmest of the the bunch, was very easy in binoculars but took a bit of concentration to see with the naked eye.

I’ve highlighted several nights of the triple planet gathering over the coming nights. Jupiter is colored yellow and Mercury pink to tell which is which. Created with Stellarium

This jam has just begun. Watch over the coming nights as the three planets move closer together to form a series of ever-changing jeweled triangles. Tomorrow night Mercury and Venus will be closest (1.4 degrees); Mercury and Jupiter on Memorial Day (2.3 degrees) and Venus and Jupiter on May 28 (1 degree).

All you need to see them is an unobstructed view to the west-northwest. You can begin your search about 30 minutes after sunset; get an early start because the planets set about an hour later. Binoculars can prove most helpful in case the sky’s hazy or if you have difficulty finding Mercury.

Left: If you could hover high above Earth’s north pole today and look down on the solar system, this is how the evening planets would be laid out. You can easily see how far they are from one another. At right, viewed from the flat plane of the solar system, they appear to bunch up. These occasional bunches caused by perspective are called conjunctions. Illustration: Bob King

As you can see from the nightly maps,  Mercury moves upward from the western horizon to join Venus, passes it and then teams up with Jupiter. Mercury moves rapidly because it orbits the sun most closely. Venus is also moving up from the west but more slowly, so it essentially stays in the same spot. Jupiter meanwhile drops down toward the western horizon. Earth’s motion around the sun is much faster than Jupiter’s causing the sun to literally “get in the way” between our two planets. From our perspective, Jupiter will soon disappear in the solar glare and won’t be seen again until early July when it reappears in the morning sky.

Although the trio may appear close to one another in the sky, they’re millions of miles from each other and the Earth. We see them together because they lie along the same line of sight for the coming week.

Watch as Venus, Jupiter and Mercury align after sunset

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The sky facing northwest this evening about 30-35 minutes after sundown. Venus and Jupiter should be relatively easy to spot provided you have an unobstructed view; Mercury might require binoculars. Stellarium

Hey, hey, hey. Three planets are now lining up in a neat row at dusk. Watch for the trio starting 30-35 minutes after sunset when they’ll be low in the northwestern sky.

The distance between Venus and Jupiter has shrunk over the past week and now stands at about 8 degrees or just shy of a fist held at arm’s length against the sky. Mercury finally joins the crew after emerging from the sun’s glare, though it will be the most challenging to see because of low elevation. As always when hunting planets in twilight, be a slacker and bring binoculars to make the job easy. Mercury will become easier to see by mid-week as it races up from the sun.

All three twilight planets appear close together near the sun in evening twilight is because they all lie in nearly the same line of sight (arrow) as seen from Earth. This view is a frame from a live orrery – click to watch the planets orbit the sun. Credit: dd.dynamicdiagrams.com

Venus is brightest at magnitude -3.4, while Jupiter and Mercury are near equals at -1.5 and -1.3 respectively. A week from now the three will all be clustered within a couple degrees of each other and form striking, triangle-shaped configurations that change night by night. I’ll have maps and times to look later this week. Get your cameras ready!

Earth’s ghostly light touches the crescent moon tonight

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The 2-day-old crescent moon shines over a bog north of Duluth, Minn. last night. Light reflected from the Earth faintly illuminates the moon’s full outline. Details: 200mm f/2.8, ISO 800, 1/2″ exposure. Photo: Bob King

Wow, the moon sure looked lovely last night. At dusk it was a sharp crescent against the blue sky, but later the entire disk was visible thanks to the the Full Earth. Full Earth? Had you been able to stand on the moon and look back in this direction, you would have seen our planet hanging like a big, blue ornament in the velvety black lunar sky. When the moon’s a sickle, light reflected from Earth – called earthshine – lights up the part of our satellite still in shadow.

Earth and moon phases complement one another. The top strip shows the moon phases and the bottom the corresponding Earth phases seen by an astronaut standing on the moon’s surface looking back at Earth. One difference: Earth appears almost 4 times bigger than the moon. Illustration: Bob King

Moon and Earth phases are complementary. A thin crescent in our sky means a person standing on the moon sees a nearly full Earth. A half moon here means a half-Earth there, and around the time of full moon, our lunar astronaut sees a crescent Earth.

A ramble across the earthlit portion of the moon in binoculars will reveal large dark areas (lunar seas) and several bright blotches – the craters Tycho, Copernicus and Aristarchus. Photo: Bob King

Sunlight reflected from our blue, cloud-streaked globe gently illuminates the full outline of the moon. Since the light is reflected rather than direct sunlight, earthlight is faint and rather mysterious-looking. From the surface of the moon, it resembles twilight here on Earth. The crescent itself is lit directly by the sun and appears brilliant in comparison.

Earthshine is twice-reflected sunlight – one bounce off the Earth to the moon and then a bounce back from the moon to Earth. Both moon and Earth absorb much of the sun’s light, which is why earthshine appears faint compared to the sunlit crescent. Illustration: Bob King

A full Earth reflects a lot of sunlight back at the moon, so earthshine is brightest when the crescent is thinnest. As the moon’s phase waxes to half and beyond, the Earth’s phase wanes, going from full to half to crescent. With less Earth to reflect sunlight, earthshine gets fainter and fainter. It also doesn’t help that the area for the Earth to illuminate shrinks as the sunlit portion of the moon grows ever larger night after night.

Jupiter (top left) and Venus (lower right) joined the crescent during twilight last night. Tonight the moon will be to the left of Jupiter. Photo: Bob King

Tonight’s crescent moon will be higher up in a darker sky, so the smoky earthlight should be even easier to see. When you step out for a look, you’ll also see a brilliant “star” a fist to the moon’s right. That’s Jupiter. If you have binoculars, take a minute to study the earthlit portion – you’ll see a surprising number of features there including several large dark areas (the lunar seas) and even a few craters, which look like bright spots.

Venus returns to the evening sky in grand style tonight

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Venus returns like a spring flower to evening twilight this month. This was the view last night 35 minutes after sunset looking low in the northwestern sky. Photo: Bob King

Guess who’s finally come out of hiding? Yep, it’s Venus, a planet we’ve seen neither hide nor hair of for months. Venus has been masked by the sun’s glare since late January for northern hemisphere sky watchers. Not anymore.

Like a child letting go of her parents, the brightest planet of them all is finally stepping away from the sun. You can see her for yourself chaperoned by a remarkably thin moon low in the northwestern sky beginning 20-30 minutes after sunset tonight.

I made my first attempt to catch a glimpse of the planet last night, figuring it might only show in binoculars. Boy, was I surprised. Although only 4 degrees high, Venus jumped right out in binoculars and was also plainly seen without optical aid. I followed the lovely “evening star” from 20 minutes past sunset for at least another 20 minutes before it sunk into the trees.

Watch for a wonderful close conjunction of returning Venus and a one-day-old crescent moon tonight. This map shows the sky facing west-northwest 30 minutes after sunset. Tomorrow night the moon will have moved up and away from the planet toward its next encounter with Jupiter. Stellarium

Tonight will be an extra special one for Venus watchers. The goddess of beauty and love will be joined by an extremely thin crescent moon for a brief time after sunset. I encourage you to find a spot with wide open view to the west-northwest to see the show.

Find your sunset time HERE and then arrive at your selected spot a few minutes after sundown. Bring binoculars so you can start scanning about 20 minutes later. Look a short distance to the left of the “sunset point”, that telltale bright glow along the horizon indicating where the sun has gone down. I don’t which you’ll see first – moon or planet – but once you find one, you’ll find the other. They should be a ravishing sight in binoculars!

By tomorrow night the moon will be well above Venus on its way toward Jupiter. Speaking  of which, Jove and Venus – with Mercury thrown in for good fun – will have their own close encounter May 27-29. The triple gathering promises to be the naked-eye highlight of the month, but more on that later.

The ever-changing geometry between Earth and Venus as the two planets orbit the sun causes Venus to go through phases just like the moon. In the evening sky, the planet is to the left or east of the sun; when visible at dawn, it’s to the right or west of the sun. Illlustration: Bob King

If the weather doesn’t cooperate tonight, you can use the moon again Saturday night to point you to the planet. Venus gleams about one fist held at arm’s length to the lower right of the lunar crescent.

As spring gives way to summer, Venus will pull away from the sun and slowly become more easily visible at dusk. Right now it’s on the far side of the sun from Earth and appears like a tiny full moon through a telescope. During the remainder of the year its phase will change from full to half (at Halloween) and finally a crescent at Christmas as the speedier planet catches up with our own.

Concealed planets exposed plus it’s spring break on Mars

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The sun and its pack of planets photographed earlier today by the coronagraph aboard the SOHO observatory. The sun (white circle) is blocked by an opaque disk so astronomers can study the streaky solar atmosphere called the corona. Credit: NASA / ESA

Half the planets have gone into hiding. Mercury is too low in the dawn sky for northern hemisphere skywatchers, and Mars, Venus and Uranus are gathered around the sun concealed by its glare. Only Jupiter and Saturn remain available for our viewing pleasure.

Still, it’s hard to keep planets hidden away when you’ve got the eyes of the Solar Heliospheric Observatory (SOHO) on your side. SOHO orbits around a stable region of space called the L1 Langrangian point where the gravity of Earth balances that of the sun.

SOHO orbits about a million miles ahead of Earth in line with the sun in a small “halo orbit” around the L1 Lagrangian point. From this vantage point it keeps the sun and Earth in view 24/7. Credit: Office of Naval Research

From this prime observing spot, scientists use SOHO’s cameras to study the sun in many wavelengths or colors of light. Special devices called coronagraphs block the overly-bright solar disk with a metal stop to allow viewing of the sun’s outer atmosphere or corona. They also show other objects in the field of view like comets and the current gang of planets – Uranus, Venus and Mars.

Since the planets are very near one another, lots of interesting lineups will happen in the coming days. Venus reaches superior conjunction on March 28 (tomorrow) when it lines up on the opposite side of the sun from Earth. Six hours later it’s only one degree (two full moon diameters) below Uranus. An hour after, Uranus is in conjunction with the sun. Then on April 6-7 Venus and Mars will be in conjunction just half a degree apart. Is this beginning to sound like a barn dance?

One thing to remember about conjunctions – the planets involved are not physically close; they only appear to be because we see them in the same line of sight. If you’d like to watch all these interesting encounters, check out SOHO’s latest coronagraph image.

Approximately every 26 months, Mars passes almost directly behind the sun from Earth’s perspective. During this time, NASA will halt communications with the two rovers. Credit: NASA/JPL-Caltech

For us, Mars’ proximity to the sun is interesting but inconsequential. Not so for the Curiosity mission. On April 17 the planet is in conjunction on the opposite side of the sun from Earth. From our perspective, Mars will appear extremely close to the sun’s brilliant disk. Radiation from solar flares and high-speed subatomic particles in the sun’s corona can disrupt radio transmissions between the two planets during close alignments like this one. To prevent compromised radio commands from reaching either Curiosity or the older Opportunity rover, mission controllers will temporarily suspend transmissions from April 9 to 26.

Wide angle view of Yellowknife Bay taken by one of Curiosity’s hazard avoidance cameras on March 27, 2013. The rover recently resumed science operations after recovery from a computer glitch. Credit: NASA/ JPL

Communications from Mars to Earth will also be reduced. To stay in touch, Curiosity will send daily beeps to Earth. Meanwhile both rovers and orbiting Mars satellites will continue science operations. Data gathered will be stored and then beamed to Earth in early May. The rovers’ spring break will be tame by earthly standards; both will stay put during the interval to prevent any shenanigans.

The bright star Sirius and planet Jupiter perform a balancing act on either side of Orion’s Belt this month and next. This may shows the sky facing southwest around 8:30 p.m. in late March.  Maps created with Stellarium

Did I mention there are still two great planets out at night? Jupiter stands high in the west-southwest at nightfall. It’s the brightest object in that direction. Saturn comes up later around 11 o’clock in the southeast about one extended fist to the lower right of Spica. The full moon will be near Spica tonight and Saturn on Thursday night. Much to see for all!

The full moon will swing by both Spica (tonight) and the planet Saturn tomorrow night. This map shows the sky facing southeast around 11:30 p.m.

St. Pat’s aurora update plus a pleasing lunar lineup tonight

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Green auroral rays topped with pink from earlier this morning near Cloquet, Minn. photographed by Matthew Moses

The sun’s wind of particles has been pounding Earth’s defensive magnetic shield since early this morning. A magnificent display of auroras erupted in response. While hurricane winds can reach over 200 mph, they’re nothing compared to solar wind speeds. Top speed for this storm happened at 5:07 a.m. CDT this morning  when electrons and protons hit the magnetosphere at 477 miles per second (767 km/s) or 1.7 million mph. Of course we’re talking about a very dilute soup of particles compared to the far denser atmosphere, hence the destructive power of a hurricane.

The colorful donut shows the extent of the auroral over at 6:53 p.m. Central time this evening recorded by the POES satellite. Red is a good indicator of strong auroral activity. Let’s hope it’s still there when the U.S. rotates under it later this evening. Credit: NOAA

The storm has continued throughout the day at high levels. Judging by recent satellite plots of the auroral ovals, those vast caps of northern and southern lights centered on Earth’s magnetic poles, residents of the Scandinavia countries, Iceland and Greenland must be experiencing a great light show at the moment.

Auroras look to continue into the evening hours tonight for southern Canada and the northern U.S. once darkness returns. The latest forecast calls for minor storms, but you never know. If it’s clear, walk your dog and keep your eyes to the sky.

Watch the moon slowly slip between Jupiter and Aldebaran tonight. This map shows the sky facing southwest around 10:30 p.m. Central time. Stellarium

Even if auroras fail to materialize, the moon has something fun in store. Tonight it will march  directly between the planet Jupiter and Aldebaran, the brightest star in Taurus the Bull. The three will be closest to a perfect lineup one atop the other around 10:30 p.m. Central time or 8:30 p.m. Pacific. If you look early and then check back a hour or two later, you’ll easily see how quickly the moon moves through the sky as it orbits the Earth.

Tip your gaze toward Jupiter and the moon tonight

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Watch for the celestial triangle of Jupiter, the waxing moon and Aldebaran high in the southern sky tonight. Maps created with Stellarium

The big events in astronomy are wonderful to watch and read about, but it’s the small stuff that makes up the bulk of sky watching. Case in point. Tonight the moon will pass between the planet Jupiter and the bright star Aldebaran in Taurus the Bull. The actual passage happens in dark skies for eastern European and Asian observers. By the time it’s dark in the U.S., the moon will have moved on to the east, and the trio will form an eye-catching triangle.

If you have a small telescope, you have a chance to see Jupiter’s four brightest moons in an odd configuration. We often see them in a nearly straight line on either side of the planet, but tonight only Io and Europa will be aligned in that fashion. Callisto floats above the planet’s south polar region, while Ganymede hovers near the north pole.

Jupiter and its four brightest moons through a small telescope tonight Feb. 18, 2013. Notice their odd arrangement, which has to do with the tilt of Jupiter’s axis.

These interesting, non-linear arrangements happen because Jupiter’s axis tilts 3.3 degrees (Earth’s is 23.5). Presently, the planet’s north pole is tipped in our direction. Since the four bright moons all orbit about Jupiter’s equator, the tilt causes the more distant ones – Callisto and Ganymede – to miss or nearly miss the planet when they pass directly in front of it.

By the time those moons move far enough to either side of Jupiter, the difference caused by the planet’s axial tilt isn’t as obvious and once again, all four moons appear approximately in a line. The closer-in moons Io and Europa always pass in front of the planet from our perspective on Earth, because the tilt isn’t enough to shift them above or below Jupiter’s disk. Every six years however, Earth’s orbital plane exactly lines up with Jupiter’s equator and all four moons parade back and forth in straight lines.

A rare double transit of Jupiter’s moon Ganymede (top) and Io on Jan. 3, 2013. Here, the sun is shining from the left, causing shadows cast by the moons to fall onto the planet’s cloud tops. Credit: Damian Peach

One last note. The moons regularly pass in front of or in back of Jupiter during their orbits. Tonight, Ganymede will be occulted or covered up by the planet starting at 9:16 p.m. CST. The event can be easily observed in any telescope. Go out about 10 minutes before and watch as Ganymede and Jupiter get closer and closer until the moon sticks to the planet’s limb like an earring.

If Jupiter were occulting a star, which is a point of light, it would disappear very quickly. Ganymede will take a minute or two because it has real girth despite its stellar appearance. You can find lots of fun occultations and other Jupiter moon events at Sky and Telescope’s online Jupiter’s Moons site.

Jupiter and moon put on a great show at 18 below

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The moon and Jupiter through a 400mm telephoto lens last night around 9:30 p.m. (CST) when they were near their closest separation. You can just make out Jupiter’s disk. Photo: Bob King

Jupiter and the moon were fabulous last night. I hope you got to see them. We were clear in Duluth, Minn. though there a price to be paid in frozen fingertips. The temperature hit -18 F at my house.

Our two celebs were so close together you could easily see the moon’s motion to the east in just 20 minutes. For a change, the air was tranquil overhead, giving steady, sharp images at the telescope. Craters like Copernicus, Plato and Tycho were crisply detailed and Europa’s shadow on Jupiter’s cloud tops looked like the most perfect of points.

Five of the 11-day-old moon’s most prominent craters are visible tonight in 8x (or higher) binoculars and small telescopes. Three of them – Copernicus, Kepler and Tycho – are surrounded by bright rays, which are aprons of impact debris. Plato has a smooth, dark, lava-flooded floor. Credit: Frank Barrett with my annotations

Tonight the moon moves further east into Taurus. As it waxes closer to full, we get more moon for our buck. That means more cool craters and alien terrain to pour over in binoculars and telescopes. I encourage you to take a look even if the weather bites. Just throw on a few more layers and laugh at the cold.

Heavy fog at -20 F over Lake Superior near the Lester River in Duluth, Minn. this morning. Cold air moving over the warmer lake condenses into tendrils of mist which gather into foggy clouds. Photo: Bob King

Beautiful Jupiter-moon conjunction on tap for tonight

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A partial halo rings the moon and Jupiter (upper left) last night Jan. 20, 2013. Tonight the moon will sit right under the planet. Photo: Bob King

Ready for another one of Jupiter’s fly-by-night meetings with the moon? Tonight’s pairing of planet and moon will be the closest yet in a series that began last fall.

Observers in North and South America will get the best views at the most convenient hour. At 9 p.m. (CST) Jupiter will be just one moon diameter (1/2 degree) north of the moon and high in the southern sky.

The waxing gibbous moon and Jupiter will be closest around 9 p.m. (CST) together tonight Jan. 21, 2013 high above the constellation Orion. Maps created with Stellarium

Their proximity also means you have the opportunity to watch the moon “move its own diameter” in a hour. With Jupiter as a reference, you’ll easily see the two approach and separate during the evening. And yes, the moon moves a moon-span in about an hour as it orbits planet Earth. Check it out yourself.


Jupiter emerges in real time from behind the moon during the Dec. 25, 2012  occultation seen in Brazil. Credit: Carlos Bella

Sky watchers living across a wide swath of South America will get an extra treat – a Jupiter occultation. Because the moon is relatively close to Earth, its position shifts slightly against the background stars depending on your location. Seen from central S. America, it’s over 1/2 degree farther north compared to the view from northern U.S., putting it on a path to occult the planet. As the moon travels eastward during the night, it will first cover and then uncover Jupiter. Click HERE for a map and list of cities and times where the occultation will be visible.

Simulated view of the moon and Jupiter – with satellites Ganymede (G), Io (I) and Callisto (C) – as seen in binoculars and small telescopes tonight. North is up, west to the right.

Binoculars will show 2 or 3 Jovian satellites tonight depending on magnification and how steadily you can hold them. Through a telescope you’ll see all three plus be able to watch the shadow of Europa pass over the planet’s cloud tops between 9:18 p.m. and 12:52 a.m. (CST). Look for a tiny black pinprick south of Jupiter’s thick South Equatorial Belt (SEB).

A glance skyward tonight is all that’s necessary to witness this delightful celestial drama unfold. Don’t miss it. Skywatchers in the mainland U.S. won’t see Jupiter and the moon snuggled up this close again until Sept. 2, 2016!

Jupiter’s poles crackle with volcano-induced auroras

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Both a bar magnet (left) and Earth are surrounded by magnetic fields with north and south poles. Earth’s field is shaped by charged particles – electrons and protons – flowing from the sun called the solar wind. Credit: Andy Washnik (left) and NASA

On Earth the aurora is intimately connected to solar activity. High speed electrons and protons from the sun find their way into the upper atmosphere by following invisible lines of magnetic force that surround our planet much like the those around an old fashioned horseshoe magnet. You can render the invisible visible by placing a magnet on a sheet of paper and sprinkling iron filings around it. Immediately they’ll align themselves in series of arcs defining the magnetic lines of force.

Solar wind particles are a bit like guided missiles. Under the right conditions, they spiral down the field lines and crash into Earth’s atmosphere, temporarily dislodging electrons in oxygen and nitrogen atoms. When the sprung electrons meet up with their parent atoms an instant later, those billions of oxygens and nitrogens emit tiny flashes of green and red light. It’s this sub-microscopic activity that’s behind a spectacular display of northern lights.

Nature often dazzles by numbers. We don’t notice a few snowflakes, but trillions of them can be whipped into a storm powerful enough to stop us in our tracks.

Jupiter’s aurora photographed in ultraviolet light in March 2007 by the Hubble Space Telescope. The bright dot at right is Io’s auroral “footprint” described below. Click to enlarge. Credit: NASA/ESA/J.Clarke

Jupiter also possesses a magnetic field or technically, a magnetosphere, but as you might guess, it’s far larger and more powerful than Earth’s. This is due both to Jupiter’s size and rapid rotation rate of just 10 hours. We can picture planets with magnetospheres as spinning magnets. Spinning a small magnet creates a small electric current but spinning a huge magnet like Jupiter at a rapid speed creates a current of 10 million volts at its north and south poles. Powerful electric fields coupled with the planet’s “animal magnetism” grab hold of any particles in the neighborhood and dash them into Jupiter’s upper atmosphere, where they spark extensive auroras.

Northern and southern lights on seen by Hubble on September 20, 1997. Electrified sulfur and oxygen atoms from Io are primarily responsible for Jupiter’s auroras, but the sun and possibly material in the planet’s high atmosphere also play a role. Click to enlarge. Credit: NASA/ESA/J.Clarke

On Earth, particles from the sun are the chief cause of the aurora, but on Jupiter they play only a small role. The planet relies largely on its moon-sized moon Io, the most volcanically active body in the solar system.

Io is the innermost of the Jupiter’s four brightest moons and orbits the planet in just 1.8 days. Astronomers have mapped more than 300 active volcanoes on this small world that spew lava across the landscape and volcanic gases into outer space at the rate of one ton per second.

Sulfur and oxygen atoms in the expelled gas are electrified (ionized) by Jupiter’s magnetic field and eventually make their way down the field lines headed for the poles. As they crash into molecules in the planet’s atmosphere, their electrons are temporarily stripped off. When the sulfur and oxygen ions eventually slow down, they snatch back their electrons and emit tiny bursts of ultraviolet and X-ray light in the process. Voila – auroras bloom over Jove’s poles!

Like blurry images in a mirror, Io, Ganymede and Europa leave an electrified impression of themselves in Jupiter’s polar aurora in this photo taken in 2000 by Hubble. Io even has a ‘tail’ that sweeps around the top of Jupiter as the planet rotates. Click to enlarge. Credit: NASA/ESA/J. Clarke

Jupiter auroras, which show up best in UV and X-rays, are thousands of times more intense than anything here on Earth. Buried within their curtains and curls are features never seen in earthly auroras. As Jupiter’s magnetic field sweeps past Io, powerful electric currents connect the moon directly with the planet’s magnetic poles. Billions of electrified sulfur and oxygen ions are swept along by the field, slamming into the polar atmosphere to create a set of bright dots or “footprints” of aurora at both poles.

Particles from Io, shown as the glowing red donut around Jupiter, get pulled into the planet’s magnetic field (blue arcs) and slam into the atmosphere to create auroras. The electrical conduits (pink) from Io, Ganymede and Europa lead to their individual “footprints”. Credit: LASP/NASA

Ganymede, the only moon in the moon in the solar system with its own magnetic field, and Europa are also connected to Jupiter’s magnetic field and sport their own polar footprints. While it’s understood how Ganymede can hook up with the planet’s field, it’s less clear with Europa. You need something to conduct electricity like Io’s ions or a magnetic field to make the connection to Jupiter. Maybe we’ll learn the answer come 2016, when the Juno space probe, launched in August 2011, is expected to arrive at Jupiter. One of its mission’s goals is to examine and take close-up photos of the planet’s mighty auroras.

(Note: Thanks to Jan Karon’s question for the inspiration for this blog.)