Planetary oddball Uranus tempts skywatchers on October nights

Uranus is one of the two “ice giant” planets, edging out Neptune as the third largest planet. Its atmosphere is mostly hydrogen and helium with enough methane to tint the planet blue. Deep inside, Uranus has a rocky core surrounded by a thick rind or slushy ice. Uranus is “only” 1.77 billion miles from Earth this October. Credit: NASA/ESA/L. Sromovsky

This week, Thursday to be exact, the planet Uranus and Earth will be at their closest for the year. This special day is called opposition and refers to Uranus appearing opposite the sun in the sky. When the sun sets, the 7th planet will crest the eastern horizon, arc across the sky the entire night and then set at sunrise.

When planets are at opposition they’re not only closest but brightest. Bright of course is a relative term. Mars at opposition can become much brighter than Sirius, the brightest star. Uranus shines meekly at magnitude 5.7 slightly above the naked eye limit. On dark nights if you know exactly where to look, you can glimpse the planet without optical aid. I’ve seen it many times; my hope is that with the help of these maps, you will too.

Engraving of 18th century astronomer William Herschel in his element.

English astronomer John Flamsteed was the first to see Uranus in 1690 but thought it was just another star in the constellation Taurus. He even gave it a name: 34 Tauri. Despite running across it at least six times he never realized he was looking at a planet and not a star.

Enter William Herschel, a German transplant living in Bath, England and passionate sky watcher who never missed a clear night. From his garden on 19 New King Street, he stumbled across what he thought was a new comet in Taurus in his homemade 6-inch reflecting telescope on Tuesday night March 13, 1781. Closer examination of the object at high magnification showed it as a fuzzy disk, distinct from the point-like stars.

Extract from William Herschel’s journal entry made on March 13, 1781. The second paragraph reads: “In the quartile near Zeta Tauri the lowest of 2 is a curious either nebulous star or perhaps a Comet.” Source: Journal of the Royal Astronomical Society

Like any good comet hunter then or now, Herschel returned to his “comet” several nights later on the 17th to see if it had moved. For all practical purposes stars are fixed, but planets and comets inch across the sky as they orbit the sun. They can’t help but give themselves away.

Herschel next reported his find to England’s Royal Astronomical Society so others could see and track the new object. Very soon, astronomers realized this was no comet but a brand new planet, the first discovered since antiquity.

Because its axis is tipped 98 degrees, Uranus orbits the sun spinning on its side. The poles alternately face the sun for 42 years at a time. Credit: Nature of the Universe

And what an odd planet! We now know that Uranus is not only the coldest planet in the solar system – even chillier than more distant Neptune – but the only one that spins on its side. Like Earth, most of the planets spin like tops with their rotation axes tilted a little this way or that, but Uranus takes it to the extreme with a tip of 98 degrees. Seen from afar, it looks like a ball rolling on its side, and that has some curious consequences when it comes to seasons.

Since Uranus takes 84 years to make one spin around the sun, each of the planet’s poles gets 42 years of continuous sunlight during the summer season followed by 42 years of winter darkness. The northern hemisphere currently faces the sun with the first day of Uranian summer due in 2028.

Because of the planet’s extreme axial tilt, we see Uranus from different perspectives over its 84-year orbit. Right now the view is “opening up” again after a near “edge-on” view in 2006. Credit: NASA/ESA/G. Bacon – STScI

“Day” is something of a misnomer. A day on the planet lasts a little more than 17 hours, but as seen from the poles, a day in the traditional sense lasts 42 years. If you could hang out at one of the poles, the sun would rise on the first day of spring, creep slowly across the sky and finally set on the first day of fall 42 years later.

Uranus comes up into view around 9:30 p.m. local time in the southeastern sky below the Great Square of Pegasus and to the right of the small constellation Aries. It’s not far from the star Delta in Pisces. Once you find Delta with eye and binoculars, you’re ready to use the detailed map below. All maps: Stellarium

Uranus is the third largest planet, edging out distant Neptune by just 85 miles. All the large outer solar system planets radiate heat from their cores which are still contracting under the force of gravity since their formation 4.5 billion years ago. Contraction creates heat which escapes the core and spills into space.

Delta heads up a little row of stars that points toward the planet Uranus. If you place Delta to one side of your binocular view, you’ll see Uranus near the other side. The planet is the same brightness as the 5.7 mag. star. Positions are shown every 5 days from Sept. 30 to Oct. 15.

Oddball Uranus gives off little internal heat and no one’s sure why. Temperatures as low as -371 degrees F (-224 C) have been recorded in its lower atmospheric layers. Scientists hypothesize that there might be some sort of barrier deep below the atmosphere that blocks heat coming from the core. That or the planet was struck by another developing planet long ago, causing it to expel its internal heat as well as knocking the axis kittywampus.

Uranus and a few of its moons as seen in the Hubble Space Telescope. The planets also has at least 13 very narrow rings composed of water ice coated by dark, organic materials. Credit: NASA/ESA

While Uranus may be challenging to see with the naked eye, it’s easily visible in binoculars even in less than ideal skies. That’s the good news. The bad news is that the planet isn’t near any bright stars that would give a beginning observer a leg up in finding it. No problem. We’ll get you there anyway.

Through a telescope magnifying about 75x you can tell you’re looking at a planet and not a star. Stars are tiny and possess a fiery radiance; Uranus looks slightly larger and “dull” in comparison. Once you crank up the power to 150x and higher, you can’t miss its tiny disk, tinted blue from atmospheric methane gas. Amateur astronomers using scopes in the 12-inch to 16-inch range can even spot two of the planets 27 known moons, Titania and Oberon.

Uranus moves slowly westward through the constellation Pisces during October. You can watch its progress in binoculars as it passes among several “fixed stars” of similar brightness. Face southeast starting around 9:30 – 10 p.m. when the planet has cleared the trees and houses and begin by locating the Great Square of Pegasus, a big, vacant square of sky with a star marking each of the four corners. Drop down one outstretched fist below the Square to find the dimmer star called Delta in the constellation Pisces. Now center your binoculars on Delta and use the map below to hone in on the planet’s location.

I wish you well in discovering the 7th planet all by yourself just as Herschel once did.

Concealed planets exposed plus it’s spring break on Mars

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.

Uranus makes a rare pass by a star in Pisces

To get oriented, face east around 10 o’clock and find the Great Square of Pegasus. Uranus is located one “square width” below and in line with the Square’s left side and forms an isosceles triangle with Delta and Omega Piscium. Charts created with Chris Marriott’s SkyMap

Last week at a star party I aimed my telescope at Uranus for the first time this season and was pleasantly surprised to find it next door to 44 Piscium (PYE-see-um), a star of identical brightness. One by one people lined up for a look. We had fun comparing the two colors – Uranus an obvious blue against the yellow-orange of 44 – and trying to figure which was the planet and which the star. That was apparently too easy, since everyone had no trouble telling them apart.

As we zoom in a little, Uranus and 44 Piscium stand out better. Delta and Omega Piscium will guide binocular users to the pair. Uranus is magnitude 6 and just visible with the naked eye from dark rural skies. Stars are shown to magnitude 7 with the view facing around 10 this evening (22nd).

Since then, Uranus has been edging closer to the star night after night. Tonight (Sept. 22) and tomorrow they’ll be at their closest and form a striking “double star” through binoculars and telescopes. How close? Only 1.4 arc minutes  or about 1/20 the diameter of the full moon. Those with excellent skies will see the pair as a single, faint, unresolved star, while binoculars will show them as a pair of close-set “eyes” staring straight back at you. In the coming nights, the planet will slowly pull away to the west but remain near 44 through the end of the month. Finding the 7th planet and seeing it groove through the sky is a very worthwhile observing project that requires only the simplest of equipment.

Our final chart is close in, so you can use it to track Uranus’ movement to the right (west) over the coming nights. Positions are shown for 10 p.m. CDT. The blue dots show the planet on the nights of closest approach.

Uranus always appears identical to a star with the naked eye and binoculars, but a small telescope magnifying 60x or higher will not only show the color difference between star and planet but also reveal Uranus as a tiny disk. 44 Piscium will remain a flickering point of light even at high power – a fine side-by-side example of the difference in appearance between a star-like planet and a star. I wonder if the colors will be visible in binoculars? Only one way to find out. Good luck!

Weird Uranus auroras seen first time from Earth

Wild leeks push through the dried leaves of the forest floor each April in Duluth's Hawk Ridge nature reserve. Photo: Bob King

The ground is snapping and popping. Ever hear this? On quiet evenings in the country in mid-spring, you can walk up to a roadside ditch along the edge of the forest and listen to green plants pushing up through last year’s leaves and grasses. It sounds like fire consuming tiny twigs. Green fire.

I used to think it was insects but I’ve looked with a flashlight and heard it for so many years I’m certain the sound is from plants on their way up and out. Not even night can hold back the call of the sun.

The sun reached out to Earth this week in the form of the aurora borealis. Uranus also displays auroras but as dots instead of arcs and curtains. Auroras were seen by the Voyager 2 spacecraft during it 1986 flyby of the planet, but this is the first time they’ve been spotted from Earth.

Uranus' northern lights have an unusual form and different location compared to Earth's due to the planet's unusually large tilt and offset magnetic field. Uranus faint ring system is also seen. Credit: Laurent Lamy

Using the Hubble Space Telescope, astronomers photographed dim dots of aurora glowing above Uranus’ pale blue cloudtops. The Uranian lights last only a few minutes at a time before fading away, making them even trickier to catch than the earthly variety.

Auroras on both Earth and Uranus are produced when charged particles (electrons and protons) from the sun enter a planet’s magnetosphere or protective magnetic envelope, and are guided into the polar atmosphere by the planet’s magnetic field.

Uranus' axis is tilted almost 98 degrees. During its 84-year orbit, first the north pole and then the south pole points toward the sun. In between, one side or another faces the sun. Credit: Smithsonian

Earth’s magnetic field is tipped just 11 degrees relative to the our axis of rotation. When the solar wind hits, the particles travel toward the north and south polar regions, which is why auroras are visible in Earth’s more northern and southern locations than nearer the equator.

Uranus is another place altogether. Its rotational axis is tilted 98 degrees compared to Earth’s modest 23.5. This means the planet literally rotates on its side like a bowling ball rolling down a lane. Its magnetic axis is way out of whack too – not only offset from the planet’s core but tilted 60 degrees relative to the rotation axis. Back during the Voyager 2 flyby, the planet’s south pole was pointed toward the sun with the magnetic poles far off to the sides. Voyager observed auroras on Uranus’ nightside resembling those on Earth.

The Earth, with its modestly-tipped rotation axis (blue arrowed line) and nearly north-pointing magnetic field axis, is a far cry from the extremes of Uranus.

Uranus has since moved along its orbit so that now its side faces the sun instead of a geographic pole. This happy circumstance means that one of the magnetic poles points directly at the sun.

When a big blast of solar wind left the sun in September 2011, the particles sped past Earth in 2-3 days, blew by Jupiter two weeks later and arrived at Uranus in mid-November, creating the odd dots of aurora that seem to lie near the equator. They’re really near the planet’s magnetic poles!

Uranus, you’re a mixed up planet, but we love you anyway. To read more about the new aurora discovery, click HERE.

Uranus passes Mercury in the dusky dusk

Mercury will be highest in the west this coming week as it slowly fades. A small telescope will show its half-moon shape. Created with Stellarium

Mars may be closest to the Earth these next few days, but Mercury’s not doing too bad either. Tomorrow it reaches it greatest elongation east of the sun in the evening sky. Provided you’ve got a decent view to the west, you should have no problem seeing the planet starting around 45 minutes after sunset, when it’s almost an outstretched fist high in the western sky. Follow the line from Jupiter and Venus down toward the horizon to point you in the right direction.

Both Mercury and Venus are showing “half moon” phases. Venus’ shape is easier to see because the planet appears almost three times larger in a telescope. Mercury travels in a tight, fast orbit around the sun and goes through phases much faster than more distant Venus. In just a week, it will have narrowed to a crescent. We’ll have to wait until the end of April before Venus is a similar crescent.

How Mercury and Venus will look through a small telescope this weekend. Created with Chris Marriott's SkyMap

Remember the Venus-Uranus match up early last month when the two planets were simultaneously visible in the same binocular field of view? I’ve got good news. It’s happening again tonight through Monday, but this time it’s Mercury’s turn. So if you missed the February opportunity to see Uranus because of clouds or commitments, and you’re up for a challenge, here’s a second chance.

Mercury and Uranus will pass each other this weekend. Uranus moves little - it's a distant planet - while Mercury moves upward. The map shows the sky facing west with north to the right. Stars are drawn to mag. 7.

These planet “handoffs” remind me of a high school relay race, where one runner passes the baton to a teammate, who runs a set distance before handing it to the next. Uranus is the baton in this interplanetary relay.

You’ll need very clear, dark-as-possible skies and 7×50 or 10×50 binoculars to see Uranus, because twilight will interfere much more than it did last month. It helps that both fit comfortably in the same field of view of most binoculars. Consider using a small telescope if you don’t succeed with binoculars.

Today they’re 3 degrees apart; tomorrow a tad closer. Closest approach of 2.5 degrees happens Monday morning in the daytime sky. Good luck – this could be a tough one. But what is life without the occasional astronomical challenge?

There’s more to Orion than 3 stars in a row

Venus and Uranus slowly separate but remain near enough to one another to easily fit inside a binocular view (yellow circle). The maps show the sky as you face west in late twilight. Stars shown to ~6.5 magnitude. Created with Stellarium

Some of us had cloudy skies last night and couldn’t see the conjunction of Venus and Uranus. Well, I’m here to tell you there’s still hope. The two will be close enough the next couple nights to easily see together in the same binocular field of view. Just use the little maps above to guide you. Conveniently, Uranus is directly below Venus tonight.

Orion painted in gold on a living room ceiling. Photo: Bob King

While I was on assignment shooting photos for the Duluth News Tribune this week, I came upon a star-studded ceiling in a subject’s living room. Orion, Cassiopeia and the Big and Little Dippers were painted in gold against a robin’s egg blue.  I felt right at home.

Orion is beautifully placed in mid-February straight up and high in the south around 8 p.m. local time. The three belt stars are the easiest to see, but there’s a good deal more to the constellation you may not have been aware of. The rectangular box of stars centered on the belt forms the general outline of the Hunter. Bright red Betelgeuse marks the top of his shoulder and equally brilliant Rigel his left foot.

If you can escape city light pollution, you’ll see plenty more of Orion beyond his bright frame. Look for his sword directly below the belt, the upraised club in his right hand and curved shield in his left.

A delightful bit of fuzz awaits your eye smack in the center of the sword – the Orion Nebula. Visible to the naked eye as a hazy spot, binoculars will show a small cloud studded with several bright stars. These stars – and thousands of others buried inside the mist – formed from the gravitational attraction of gases. They’re literally newborns compared to most of the stars visible to the naked eye.

Orion represents the mythological Hunter figure. He comes equipped with the best equipment of the era of his creation thousands of years ago. Click photo to learn more about the constellation. Picture at right: Bob King

I’ve always found it funny that for so grand a figure as Orion his head is so tiny, but that’s the way things go when you’re creating constellations – you use what you’ve got at hand.

Venus-Uranus closest tonight and a black hole lunches on asteroids

Uranus near Venus last night Feb. 8 around 7 o'clock. Tonight the two planets will be even closer. See diagram below. Details: 200mm lens at f/2.8, ISO 1600 and 4" second exposure. Photo: Bob King

Tonight’s a good night to be out at the end of twilight. Why? That’s when you can see Venus and Uranus side by side in a pair of binoculars. They’ve been approaching each other the past few nights and will be closest tonight at 8 p.m. CST.

Venus and Uranus will be only 0.3 degrees apart this evening in the western sky. To see fainter Uranus, be sure to wait until the sky is fairly dark otherwise it might be lost in twilight's glow.

Venus is the brighter and lower of the two brilliant “stars” in the southwestern sky during evening twilight. The other is Jupiter. I looked at Venus in 8×40 binoculars last night and had no trouble seeing Uranus nearby. If you’d like to add a new planet to your life list, binoculars will do the job. And if you’ve never seen the tiny disk of Uranus in a telescope, just point your instrument at Venus and both will be in the same field of view. Uranus will lie to the left or south of the bright planet. Use a magnification of 75x or higher to see it clearly.

A 10-minute sequence of the moon rising over Lake Superior last night. The atmospheric distortions are almost comical. Details: 400mm lens, f/5.6, various exposures at ISO 800. Photo: Bob King

On the way home from work last night I stopped along Skyline Parkway in Duluth to wait for the moon to rise. The road provides a wide vista of Lake Superior and the northern Wisconsin shoreline.

Not long after finishing a series of Venus-Uranus photos, the reddened and “squished” moon rose in the southeast. Due to layers of thick air near the horizon and atmospheric turbulence, the moon look positively battered. Twice I saw obvious notches along its edge as if someone had kicked and dented the poor thing. For a brief few seconds its entire outline was flattened in so many places it looked more like a polygon than a circle.

If time and circumstance would allow, I’d watch a lot more moonrises. Not only does the sky lay this amazing orange egg, but moonrise, as opposed to a blinding sunrise, lets us study so many atmospheric curiosities with little more than the naked eye and binoculars.

At left is a picture of the center of the Milky Way in X-ray light. The illustrations at right show asteroids getting torn up and vaporized by the black hole Sgr A*. Credits: X-ray: NASA/CXC/MIT/F. Baganoff et al.; Illustrations: NASA/CXC/M.Weiss

Black holes, those invisible distorters of the spacetime continuum, are back in the news this week. NASA’s orbiting Chandra X-ray observatory discovered that Sgr A* (Sagittarius A star), the supermassive black hole in the center of the Milky Way Galaxy, has been munching on asteroids. The hole packs some 2.6 million times the mass of the sun into a space only as wide as Earth’s distance from the sun. And don’t forget — it’s completely invisible. The powerful gravitation exerted by this infinitely compressed object is strong enough to literally imprison light.

For the past several years, Chandra has been recording bursts of X-rays from Sgr A* several times a day. Researchers suggest that the black hole is surrounded by a cloud of material that includes trillions of asteroids stripped from stars that strayed near the hole. When an asteroid passes about 100 million miles from Sgr A* it gets shredded by the hole’s intense gravity and then vaporized by friction. Spirally into oblivion, it emits a last gasp of brilliant X-rays … and then no more. If you’re as interested as I am in black holes and want to read the rest of the story, please click HERE.

Venus and Uranus ride piggyback this week

You can't miss Venus shining in the western sky during twilight this month. Photo: Bob King

Venus is amazing! The first “star” to come out at night, it blazes in the western sky at nightfall. While we associate clouds with dark days, the perpetual cloud cover of Venus is one of the main reasons it’s so bright. Clouds are great reflectors of light, especially when you’re looking at them from the outside.

The second reason for Venus’ brilliance is how close the planet is to Earth compared to other cloudy planets like Jupiter and Saturn. Jupiter is 11 times larger and would far outshine Venus at the same distance.

These two maps show Venus and Uranus as you'd see them in binoculars facing west during late twilight. They're 4 degrees apart this evening. You can gauge Venus' motion using my "Little Box" of stars, a small pattern of stars in Pisces near the planets. Maps created with Chris Marriott's SkyMap

Only a few weeks ago, Venus and Neptune passed near one another, making it easy to find the faintest planet by way of the brightest. This week Venus meets up with Uranus, creating another wonderful opportunity to see a remote planet with little more than a pair of binoculars.  Because it’s much brighter than Neptune, it’ll be that much easier to see. Just aim your binoculars at Venus in late twilight and use the maps to point you to the right spot. Uranus will look exactly like a star, but a small telescope magnifying around 75x-100x will reveal its tiny, blue-green disk. The maps show stars to magnitude 6.5 – a little fainter than Uranus.

On Thursday around 8 p.m. CST, when both planets are in conjunction and closest together, they’ll only be 0.3 degrees apart. That’s less than one moon diameter. Not only will they look like a “double planet” in binoculars, they’ll both easily fit together in the same field of view of a low power telescope. Definitely an eye-catcher! Despite how close together they’ll appear, Venus will be 99 million miles from Earth and Uranus almost 2 billion. Try to picture that third dimension of space when you’re peering at them through the eyepiece.

Things really get tight on Wednesday and then on Thursday when the two planets are closest. Never has finding Uranus been easier.

The maps show the planets’ positions as you face west around 6:30 p.m. CST. Don’t worry if you’re time is different by a few hours; their positions won’t change much in such a short time.

Notice that Venus continues moving upward and away from the sun this week, while Uranus slowly drops to the west. The reason they will get so close together is that both follow the same path in the sky called the ecliptic. This is also the highway traveled by the sun and moon. When everyone’s driving the same road in and out of town, sooner or later you pass one another. The same happens with the planets and moon as they cruise along the ecliptic through the zodiac constellations.

Tonight Venus and Uranus are separated by about 4 degrees, an amount that easily fits in a typical binocular field of view. That distance shrinks with each passing night. I hope you’ll be able to spot the pair at least once in the coming week. Good luck!

Crazy Uranus knocked silly by a one-two punch

Uranus and its faint ring system are seen in this composite image by the 10-meter Keck Telescope at near infrared wavelengths. Credit: Lawrence Sromovsky, Univ. of Wisconsin-Madison /Keck Observatory

Uranus is certainly a weird planet. Beneath its atmosphere of hydrogen and helium tinted aqua by clouds of methane lies a thick layer of water, ammonia and methane ices. At the bottom of it all is a rocky core estimated at half the size of Earth. We might picture it as a jawbreaker floating in a big slushy wrapped in blue mist. But that’s not all.

The planet, four times the size of Earth and nearly 2 billion miles from the sun, is tipped on its side to the tune of 98 degrees. For comparison, Earth’s axis is angled just 23.5 degrees so we – and all the other planets – look like spinning tops. Contrary Uranus rolls around its orbit like a bowling ball on an alley with its equator nearly straight up and polar axis sticking out the sides.

To account for the crazy tilt, astronomers postulate a collision with a large, planet-sized body soon after the formation of Uranus from the dusty, rocky debris orbiting the sun called the protoplanetary disk. One problem with this scenario is that the disk should have only contained smaller objects that were in the process of accreting or gathering together under the influence of gravity to form the planets we know and love.

Uranus and some of its 27 moons photographed by the Hubble Space Telescope. They revolve counterclockwise as seen from the planet's north pole. Credit: NASA/ESA

In a new study, Alessandro Morbidelli, of the Observatoire de la Cote d’Azur in Nice, France, used computer simulations to find that two smaller collisions would have done the job nicely.

“The standard planet formation theory assumes that Uranus, Neptune and the cores of Jupiter and Saturn formed by accreting only small objects in the protoplanetary disk,” said Morbidelli. “They should have suffered no giant collisions.”

If only one big smack happened, it turns out that Uranus’ moons would be orbiting the planet backwards (clockwise seen from the north) instead of how we see them today. But if two smaller collisions were involved, the moons end up going the right way. This jives with the idea that only smaller bodies populated the protoplanetary disk.

To climb your way to Uranus, look about three outstretched fists to the upper right of Jupiter to spot Gamma in the Great Square. Jupiter, Gamma and Alpha form straight line. From there, use binoculars to navigate from Gamma to the star Omega in Pisces and then use the more detailed map below to complete your journey to Uranus. Created with Stellarium

Uranus is currently in the constellation Pisces the Fish and well-placed for viewing from 9 p.m. on. At magnitude 5.7, Uranus is faintly visible with the naked eye from a dark rural location, but we’ll spare ourselves the squinting and use binoculars to make it easy. If you’ve never seen the planet orbits the sun in the same amount of time as a typical human lifetime – 84 years – maybe it’s time for a visit. I wish I could say Uranus is right next to a bright star and easy to look up, but it’s not. Don’t fret, we’ll get you there.

In this closeup map, start with Omega, which is to the left of a small asterism of stars called the "Circlet". If you place Omega at the top of your view, Uranus will be the brightest "star" near the bottom. It's next to a slightly fainter star I've marked. Created with Chris Marriott's SkyMap software

Face east and find brilliant Jupiter, then shoot a line up to Gamma Pegasi, the lower left corner star in the Great Square of Pegasus. Now grab your binoculars and look a little more than one binocular field of view (about 5 degrees) to the lower right of Gamma to find Omega. Omega is 4th magnitude and visible from suburban and rural skies with the naked eye. With Omega in view, look toward the bottom of your binocular field and you’ll see two stars – the brighter one on top is the planet Uranus, the fainter is a star.

That star is handy, because you can use it to gauge the planet’s slow movement to the west in the coming months. If you own a telescope, the planet mimics what the Earth must also look like from afar – a tantalizing blue disk. Magnifications of 75x and up will easily show it. Bon voyage! I hope you enjoy your visit to the 7th planet.

Crazy halos plus Jupiter plays tag with Uranus

A corona forms around the moon last night as clouds pass by. Photo: Bob King

As if to make up for its absence during the recent total lunar eclipse, the moon threw sky watchers a bone last night with a splendid show of color and clouds. Ever-changing colorful coronas ringed the moon as low clouds from Lake Superior tore across its face. A corona is a little colored disk centered on the moon or sun, usually bluish-white in the middle, fringed with red and surrounded by a bluish-green disk. It resembles a colored  bulls-eye of light.

Coronas form when very fine water droplets or ice crystals in clouds diffract light from the sun or moon. The droplets are so tiny, they’re similar in size to the waves of light itself. Light waves scatter off the droplets, and like waves in a pond, cross through one another. Where two wave crests meet and reinforce each other, a bright fringe or circle forms. Where a trough and a crest meet, a dark fringe is created. Each color in white light is diffracted a little differently by the droplets, creating a series of small colorful rings of varying brightness. Red light is diffracted to the outside of a corona, while blue fills the space in between. Click HERE to see photos of a spectacular corona from last year.

Last night's weird halo around the moon. It was thinner than usual and oval-shaped instead of circular. Photo: Bob King

You’ve probably seen a few coronas before but may not have been aware of them. I’m guessing you’ve probably also seen a ring around the sun or moon called a halo. These form when pencil-shaped ice crystals in high cirrus or cirrostratus refract or bend light into a circle with a radius of 22 degrees – that’s about the width of two fists at arm’s length.

In between last night’s coronas, a halo made an appearance for a minute or two and then disappeared. I finally managed to get my camera out and catch one image of it. Take a closer look at the photo above. Halos are almost always circular, but this one is squashed – longer left-to-right than top-to-bottom. I noticed this with my eye as well. It was also unusually thin in parts unlike a typical halo. Anyone have any idea what might have caused this? I’ve looked and can’t find an answer – yet. At the time the picture was taken, low clouds were passing by and light snow was falling.

These photos show the two opposite hemispheres of Jupiter. While the South Equatorial Belt (SEB) is still not nearly as dark as the north belt, it's visible now in 4-inch and larger telescopes. The SEB is thicker and and pitched at any angle in one hemisphere (left), but "pencil thin" in the other, where is passes under the Great Red Spot (right). Credit: Gary Walker (left) and Efrain Morales.

Winter is a great season for halos, coronas, light pillars and other sky phenomena involving ice. It’s also still prime time for Jupiter watching. If you’ve been following the planet through your telescope, you may have already seen the newly-returning South Equatorial Belt, one of two prominent dark clouds belts that stripe the planet’s face. The dark plume that marked the beginning of its return in fall has evolved into a complete belt visible all around the planet. Incredible to see how such enormous features on Jupiter can change in a relatively short period of time.

By good fortune, Jupiter is passing Uranus over the next few weeks. During that time, both planets will be easily visible near one another in the same binocular field of view. The stars shown are 20 Piscium and 24 Piscium, both about the same brightness as Uranus. Jupiter's position is shown weekly through Jan. 12. Uranus moves much more slowly, traveling only the length of the arrow from Dec. 22 to Jan. 12. Created with Chris Marriott's SkyMap software

With the moon now rising later each night, we’re once again entering a period of dark skies, perfect for enjoying a starry sky and seeking interesting celestial objects. One of them is the planet Uranus, and you don’t need a scope to see it. Any pair of binoculars will do the trick thanks to Jupiter being in the neighborhood. The map above shows the motion of both planets in the next few weeks. Right now they’re less than 1 1/2 degrees apart and will be closest on the night of January 3 at just half a degree.

Go out at nightfall (around 6-6:30 p.m. for the northern states) and point your binoculars at that super-bright “star” high in the southern sky. Yep, that’s Jupiter. Look to the planet’s upper left for a “star” of similar brightness to 20 and 24 shown in the map. Congratulations – that’s Uranus, the 7th planet! Though they appear close, Jupiter is 460 million miles away while Uranus is another 1.5 billion miles beyond that. If you have a telescope, you can star hop your way to Uranus from Jupiter. A magnification of about 100x will show its tiny, pale blue disk.