Tag Archives: Saturn

Are there waves on Titan’s Ligeia Sea?

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Titan’s Ligeia Mare, a sea of liquid ethane and methane 260 miles (420 km) across, is comparable to Lake Superior on Earth – with a difference. The “water” in Ligeia Sea is liquid ethane and methane. Credit: NASA

Cassini will soon make its next flyby of the planet’s largest moon Titan to look for waves on the surface of Ligeia Mare (lie-JEE-uh MAH-ray), a large sea of bitterly-cold liquid ethane in the moon’s north polar region.

Titan’s great distance from the sun ensures that the average temperature there hovers at -290 F (-179 C), cold enough for ethane and methane, which are gases here on Earth, to condense as liquids.

On May 23, the probe will cruise just 603 miles (970 km) above the lake and bounce radio waves off its surface to fathom its surface texture. No one’s sure if the liquid natural gas is thick and flat like molasses or more like lake water here on Earth. Will we someday find rapids, waterfalls? I’m hoping for some cool images of waves. Row, row, row your boat.


Watch as Saturn’s B-ring, the bright ring at upper right, expands and contracts. 39 images taken over 1 hour and 40 minutes were used to create the video.

Also on Cassini’s to-do list was the creation of a movie of Saturn’s bright B-ring in order to better understand how the planet’s moons shape its rings. In the video, you can see the ring expand and contract. Look closely and halfway through the movie you’ll also notice an arc of brighter material sweep by just within the ring’s edge. High-resolution pictures show vertical structures in the ring plane here towering up to 2.2 miles (3.5 km) high.

What you’re seeing are ring particles – made of water ice – hovering above the ring plane. As they stream past an invisible moonlet embedded in the B-ring, the moon’s gravity temporarily squeezes them together and lifts them up to form an orbiting arc. The moonlet – estimated at 1,000 feet (300 m) across, was found sometime later, betrayed by the shadow it cast when Saturn’s rings were “level” with the sun at its 2009 equinox.


A low-angle view of Saturn’s B-ring (foreground) made by Cassini. Watch as it swells outward and then shrinks inward.

In the second video, the low-angle perspective makes the expansion and contraction of the B-ring even easier to see. Scientists have found four separate, independent movements of ring particles that create the hula-hoop-like wobble.

The repeated pulls of the inner moon Mimas on B-ring particles as they orbit Saturn creates one of the swellings. The other three travel around the ring with different speeds and are caused when random motions of icy ring particles reinforce one another to create a wave that flows outward to the boundary of the B-ring. From there it’s reflected back to the inner part of the ring, which in turn reflects it out again like waves bouncing around in a bathtub. Repeated back-and-forth bounces cause sections of the B-ring to expand and contract to the tune of 120 miles (200 km).

Small pieces of ice. Amazing what they’re capable of when their random motions work in tandem. Even the 15,800 mile (25,500 km) B-ring must bow (and bend) to their will.

 

Saturn and the Seeliger Effect: Seeing is believing

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When an outer or superior planet lines up beyond Earth on the same side as the sun, it’s at opposition and closest to Earth for the year. Saturn reached opposition this past weekend. When the same planet lines up with the Earth on the opposite side of the sun, it’s in conjunction and invisible in the solar glare. Illustration: Bob King

This weekend we looked at Saturn from the unique perspective called opposition, when a planet is directly opposite the sun in the sky. Seen from space, Saturn is lined up with Earth on the same side as the sun. Seen from the ground, the planet rises at sunset, remains visible all night and doesn’t set until the sun rises the next morning. Talk about opposites – the two bodies can’t get any farther apart.

Opposition only happens with the outer planets – Mars through Neptune. Since they’re farther from the sun than Earth, they can periodically sneak up behind us.  Mercury and Venus, being closer to the sun, can’t take a walk around our backside and therefore never appear opposite the sun in the sky. Traditionally, the planets that orbit beyond Earth are called “superior” while Mercury and Venus are “inferior” or inner planets.

What a dramatic difference opposition makes! Compare Saturn’s rings on April 28 and back on March 2. The opposition or Seeliger Effect is obvious. Notice that the globe remains unchanged. Click to see more Go’s Saturn photos. Credit: Christopher Go

As described in this Friday’s blog, our opposition perspective on Saturn affords a unique view of its rings. For a few days around this time, the rings become considerably brighter than the body of the planet. The photo illustrates it dramatically, but you can also see it with your own eyeballs as amateur astronomer Richard Keen of Coal Creek Canyon, Colorado did through his 12.5-inch telescope this weekend:

“The rings were markedly brighter than the ball of the planet, while usually they’re about the same brightness. The contrast lines between where ball of the planet hides the far side ring, and between the near side ring and the planet, were sharper, too.”

Several factors contribute to the brightening, but a key one is called the opposition effect. When we face with our backs to the sun, objects in front of us are squarely lit by sunshine streaming over our shoulders.  Any shadows cast by rocks, bumps or irregularities are hidden directly behind the objects. Without shadows to ‘darken’ the scene, the view directly in front of us peaks in light intensity.

Something similar happens when we look at Saturn’s rings during the days leading up to and after opposition. The sun streams past the Earth (our shoulders) and shines directly onto the ring particles. With their shadows temporarily hidden, the rings surge in brightness compared to the planet’s globe.

Hugo von Seeliger

This brightness enhancement  was first studied by German astronomer
Hugo von Seeliger (1849-1924) who proposed that the disappearance of shadows as the cause for the rapid brightening of the rings. Seeliger saw it as confirmation that the rings were made of individual pieces rather than a series of solid disks.

The opposition surge is also the primary reason the full moon is so much brighter than the moon the night before or after.

Saturn comes to opposition once a year, but the full moon is at opposition (opposite the sun in the sky) about once a month. During the hours before full phase, it brightens by more than 40% and fades an equal amount hours after full.

From our perspective on Earth, the full moon is squarely lit by the sun. With all shadows removed, the moon experiences an extra surge in brightness. At other lunar phases, shadows play an important role in dimming the moon. Photos: Bob King

What’s going on? Like the ice crystals in Saturn’s rings, the moon dust and grit hide shadows best when the sun shines down squarely upon them. Also any divots or pits on the moon’s surface that might otherwise be filled with shadow are fully – if briefly – illuminated by sunlight.

While “shadow hiding” is an important reason for these surges, the phenomenon of coherent backscatter also plays a role in the moon, Saturn’s rings and other planets and asteroids with rocky, dusty surfaces. When a light source shines at a very direct angle at material made of a multitude of tiny, dust-like particles, multiple reflections combine to produce a single brighter reflection directly back at the observer.

So now I’m eager for clear skies to see all this for myself. Hopefully, you’ll have a chance to do the same.

Saturn biggest, brightest, closest this weekend

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Saturn and Spica come into easy view in the southeastern sky around 10 o’clock local time in late April. Add brilliant Arcturus and you’ve got a triangle of three bright celestial objects. Arcturus is about three and a half “fists” above Saturn. Maps made with Stellarium

This Sunday the King of the Rings comes to opposition when it will be closest to Earth and bigger and brighter than at any other time this year. You’ll find the Saturn in the company of Virgo’s brightest star Spica low in the southeastern sky at nightfall.

Opposition literally means “opposite the sun”, and that’s exactly where you’ll find the planet, rising in the east as the sun sets in the west. On April 28 it will be out all night, finally departing at the western horizon at sunrise.

Saturn lines up with the sun on the same side as the Earth this weekend. We’re 180 million miles closer the ringed planet compared to Nov. 6 when it’s on the opposite side of the sun and farthest from Earth. Closer means bigger and brighter. Illustration: Bob King

Spica and Saturn will get your attention around 10 o’clock in late April and by early evening in May. Located in the dim constellation of Libra the Scales, Saturn’s a little more than a fist held at arm’s length to the left or east of Spica and nearly a full magnitude brighter. You’ll easily see the difference.

A fair share of the planet’s light comes from it rings. They’re made of chunks of reflective water ice ranging in size from a fraction of an inch up to tens of feet. Since the rings are tipped open at a good angle in 2013 (18-19 degrees), Saturn is brighter now than it’s been in many years.

Saturn photographed on April 24, 2013 from Buena Vista, Georgia. Three rings and Cassini’s Division are visible in small to medium-sized telescopes. Credit: Brian Combs

Saturn’s juxtaposition with Spica presents a nice opportunity to see one of the differences between a planet and star. On nights when the atmosphere overhead is buffeted by winds and eddies, Spica will appear to twinkle as its light is yanked this way and that by turbulence. Saturn, which has a substantial size compared to a point-like star, is much less affected by the airy tumult and usually appears tranquil and steady.

One of life’s greatest small pleasures is seeing the ringed planet through a telescope. Nothing can compare. Most people say it looks fake – that’s because it’s one of the few things in the sky that looks like its photograph. In 10x and higher power binoculars you can tell Saturn’s not round like Jupiter. Because we see the rings tipped partway toward us, they stick out from either side of the planet, giving it an oval shape.To see them distinctly and separate from the ball of the planet requires only a small telescope magnifying 40x or higher.

Saturn’s tilted axis means we get to see an ever changing presentation of its rings as the planet revolves around the sun in a 29.5 year orbit. Credit and copyright: thChieh

Unlike the speedier inner solar system planets, Saturn takes 29.5 years to make one cycle around the sun and spends 2-3 years in each zodiac constellation. Because Saturn’s axis is tipped much like Earth’s, we see alternate faces of the ring during its orbit. For the next dozen years, we’ll be looking at the north side. Come 2025, the rings will be edgewise to Earth and appear thin as a thread before they open up again and reveal their south face starting in 2026. An entire cycle takes  - you guessed it – 29.5 years.

Saturn’s rings are open fairly wide in 2013 with a tip of 18-19 degrees. Maximum happens in 2017. We’re currently viewing the north face of the rings. Credit: Tom Ruen

This coming month the rings are tipped invitingly wide at 18 degrees; maximum tilt of 27 degrees happens in 2017. As you increase magnification in your telescope, you’ll see that the one big ring divides into two or three concentric rings.

Even a small scope will show the dark gap called Cassini’s Division separating the thinner A ring from the wide, bright B ring. If you use a 6-inch or larger telescope, you can pick out the dusky C ring interior the A-B pair. Use 100x and up and look for a grey shading where it crosses the edge of Saturn’s globe. Further divisions in the rings require at least an 8-inch scope and preferably a 12-inch.

Ah, then there are Saturn’s wonderful family of moons. Titan, the biggest and brightest, is a snap to see in any telescope. Even a 6-inch will reveal its orange color caused by chemical smog in the moon’s atmosphere. Rhea, Iapetus, Dione and Tethys can be captured in a 6-inch telescope as well, but Enceladus will probably require 8-incher, since it’s so close to the planet and difficult to pick out from the rings’ glare.

To know when and where to look for Saturn’s moons, check out Sky and Telescope’s Javascript utility Saturn’s Moons or download SaturnMoons for iPhone for $2.99.

You can also watch for the Seelinger Effect, which happens for several nights around Saturn’s opposition. The ring particles are very effective at reflecting sunlight back to the observer when the sun is shining directly at them (called “backscattering”). This causes the rings to brighten noticeably compared to the ball of the planet.

This is how Saturn and four of its moons will look around 11 p.m. CDT this Sunday night April 28. Be sure to take a close look at the brightest, Titan, to see if you can tell its color. South is up, the way most telescopes show the sky. Illustration: Bob King

Check it out and see for yourself. Speaking of the planet, Saturn has cloud belts like Jupiter though they’re much more subtle. The belts of the southern hemisphere are hidden by the rings, but the last time I checked, I could easily see the planet’s dark North Equatorial Belt about halfway between the ring plane and north pole.

A great storm raged in Saturn’s northern hemisphere during 2011visible in modest-sized telescopes. Credit: NASA/JPL-Caltech

Watch for any unusual white patches to develop – Saturn occasionally has storms that bring up fresh material from below the cloud desk. High winds over 1,000 mph can spread the clouds into white spot big enough to see in even a small telescope. A huge storm two and a half years ago grew large enough to chase its tail and encircle the entire planet!

Saturn, Spica and a Pink Moon partial eclipse

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The moon will be only a degree or two southeast of the star Spica tonight. Tomorrow night (April 25) the Full Pink Moon hangs below the planet Saturn. The map shows the sky facing southeast around 10 o’clock local time. Created with Stellarium

The nearly full moon passes just south of Virgo’s brightest star Spica tonight. For sky watchers across a wide swath of South America and Africa, the moon will do better than that by coming up right alongside and then blocking the star from view. When one celestial body cloaks another, it’s called an occultation.

If you live within the slinky-like path, you’ll see the moon cover or occult Spica tonight. The star will graze the  moon’s northern edge for observers along the path’s northern boundary; the moon’s southern edge along the southern boundary. Times shown are Universal Time (Greenwich TIme). Credit: U.S. Navy

Depending on where you live within the occultation path, Spica could disappear for nearly an hour or just graze the edge of the moon, ducking in and out from behind mountain peaks as the moon slowly travels eastward in its orbit.

Click HERE for a more detailed map.

Tomorrow night we’ll enjoy the Full Pink Moon, named after moss pink (a.k.a. ground phlox), an early spring flower of eastern North America. Other names for April’s full moon include Sprouting Grass Moon, Egg Moon and Fish Moon.

Many parts of the country are seeing their first wildflowers of the season. My first was a dandelion that bravely raised its head from a crack in the asphalt in a downtown alley.

With a bit of imagination you can fancy a variety of characters in the full moon’s blotchy face. Top row: old man carrying sticks, a face. Bottom: woman’s face, rabbit, another face.

You can always find the time of moonrise for your town by clicking over to the U.S. Naval Observatory’s Complete Sun and Moon Date for One Day site. As you watch the moon over the next few nights, do you see a face, a rabbit, an old man carrying a load of sticks? Our eyes form these patterns from the moon’s lighter-toned ancient crust called the lunar highlands and the darker lava plains known as the lunar “seas”.

Visibility map of Thursday’s partial lunar eclipse. Credit: Fred Espanek / NASA

The Pink Moon will briefly assume a dimmer countenance for sky watchers in Europe, Africa and Asia when it undergoes a minor partial eclipse tomorrow night. Only 1.5% of the moon will tread into Earth’s dark inner shadow (umbra) during maximum eclipse with the entire event lasting just 27 minutes.

The moon’s path through Earth’s outer shadow (penumbra) and inner umbra during Thursday night’s eclipse. Times are Universal (Greenwich – England Time). At maximum or greatest eclipse, the top of the moon will look shaved off. Click image for more information. Credit: NASA

While lacking the drama of a deeper partial or total eclipse, it should be fun to watch especially in eastern Europe and Africa where It happens during convenient early evening hours. Keen-eyed sky gazers will notice some dimming of the moon even before it dips into the darker umbra as it first passes through the outer penumbral shadow.

The moon first touches the penumbra at 6:03 p.m. Greenwich time and umbra at 7:54. It leaves the umbra at 8:21 p.m. and the penumbra at 10:11.

The next lunar eclipse for North American will be a very minor penumbral one on May 24. That’s it until next year when the Americas and other regions of the world will be treated to a total lunar eclipse on April 15, 2014.

Glow and glow alike – Saturn and Earth share aurora link

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Artist illustration of the northern auroral oval on planet Earth. Credit: NASA

Auroras will do what they will do, forecast or no. Two days ago, NOAA space weather forecasters predicted a quiet night last night, but there’s no question the aurora was out. We received a couple reports plus the usual online indicators were hopping with activity. All that was shut out here by clouds and rain, but observers in the northern U.S. with clear skies and a bent for staring into them saw the aurora last night.

Tonight a minor flurry of auroras may happen once again, so be on the lookout. Anytime you see the northern lights, keep in mind you’re looking at one small section of a much larger structure called the auroral oval. These “crowns” of glowing gases are centered about 70 miles high over Earth’s north geomagnetic pole in the Canadian Arctic and over the south geomagnetic pole in Antarctica.

Satellite photos of the auroral oval taken every six minutes over a half hour. The oval is dynamic, changing in brightness and width in response to particle flows from the sun. Credit: NASA

The ovals are where electrons and protons in the solar wind are funneled by our planet’s magnetic field into the upper atmosphere. There they crash into and energize nitrogen and oxygen molecules; rays and colors are produced when the excited atoms emit tiny bursts of light as they return to their “rest” states. I like to visualize them as an ever-shifting interface between sun and Earth – a place where two worlds touch on a subatomic level.

The ovals do not rotate with the Earth but stay in place as the Earth rotates under them. They’re not perfectly circular halos either. The northern oval sags furthest south toward the equator around local midnight, making that the usual optimum time for aurora viewing.

On February 18, 2012 the oval expanded southward well into the U.S. making for a great display. Credit: NOAA

Still, much of the U.S. rarely experience auroras because the oval doesn’t reach that far south except during powerful solar storms.

Like stretching a rubber band, the auroral oval expands with strong influxes of particles from the sun during times of high solar actitvity. When the sun is “quiet”, the ovals skinnify and shrink back toward the poles.

Back in January I described Jupiter’s auroral ovals and how they’re caused not by interaction with the sun’s wind but by sulphur spewed from active volcanoes on the moon Io. Caught up in the planet’s rapid 10-hour rotation, electrified sulfur atoms follow Jupiter’s magnetic field until they crash into the planet’s upper atmosphere, setting it aglow. Big Jove’s own aurora-making machine doesn’t need much help from the sun.

Hubble Space telescope photo in UV light showing Saturn’s north and south ovals. Credit: NASA/ESA

Saturn’s different. It’s poles are capped by auroral crowns, but unlike Jupiter they’re created primarily by fluctuations in the zappy solar wind.

When the wind blows hard and points in a favorable direction, Saturn responds with expanding ovals. When weak, the ovals ratchet back poleward. Sound familiar? Saturn’s oval mimics that of planet Earth.

Enceladus sends beams of electrons down to Saturn’s upper atmosphere creating an auroral footprint. Credit: NASA/ Cassini Imaging Team

There are a couple key differences. Hydrogen gas dominates Saturn’s upper atmosphere. When excited by incoming electrons, it glows deep ruby red unlike the more common green auroras produced by oxygen molecules here on Earth. Some photos show it as blue – that’s because they’re taken in ultraviolet light, where the aurora stands out better against sunlight reflected by the planet’s cloud tops.


Listen to the hiss-like radio noise generated by electrons moving along magnetic field lines from Enceladus to a glowing patch of ultraviolet light on Saturn. The sound is typically inaudible to the human ear, but has been amplified electronically. 

There’s also a faint “footprint” of auroral light just beyond the oval’s edge courtesy of the moon Enceladus. Enceladus spews water vapor from cracks in its icy crust at the rate of 400 lbs. (200 kg) per second which becomes electrically-charged when it interacts with Saturn’s magnetic field. As Enceladus revolves around the planet, that cloud of particles – called a plasma – stimulates a rain of electrons to plummet down one of the planet’s magnetic field lines straight into the atmosphere to form a patch of aurora. Jupiter’s moon Io does the same thing.

Saturn now rises in the southeastern sky around 11 p.m. in the constellation Virgo. The next time the aurora’s aflame on our planet, you can picture something very similar happening nearly a billion miles away.

Cross the “snow line” to Saturn and relish its ancient ice

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NASA’s Cassini spacecraft on July 29, 2011, shows Saturn’s A and F rings and five of its moons. From left, the moons are Janus, Pandora, Enceladus, Mimas and Rhea. Saturn is hidden at right behind Rhea. Credit: NASA/JPL-Caltech/Space Science Institute

Wipe the dust from an antique and you can begin to appreciate its vintage and workmanship. See beneath the space-worn colors of Saturn’s rings and moons and you might just get a glimpse of the primeval solar system. A new analysis of data from NASA’s Cassini spacecraft suggests that the Saturn system is tinted by “pollutants”.

Geysers of water ice crystals erupt from fissures in Enceladus’ south polar region in this photo taken by Cassini. Credit: NASA/JPL-Space Science Institute

The inner moons get whitewashed as they pass through water sprayed by geysers from the moon Enceladus. More distant moons wear a pale coating of red from particles of dust shed by Phoebe; the farther out they are from Saturn, the redder they appear.

Phoebe is an outer moon that may have once resided in the far-off Kuiper Belt beyond the planet Neptune before it was captured by the ringed planet.

Parts of the Saturn’s B-ring also appear faintly red perhaps from meteoroids that pepper the icy ring particles. Iron is a very common constituent of meteorites. Scientists think the reddish color could be either oxidized iron – better known as rust – formed when oxygen and iron combine in the presence of water -  or polycyclic aromatic hydrocarbons (PAHs), organic molecules common in tars and oil.

PAHs form in the atmospheres of aging, expanding stars when carbon and oxygen atoms are spat out into space. As they cool, the atoms bind together to form simple organic molecules and PAHs.

The precursors to the planets, called planetesimals, were mostly rocky stuff in the inner solar system within the snow or frost line. The outer planets formed from planetesimals composed of a mixture of rock and ice. Credit: Univ. of Colorado

Despite their diverse colors, data from Cassini’s visual and infrared mapping spectrometer (VIMS), which penetrates below the chemical veneer, found deep similarities. VIMS detected lots of water ice in both moons and rings, too much to have been deposited by recent comet collisions. The authors concluded that the ice must have formed around the birth of the solar system. How do you keep ice around that long? You either live in Duluth, Minn. or form it beyond the “snow line”, where temperatures are cold enough to keep things frozen almost forever.

Our solar system’s snow line starts at around 5 times the Earth’s distance from the sun or roughly at Jupiter’s distance. Indeed it’s the snow line which separates the inner terrestrial planets from the giant gas planets of the outer. Drop this side of the line and water either melts or vaporizes.

Saturn’s small 84-mile-long moon Prometheus creates a knot in the F-ring through its gravitational interaction with the icy ring particles. Prometheus may have formed from ring material. Credit: NASA/JPL-Space Science Institute

Cassini turned up another interesting fact. Saturn’s moon Prometheus has a similar reddish tint as the rings, hinting that it may have formed from ring material:

“The similar reddish tint suggests that Prometheus is constructed from material in Saturn’s rings,” said co-author Bonnie Buratti, a VIMS team member based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Scientists had been wondering whether ring particles could have stuck together to form moons — since the dominant theory was that the rings basically came from satellites being broken up.”

Saturn’s icy ring particles range in size from less than a millimeter to around 10 feet across. Credit: NASA/JPL-Space Science Institute

With Prometheus, the process may have worked the other way around, testing our assumptions once again.

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.

Planetary perspectives inspire appreciation for the little things

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Venus is the bright “star” seen among Saturn’s rings in the photo taken by Cassini late last year. The bright arc is Saturn’s atmosphere glowing in backlit sunlight. Light reflected from the rings faintly illuminates the planet. Click to enlarge. Credit: NASA/JPL-CalTech

Nothing beats stepping back to gain a little perspective. NASA recently released a pretty picture of Venus peering through Saturn’s rings. The photo was taken on Nov. 10, 2012 when the Cassini spacecraft orbited the shadowed side of the ringed planet, so we see the rings and atmospheric edge of Saturn backlit by the sun. Venus is a pinprick of light nearly a billion miles away shining through the veil of icy bits that compose the rings.

Venus as seen this morning March 6, 2013 by SOHO’s camera. An opaque disk covers the sun (white circle) allowing astronomers to study the streaky solar atmosphere called the corona.  Venus is currently about 159 million miles from Earth. Credit: NASA/ESA

We also have a more recent photo of Venus taken by the Solar and Heliospheric  Observatory (SOHO) from a different point of view. This picture was taken earlier this morning and shows Venus nearby southwest of the sun. SOHO is parked near the L1 Lagrange point, a spot in space 1 million miles forward of Earth in the direction of the sun. Here the planet’s gravity balances that of the more distant sun allowing the craft to hover in equilibrium with its eye ever focused on the sun. Due to gravitational tugs from the moon and planets, SOHO fires its thrusters every few months to remain in position.

As Venus revolves around the sun, we see it pass through phases just like the moon. Today Venus is near the sun in the sky and appears like a nearly full moon. On the 28th it will be in conjunction and farthest from Earth on the opposite side of the sun. Illustration: Bob King

Venus might look like it’s in the foreground in the SOHO image, but it’s really in the background. On March 28 the planet will pass through superior conjunction when it will appear closest to the sun but located on the farside of its orbit behind it. After that date Venus begins its slow trek back into the evening sky as it comes round to the left or east of the sun. Watch for it to re-appear at dusk in late May.

Venus and Earth are nearly invisible in this wide angle view that includes the sun taken by the Voyager 1 spacecraft in 1990. Click to see the BIG version. Credit: NASA

A tight crop of the wide Voyager 1 photo clearly shows the pale blue dot of Earth. It’s caught in a streak of lens flare caused by the camera pointing directly at the sun. Everything we care about most deeply is contained in that minute fleck of light. Credit: NASA

Let’s pull back a bit more. What do Venus (and Earth) look like from 4 billion miles away, the way the Voyager 1 space probe saw them on Valentine’s Day 1990? Dots of course! Take a close look and you just might be able to see them in the photo. They’re much more obvious the full-resolution image, which can be had for a click.

Earth and the moon from 114 million miles away in the vicinity of Mercury photographed in 2010 by MESSENGER. Click to enlarge. Credit: NASA

Before we wrap up, let’s move in again a little closer and enjoy a picture of the dynamic duo of moon and Earth taken by the Mercury MESSENGER spacecraft from 114 million miles away. While not shot from the planet Mercury, the perspective is nearly identical. Doesn’t it make you feel a little exposed looking at these photos? I mean, there’s so much nothing out there compared to the bits of something. Time to hug my kids again.

Saturn and moon match up tomorrow morning

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Saturn and last quarter moon hang together in the southern sky tomorrow morning Feb. 3, 2013 at dawn. Time shown is 6 a.m. local time facing south. Farther east, the summer star Antares and Scorpius are visible. Created with Stellarium

We’ve only had one bright planet adorn the evening sky this winter – Jupiter. He’s certainly generous with his moons, clouds belts and brilliant display, but he’ll soon have company. The planet Saturn edges 4 minutes closer to the evening sky every night.

The ringed one rises around 12:45 a.m. tomorrow morning but by month’s end pops up at 11 o’clock. Either time may be too late for many, but if you’re an early-riser, consider peeking out your window at dawn tomorrow. Like fruit hanging from a twig, the last quarter moon will dangle below Saturn. Although not a particularly close conjunction, the two will be near enough to catch your attention. Closest approach of 3.4 degrees occurs around 1 a.m. (CST).

Saturn photographed on Dec. 27, 2012. The planet is covered in clouds of ammonia ice crystals, some of which are arranged in colorful bands. The rings are composed of countless, individual icy “moonlets”. The dark Cassini’s Division separates the A and B rings. Credit: Damian Peach

If you’re feeling brave, take your scope out for a look at its marvelous tipped rings in the dawning sky. Some of my favorite views of planets have been at dawn or dusk. Seen against a deep blue sky, Saturn’s natural glare is lessened and the view more natural and satisfying. Examine the rings closely and you may be able to spot the hairline gap between the outer, narrower A ring and broader interior B ring. The apparently empty space is named Cassini’s Division in honor of 17th century Italian astronomer Giovanni Cassini who discovered the gap in 1675. Under good conditions even a small 3-inch telescope will show the 3,000-mile-wide vacancy. Gravitational interactions by the moon Mimas clear out ring particles to create the gap.

Giovanni Cassini (1624-1712) was an Italian astronomer but moved to France to become director of the Paris Observatory in 1671.

Cassini has many firsts to his credit. He discovered four of Saturn’s moons, co-discovered Jupiter’s Great Red Spot and determined the rotation periods of Jupiter and Mars by careful study of their surface and cloud features. With the help of his assistant Jean Richer, he triangulated the distance to Mars in 1672. Once Mars’s distance was known, Cassini could easily calculate the distances to all the other planets, since the ratio of their distances to the sun was already known through geometry.

He did well. His measurement of the Earth-sun distance was off by just 7%.

It’s no wonder then why his name was chosen for the Cassini mission to Saturn which has been orbiting that planet and its family of moons since July 1, 2004. New pictures are taken all the time, many of which I’ve featured in this blog. Like Cassini himself, his namesake continues blazing a path of discovery.

This set of images from NASA’s Cassini mission shows the evolution of a massive thunder-and-lightning storm that circled all the way around Saturn and fizzled when it ran into its own tail. The storm was first detected on Dec. 5, 2010. Click to see more photos. Credit: NASA/JPL-Caltech

Recently NASA released a series of photos showing Saturn’s monster storm, the biggest ever recorded in the planet’s northern hemisphere, that began around Dec. 5, 2010 and finally ran out of steam 267 days later. It’s been compared to a hurricane on Earth with its powerful winds, lighting and thunder though on a far grander scale.

Earthly hurricanes derive their energy from warm oceanic waters, while Saturn funnels its power from warm, rising gases in its enormous atmosphere. But there the similarity ends. With no land masses to get in the way and sap the storm of its fury, the leading edge of Saturn’s “hurricane” circled the full 190,000 miles of the planet’s circumference and met up again with its tail! Some have compared it to the mythical serpent Ouroboros eating its own tail. An apt image if there ever was one.

Of course, Cassini was there snapping away the entire time. To read more about the big storm and see additional photos, I invite you to click HERE.

Sun blows Earth a kiss – will she blush?

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Three views over 2 1/2 hours of a coronal mass ejection or CME as it burst off of the sun headed for Earth this morning Jan. 13, 2013. The images were captured by NASA’s Solar Terrestrial Relations Observatory (STEREO). Credit: NASA/STEREO

The sun hurled a coronal mass ejection (CME) in Earth’s direction this morning at 1:24 a.m. (CST). This proton-electron particle spray may reach us within 1 to 3 days and possibly make the Arctic sky blush with auroras. We’ll have to wait and see.

Since this CME left the sun at only 275 miles per second, it’s not likely to kick up a big storm. The biggest blasts can send particles our way at nearly ten times that. If they succeed in connecting with Earth’s magnetic envelope, the magnetosphere, electrons and occasionally protons spiral down along magnetic field lines into our atmosphere to produce auroras. We don’t have to worry about these guys hitting us directly on the ground; we’re protected by the planetary magnetic field and the air above us.

Saturn’s tiny moon Daphnis (the point of light) clears the 26-mile-wide Keeler Gap, named after 19th century American astronomer James Keeler, in Saturn’s rings. The gravity of the moon also creates the ripples seen along either side of the vacancy. Credit: NASA/JPL-Caltech SSI

One of my favorite things to do is dig through image archives looking for gems to share. A recent photo of Saturn’s 5-mile-diameter moon Daphnis raising sawtooth-like waves in Saturn’s Keeler Gap caught my eye. The picture, taken by the Cassini spacecraft last August and released in late December 2012, shows a lovely series of ripples on either side of the Keeler Gap, a debris-free zone about 26 miles wide near the outer edge of Saturn’s A-ring.

Closeup of Daphnis and its gravitational wake photographed by Cassini on July 5, 2010 from a distance of 45,000 miles.  Click to enlarge. Credit: NASA/JPL/SSI/ color composite by Gordan Ugarkovic

As it circles the planet on an inclined orbit, Daphis’ gravity tugs on the icy ring particles to clear a gap and create the ripples. The rings are only about 33 feet thick despite their vast extent and consist primarily of individual chunks of ice in their own slightly different but unique orbits about the ringed planet.

Although difficult to see in the picture, the ripples rise up about 1 mile above the ring plane. Notice there are two sets. Material along the inner edge of the gap orbits faster than the moon, so that the ripples precede Daphnis in its orbit. Material on the outer edge moves slower than the moon, creating a set of trailing waves.

Nature has many sculptors and tools with which to fashion the most delightful of cosmic structures. Put a smidge of a moon in the right place and it’s not long before something marvelous happens.