Mars and Saturn boogaloo with Zubenelgenubi

Mars and Saturn are now only about 7 degrees apart (a little more than three fingers) low in the southwestern sky at dusk. This view shows the sky about 90 minutes after sunset. Between the two, you can spot the dimmer star Zubenelgenubi, the brightest star in the constellation Libra the Scales. Stellarium

Evening planets Saturn and Mars are fading and dropping lower in the western sky as August ticks toward September. Remember when Mars was brighter than Arcturus this spring? Planets. They never sit still. Their light’s never constant. We love watching them change, which is why our ancient ancestors knew immediately they were different from the static stars.

From my house, I need to be vigilant to spot Saturn and Mars before they’re lost in the treetops. That means getting out about an hour after sunset in fading twilight and finding an open spot where I can look low in the southwestern sky.

You may have noticed that the two have slowly been drawing together over the past few weeks. Mars, much closer to Earth than Saturn, moves more quickly across the sky. It’s been ‘chasing’ slower Saturn for some time now.

Mars gets closer to Saturn with each passing night until August 25 when they’ll be in conjunction just 3.4 degrees apart (twice as close as tonight). Watching Mars move against much slower Saturn makes a fun and easy observing project. Stellarium

Tonight, the two planets will be 7 degrees apart on either side of Libra the Scales’ brightest star, Zubenelgenubi (zoo-BEN-el-je-NEW-bee). The name, a delight to pronounce, is pure Arabic and means ‘southern claw’. Libra’s stars used to belong to neighboring Scorpius and both it and nearby Zubeneschamali (northern claw) remind of us of times long ago when Libra belonged to Scorpius.

Zubenelgenubi (a.k.a. Alpha Librae) is a double star that observers with keen vision can split with the naked eye. Most of us will find that a pair of binoculars will make the job much easier.

Mars will soon pass its slower brother but not before the two are in conjunction and closest together on the evening of August 25th. Watching two planets pass in the night is fun and instructive – it makes us aware that everything in our solar system’s on the move.

This weekend we’ll look at another even more amazing planetary conjunction coming up very soon – Jupiter and Venus on August 18.

Crescent moon joins a planet parade / Opportunity ready for marathon run

The moon scoots by two bright stars and two bright evening planets in the next few nights. This map shows the sky facing southwest in late evening twilight. Stellarium

The moon joins a lineup of planets and bright stars hung like tiki lamps across the southwestern sky at dusk. Watch for it to pass near fading Mars Saturday evening and Saturn on Monday.

The Martian landscape photographed by on July 30, 2014. The rover is exploring south along the west rim of Endeavour Crater heading toward a notch called ‘Marathon Valley’ about 1.2 miles (2 kilometers) away. Credit: NASA/JPL

While you’re gazing at the Red Planet, know that the Opportunity rover made news this week when it set a record for the most miles ever driven off-planet, tallying a satisfying 25 miles (40 km) of Martian travels. The previous record was held by the Soviet Union’s Lunokhod 2 rover when it ambled across 24.2 miles of the moon’s surface in 1973.

Out of this world distance records compared. Credit: NASA

Opportunity surpassed that record on Monday July 28 when it registered 25.01 miles en route to a notch called Marathon Valley along the west rim of Endeavour Crater. Mission controllers would like to get a look at clay minerals there that have been spotted from orbit.

Lunokhod 2 crater photographed by Opportunity last spring. The crater’s 20 feet (6 meters) in diameter. Credit: NASA/JPL

When it reaches the Valley it will have completed 26.2 miles (42 km), the official distance of a marathon. When you consider that Opportunity and its sister probe Spirit were only intended to function for 90 days, the current record-breaking feat and upcoming marathon completion are that more remarkable.

101 geysers erupt from Enceladus’ salty deeps

At least 20 geysers blast icy particles and water vapor from cracks in the icy crust of Saturn’s moon Enceladus. Scientists recently confirmed the geyser material derives from a salty ocean beneath the moon’s surface. Credit: NASA/JPL

Future astronauts better watch where their step when exploring the south polar terrain of Saturn’s icy moon Enceladus. A geyser could pop up anywhere.

This graphic shows a 3-D model of 98 geysers whose source locations and tilts were found in a Cassini imaging survey of Enceladus’ south polar terrain by the method of triangulation. Credit: NASA/JPL-Caltech/Space Science Institute

NASA’s Cassini spacecraft have identified 101 distinct geysers erupting on Saturn’s icy moon Enceladus. Cassini has studied and photographed the moon’s intriguing ‘tiger stripe’ fractures for over 7 years and discovered that each of them coincides with a particular hot spot within a fracture.

Three competing hypotheses were put forward to explain how geysers might happen on an ice-covered moon nearly a billion miles from the warmth of the sun.

#1 – Tidal flexing: As Enceladus revolves around Saturn, the planet’s enormous gravity flexes the little moon, heating up its interior and melting ice into water which escapes as vapor through openings in the icy crust.
#2 – Frictional heating: Back-and-forth rubbing of opposing walls of the fractures generate frictional heat that turns ice into geyser-forming vapor and liquid. Same principle as rubbing your hands together to create heat.
#3 – Jaws of ice: The opening and closing of the fractures caused by Saturn’s gravitational might exposes water from below when then quickly vaporizes in the moon’s vacuum.

This artist’s rendering shows a cross-section of the ice shell immediately beneath one of Enceladus’ geyser-active fractures, illustrating how water works its way to the moon’s surface. Credit: NASA/JPL-Caltech/Space Science Institute

But a detailed study by Cassini in 2010 appears finally to have netted the correct explanation. The probe’s heat-sensing instruments matched the geysers’ locations with small-scale hot spots only a few dozen feet across - too small to be produced by frictional heating, but the right size to be the result of condensation of vapor on the near-surface walls of the fractures.

“Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa,” said Carolyn Porco, leader of the Cassini imaging team and lead author of the first scientific paper on the discovery. “It also told us the geysers are not a near-surface phenomenon, but have much deeper roots.”

Researchers concluded the only logical source of the material forming the geysers is the sea now known to exist beneath the ice shell. They also found that narrow pathways through the ice shell can remain open from the sea all the way to the surface, if filled with liquid water. This implies, at least in my mind, that liquid water might exist as pools in hot spots encircled by thick rims of ice (condensed water vapor) on the moon’s chill -330° F (-201° C) surface.

Imagine standing nearby watching fountains of vapor turn to ice crystals before your eyes and sparkling like diamond dust against the black starry sky.

Source: JPL

Rocky moon meets the ringed planet tonight

Look to the waxing gibbous moon tonight July 7 and you’ll see the planet Saturn about 1 degree above it. This map shows the sky around 10 o’clock local time. Stellarium

Forgive this ultra-brief appearance, but I’ve been exploring a virtually unknown astronomical paradise the past few days – Las Vegas! Although it seems incongruous, given Vegas’ image, the Las Vegas Astronomical Society has a very active presence here.

A recent photo posted by the Cassini spacecraft photo group shows Saturn’s magnificent rings, polar vortex and the jet stream-created polar hexagon. The hexagon, which is wider than 2 Earths, forms a six-lobed, stationary wave that wraps around the north polar regions at a latitude of roughly 77 degrees North. Credit: NASA/JPL-Caltech

The group planned a public outing for the Mars-moon conjunction on July 5 but were clouded out. Maybe tonight their members will get a clear sky for the Saturn-moon conjunction. I’ll be in a plane at 35,000 feet for the event crossing my fingers I get a window seat on the ‘right’ side.

Celestial fireworks light up the sky on the Fifth of July

The crescent moon shines in the southwestern sky tonight July 2 not far from Leo’s brightest star Regulus. It’s headed for two fine conjunctions later this week. Stellarium

We celebrate Independence Day this Friday the 4th with parades and good food topped off with colorful fireworks. Consider that the opening act. Festivities continue into the weekend with two spectacular conjunctions of the moon and planets.

Saturday evening July 5 allow your gaze to wander up to the first quarter moon. Levitating above it will be a bright red light – the planet Mars! They’ll be close. From most of the central and eastern U.S. and Canada the two are separated by just a half degree or one moon diameter. Look a short distance to the left of moon and you’ll also spot Virgo’s brightest star Spica.

The first quarter moon pays a close visit to Mars on Saturday July 5 and then passes Saturn two nights later. The views show the scene from the central U.S. around the start of nightfall. Stellarium

If you live farther south, the moon will inch closer to Mars. From sizzling Miami, the duo’s only a 1/3 of a moon apart, while the moon will completely cover or occult Mars for up to an hour across a wide swath of South America. Click HERE for a map and times showing where and when the occultation will occur.

Though Mars isn’t quite as bright as it was at opposition in April, it’s still brighter than its color rival Betelgeuse in Orion. With haze-free skies and a pair of binoculars you might be able to see it atop the moon a short time before sunset. Certainly worth a try.

Everybody loves an encore after a great performance, and the moon’s happy to oblige. Two nights later on July 7 it glides about a degree (two diameters) directly below Saturn. Once again, the moon will occult the planet as seen from the southern half of South America. While these sky events aren’t exactly stars exploding before our very eyes, their quiet beauty is worth our admiration.

Cassini at Saturn – 10 years of beauty and discovery

Saturn and its rings photographed with Earth (lower right) in the background on July 19, 2013. Click for a full, hi-res view. Credit: NASA/JPL-Caltech/SSI

Today marks the 10th anniversary of NASA’s Cassini mission to Saturn. Originally slated for four years, the mission was granted two extensions and will continue through September 2017. Now dubbed the ‘Cassini Solstice Mission’, it’s named for the Saturnian solstice which occurs in May that year. All the extra time granted to keep the probe running has allowed astronomers to study seasonal changes during Saturn’s 29.5 year orbit of the sun. Saturn has seasons just like Earth, but they’re leisurely affairs, each lasting about 7.5 years.

This image shows the first flash of sunlight reflected off a hydrocarbon lake on Saturn’s moon Titan on July 8, 2009. The glint off a mirror-like surface is known as a specular reflection. Click to enlarge. Credit: NASA/JPL-Caltech

Cassini has not only made a remarkable number of new discoveries but returned what many of us consider the most beautiful photos every taken of another world. Planetary scientist Carolyn Porco, who leads the Cassini imaging team, has a knack for capturing images of both scientific import and spectacular beauty. How can you help it when your subject’s the most picturesque celestial body in the known universe?

First color image of Titan’s surface taken by the Huygens lander. The two icy rocks below center  measure about 6 inches across (left) and 1.5 inches (right). They’re about a yard from the spacecraft. Click for more details. Credit: NASA/JPL-Caltech

Here’s a short list of Cassini’s most notable discoveries since arriving in 2004:

* Titan revealed as a colder analog of Earth with rivers, lakes, seas filled by rainstorms of liquid hydrocarbons like ethane and methane and an atmosphere composed primarily of nitrogen.

* First landing by the Huygens probe – dispatched by Cassini – on a moon orbiting another planet. Huygens touched down on Titan after parachuting to its surface on Jan. 14, 2005.

* Discovery of active, icy plumes on the Saturnian moon Enceladus that appear to originate from a 6-mile-deep subsurface ocean confirmed just this spring. Enceladus joins Jupiter’s moon Europa and Mars as potential habitats for life.

Vertical structures rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken 2 weeks before the planet’s August 2009 equinox. The structures tower as high as  1.6 miles (2.5 km) above the plane of the rings, much higher than their general thickness of just 30 feet (10-m). Click to enlarge. Credit: NASA/JPL-Caltech

* Spectacular closeup photos revealing the individual characteristics of many of Saturn’s moons as well as active and dynamic structures within the planet’s rings like vertical ‘ice pillars’ and the birth of a new moon.

* First complete view of the north polar hexagon and discovery of giant hurricanes at both of Saturn’s poles.

* Close up study of the planet’s massive thunderstorm from first detection on Dec. 5, 2010 into 2013.

Enceladus shows off its plumes to NASA’s Cassini spacecraft cameras. Click to enlarge. Credit: NASA/JPL-Caltech/SSI

There’s so much more, much of it reported here over the years. If you’d like to go deeper, start at the Cassini Solstice Mission homepage. Be sure you check out some of the favorite Cassini images selected by members of the team.

The spacecraft has been remarkably trouble-free, and from an
engineering standpoint, the main limiting factor for Cassini’s lifetime
now is how much propellant is left in its tanks. Future studies include examining the rings and moons in ever greater detail.

Care to see more photos? Click to view the Cassini Imaging Diary.

Two asteroids approach in the night / See Saturn’s elusive moon Iapetus

Map showing Ceres and Vesta as they approach each other closely this coming week. Both asteroids are near the easy-to-find star Zeta in Virgo not far from bright Mars (see map below). Although the asteroids appear very close together in the sky, they’re really about 51 million miles apart with Vesta in the foreground. Click to enlarge. Source: Chris Marriott’s SkyMap

This coming week there will be something for everyone in the night sky whatever instrument you choose: telescope, binoculars or naked eyeballs.

The biggest asteroid, Ceres, and brightest, Vesta, have been on converging paths since early spring. Right now they’re about a moon diameter (1/2 degree) apart and closing with each passing night. Saturday night July 5 – one week from today –  they’ll be three times closer yet, separated by just 10 arc minutes. To see this double asteroid treat a pair of 35 or 50mm binoculars should do the trick.

Use this wider view to help get oriented. Our two featured asteroids are near the 3rd magnitude star Zeta Virginis just above the bright pair of Mars and Spica. The map shows the sky around 10 p.m. local time tonight June 28, 2014 for the central U.S. Stellarium

Just as moon routinely has conjunctions with bright planets and stars during its monthly round through the zodiac, Vesta and Ceres will be in conjunction one directly atop the other on July 5. Vesta will shine at 7th magnitude and be easy to spot in binoculars; fainter Ceres at magnitude 8.3 will take a little more effort. Since asteroids are too small and far away to show as disks in most telescopes, the pair will look like a temporary ‘double star’ in all instruments.

Double your conjunction fun on Saturday night July 5. The same night Ceres and Vesta are closest, the moon and Mars form a tight duo nearby. From parts of South America, the moon will cover or occult the Red Planet. Stellarium

Another celestial duo debuts on the very same night the asteroids are closest. For observers in the U.S. and Canada, the moon, some 7 degrees south of Vesta-Ceres, passes only a half degree from Mars. Two conjunctions in the same small pocket of sky on the same night!

For U.S. observers, this all happens the night after the July 4 Independence Day fireworks. Could July start with more of a bang?

Another telescopic delight is happening a stone’s throw from Mars around the planet Saturn. Of the 62 known moons of the ringed planet, one of the most peculiar is 907-mile-wide Iapetus, which orbits well beyond the more familiar telescopic moons Titan, Rhea, Tethys and Dione.

Ever seen Saturn’s peculiar moon Iapetus? Right now it’s west of the planet and bright — second only to the moon Titan. Click to enlarge. Source: Starry Night

Iapetus has two faces really. One is shiny white and bright as snow, the other dark as the sky above Gotham City. The moon takes 79 days to complete one orbit around Saturn and like our own moon, keeps one face locked toward the planet. When it orbits east of Saturn, Iapetus shines dimly at magnitude +12 because its dark side faces us. But when it’s off to the west of the planet, the brilliant side turns our way and we see it shine two magnitudes brighter.

Saturn’s moon Iapetus, 907 miles (1,460 km) in diameter, has a dual personality. One hemisphere is covered with bright ice, the other with darker material possibly ejected by impacts on the more distant moon Phoebe. Credit: NASA / JPL / Space Science Institute

Greatest brightness occurs at the time of greatest distance west of the planet which happens on July 3. You can use the map above to help you follow the moon through its cycle of bright to dim. For more information, please see this recent article in Sky and Telescope.

Magnetic collapse makes Saturn’s auroras dance the cha-cha

Images of auroras over Saturn’s north pole in ultraviolet light with the Hubble Space Telescope capture moments when Saturn’s magnetic field is affected by bursts of particles streaming from the Sun. Click to enlarge. Credit: NASA, ESA, Jonathan Nichols (University of Leicester)

Saturn shines brightly in the late May evening sky. You can see it now at nightfall by following an arc starting with fiery Mars and passing through Spica. Continue and you’ll end up at Antares, the alpha luminary in Scorpius. Did you know that it also shimmers with auroras too just like the Earth?

Recent Hubble Space Telescope photos taken in ultraviolet light, where the aurora shines brightly, show bursts of light shooting around Saturn’s polar regions traveling at more than three times faster than the speed of the gas giant’s roughly 10-hour rotation period.

Saturn’s auroras shine brightly in UV but would appear deep red at the bottom and violet at top with the naked eye. That’s because hydrogen gas dominates the planet’s atmosphere and emits light in different colors when bombarded by the energetic electrons in the solar wind. On Earth, excited oxygen and nitrogen molecules produce the more familiar greens, reds and blues of northern lights.

A magnetosphere is that area of space around a planet that’s controlled by the planet’s magnetic field. The shape of the Earth’s magnetosphere is the direct result of being blasted by solar wind, compressed on its sunward side and elongated on the night side forming a magnetotail. Saturn’s is similar. Credit: NASA

University of Leicester researchers recently discovered an amazing connection between Saturn’s and Earth’s auroras. Both planets are surrounded by teardrop-shaped magnetic domains called magnetospheres generated by the churning of materials within their cores. In each case, the side facing the sun is compressed and flattened, while the other side is drawn out into a long tail called a magnetotail.

“Our observations show a burst of auroras that are moving very, very quickly across the polar region of the planet. We can see that the magnetotail is undergoing huge turmoil and reconfiguration, caused by buffering from solar wind,” said Jonathan Nichols, of the University of Leicester’s Department of Physics and Astronomy, who led the Hubble observations.


NASA’s THEMIS Spacecraft See magnetic reconnection / collapse in Earth’s magnetotail

What’s happening – and you can see it clearly in the video above – is that the incoming solar wind connects to and ‘peels back’ a portion of the magnetic field on the dayside of both Earth and Saturn. When the lines pinch together and reconnect on the back or magnetotail-side, a torrent of solar electrons is funneled into the upper atmospheres of both planets. Voila – aurora borealis! Here’s another video showing it from a slightly different perspective.


Dance of Saturn’s auroras

“The particular pattern of auroras that we saw relates to the collapsing of the magnetotail,” Nichols added. “We have always suspected this was what also happens on Saturn. This evidence really strengthens the argument.”

Cool beyond cool. Earth and Saturn are auroral buddies.

Follow the arc from fiery Mars in the south through Spica to find Saturn. Keep going all the way to Antares. All four are magnitude 1 or brighter. The map shows the sky around 10:30 p.m. local time facing south. Stellarium

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

Full Flower Moon blooms and hides Saturn this week

Saturn and the moon Tuesday and Wednesday nights (May 13-14) just before midnight as viewed from the U.S. Midwest. Stellarium

38 degrees today in Duluth with a chill wind off Lake Superior. Must be May again. Time for the Flower Moon, the traditional name given to May’s full moon. Such a lovely moniker but nearly always lost on this frozen outpost I call home.

Tonight the moon’s in that awkward phase between half and full called gibbous, but tomorrow night it will shine nearly full and round in the southern sky just a few degrees to the right or west of Saturn. When full on the 14th, the moon will move to the opposite side of the planet.


Moon-Saturn occultation from Perth, Australia Feb. 22, 2014 captured by Colin Legg

While a moon-planet conjunction isn’t unusual, an occultation is. This time around, skywatchers in Australia and New Zealand are in the right location to watch the moon hide or ‘occult’ Saturn for about an hour early Weds. evening May 14 Australian time.

U.S. and Canadian observers can watch the waxing moon slowly approach Saturn overnight Tuesday. The best views will be had at the onset of dawn on the West Coast where only a degree (two full moon diameters) will separate the two early Wednesday.

If you could move fast enough to the west to avoid encroaching daylight and south to raise the moon a tad higher against the starry backdrop, you’d find yourself in Australia Wednesday night watching the moon slowly slide over the planet Saturn.

An earlier Saturn disappearance.

Planet occultations are awesome events to watch through a telescope because they give us an inkling of what it’s like to see a planet ‘set’ and ‘rise’ over an alien landscape, a place other than Earth.

What am I talking about? As the moon approaches Saturn, the planet will appear to ‘set’ as the bright edge of the moon encroaches and slowly nibbles away at Saturn until only a ringtip remains. Once the planet disappears, observers must wait about an hour for it to reappear on the moon’s other side, when it ‘rises’ from the limb by degrees until it’s in the clear once more. A wonderful sight!

I’ve seen occultations of Jupiter and Saturn and wouldn’t miss another except for the expense and time of flying to Australia. Closer to home, I’m game anytime.

Happily, we all can be close to home for this event. Astrophysicist Gianluca Masi will broadcast the occultation live online from his Virtual Telescope website beginning at 10:15 a.m. Universal Time May 14 or 6:15 a.m. EDT, 5:15 a.m. CDT, 4:15 MDT and 3:15 PDT. Yes, that’s early, but I know some of you may want to catch it.

Map showing where the Saturn occultation is visible. Some cities, like Darwin, will see Saturn graze the edge of the moon. Click to find times for individual cities. Times will be in Universal Time. Add 9.5 hours for Australian Central Standard Time. Credit: IOTA

Meanwhile, if you live in Australia or New Zealand and are reading this, click the map above for a list of times for individual cities when Saturn disappears and reappears.

The moon and its close companion, double star Zubenelegenubi, as they’ll appear early Tuesday evening. Stellarium

Six more moon-Saturn occultations occur this year but none are visible in North America. Curious about future events? Peruse this list when you have a few free minutes.

Even if northerners have to wait a while for the next planetary occultation, we can still enjoy Saturn flirting with the Flower Moon two nights in a row. Plus there’s a consolation prize! Look at the moon through binoculars tomorrow night (May 13) and less than a moon-diameter south you’ll spot the best-named double star in the whole sky: Zubenelgenubi (zoo-BEN-el-je-NEW-bee). Even binoculars can split this one.