Bob King, Author at Universe Today

September 9, 2014December 23, 2015 by Bob King

Bumper Car Moonlets Crash and Crumble in Saturn’s F Ring

A map of Saturn's F ring from 2006 shows one of the few bright, extended clumps (indicated by a green box) seen during six years of observation by Cassini. Image credit: NASA/JPL-Caltech/SSI

Nothing stands still. Everything evolves. So why shouldn’t Saturn’s kookie, clumpy F ring put on a new face from time to time?

A recent NASA-funded study compared the F ring’s appearance in six years of observations by the Cassini mission to its appearance during the Saturn flybys of NASA’s Voyager mission, 30 years earlier.

Example of a kink in part of Saturn's F ring. While the ring is held together by the shephard moons Prometheus and Pandora, which orbit just inside and outside the ring, embedded moonlets are believed responsible for the kinks and clumps. Credit: NASA — A kink in part of Saturn’s F ring. While the ring is held together by the shepherd moons Prometheus and Pandora, which orbit just inside and outside the ring, embedded moonlets are believed responsible for the kinks and clumps. The rings is several hundred kilometers wide. Credit: NASA

While the F ring has always displayed clumps of icy matter, the study team found that the number of bright clumps has nose-dived since the Voyager space probes saw them routinely during their brief flybys 30 years ago. Cassini spied only two of the features during a six-year period.

Scientists have long suspected that moonlets up to 3 miles (5 km) wide hiding in the F ring are responsible for its uneven texture. Kinks and knots appear and disappear within months compared to the years of observation needed changes in many of the other rings.

Saturn's F ring is extremely narrow compared to the historic A, B and C rings. It measure just a few hundred kilometers across. Credit: NASA/Cassini — Saturn’s F ring is extremely narrow compared to the historic A, B and C rings. It measures just a few hundred kilometers across. Credit: NASA/Cassini

“Saturn’s F ring looks fundamentally different from the time of Voyager to the Cassini era,” said Robert French of the SETI Institute in Mountain View, California, who led the study along with SETI Principal Investigator Mark Showalter. “It makes for an irresistible mystery for us to investigate.”

A 2007 artist impression of the aggregates of icy particles that form the 'solid' portions of Saturn's rings. These elongated clumps are continually forming and dispersing. The largest particles are a few metres across.They clump together to form elongated, curved aggregates, continually forming and dispersing. Credit: NASA/JPL/Univ. of Colorado — A 2007 artist impression of small boulder-like chunks of ice that comprise Saturn’s rings. The largest are about 10-12 feet across.They clump together to form elongated, curved aggregates, continually forming and dispersing. Credit: NASA/JPL/Univ. of Colorado

Because the moonlets lie close to the ring and cross through it every orbit, the research team hypothesizes that the clumps are created when they crash into and pulverize smaller ring particles during each pass. They suspect that the decline in the number of exceptionally bright kinks and the clumps echoes a decline in the number of moonlets available to do the job.

So what happened between Voyager and Cassini? Blame it on Prometheus. The F ring circles Saturn at a delicate point called the Roche Limit. Any moons orbiting closer than the limit would be torn apart by Saturn’s gravitational force.

A possible culprit! Prometheus measures 74 miles (119 km) across and orbits the inner edge of Saturn's F ring. Credit: NASA — The culprit? Prometheus measures 74 miles (119 km) across and orbits the inner edge of Saturn’s F ring. Credit: NASA

“Material at this distance from Saturn can’t decide whether it wants to remain as a ring or coalesce to form a moon,” said French. “Prometheus orbits just inside the F ring, and adds to the pandemonium by stirring up the ring particles, sometimes leading to the creation of moonlets, and sometimes leading to their destruction.”

Every 17 years the orbit of Prometheus aligns with the orbit of the F ring in a way that enhances its gravitational influence. The researchers think the alignment spurs the creation of lots of extra moonlets which then go crashing into the ring, creating bright clumps of material as they smash themselves to bits against other ring material.

Sounds like a terrifying version of carnival bumper cars. In this scenario, the number of moonlets would gradually drop off until another favorable Prometheus alignment.

The Voyagers encounters with Saturn occurred a few years after the 1975 alignment between Prometheus and the F ring, and Cassini was present for the 2009 alignment. Assuming Prometheus has been “working” to build new moons since 2009, we should see the F ring light up once again with bright clumps in the next couple years.

Cassini will be watching.

September 8, 2014December 23, 2015 by Bob King

Guide to Tonight’s Big Harvest Moon

"The Harvest Moon", a circa 1833 oil painting by Samuel Palmer. Closely spaced moonrises meant extra light to bring in the crops in the days before electric lighting.

Tonight, September 8, the Harvest Moon rises the color of a fall leaf and spills its light across deserts, forests, oceans and cities. The next night it rises only a half hour later. And the next, too. The short gap of time between successive moonrises gave farmers in the days before electricity extra light to harvest their crops, hence the name.

The Harvest Moon is the full moon that falls closest to the autumnal equinox, the beginning of northern autumn. As the moon orbits the Earth, it moves eastward about one fist held at arm’s length each night and rises about 50 minutes later. You can see its orbital travels for yourself by comparing the moon’s nightly position to a bright star or constellation.

This full Moon is also a Proxigean or Perigee Full “Supermoon” (find out more about that here), which means the Moon is in a spot in its elliptical orbit where it is closer to Earth near the time it is full, making it look up to 15% larger than average full Moon.

Around the time of Harvest Moon, the full moon's path is tilted at a shallow angle to the eastern horizon making with successive moonrises only about a half hour apart instead of the usual 50 minutes. Source: Stellarium — Around the time of Harvest Moon, the full moon’s path is tilted at a shallow angle to the eastern horizon making with successive moonrises only about a half hour apart instead of the usual 50 minutes. Source: Stellarium

50 minutes is the usual gap between moonrises. But it can vary from 25 minutes to more than an hour depending upon the angle the moon’s path makes to the eastern horizon at rise time. In September that path runs above the horizon at a shallow angle. As the moon scoots eastward, it’s also moving northward this time of year.

This northward motion isn’t as obvious unless you watch the moon over the coming week. Then you’ll see it climb to the very top of its monthly path when it’s high overhead at dawn. The northward motion compensates for the eastward motion, keeping the September full moon’s path roughly parallel to the horizon with successive rise times only ~30 minutes apart.

The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in spring, the path tilts steeply southward, delaying successive moonrises by over an hour. In September, the moon’s path is nearly parallel to the horizon with successive moonrises just 20+ minutes apart. Times are shown for the Duluth, Minn. region. Illustration: Bob King — The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in spring, the path tilts steeply southward, delaying successive moonrises by over an hour. In September, the moon’s path is nearly parallel to the horizon with successive moonrises just 30+ minutes apart. Times are shown for the Duluth, Minn. region. Illustration: Bob King

Exactly the opposite happened 6 months earlier this spring, when the moon’s path met the horizon at a steep angle. While it traveled the identical distance each night then as now, its tilted path dunked it much farther below the horizon night to night. The spring full moon moves east and south towards its lowest point in the sky. Seen from the northern hemisphere, that southward travel adds in extra time for the moon to reach the horizon and rise each successive night.

If all this is a bit mind-bending, don’t sweat it. Click HERE to find when the moon rises for your town and find a spot with a great view of the eastern horizon. You’ll notice the moon is orange or red at moonrise because the many miles of thicker atmosphere you look through when you gaze along the horizon scatters the shorter bluer colors from moonlight, tinting it red just as it does the sun.

A series of photos of the full moon setting over Earth's limb taken by from space by NASA astronaut Don Pettit on April 16, 2003. Refraction causes a celestial object's light to be bent upwards, so it appears higher than it actually is. The bottom half of the moon, closer to the horizon, is refracted strongest and "pushed" upward into the top half, making it look squished. Credit: NASA — A series of photos of the full moon setting over Earth’s limb taken by from space by NASA astronaut Don Pettit on April 16, 2003. Refraction causes a celestial object’s light to be bent upwards, so it appears higher than it actually is. The bottom half of the moon, closer to the horizon, is refracted strongest and “pushed” upward into the top half, making it look squished. Credit: NASA

The moon will also appear squished due to atmospheric refraction. Air is densest right at the horizon and refracts or bends light more strongly than the air immediately above it. Air “lifts” the bottom of the moon – which is closer to the horizon – more than the top, squishing the two halves together into an egg or oval shape.

How we perceive the moon's size may have much to do with what's around it. In this illustration, most of us seen the bottom moon as smaller, but they're both exactly the same size. Crazy, isn't it? Credit: NASA — How we perceive the moon’s size may have much to do with what’s around it. In this illustration, most of us seen the bottom moon as smaller, but they’re both exactly the same size. Crazy, isn’t it? Credit: NASA

You may also be entranced Monday night by the Moon Illusion, where the full moon appears unnaturally large when near the horizon compared to when viewed higher up. No one has come up with a complete explanation for this intriguing aspect of our perception, but the link above offers some interesting hypotheses.

Can you see craters with your naked eye? Yes! Try tonight through Wednesday night. Plato is the trickiest. Credit: Bob King

Finally, full moon is an ideal time to see several lunar craters with the naked eye. They’re not the biggest, but all, except Plato, are surrounded by bright rays of secondary impact craters that expand their size and provide good contrast against the darker lunar “seas”. Try with your eyes alone first, and if you have difficulty, use binoculars to get familiar with the landscape and then try again with your unaided eyes.

In contrast to the other craters, Plato is dark against a bright landscape. It’s a true challenge – I’ve tried for years but still haven’t convinced myself of seeing it. The others are easier than you’d think. Good luck and clear skies!

If you don’t have clear skies, Slooh will broadcast the “Super Harvest Moon” live from the Institute of Astrophysics of the Canary Islands, off the coast of Africa. Slooh’s live coverage will begin at 6:30 PM PDT / 9:30 PM EDT /01:30 UTC (8/9) – International times here. Slooh hosts are Geoff Fox and Slooh astronomer Bob Berman. Viewers can ask questions during the show by using hashtag #Sloohsupermoon. Watch below:

September 7, 2014December 23, 2015 by Bob King

Speed Demon Asteroid Sprints Safely Past Earth Today

Asteroid 2014 RC photographed 30 minutes before closest approach to Earth today. During this one-minute-long time exposure the asteroid covered more than 3/4 degree of sky. Credit: Ernesto Guido, Nick Howes, Martino Nicolini

Earth-approaching asteroid 2014 RC ripped pass Earth today, got its orbit refashioned by our planet’s gravity and now bids us adieu. I thought you’d like to see how fast this ~60-foot-wide (20-meter) space rock moved across the sky. The team of observers at Remanzacco Observatory in Italy photographed it remotely with a telescope set up in Australia. 30 minutes before closest approach to Earth of 25,000 miles (40,000 km), 2014 RC was traveling at the rate of 49.5 arc minutes (1.6 times the diameter of the full moon) per minute.

2014 RC accelerates across the sky from 4 a.m. to 4 p.m EDT in this path created by Gianluca Masi using SkyX Pro software and the latest positions from JPL. he asteroid’s intrinsic speed was not exceptional, but because it came so close to Earth, it covered a huge swath of sky in a hurry.

At the time, the asteroid glowed at magnitude +11.2, bright enough to see in a 4.5 inch telescope even in the bright moonlit sky at the time. Let’s try to get a feel for its speed. Just to keep 2014 RC centered in the field of view, you’d have to continually move the telescope to follow it as it you were tracking an airplane or satellite. What a thrill it must have been for observers in Australia and New Zealand who got the ride of their life across the heavens hanging onto this fleet rock with their eyeballs. In an hour’s time, centered on closest approach, the asteroid traveled approximately 48º. That more than twice the length of the constellation Orion!

The orbit of 2014 RC occasionally brings it close to Earth as it did today September 7, 2014. Credit: NASA/JPL-Caltech — The orbit of 2014 RC occasionally brings it close to Earth as it did today September 7, 2014 when it passed less than 1/10 the distance of the moon to the Earth. The asteroid orbits the sun every 1.5 years. Credit: NASA/JPL-Caltech

As 2014 RC blew by, its orbit was bent by Earth’s gravity and sent on a new trajectory. If this sounds familiar, we deliberately performed the same maneuver with the Voyager I and II spacecraft back in the late 1970s and early 1980s. A rare planetary alignment allowed scientists to swing the probes near Jupiter and Saturn to gain speed and shape their orbits for future encounters. Such gravity assist maneuvers are now commonplace.

The dot behind the hubbub. Gianluca Masi, who runs the Virtual Telescope Project, tracked 2014 RC during his time exposure, so it shows up as a tiny dot instead of a streak. Credit: Gianluca Masi — Space rock exposed! Gianluca Masi, who runs the Virtual Telescope Project, tracked 2014 RC during his time exposure, so it shows up as a tiny dot instead of a streak. Credit: Gianluca Masi

No doubt 2014 RC will approach Earth again, but no threatening encounters are in the cards for at least 100 years. For now we’re grateful it passed safely while inspiring wonder at what the solar system can throw at us.

Update: here’s an additional set of images from Peter Lake from Australia. You can see more on his blog here.

Three 30 second exposures at different times during Asteroid 2014 RC's pass by Earth on September 7, 2014. Credit and copyright: Peter Lake. — Three 30 second exposures at different times during Asteroid 2014 RC’s pass by Earth on September 7, 2014. Credit and copyright: Peter Lake.

September 5, 2014December 23, 2015 by Bob King

New Mosaic Reveals Jets Blasting from Rosetta’s Comet

Two jets of gas and dust blast from Comet 67P/C-G in this reassembled and enhanced mosaic made from four photos taken by Rosetta's navigation camera on September 2, Credit: ESA/Rosetta/ Navcam/Bob King

Hidden among the four new images of Comet 67P/Churyumov-Gerasimenko released by ESA this week are a pair of dusty jets shooting from the nucleus of Comet Churyumov-Gerasimenko. The photos were taken September 2, 2014 and posted as a mosaic of four separate images. I re-assembled the four, albeit imperfectly, and added some additional contrast to better show the dual geyser of ice crystals mixed with dust venting from the nucleus.

Four image montage of comet 67P/C-G, using images taken on 2 September. Credits: ESA/Rosetta/NAVCAM — Original four image montage of comet 67P/C-G, using images taken on September 2. The dark spot at center is imaging artifact. Credits: ESA/Rosetta/NAVCAM

An earlier Rosetta photo taken of Comet 67P/ Churyumov-Gerasimenko from a great distance and deliberately overexposed showed jets of dust-laden vapor shooting from the comet, but this is the first image I’m aware of that shows both the comet’s surface and its much fainter exhalations.

Jets or sprays of vaporizing ice are what gives a comet its lively appearance. Dust released with water vapor is ultimately pushed back by the pressure of sunlight to grow 67P/C-G’s dust tail. Ultraviolet light from the sun causes volatiles within the vapor to fluoresce a pale blue, creating a second ion or gas tail. The coma or comet atmosphere is a mix of both.

Rosetta took a long-exposure image with its wide-angle camera on August 2, 2014, to observe jets of dust escaping from the comet. The photo was taken from a distance of 550 kilometers. ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA — On August 2, 2014 at distance of 342 miles (550 km), Rosetta took this wide-angle view of the comet and jets of dust and vapor shooting into space.
ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

We can expect the jets to grow stronger and hopefully more numerous as 67P/C-G approaches perihelion in August 2015. Because the spacecraft is maneuvering into orbit between the comet and sun, we don’t get the best view of jetting activity. The comet nucleus, illuminated by sunlight, drowns out the fainter jets. Rosetta will make an excursion to the nightside on September 24. Assuming the jets remain active, we might see them backlit by the sun as bright beams extending from the darkened nucleus into space.

September 5, 2014December 23, 2015 by Bob King

What Comets, Parking Lots and Charcoal Have in Common

Illustration of Comet 67P/C-G brought down to Earth in the city of Los Angeles, Calif. Compare to the same image (below) as viewed in space. Credit: ESA and anosmicovni

All the pictures we’ve seen of Rosetta’s target comet 67P/C-G show it reflecting brightly against the background of outer space. And well they should. Space is black as night. But if we were to see the comet against a more familiar earthly backdrop, we’d be shocked by its appearance. Instead of icy white, Rosetta’s would appear the color of a fresh asphalt parking lot. Most comets, including Rosetta’s, are no brighter than the charcoal briquettes you use to grill hamburgers.

Astronomers rank an object’s reflectivity by its albedo (al-BEE-do). A body that reflects 100% of the light is said to have an albedo of 1.0. Venus’ albedo is .75 and reflects 75% of the light it receives from the sun, while the darker Earth’s average is 30%. Trees and the darker-toned continents reflect much less light compared to Venus’ pervasive cloud cover. In contrast, the coal-dark moon reflects only 12% of the sunlight falling on it and fresh asphalt just 4% – smack in the middle of the 2-6% range of most known comets.

Photo of Comet 67P/C-G taken by Rosetta on August 6, 2014. Credit: ESA — Photo of Comet 67P/C-G taken by Rosetta on August 6, 2014. Against the blackness of space, it appears whitish-grey. Credit: ESA

The brightest object in the solar system is Saturn’s icy moon Enceladus with a reflectivity of 99%. So why are comets so dark? It’s funny because before we sent the Giotto spacecraft to snap close-up pictures of Halley’s Comet in 1986, astronomers thought comets, being made of reflective ice, were naturally white. Not Halley and not every comet seen up close since then.

Comets are as dark as charcoal but appear light only because the sun illuminates them against the blackness of outer space. The same charcoal, when viewed in normal light on Earth, appears black. Credit; Bob King — Comets are as dark as charcoal but appear light only because the sun illuminates them against the blackness of outer space. I shone a flashlight on a charcoal briquette (left) to simulate comet lighting. The same charcoal, when viewed in normal light, appears black. Credit; Bob King

Astronomers hypothesize that a comet grows a dark ‘skin’ both from accumulated dust and irradiation of its pristine ices by cosmic rays. Cosmic rays loosen oxygen atoms from water ice, freeing them to combine with simple carbon molecules present on comets to form larger, more complex and darker compounds resembling tars and crude oil.

Comet colored parking lots have been the rage for years. Both comets and fresh asphalt reflect about the same amount of light. Credit: Bob King

Over time, the comet can become insulated by dust and complex organic materials. Combined with a loss of ice to vaporization at each repeated swing past the sun, they stop outgassing and become inert or defunct comets similar to asteroids. And that might not be the end of the story. Occasionally, a dead comet or an object originally discovered as an asteroid can unexpectedly fire back up after years of inactivity and become a comet again temporarily. Astronomers call these peculiar critters ‘damocloids’.

One wonders what you’d see if you could slice open a 67P/Churyumov-Gerasimenko. Would it resemble an Oreo cookie with a dark exterior and creamy white inside? One of NASA’s instruments aboard Rosetta named Alice began mapping the comet last month. In its first far ultraviolet spectra of the surface, we learned just this week that 67P is “darker than charcoal black”. Alice also detected hydrogen and oxygen in the comet’s coma, or atmosphere.

Oreo cookies - a model of a comet nucleus? Credit: Evan-Amos — Oreo cookies – a model of a comet nucleus? Credit: Evan-Amos

Rosetta scientists also discovered the comet’s surface so far shows no large water-ice patches. The team expected to see ice patches on the comet’s surface because it’s too far away for the sun’s warmth to turn its water into vapor.

“We’re a bit surprised at just how unreflective the comet’s surface is and how little evidence of exposed water-ice it shows,” said Alan Stern, Alice principal investigator at the Southwest Research Institute in Boulder, Colorado.

Hmmm … maybe it really is a giant cookie.

September 4, 2014December 23, 2015 by Bob King

Get Ready for Sunday’s Close Flyby of Asteroid 2014 RC

This graphic depicts the passage of asteroid 2014 RC past Earth on September 7, 2014. At time of closest approach, the space rock will be about one-tenth the distance from Earth to the moon. Times indicated on the graphic are Universal Time. Subtract 4 hours for Eastern Daylight Time. Credit: NASA/JPL-Caltech

Guess who’s dropping by for a quick visit this weekend? On Sunday, a 60-foot-wide (20-meters) asteroid named 2014 RC will skim just 25,000 miles (40,000 km) from Earth. That’s within spitting distance of all those geosynchronous communication and weather satellites orbiting at 22,300 miles.

Size-wise, this one’s similar to the Chelyabinsk meteorite that exploded over Russia’s Ural Mountains region in February 2013. But it’s a lot less scary. 2014 RC will cleanly miss Earth this time around, and although it’s expected back in the future, no threatening passes have been identified. Whew!

2014 RC will pass along the outer edge of the geosynchronous satellite belt, home to many weather and communications satellites. The chance of a hit is close to infinitesimal. Click for more information and detailed finder charts. Credit: SatFlare

NEOs or Near Earth Asteroids are defined as space rocks that come within about 28 million miles of Earth’s orbit. Nearly once a month astronomers discover an Earth-crossing asteroid that passes within the moon’s orbit. In spite of hype and hoopla, none has threatened the planet. As of February 2014, we know of 10,619 near-Earth asteroids. It’s estimated that 93% of all NEOs larger than 1 km have been discovered but 99% of the estimated 1 million NEOs 100 feet (30-meters) still remain at large.

No surprise then that new ones pop up routinely in sky surveys. Take this past Sunday night for example, when the Catalina Sky Survey nabbed 2014 RA, a 20-foot (6-meter) space rock that whistled past Earth that evening at 33,500 miles (54,000 km). It’s now long gone.

Artist view of an asteroid (with companion) passing near Earth. Credit: P. Carril / ESA

2014 RC was picked up on or about September 1-2 by both the Catalina Sky Survey and Pan-STARRS 1 survey telescope atop Mt. Haleakala in Maui. The details are still being worked out as to which group will take final discovery credit. Based on current calculations, 2014 RC will pass closest to Earth around 2:15 p.m. EDT (18:15 UT) on Sunday, September 7th. When nearest, the asteroid is expected to brighten to magnitude +11.5 – too dim for naked eye observing but visible with a good map in 6-inch and larger telescopes.

Seeing it will take careful planning. Unlike a star or planet, this space rock will be faint and barreling across the sky at a high rate of speed. Discovered at magnitude +19, 2014 RC will brighten to magnitude +14 during the early morning hours of September 7th. Even experienced amateurs with beefy telescopes will find it a challenging object in southern Aquarius both because of low altitude and the unwelcome presence of a nearly full moon.

64-frame movie showing Toutatis tumbling through space only 4.3 million miles from Earth on Dec. 12-13. Credit: NASA/Goldstone radar

Closest approach happens in daylight for North and South America , but southern hemisphere observers might spot it with a 6-inch scope as a magnitude +11.5 “star” zipping across the constellations Pictor and Puppis. 2014 RC fades rapidly after its swing by Earth and will quickly become impossible to see in all amateur telescopes, though time exposure photography will keep the interloper in view for a few additional hours.

Most of us won’t have the opportunity to run outside and see the asteroid, but Gianluca Masi and his Virtual Telescope Project site will cover it live starting at 6 p.m. EDT (22:00 UT). Lance Benner, who researches radar imaging of near-Earth and main-belt asteroids, hopes to image 2014 RC with 230-foot (70-m) radar dish at the Goldstone complex on September 5-7 and possibly the big 1,000-foot (305-m) radar dish at Arecibo. Both provide images based on radar echoes that show asteroids up close with shapes, craters, ridges and all.

August 31, 2014December 23, 2015 by Bob King

Tonight’s Moon-Mars-Saturn Trio Recalls Time of Terror

The crescent moon, Saturn and Mars will form a compact triangle in the southwestern sky in this evening August 31st. 3.5º separate the moon and Saturn; Mars and Saturn will be 5º apart. Stellarium

Check it out. Look southwest at dusk tonight and you’ll see three of the solar system’s coolest personalities gathering for a late dinner. Saturn, Mars and the waxing crescent moon will sup in Libra ahead of the fiery red star Antares in Scorpius. All together, a wonderful display of out-of-this-world worlds.

Four dark lunar seas, also called 'maria' (MAH-ree-uh), pop out in binoculars. Four featured craters are also highlighted - the triplet of Theophilus, Cyrillus and Catharina and Maurolycus, named after Francesco Maurolico, a 16th century Italian scientist. Credit: Virtual Moon Atlas / Christian LeGrande, Patrick Chevalley — Four dark lunar seas, also called ‘maria’ (MAH-ree-uh), pop out in binoculars. Four featured craters are also highlighted – the triplet of Theophilus, Cyrillus and Catharina and Maurolycus, named after Francesco Maurolico, a 16th century Italian scientist. Credit: Virtual Moon Atlas / Christian LeGrande, Patrick Chevalley

If you have binoculars, take a closer look at the thick lunar crescent. Several prominent lunar seas, visible to the naked eye as dark patches, show up more clearly and have distinctly different outlines even at minimal magnification. Each is a plain of once-molten lava that oozed from cracks in the moon’s crust after major asteroid strikes 3-3.5 billion years ago.

Larger craters also come into view at 10x including the remarkable trio of Theophilus, Cyrillus and Catharina, each of which spans about 60 miles (96 km) across. Even in 3-inch telescope, you’ll see that Theophilus partly overlaps Cyrillus, a clear indicator that the impact that excavated the crater happened after Cyrillus formed.

Close-up of our featured trio of craters. Sharpness indicates freshness. Comparing the three, the Theophilus impact clearly happened after the others. Craters gradually become eroded over time from micrometeorite impacts, solar wind bombardment, moonquakes and extreme day-to-night temperature changes. Credit: Damian Peach

Notice that the rim Theophilus crater is still relatively crisp and fresh compared to the older, more battered outlines of its neighbors. Yet another sign of its relative youth.

Astronomers count craters on moons and planets to arrive at relative ages of their surfaces. Few craters indicate a youthful landscape, while many overlapping ones point to an ancient terrain little changed since the days when asteroids bombarded all the newly forming planets and moons. Once samples of the moon were returned from the Apollo missions and age-dated, scientists could then assign absolute ages to particular landforms. When it comes to planets like Mars, crater counts are combined with estimates of a landscape’s age along with information about the rate of impact cratering over the history of the solar system. Although we have a number of Martian meteorites with well-determined ages, we don’t know from where on Mars they originated.

At least three different impact sequences are illustrated in this photo. Maurolycus appears to lie atop an older crater, while younger, sharp-rimmed craters pock its center and southern rim. Even a 3-inch telescope will show signs of all three ages. Credit: Damian Peach

Another crater visible in 10x binoculars tonight is Maurolycus (more-oh-LYE-kus), a great depression 71 miles (114 km) across located in the moon’s southern hemisphere in a region rich with overlapping craters. Low-angled sunlight highlighting the crater’s rim will make it pop near the moon’s terminator, the dividing line between lunar day and night.

Like Theophilus, Maurolycus overlaps a more ancient, unnamed crater best seen in a small telescope. Notice that Maurolycus is no spring chicken either; its floor bears the scares of more recent impacts.

Putting it all into context, despite their varying relative ages, most of the moon’s craters are ancient, punched out by asteroid and comet bombardment more than 3.8 billion years ago. To look at the moon is to see a fossil record of a time when the solar system was a terrifyingly untidy place. Asteroids beat down incessantly on the young planets and moons.

Despite the occasional asteroid scare and meteorite fall, we live in relative peace now. Think what early life had to endure to survive to the present. Deep inside, our DNA still connects us to the terror of that time.

August 30, 2014December 23, 2015 by Bob King

Caterpillar Comet Poses for Pictures En Route to Mars

Comet C/2013 A1 Siding Spring passed between the Small Magellanic Cloud (left) and the rich globular cluster NGC 130 on August 29, 2014. Credit: Rolando Ligustri

Now that’s pure gorgeous. As Comet C/2013 A1 Siding Spring sidles towards its October 19th encounter with Mars, it’s passing a trio of sumptuous deep sky objects near the south celestial pole this week. Astrophotographers weren’t going to let the comet’s picturesque alignments pass without notice. Rolando Ligustri captured this remarkable view using a remote, computer-controlled telescope on August 29th. It shows the rich assemblage of stars and star clusters that comprise the Small Magellanic Cloud, one of the Milky Way’s satellite galaxies located 200,000 light years away.

A photo taken one day earlier on August 28th captures the comet and NGC 362 in a tight pairing. Credit: Damian Peach — A photo taken one day earlier on August 28th captures the comet and NGC 362 in close embrace. Credit: Damian Peach

Looking like a fuzzy caterpillar, Siding Spring seems to crawl between the little globular cluster NGC 362 and the rich swarm called 47 Tucanae, one of the few globulars bright enough to see with the naked eye. C/2013 A1 is currently circumpolar from many locations south of the equator and visible all night long. Glowing at around magnitude +9.5 with a small coma and brighter nucleus, a 6-inch or larger telescope will coax it from a dark sky. Siding Spring dips farthest south on September 2-3 (Dec. -74º) and then zooms northward for Scorpius and Sagittarius. It will encounter additional deep sky objects along the way, most notably the bright open cluster M7 on October 5-6, before passing some 82,000 miles from Mars on October 19th.

Map showing Comet Siding Spring's recent and upcoming travels near the Small Magellanic Cloud. Positions are shown nightly for Alice Springs, Australia. Source: Chris Marriott's SkyMap — Map showing Comet Siding Spring’s recent and upcoming travels near the Small Magellanic Cloud. Positions are shown nightly for Alice Springs, Australia. Source: Chris Marriott’s SkyMap

While the chance of a Mars impact is near zero, the fluffy comet’s fluffy coma and broad tail, both replete with tiny but fast-moving (~125,000 mph) dust particles, might pose a hazard for spacecraft orbiting the Red Planet. Assuming either coma or tail grows broad enough to sweep across the Martian atmosphere, impacting dust might create a spectacular meteor shower. Mars Rover cameras may be used to photograph the comet before the flyby and to capture meteors during its closest approach. NASA plans to ‘hide’ its orbiting probes on the opposite side of the planet for a brief time during the approximately 4-hour-long encounter just in case.

Today, Siding Spring’s coma or temporary atmosphere measures about 12,000 miles (19,300 km) wide. While I can’t get my hands on current dust production rates, in late January, when it was farther from the sun than at present, C/2013 A1 kicked out ~800,000 lbs per hour (~100 kg/sec). On October 19th, observers across much of the globe with 6-inch or larger instruments will witness the historic encounter with their own eyes at dusk in the constellation Sagittarius.

August 19, 2014December 23, 2015 by Bob King

Australian Amateur Terry Lovejoy Discovers New Comet

The small fuzzy potential comet is at center in this photo taken discovered by Terry Lovejoy. Credit: copyright Alain Maury and Joaquin Fabrega

It’s confirmed! Australian amateur astronomer Terry Lovejoy just discovered his fifth comet, C/2014 Q2 (Lovejoy). He found it August 17th using a Celestron C8 fitted with a CCD camera at his roll-off roof observatory in Brisbane, Australia.

Image triplet taken by Terry Lovejoy on which he discovered the comet. The comet moves slightly counterclockwise around the larger fuzzy spot. Credit: Terry Lovejoy — Image triplet taken by Terry Lovejoy of his comet discovery. The comet moves slightly counterclockwise around the larger fuzzy spot over the time frame. Credit: Terry Lovejoy

“I take large sets of image triplets, i.e 3 images per star field and use software to find moving objects,” said Lovejoy. “The software I use outputs suspects that I check manually by eye.”

Most of what pops up on the camera are asteroids, known comets, or false alarms but not this time. Lovejoy’s latest find is a faint, fuzzy object in the constellation Puppis in the morning sky.

Sky as seen from central South America showing the approximate location of the new comet on August 19 in Puppis near the bright star Canopus. Stellarium — Sky as seen from central South America showing the approximate location of the new comet (purple circle) on August 19 in Puppis near the bright star Canopus. The view shows the sky facing southeast just before the start of dawn. Stellarium

Glowing a dim magnitude +15, the new comet will be a southern sky object until later this fall when it swings quickly northward soon around the time of perihelion or closest approach to the sun. Lovejoy’s find needs more observations to better refine its orbit, but based on preliminary data, Maik Meyer, founder of the Comets Mailing List, calculates a January 2, 2015 perihelion.

Another photo of C/2014 Q2 taken on August 19, 2014. Credit: Jean-François and Alain Maury

On that date, it will be a healthy 84 million miles from the sun, but one month earlier on December 7, the comet could pass just 6.5 million miles from Earth and be well placed for viewing in amateur telescopes.

Everything’s still a little up in the air right now, so these times and distances are likely to change as fresh observations pour in. Take all predictions with a major grain of salt for the moment.

photographed by NASA astronaut Dan Burbank, Expedition 30 commander, onboard the International Space Station on Dec. 22, 2011. Credit: NASA — Comet Lovejoy (C/2011 W3) photographed by NASA astronaut Dan Burbank, onboard the International Space Station on Dec. 22, 2011 from 250 miles up. Credit: NASA

You might remember some of Terry’s earlier comets. Comet Lovejoy (C/2011 W3), a Kreutz sungrazer discovered in November 2011, passed just 87,000 miles above the sun’s surface. Many astronomers thought it wouldn’t survive the sun’s heat, yet amazingly, although much of its nucleus burned off, enough material survived to produce a spectacular tail.

More recently, Comet Lovejoy (C/2013 R1) thrilled observers as it climbed to naked eye brightness last November, managing to do the impossible at the time and draw our eyes away from Comet ISON.

Congratulations Terry on your new find! May it wax brightly this fall.

* Update: The latest orbit calculation from the Minor Planet Center based on 24 observations now puts perihelion at 164.6 million miles (265 million km) on February 14, 2015. Closest approach to Earth of 93.2 million miles (150 million km) will occur in January.

August 10, 2014December 23, 2015 by Bob King

Fear Not the Moon, Perseids Always a Great Show

The annual Perseid meteor shower radiates from a point in the constellation Perseus just below the W of Cassiopeia. Rates are usually about 100-120 meteors per hour from a dark, moonless sky at peak but will be cut in half due to moonlight this time around. This map shows the sky facing east around midnight Aug. 12-13. Source: Stellarium

Get ready for the darling of meteor showers this week — the Perseids. Who can deny their appeal? Not only is the shower rich with fiery flashes of meteoric light, but the meteors come in August when the weather’s couldn’t be more ideal. Peak activity is expected Tuesday night, Aug. 12-13, when up to 100 meteors an hour might be seen.

Ah, but there’s a rub. This year the moon will be only two days past full and radiant enough to drown out the fainter shower members. We’re more likely to see something like 30 meteors an hour, maybe fewer. But all it takes is one bright meteoric flash to make it all worthwhile. Nothing gets the heart pumping like a bright Perseid and the anticipation of the next.

While more meteors are surely more exciting, it’s not a number thing, but the experience of the raw event that makes all the difference. Sure beats sitting in front of a computer screen or watching the latest rerun of The Big Bang Theory, right?

A fine Perseid flashes straight out of the radiant on August 12, 2013. The fuzzy-starry clump near the start of the trail is the Double Cluster. Credit: Bob King — A fine Perseid flashes straight out of the radiant on August 12 last year. The two bright dots above the start of the trail form the well-known Perseus Double Cluster. Credit: Bob King

Find a place away from glaring lights to allow your eyes to adapt to the darkness. That way you’ll see more meteors. While the Perseids spit out the occasional fireball, most shower members are going to be closer in brightness to the stars of the Big Dipper. Some leave “smoke” trails called meteor trains. They’re actually tubes of glowing air molecules created as the meteoroid particles speed through the atmosphere at 130,000 mph. Though ‘shooting stars’ can look surprisingly close by, they typically burn up 60-70 miles overhead.

Perseid meteors radiate from the constellation Perseus (hence the name) located a short distance below the “W” of Cassiopeia in the northeastern sky. To know for sure if you’ve seen the genuine item and not a random meteor, follow the trail backward — if it points toward the northeast, you’ve got a ringer!

Perseid meteor ISS Ron Garan Aug13_2011 — A remarkable orbital view of a Perseid (right, center) burning up in Earth’s atmosphere photographed by astronaut Ron Garan on Aug. 13, 2011. The star Arcturus is directly above the bright trail. Credit: Ron Garan / ISS Expedition 28 crew / NASA

You can watch for Perseids all week long, but peak activity begins Tuesday evening and continues through dawn Wednesday. The later you stay up, the more meteors you’ll spot because the radiant or point in the sky from which the meteors appear to radiate rises higher with every hour. The higher the radiant, the fewer meteors that get cut off by the horizon.

Composite of bright Perseid meteors recorded by NASA all-sky cameras in 2011. Each is a grain of rock shed from the tail of comet 109P/ Swift-Tuttle. Every year in mid-August, Earth passes through the comet’s debris trail as it orbits around the sun. Any particles we smack into burn up as meteors about 60-70 miles overhead. Credit: NASA — Composite of bright Perseid meteors recorded by NASA all-sky cameras in 2011. Each is a grain of rock shed from the tail of comet 109P/Swift-Tuttle. Every year in mid-August, Earth passes through the comet’s debris trail as it orbits around the sun. Credit: NASA

The observing equipment you were born with and a comfortable chair are all you need to make the most of the event. OK, it’s nice to have a friend along, too, to share the ‘wow’ moments and keep from falling asleep. Sometimes I’m too lazy to haul out a chair and instead sprawl out on the deck or grass. Others prefer their Perseids from a steaming hot tub.

A 2010 Perseid meteor streaks over the European Southern Observatory's Very Large Telescope (VLT). Credit: ESO — A 2010 Perseid meteor streaks over the European Southern Observatory’s Very Large Telescope (VLT). Credit: ESO

Left-behind sand, seed and pebble-sized particles from comet 109P/Swift-Tuttle are responsible for all the fun. Discovered in 1862, the comet circles the sun every 120 years. Over millennia, 109P has left a stream of debris along its orbit, which the Earth passes through every year in mid-August. Comet grit hits our atmosphere like bugs smacking a car windshield and vaporize in a flashes of light or meteors.

Normally I’d recommend facing east or southeast to watch the shower, but with the moon dominating that direction, look off to the northeast, north or southwest to keep from getting zapped by that old devil moonlight. Even a little dark adaption will help boost your Perseid count. Once situated, sit back, look up and enjoy each and every sparkler that drops from the sky.

And don’t forget to take in the big picture show rolling by. The sky’s a giant calendar that begins with the mid-summer constellations at nightfall and advances through the fall stars to the onset of winter with the rising of Orion at dawn. Let the months fall away as the Earth turns you toward the sun.