Some of you have asked about a new map for locating famed Comet L4 PANSTARRS as it treks through Cepheus headed for the North Star. Well, here ya’ go. PANSTARRS currently shines around magnitude 7 and should still be easily visible in 50mm or larger binoculars as a faint fuzzy spot with perhaps a hint of tail. The comet’s visible all night long for observers at mid-northern latitudes. Share your impressions with us via Comments if you see it.
You’ve probably seen and heard at least one video of February’s fireball exploding over Cheylabinsk, Russia. The shock wave from entry and subsequent break up of the meteoroid blew out thousands of windows, caused part of a building to collapse and set off countless car alarms.
Scientists estimate the incoming object measured about 55 feet (17m) across – as big as a 5-story building – weighed 7,000 tons and blazed across the sky at over 40,000 mph (64,000 kph). The shock pressure and heat upon entry converted much of the mass into dust, seen as a smoky “contrail”, and the rest into thousands of small meteorites that pocked snow drifts in the surrounding countryside.
While the Chelyabinsk event was the most impressive witnessed meteor in more than 100 years, its effects were even more far-reaching. Almost 6,000 miles (9,600 km) away in Lilburn, Georgia a full 10 hours after the explosion, infrasound sensors recorded multiple rumbles from the object’s impact with the air.
Infrasound, a very low frequency sound wave that can travel long distances, can’t be heard by human ears but can be detected with sensors. When a large meteor enters the atmosphere it sends ripples of infrasound through the atmosphere and around the planet revealing information about its speed, direction of travel and how much energy it contains.
Lilburn is home to one of nearly 400 seismic/infrasound stations in use in the eastern United States. They are part of a large-scale project named Earthscope, an initiative funded by the National Science Foundation that studies the Earth’s interior beneath North America. Although the stations mostly record seismic waves from earthquakes, they also are sensitive to long-period waves of infrasound.
Georgia Tech faculty member Zhigang Peng took the Lilburn infrasound data, sped it up and amplified it so we can heard the reverberations created by the falling meteoroid as it plowed through the atmosphere.
“The sound started at about 10 hours after the explosion and lasted for another 10 hours in Georgia,” said Peng. Like a tsunami set in motion by an earthquake, the Chelyabinsk meteoroid created a series of tsunami-like waves in the atmosphere itself. Both travel at nearly the same speed.
Peng has used the same process to convert seismic waves and underground nuclear explosions into audible sound. Click above for a listen. Check out this site for more exploding Chelyabinsk videos.
Up for another early morning meteor shower? Then get ready for the Eta Aquarids (AY-tuh ah-QWAR-ids) which peak tomorrow in the quiet hours before dawn. This is a fairly big event for southern hemisphere observers who might see up to one meteor a minute during tomorrow morning’s maximum. The radiant or point in the sky from which the meteors will appear to originate is much higher for southern latitudes. Morning twilight also begins later allowing for more viewing time.
The higher the radiant, the more meteors. A low radiant means most of a shower’s meteors are out of view, streaking away below the horizon. At latitude 50 degrees north the viewing window lasts 1 1/2 hours with the radiant low in the southeastern sky; at 40 degrees north, it’s a little more than 2 hours. If you live in the southern U.S. you’ll have nearly 3 hours of viewing time with the radiant 35 degrees high.
Across the middle north latitudes expect to see about 10 very fast meteors an hour. Eta Aquarids, which are the dusty remains of numerous visits of Halley’s Comet to the inner solar system, tear across the sky at over 147,000 mph (237,000 km/hr). Slower meteors are often yellow or orange; these will flare white as they’re incinerated by the atmosphere.
Earth crosses Halley’s orbit twice a year. Each time, bits of the comet collide with our atmosphere and burn up. In mid-October we’ll encounter Halley’s orbit again and re-visit the comet’s dust trail as the Orionid meteor shower.
Tomorrow morning the crescent moon will also be out – it eases up over the tree line about the time dawn begins – and a special guest, Comet Lemmon, located about one “fist” to the moon’s left. While visible in binoculars as a dim, fuzzy patch of light, a telescope should show the comet’s bright head and diffuse tail. The radiant is located near the star Eta Aquarii well to the right of the familiar Great Square of Pegasus.
Meteor shower members can appear in any part of the sky, but if you trace their paths in reverse, they’ll all point back to the radiant. Other random meteors you might see are called sporadics and not related to the Eta Aquarids.
For most mid-northern sky watchers, the best time to watch will be about 2 1/2-3 hours before sunrise. (Find your sunrise time HERE). Even if Aquarius is very low or hasn’t risen yet, you can still catch a few meteors before twilight brightens the sky. You might even get lucky and spot an Earth-grazer, a slow-moving meteor skimming the upper atmosphere nearly parallel to the ground. They’re best seen around the time the radiant rises. Keep an eye out for them.
The Eta Aquarid shower has a broad peak, so if it’s cloudy tomorrow, try again on Monday or Tuesday. You’re likely to catch at least a few. All you need for equipment are your eyes, a comfy lawnchair and a reasonably dark sky. Face east or south for the best view. Good luck!
Sometimes you have to stop what you’re doing and share a cool photo with your friends. Once a week I get an e-mail announcement with photo updates from the Mars Reconnaissance Orbiter (MRO), a NASA probe orbiting Mars since 2006. MRO’s main mission is to map the planet’s surface in detail with its high resolution camera; it’s also been studying Mars’ atmosphere, climate and geology.
The photo shows something I especially love about nature – how beautiful patterns evolve by natural happenstance. Here, boulders perched in an alcove within a crater wall tumbled down the slope until coming to rest near the crater’s floor. The long, dotted tracks help us picture each bounce as gravity did its magic and teased one boulder after another down the incline.
“Mass wasting” – the downhill movement of rocks and particles due to the force of gravity - is the technical term for what you’re seeing, and it’s as prevalent on Mars as on Earth. Landslides, avalanches and debris flows are familiar manifestations of mass wasting.
On Mars two of the most common forms of the process are rock landslides and dust and sand avalanches, also called “slope streaks”. Any numbers of things can trigger an avalanche. Erosion from Martian winds, subsurface water flows or vaporizing ice can steepen and widen a crater’s wall, undercutting the rim where the boulders have been in repose for millions of years. When the tipping point is reached, gravity’s tug can nudge them over the edge and down the slope.
Marsquakes and weakening of rocks from the day-night freeze-thaw cycle also play important roles in jimmying boulders loose and setting them in motion.
Last weekend I came across a delightful example of mass wasting along the north shore of Lake Superior. While crossing a pebble beach I was stopped in my tracks by a 4-foot-wide stream slicing across the strand as it hurried toward the lake. The current cut so quickly through the loose rock, pebbles along its banks tumbled continuously into the fast-moving water and were swept into the lake.
Looks like Comet PANSTARRS has company.This week Comet Lemmon begins nudging its way into the early dawn sky. Watch it to slowly climb up the eastern side of the Great Square of Pegasus in the coming weeks. Both comets are now below the naked eye limit and glow around 7th magnitude.
From a dark sky 7×50 and 10×50 binoculars will easily show Lemmon as a fuzzy spot, and you might even spot a long, thin tail. The comet slowly fades during the month while rising higher and becoming easier to see in the morning sky. You can use the map here to help guide you to it; for more details, check out this recent article I wrote that appeared in Universe Today.
Midnight. Too late for a look at the sky? Not if you hungry for a token of summer. It’s out there alright – the Summer Triangle. It’s unclear who named this giant triangle formed by three of summer’s brightest stars – Vega, Deneb and Altair – but its usage has been around since at least the 1920s. The first person we know of to connect the three stars in a triangle, even though he didn’t give the figure a name, was the German astronomer Johann Bode back in 1816. Bode created some of the most beautiful star atlases ever made.
Sometime in the late 1920s Austrian astronomer and prolific astronomy popularizer Oswald Thomas described these stars as the “Grosses Dreieck” (Great Triangle) and later in 1934 as the “Sommerliches Dreieck” (Summerly Triangle). Another great name in astronomy, England’s Patrick Moore, who passed away last December, described the trio as the Summer Triangle starting in the 1950s in his many books and lectures.
Tonight you’ll see the famed asterism crest the eastern horizon around midnight. Vega, the westernmost of the three and earliest to rise, sparkles in the northeast by 10 p.m. Deneb’s up by 11 and joined by Altair shortly before midnight. Although tipped on its side and slung low in the east in early May, by month’s end, the triangle stands higher and becomes visible at nightfall.
From July through September the Summer Triangle rules the sky, standing upright in the south balanced on its southermost apex Altair. That’s how it got its name of course, since it’s most obvious in the mid to late summer months. Come October and November, the figure scootches over to the west and by December it’s gone – just in time for winter.
The brightest of the three pivotal stars is Vega in the constellation Lyra the Harp. All Lyra’s stars are dim, but Vega more than compensates with a radiance as pure and white as burning magnesium.
To find Deneb, the brightest star in Cygnus the Swan or Northern Cross, reach your balled fist to the sky and look ‘two fists’ to the lower left of Vega. Altair in Aquila the Eagle is way down to the lower right. Three-plus fists will get you there. Vega, Deneb and Altair are all easy to see even from a middle-sized city and suburban areas.
An additional treat awaits the eyes of rural observers or those who make a drive to the country. The Summer Triangle frames a bright section of the Milky Way, and with the moon out of the way for the next couple weeks, it’s worth the time to witness this most impressive sight.
I don’t know about you, but winter was too long in the tooth around here, so every time I see those three bright stars and swirly Milky Way I get jazzed for summer nights ahead.
“Bullet hole – a small stone from the universe went through our solar array,” tweeted space station Commander Chris Hadfield yesterday. ”Glad it missed the hull.”
Hadfield photographed the small puncture in the array caused by either a tiny meteoroid or a piece of man-made space junk. There’s plenty of both to go around. Earth gets peppered by over 40 tons of asteroid dust and grit every day.
Man-made orbital debris from decades of rocket launches plus a considerable amount of additional space trash from two anti-satellite tests (in 1985 by the U.S. and 2007 by China) and a 2009 collision of an Iridium communications satellite and Russian military satellite orbit Earth across a wide spread of altitudes.
Some 20,000 pieces of debris larger than 2 inches (5 cm) are tracked by NORAD radar and at least 500,000 pieces 1/2-inch (1 cm) and larger occupy low Earth orbit between 99 and 1,200 miles high. It’s here where the space station circles the planet at over 17,000 mph 250 miles overhead.
For perspective, a marble-sized object moving with a relative speed of 10,500 mph (17,000 km) to a satellite or ISS would deliver as much energy as a small hand grenade.
The space station proper is protected by its hull from small hits by millimeter-sized objects. Presumably this “bullet” was small enough to not pose a danger. Had it struck Earth’s atmosphere, the bit of debris would have burned completely as a meteor. In orbit, the “skin” that protects astronauts is thin in comparison.
Mars has finally cleared the sun. That puts us back in touch with the two Martian rovers Curiosity and Opportunity and the three functioning satellites, Mars Reconnaissance Orbiter (MRO), Mars Odyssey, and Mars Express.
Communications between Mars and Earth were suspended between April 9 and April 26 when Mars was in (or near) conjunctionwith the sun. As seen from Earth, the planet passed very close to the brilliant solar disk. Any commands and communications sent around the time of conjunction risk being corrupted by charged particles and solar flares in the line of sight between Mars and Earth. Since one bad command could potentially cripple a rover or satellite, NASA imposed a communications blackout for most of April.
According to Guy Webster, Jet Propulsion Lab (JPL) spokesperson, NASA finally heard again from the rovers over the weekend. Curiosity weathered the hiatus well, but Opportunity booted itself into standby mode when it sensed something amiss on April 22, possibly during a routine camera scan of the clarity of the atmosphere. Fresh commands should solve the problem.
“Both are healthy,” said Webster. Contact so far has been one-way — from rovers to Earth. Starting Wednesday May 1 data gathered during the blackout will follow. Reid Thomas, Deputy Mission Manager of JPL, anticipates about 40 gigabits from the Mars Reconnaissance Orbiter and about 12 gigs from Curiosity. Just a little homework assignment during the month-long “vacation”.
We’ve grown so accustomed to the steady stream of Curiosity’s discoveries on the Red Planet some of us have been experiencing withdrawal pangs. They’ll soon come to an end as mission controllers get back in the rover’s driver seat in May.
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.
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.
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.
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.
The spectacular fireball over Chelyabinsk, Russia in February and a more recent meteorite fall through the roof of a home in Wolcott, Connecticut last Friday remind us the solar system is still littered with debris left over from its formation 4.6 billion years ago.
During and immediately after the formation of the planets, meteorite bombardment was nonstop. Since then the impact rate has dropped dramatically – a good thing for life – but continues to this day as a steady rain of everything from fine dust to the occasional teeth-rattling meteorite strike.
Besides Earth, amateur and professional astronomers have recorded meteorite or comet strikes on the moon and Jupiter. Now we can add Saturn to the list. Detailed study of thousands of images sent back to Earth by the Cassini spacecraft have turned up nine meteoroid strikes on Saturn’s rings in 2005, 2009 and 2012.
Think of the rings as a giant meteoroid detector/collector. If Earth gathers some 37,000-78,000 tons of space debris per year (mostly as dust but approx. 3-8 tons as rocks weighing 1/3 ounce to 2.2 lbs.), Saturn’s rings, with a surface area 100 times that of our planet, is more like humpback whale during feeding season.
Meteoroids pummeling the rings range in size from about a half-inch to several yards (one cm to several meters). When they bash into the icy ring particles they self-destruct, creating clouds of dust and ice in the process. The material is then sorted according to its distance from the planet – closer debris orbits more quickly, material further out more slowly. Soon the dust cloud gets stretched into an elongated bright streak that Cassini can photograph as it looks down (or up) onto the ring plane.
“These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth — two very different neighborhoods in our solar system — and this is exciting to see,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
It’s fascinating to realize that the sight of a meteor in Earth’s starry skies finds its counterpart among the icy boulders of Saturn’s rings nearly a billion miles afield.