Astronomy Archives

October 15, 2014December 23, 2015 by David Dickinson

Comet A1 Siding Spring vs Mars: Views in Space and Time

Oh, to be a stranded astronaut on the surface of the planet Mars this week. There’s a great scene from Andy Weir’s recent novel The Martian where chief protagonist Mark Watney uses the swift moving moons of Phobos and Deimos to roughly gauge his direction while travelling across the expansive Martian desert.

This week, the skies over Mars will also be graced by an unforgettable and spectacular sight: the extremely close passage of Comet C/2013 A1 Siding Spring. The first comet discovered in 2013, A1 Siding Spring was spotted by veteran comet hunter Robert McNaught from the Siding Spring Observatory in Australia. Dozens of comets are discovered in any given year, but this one soon gained the attention of astronomers when it was found that the comet could possibly hit Mars in October 2014.

And although further observations refined A1 Siding Spring’s orbit and ruled out such an impact, the particulars of the close passage of the comet past Mars are still stunning: A1 Siding Spring will pass within 87,000 miles (139,500 kilometres) from the center of Mars on Sunday, October 19^th at 18:27 Universal Time (UT) or 2:27 PM EDT.

And although we’ve yet to set “boots” on Mars, a fleet of spacecraft arrayed throughout the inner solar system are set to study the comet from both near and far. NASA has taken measures to assure that spacecraft in orbit are afforded maximum protection from incoming cometary debris, and the exciting possibility exists that we’ll be able to study first-hand the interaction of the comet’s tail with the Martian atmosphere.

Credit NASA — Mars-based spacecraft set to observe Comet A1 Siding Spring: a scorecard. Credit: NASA.

Universe Today has written extensively on the scientific efforts to study the event, how to observe the comet from Earth, and the unprecedented amateur and professional campaign in progress to witness the close pass.

What we’d like to do now is imagine the unparalleled view under alien skies as the comet slides gracefully overhead.

The nucleus of A1 Siding Spring is thought to be 700 metres across, and the coma extends 19,300 km in diameter. The comet’s closest passage is just under six times the distance of Mars’ outer moon Deimos, and at closest approach, the coma will appear almost 8 degrees in size to any would-be Martian — that’s 16 times the diameter of a Full Moon as seen from the Earth — and will be crossing the skies at a staggering 1.5 degrees a minute. You would be able to easily see the motion of the comet as it moves across the Martian sky with the unaided (well, space suit helmet protected) eye after just a few dozen seconds worth of watching! The comet’s magnitude may reach -5 as seen from Mars, though that would also be extended over its huge expanded surface area.

The enormous tail of the comet would also span the sky, and NASA has already released several mind blowing simulations to this effect. We’ve also constructed some brief simulations using Starry Night that show the view of the encounter from Earth, Phobos, and the perspective from the comet itself:

There’s also been some discussion as of late that A1 Siding Spring has slowed down in terms of its predicted brightening, though this is not unusual or unexpected.

From Acidalia Planitia (the setting for The Martian) located in the mid-northern latitudes on the surface of Mars, the comet would be a fine morning object, sitting 48 degrees above the northeastern horizon at dawn at closest passage for one morning only, and perhaps staying visible even after sunrise. Earth would be in the picture too, shining at magnitude -2.5 in the Martian dawn.

And the view from the comet? Now that would be a truly spectacular ride, as Mars swells to 3 degrees in diameter as it approaches and recedes. The comet itself is on a million year plus orbit, never to again visit the realm of the inner solar system in our lifetimes.

Such a view has never been seen in recorded history from the Earth. The closest confirmed passage of a large comet near our planet was Comet D/1770 L1 Lexell, which passed over 15 times more distant than A1 Siding Spring from Mars, at 2.2 million km from Earth on July 1^st, 1770. Note that an even closer cometary passage in 1491 remains unverified. In more recent times, Comet Hyakutake passed 15.8 million km from Earth on March 25^th, 1996, with a tail that spanned half the sky as seen from a dark sky site, and long-time comet observers might also remember the 1983 passage of Comet IRAS-Araki-Alcock, which passed just 4.7 million kilometres from the Earth.

A1 Siding Spring imaged from Earth on October 11th, 2014. Credit: Efrain Morales Rivera.

And then there was the historic impact on Comet Shoemaker-Levy 9 into Jupiter in 1994, reminding us that cosmic catastrophes can and do indeed occur… the upper size limit estimate for the nucleus of A1 Siding Spring compares to 70% the size of Fragment G, and an impact on Earth or Mars of such a dirty snowball would be a very bad day, for rovers or the humans. An extinction level event such as the Chicxulub impactor, however, was estimated to be much larger, at about 10 km in size.

Thankfully, we’ve merely got a front row seat to the show this weekend, and our planet is not the main event. From Earth, Comet A1 Siding Spring will be a binocular object, shining at magnitude +9 as it passes 3’ from +0.9 magnitude Mars. Both will be visible briefly in dusk skies, and the Virtual Telescope Project also plans to broadcast the event live starting at 16:45 UT on October 19th.

Don’t miss the historic passage of Comet A1 Siding Spring past Mars… by this time next week, we fully expect more images of the comet — both amateur and professional — to grace the cyber-pages of Universe Today!

Imaging A1 Siding Spring and/or Mars? Send those astro-pics into Universe Today at our Flickr forum.

October 13, 2014December 23, 2015 by David Dickinson

Get Ready for the Fireballs of October

A recent fireball captured over the UK on October

On October 31^st 2005, trick-or-treaters across the central U.S. eastern seaboard were treated to a brilliant fireball, a celestial spectacle that frequently graces October skies.

Mid- to late October is fireball season, a time when several key meteor showers experience a broad peak. We’re already seeing an uptick in fireball activity as monitored by numerous all-sky cameras this month, including NASA’s system positioned across the United States. Three lesser known but fascinating showers are the chief culprits.

The main meteor shower on tap for the month of October is the Orionids. This shower radiates from the Club of the constellation Orion, and is the product of that most famous comet of them all, 1P Halley. Halley’s Comet is actually the source of two annual meteor showers, the October Orionids and the May Eta Aquarids. We’re seeing the inward stream of Halley debris in October, and Orionid velocities average a swift 66 kilometres a second. The radiant rides highest for northern hemisphere observers at 4 AM local, and 2014 sees an estimated zenithal hourly rate (ZHR) of 20 predicted to arrive on the mornings of October 21^st through the 22^nd. The Orionids experience a broad peak spanning October 21^st through November 7^th, and 2014 sees the peak arrive just two days prior to the Moon reaching New phase. The Orionids have exhibited an uptick in activity as high as 50-75 per hour from 2005-2007, and it’s been suggested that a 12 year peak cycle may govern the Orionids, as the path of meteoroid debris stream is modified by the gravitational influence of the giant planet Jupiter.

Two other nearby radiants in the sky also produce an exceptionally large number of fireballs in late October: the Southern Taurids and Northern Taurids. These are complex streams laid down by the periodic comet 2P Encke, which possesses the shortest orbital period of any comet known at 3.3 years. Though the ZHR for both is only slightly above the background sporadic rate for northern hemisphere Fall at about five per hour, the Taurids also produce a high ratio of fireballs. The southern Taurids peak in early October and are already active, and the Northern Taurids peak in late October through early November, earning them the nickname the “Fireballs of Halloween”. Unlike many meteor showers, the Northern Taurids are approaching the Earth from behind in our orbit and have a slow relative atmospheric entry velocity of 28 kilometres per second. This makes for long, stately meteor trains often visible in the evening hours before local midnight.

The Taurids also seem to exhibit a seven year periodicity that begs for further study. 2008 was a fine year for Taurid fireballs… could 2015 be next?

Of course, the exact definition of a “fireball” meteor varies by source, though we prefer the definition of a fireball as a meteor brighter than magnitude -3. A fireball reaching -14 (a Full Moon equals magnitude -13, about 2.5 times fainter) is often termed a bolide.

Halley's orbit — Comet 1P/Halley’s orbital path through the inner solar system. (Credit: NASA/JPL).

Observing meteor showers such as the Orionids is as simple as sitting back and patiently watching the skies. Our own personal rule while starting a meteor vigil is to scan the skies for 10 minutes; one or more meteor sightings is a good sign to keep on watching, while no meteors means it’s time to pack it in and instead maybe write about astronomy. Dark, moonless skies are key, and you can report how many meteors you see to the International Meteor Organization. Be sure to keep a pair of binoculars handy to examine any lingering smoke trails post-fireball passage.

The positions of the radiants of the Orionids and the Taurids, with peak dates. Credit: Stellarium.

Of course, seeing a Taurid fireball is largely a matter of luck and looking at the right place in the sky at the right time. All-sky cameras work great in this regard, and many amateurs now use tripod mounted DLSRs set to take wide-field exposures of the sky automatically throughout the night. Just watch out for dew! Nearly every meteor we’ve caught on camera turned up only in post review, a testament to how much of the sky a lone pair of eyes still misses.

Spot a fireball? The American Meteor Society maintains a great online database of recent sightings and reports. Keep in mind, lots of “meteor-wrongs” inevitably crop up on Facebook and Twitter during any event, posted by folks eager for likes and retweets. Faves of such spoofers are: the Peekskill meteor train, the reentry of Hyabusa, Mir, and scenes (!) from the movie Armageddon. We’ve seen ‘em all passed off as legit, though you’re more than welcome to try and be original… a majority of initial meteor images almost always come from dash cams (remember Chelyabinsk?) and security cameras.

Finally, in addition to fireballs, there’s another astronomical tie-in for Halloween, as it’s one of four cross-quarter tie-in days approximately mid-way between a solstice and an equinox. The other three are: Lammas Day (August 1st), Groundhog’s Day (February 2nd) and May Day (May 1^st). We just think that it’s great — if a bit paradoxical — to see modern day suburbanites dress up as ghouls and goblins as they reenact archaic rites and holidays…

Don’t forget to keep an eye out for the fireballs of October this Halloween!

October 13, 2014December 23, 2015 by Shannon Hall

A New Look at Dark Matter — Is the Milky Way Less of a Behemoth Than Previously Thought?

This annotated artist's conception illustrates our current understanding of the structure of the Milky Way galaxy. Image Credit: NASA

Astronomy is notorious for raising more questions than it answers. Take the observation that the vast majority of matter is invisible.

Although astronomers have gathered overwhelming evidence that dark matter makes up roughly 84 percent of the universe’s matter — providing straightforward explanations for the rotation of individual galaxies, the motions of distant galaxy clusters, and the bending of distant starlight — they remain unsure about any specifics.

Now, a group of Australian astronomers thinks there’s only half as much dark matter in the Milky Way as previously thought.

In 1933, Swiss astronomer Fritz Zwicky observed the Coma cluster — a galaxy cluster roughly 320 million light-years away and nearly 2 light-years across — and found that it moved too rapidly. There simply wasn’t enough visible matter to hold the galaxy cluster together.

Zwicky decided there must be a hidden ingredient, known as dunkle Materie, or dark matter, that caused the motions of these galaxies to be so large.

The rotation curve of the Milky Way. Image Credit: Kafle et al.

Then in 1978, American astronomer Vera Rubin looked at individual galaxies. Astronomers largely assumed galaxies rotated much like our Solar System, with the outer planets rotating slower than the inner planets. This argument aligns with Newton’s Laws and the assumption that most of the mass is located in the center.

But Rubin found that galaxies rotated nothing like our own Solar System. The outer stars did not rotate slower than the inner stars, but just as fast. There had to be dark matter on the outskirts of every galaxy.

Now, astronomer Prajwal Kafle, from The University of Western Australia, and his colleagues have once again observed the speed of stars on the outskirts of our own galaxy, the Milky Way. But he did so in much greater detail than previous estimates.

From a star’s speed, it’s relatively simple to calculate any interior mass. The simple equation below shows that the interior mass (M) is equal to the distance the star is from the galactic center (R) times its velocity (V) squared, all divided by the gravitational constant (G):

Kafle and his colleagues used messier physics accounting for the sloppiness of the galaxy. But the point holds, with a star’s velocity, you can calculate any interior mass. And with multiple stars’ velocities you’re bound to be more accurate. The team found the dark matter in our galaxy weighs 800 billion times the mass of the Sun, half of previous estimates.

“The current idea of galaxy formation and evolution … predicts that there should be a handful of big satellite galaxies around the Milky Way that are visible with the naked eye, but we don’t see that,” said Kafle in a news release. This is typically referred to as the missing satellites problem, and it has evaded astronomers for years.

“When you use our measurement of the mass of the dark matter the theory predicts that there should only be three satellite galaxies out there, which is exactly what we see; the Large Magellanic Cloud, the Small Magellanic Cloud and the Sagittarius Dwarf Galaxy,” said Kafle.

These new measurements might prove the Milky Way is not quite the behemoth astronomers previously thought. They also help explain why there are so few satellite galaxies in orbit. But first the results will have to be confirmed as they stand up against numerous other ways to weigh the dark matter in our galaxy.

The results have been published in the Astrophysical Journal and are available online.

October 11, 2014December 23, 2015 by Jason Major

Watch the “Blood Moon” Eclipse from Mercury

Earth and the Moon imaged by the MESSENGER spacecraft on Oct. 8, 2014

Yes, it’s another time-lapse of the October 8 lunar eclipse that was observed by skywatchers across half the Earth… except that these images weren’t captured from Earth at all; this was the view from Mercury!

The animation above was constructed from 31 images taken two minutes apart by the MESSENGER spacecraft between 5:18 a.m. and 6:18 a.m. EDT on Oct. 8, 2014.

“From Mercury, the Earth and Moon normally appear as if they were two very bright stars,” said Hari Nair, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory, which developed and operates the MESSENGER mission for NASA. “During a lunar eclipse, the Moon seems to disappear during its passage through the Earth’s shadow, as shown in the movie.”

According to Nair the images have been zoomed by a factor of two and the Moon’s brightness has been increased by a factor of about 25 to enhance visibility. Captured by MESSENGER’s narrow-angle camera, Earth and the Moon were 0.713 AU (106.6 million km / 66.2 million miles) away from Mercury when the images were acquired.

Want to see some great photos of the eclipse shared by talented photographers around the world? Click here.

The Oct. 8 “Hunter’s Moon” eclipse was the second and last total lunar eclipse of 2014. The next will occur on April 4 of next year… but by that time MESSENGER won’t be around to witness it.

Launched August 3, 2004, MESSENGER entered orbit at Mercury on March 18, 2011. It is currently nearing the end of its missions as well as its its operational life, but we still have several more months of observations to look forward to from around the Solar System’s innermost planet before MESSENGER makes its final pass and ultimately impacts Mercury’s surface in March 2015.

Video credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Source: MESSENGER news release

October 10, 2014December 29, 2015 by Tim Reyes

Nearby Galaxy Holds First Ultraluminous X-Ray Source that is a Pulsar

Artist's illustration of a rotating neutron star, the remnants of a super nova explosion. Credit: NASA, Caltech-JPL

A research team led by Caltech astronomers of Pasadena California have discovered an ultraluminous X-ray (ULX) source that is pulsating. Their analysis concluded that the source in a nearby galaxy – M82 – is from a rotating neutron star, a pulsar. This is the first ULX source attributed to a pulsar.

Matteo Bachetti of the Université de Toulouse in France first identified the pulsating source and is the lead author of the paper, “An ultraluminous X-ray source powered by an accreting neutron star” in the journal Nature. Caltech astronomer Dr. Fiona Harrison, the team leader, stated “This compact little stellar remnant is a real powerhouse. We’ve never seen anything quite like it. We all thought an object with that much energy had to be a black hole.”

What is most extraordinary is that this discovery places even more strain on theories already hard pressed to explain the existence of ultraluminous X-Ray sources. The burden falls on the shoulder of the theorists.

The NuStar Space Telescope launched into Earth orbit by a Orbital Science Corp. Pegasus rocket, 2012. The Wolter telescope design images throughout a spectral range from 5 to 80 KeV. (Credit: NASA/Caltech-JPL)

The source of the observations is the NuSTAR space telescope, a SMEX class NASA mission. It is a Wolter telescope that uses grazing incidence optics, not glass (refraction) or mirrors (reflection) as in visible light telescopes. The incidence angle of the X-rays must be very shallow and consequently the optics are extended out on a 10 meter (33 feet) truss. NuSTAR records its observations with a time stamp such as taking a video of the sky. The video recording in high speed is not in visible everyday light but what is called hard x-rays. Only gamma rays are more energetic. X-rays emanate from the most powerful sources and events in the Universe. NuStar observes in the energy range of X-Rays from 5 to 80 KeV (electron volt)while the famous Chandra space telescope observes in the .1 to 10 KeV range. Chandra is one NASA’s great space telescope, was launched by the Space Shuttle Columbia (STS-93) in 1999. Chandra has altered our view of the Universe as dramatically as the first telescope constructed by Galileo. NuSTAR carries on the study of X-rays to higher energies and with greater acuity.

ULX sources are rare in the Universe but this is the first pulsating ULX. After analysis, they concluded that this is not a black hole but rather its little brother, a spinning neutron star as the source. More specifically, this is an accreting binary pulsar; matter from a companion star is being gravitationally attracted by and accreting onto the pulsar.

The Crab Nebula Pulsar, M1. Both are sequences of observations that show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech) — The prime example of a pulsar – the Crab Nebula Pulsar, M1. These actual observations show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second, not seen here, a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech)

Take a neutron star and spin it up to anywhere from 700 rotations per second to a mere one rotation every 10 seconds. Now you have a neutron star called a pulsar. Spinning or not, these are the remnants of supernovae, stellar explosions that can outshine a galaxy of 300 billion stars. Just one teaspoon of neutron star material weighs 10 million tons (9,071,847,400 kg). That is the same weight as 900 Great Pyramids of Giza all condensed to one teaspoon. As incredible a material and star that a neutron star is, they were not thought to be the source of any ultraluminous X-Ray sources. This view has changed with the analysis of observations by this research team utilizing NuSTAR. The telescope name – NuSTAR – stands for Nuclear Spectroscopic Telescope Array.

There is nothing run of the mill about black holes. Dr. Stephen Hawking only conceded after 25 years, in 2004 (the Thorne-Hawking Bet) that Black Holes exist. And still today it is not absolutely certain. Recall the Universe Today weekly – Space Hangout on September 26 – “Do Black Holes exist?” and the article by Jason Major, “There are no such things as Black Holes.”

Pulsars stars are nearly as exotic as black holes, and all astronomers accept the existence of these spinning neutron stars. There are three final states of a dying star. Stars like our Sun at the end of their life become very dense White Dwarf stars, about the size of the Earth. Neutron stars are the next “degenerate” state of a dying exhausted star. All the electrons have merged with the protons in the material of the star to become neutrons. A neutron star is a degenerate form of matter effectively made up of all neutron particles. Very dense, these stars are really small, the size of cities, about 16 miles in diameter. The third type of star in its final state is the Black Hole.

The Crab Nebula was first observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova, Chinese astronomers observed in 1054 A.D and holds the second Pular discovered (1968). — The Crab Nebula was first observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova that Chinese astronomers observed in 1054 A.D, it holds the second Pulsar discovered (1968).

A spinning neutron star creates a magnetic field, the most powerful of such fields in the Universe. They are like a dipole of a bar magnet and because of how magnetic fields confine the hot gases – plasma – of the neutron star, constant streams of material flow down and light streams out from the magnetic poles.

Recently, the Earth has had incredible northern lights, aurora. These lights are also from hot gases — a plasma — at the top of our atmosphere. Likewise, hot energetic particles from the Sun are funneled down into the magnetic poles of the Earth’s field that creates the northern lights. For spinning neutron stars – pulsars – the extreme light from the magnetic poles are like beacons. Just like our Earth, the magnetic poles and the spin axis poles do not coincide. So the intense beacon of light will rotate around and periodically point at the Earth. The video of the first illustration describes this action.

Messier object - M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar. — Messier object – M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar.

The light beacons from pulsars are very bright but theory, until now, has been supported by observations. No ultraluminous X-ray sources should be pulsars. The newly discovered pulsar is outputting 100 times more energy than any other. Discoveries like the one by these astronomers utilizing NuSTAR is proof that there remains more to discover and understand and new telescopes will be conceived to help resolve questions raised by NuSTAR or Chandra.

How to See Comet Siding Spring as it Encounters Mars

Comet C/2013 A1 Siding Spring passes just north of the sparking Butterfly Cluster on October 9. Credit: Rolando Ligustri

With excitement building as Comet Siding Spring rapidly approaches the Red Planet, we’ll soon have the opportunity to spot it through our own telescopes. Dark skies return this week with the moon now past full and rising later each night. Until recently, the comet could only be seen by skywatchers living in southern latitudes. Now it’s popped high enough above the southern horizon to see from mid-northern latitudes, albeit low in the sky. Observers with 8-inch (20 cm) or larger telescopes can follow the comet as it travels from Scorpius north to Ophiuchus and its encounter with Mars on October 19.

adsfdf — JPL Horizons light curve for Comet C/2013 A1 Siding Spring shows it brightening as it approaches Earth and then fading after late September. For our purposes we’re interested in the purple squares which are visual magnitude estimates of the whole comet submitted to the Comet Observation Database. Recently, the comet has faded faster than predictions. Click for more details. Credit: CIOC

Until late September, the comet had been brightening as forecast based on the simple principle that the closer an object is to Earth the brighter it appears in the sky. Siding Spring came just shy of 1 A.U. of Earth in early September and has since been slip-sliding away. All through the first weeks of September it glowed at magnitude +9-10 and could be spotted in small telescopes trekking across the south polar constellations. Now on the cusp of its big moment with Mars, Siding Spring has been fading faster than expected.

It could be running low on exposed ice or concluding a long, slow outburst. Maybe it’s as simple as our changing perspective on the comet’s tail – we see it from the side now instead of looking down the tail where reflective dust piles up along our line of sight. No one knows exactly why, but given that comets are famous for their unpredictability due to their fragile nature and the varying rates at which they sputter away ice and dust, we shouldn’t be too surprised.

The paths of Mars and Comet Siding Spring are clearly on a (near) collision course! Watch over the coming nights as they draw ever closer. Source: Chris Marriott's SkyMap — The paths of Mars and Comet Siding Spring are clearly on a (near) collision course! Watch over the coming nights as they draw ever closer. This map shows the sky facing southwest at nightfall from Kansas City, Missouri. From the central U.S. the comet will be about 13-15º high but only ~5-8º altitude in the northern border states. Source: Chris Marriott’s SkyMap

So what does that mean for observers? The most recent observations put the comet at about magnitude +11 with a loosely condensed coma and diameter of about one arc minute or a little larger than Jupiter appears in a telescope. It’s a small, relatively faint object now but should be visible in 8-inch and larger telescopes from a dark sky assuming it doesn’t “drop off the deep end” and fade even faster. With Mars nearby, finding the general location of Siding Spring is easy. The maps will help you pinpoint it.

Daily positions of Comet Siding Spring October 10-20 from the central U.S. at nightfall. Stars shown to magnitude +11.5. Closest approach to Mars is October 19. Brighter stars like 3 Sagittarii, 44 and 51 Ophiuchi and Theta Ophiuchi are labeled. Source: Chris Marriott's SkyMap — Daily positions of Comet Siding Spring October 10-20 from the central U.S. at nightfall. Stars shown to magnitude +11.5. Closest approach to Mars is October 19. The brighter stars 3 Sagittarii, 44 and 51 Ophiuchi and Theta Ophiuchi are labeled. Click for large version to print and use at the telescope. Source: Chris Marriott’s SkyMap

The good news is that the comet is heading straight north and getting higher in the sky every night. The bad news is that it’s also dropping westward each evening mostly negating its northerly altitude gains. Those in the southern U.S. will have the best viewing window with Siding Spring 20º high at nightfall (14º in the central states and 6º in the north). To ensure success, find a spot with a wide open view as far down to the southwestern horizon as possible. You’ll make best use of your time and see the comet highest if you set up during evening twilight and begin searching as soon as the sky is dark. Given that Mars is 1st magnitude and the comet has faded more than expected, it may be difficult to see against the planet’s glare on the 19th. Not that I want to dissuade you from trying, but the nights leading up to and after the encounter will prove better for comet spotting.

Need to get in closer yet? This map shows Mars and Comet Siding Spring on five nights closer to its flyby with stars to magnitude +12. Time and location are the same as the map above. Click for larger version. Source: Chris Marriott's SkyMap — Need to get in closer? This more detailed map shows Mars and Comet Siding Spring nightly October 15-20 with stars to magnitude +12. Time and location are the same as the map above. Click for larger version. Source: Chris Marriott’s SkyMap

The fluffball passed the glittery Butterfly Cluster (M6) in Scorpius on October 9 displaying an attractive curved tail pointing southeast. Tim Reyes of Universe Today calculated the current tail length at ~621,000 miles (1 million km) with a coma ~19,900 miles across (32,000 km). Closest approach occurs around 1:28 p.m. Central Daylight Time (18:28 UT) October 19 when the comet will miss Mars by only 88,000 miles (141,600 km). Dust particles leaving the coma will rip by the planet at ~125,000 mph (56 km/sec). Will they pass close enough to set the Martian sky a-sparkle with meteors?

Not only will the Mars orbiters gather information about the comet and its dust before, during and after the encounter, a fleet of additional telescopes will be making the most of the rare opportunity. Credit: NASA — Not only will the Mars orbiters gather information about the comet and its dust before, during and after the encounter, a fleet of additional telescopes will make the most of the rare opportunity. Credit: NASA

According to a recent NASA press release, the period of greatest risk to orbiting spacecraft will start about 90 minutes after the closest approach of the comet’s nucleus and will last about 20 minutes, when Mars will come closest to the center of the widening trail of dust flying from the comet’s nucleus. Since the comet will barely graze the planet, dust impacts on orbiting spacecraft may or may not happen.

Back on Earth we can watch the daredevil pass by telescope or catch it live on the Web here:

* SLOOH: broadcast begins Sunday Oct. 19 at 9:51 a.m. CDT (14:51 UT)

* Gianluca Masi’s Virtual Telescope: streaming begins Sunday, Oct. 19 at 11:45 a.m. CDT (16:45 UT)

October 9, 2014December 23, 2015 by Tammy Plotner

Radio Telescopes Help Astronomers Tune In To Nova Generated Gamma Rays

When the nova stops blowing a wind, and the material drifts off into space, the fireworks are finished. Credit: Bill Saxton, NRAO/AUI/NSF

Over two years ago, the Fermi-LAT Collaboration observed an “ear and eye opening” event – the exact location where a stellar explosion called a nova emitted one of the most energentic forms of electromagnetic waves… gamma rays. When it was first detected in 2012, it was something of a mystery, but the findings could very well point to what may cause gamma ray emissions.

“We not only found where the gamma rays came from, but also got a look at a previously-unseen scenario that may be common in other nova explosions,” said Laura Chomiuk, of Michigan State University.

A nova? According to the Fermi researchers, a classical nova results from runaway thermonuclear explosions on the surface of a white dwarf that accretes matter from a low-mass main-sequence stellar companion. As it gathers in material, the thermonuclear event expels debris into surrounding space. However, astronomers didn’t expect this “normal” event to produce high energy gamma rays!

Explains the Fermi-LAT team: “The gamma-ray detections point to unexpected high-energy particle acceleration processes linked to the mass ejection from thermonuclear explosions in an unanticipated class of Galactic gamma-ray sources.”

While NASA’s Fermi spacecraft was busy watching a nova called V959 Mon, some 6500 light-years from Earth, other radio telescopes were also busy picking up on the gamma ray incidences. The Karl G. Jansky Very Large Array (VLA) was documenting radio waves coming from the nova. The source of these emissions could be subatomic particles moving at nearly the speed of light interacting with magnetic fields – a condition needed to help produce gamma rays. These findings were backed up by the extremely-sharp radio “vision” of the Very Long Baseline Array (VLBA) and the European VLBI network. They revealed two knots in the radio observations – knots which were moving away from each other. Additional studies were done with e-MERLIN in the UK, and another round of VLA observations in 2014. Now astronomers could begin to piece together the puzzle of how radio knots and gamma rays are produced.

According to the NRAO news release, the white dwarf and its companion give up some of their orbital energy to boost some of the explosion material, making the ejected material move outward faster in the plane of their orbit. Later, the white dwarf blows off a faster wind of particles moving mostly outward along the poles of the orbital plane. When the faster-moving polar flow hits the slower-moving material, the shock accelerates particles to the speeds needed to produce the gamma rays, and the knots of radio emission.

“By watching this system over time and seeing how the pattern of radio emission changed, then tracing the movements of the knots, we saw the exact behavior expected from this scenario,” Chomiuk said.

A nova does not explode like an expanding ball, but instead throws out gas in different directions at different times and different speeds. When this gas inevitably crashes together, it produces shocks and high-energy gamma-ray photons. The complex explosion and gas collisions in nova V959 Mon is illustrated here. In the first days of the nova explosion, dense, relatively slow-moving material is expelled along the binary star system's equator (yellow material in left panel). Over the next several weeks, fast winds pick up and are blown off the binary, but they are funneled along the binary star system's poles (blue material in central panel). The equatorial and polar material crashes together at their intersection, producing shocks and gamma-ray emission (red regions in central panel). Finally, at later times, the nova stops blowing a wind, and the material drifts off into space, the fireworks finished (right panel). CREDIT: Bill Saxton, NRAO/AUI/NSF — A nova does not explode like an expanding ball, but instead throws out gas in different directions at different times and different speeds. When this gas inevitably crashes together, it produces shocks and high-energy gamma-ray photons. The complex explosion and gas collisions in nova V959 Mon is illustrated here. In the first days of the nova explosion, dense, relatively slow-moving material is expelled along the binary star system’s equator (yellow material in left panel). Over the next several weeks, fast winds pick up and are blown off the binary, but they are funneled along the binary star system’s poles (blue material in central panel). The equatorial and polar material crashes together at their intersection, producing shocks and gamma-ray emission (red regions in central panel). Finally, at later times, the nova stops blowing a wind, and the material drifts off into space, the fireworks finished (right panel). CREDIT: Bill Saxton, NRAO/AUI/NSF

But the V959 Mon observations weren’t the end of the story. According to Fermi-LAT records, in 2012 and 2013, three novae were detected in gamma rays and stood in contrast to the first gamma-ray detected nova V407 Cygni 2010, which belongs to a rare class of symbiotic binary systems. Despite likely differences in the compositions and masses of their white dwarf progenitors, the three classical novae are similarly characterized as soft spectrum transient gamma-ray sources detected over 2-3 week durations.

“This mechanism may be common to such systems. The reason the gamma rays were first seen in V959 Mon is because it’s close,” Chomiuk said. Because the type of ejection seen in V959 Mon also is seen in other binary-star systems, the new insights may help astronomers understand how those systems develop. This “common envelope” phase occurs in all close binary stars, and is poorly understood. “We may be able to use novae as a ‘testbed’ for improving our understanding of this critical stage of binary evolution,” explains Chomiuk.

Original Story Source: Radio Telescopes Unravel Mystery of Nova Gamma Rays from National Radio Astronomy Observatory. Chomiuk worked with an international team of astronomers. The researchers reported their findings in the scientific journal “Nature”.

October 8, 2014December 23, 2015 by Tim Reyes

Comet Siding Spring: Close Call for Mars, Wake Up Call for Earth?

Five orbiters from India, the European Union and the United States will nestle behind the Mars as comet Siding Springs passes at a speed of 200,000 km/hr (125,000 mph). At right, Comet Shoemaker-Levy 9 impacts on Jupiter, the Chelyabinsk Asteroid over Russia. (Credits: NASA,ESA, ISRO)

It was 20 years ago this past July when images of Jupiter being pummeled by a comet caught the world’s attention. Comet Shoemaker-Levy 9 had flown too close to Jupiter. It was captured by the giant planet’s gravity and torn into a string of beads. One by one the comet fragments impacted Jupiter — leaving blemishes on its atmosphere, each several times larger than Earth in size.

Until that event, no one had seen a comet impact a planet. Now, Mars will see a very close passage of the comet Siding Spring on October 19th. When the comet was first discovered, astronomers quickly realized that it was heading straight at Mars. In fact, it appeared it was going to be a bulls-eye hit — except for the margin of error in calculating a comet’s trajectory from 1 billion kilometers (620 million miles, 7 AU) away.

It took several months of analysis for a cataclysmic impact on Mars to be ruled out. So now today, Mars faces just a cosmic close shave. But this comet packs enough energy that an impact would have globally altered Mars’ surface and atmosphere.

So what should we Earthlings gather from this and other events like it? Are we next? Why or why not should we be prepared for impacts from these mile wide objects?

For one, ask any dinosaur and you will have your answer.

Adding Siding Spring to the Comet 67P atop Los Angeles provides a rough comparison of sizes. This images was expanded upon U.T.'s Bob King - "What Comets, Parking Lots and Charcoal Have in Common". (Credit: ESA, anosmicovni) — An illustration of the Siding Spring comet in comparison to the Comet 67P atop Los Angeles. The original image was the focus of Bob King’s article – “What Comets, Parking Lots and Charcoal Have in Common“. (Credit: ESA, anosmicovni)

One can say that Mars was spared as were the five orbiting spacecraft from India (Mars Orbiter Mission), the European Union (Mars Express) and the United States (MOD, MRO, MAVEN). We have Scottish-Australian astronomer Robert McNaught to thank for discovering the comet on January 3, 2013, using the half meter (20 inch) Uppsala Southern Schmidt Telescope at Siding Spring, Australia.

Initially the margin of error in the trajectory was large, but a series of observations gradually reduced the error. By late summer 2014, Mars was in the clear and astronomers could confidently say the comet would pass close but not impact. Furthermore, as observations accumulated — including estimates of the outpouring of gases and dust — comet Siding Spring shrunk in size, i.e. the estimates of potentially tens of kilometers were down to now 700 meters (4/10th of a mile) in diameter. Estimates of the gas and dust production are low and the size of the tail and coma — the spherical gas cloud surrounding the solid body — are small and only the outer edge of both will interact with Mars’ atmosphere.

The mass, velocity and kinetic energy of celestial bodies can be deceiving. It is useful to compare the Siding Spring comet to common or man-made objects.

Yet, this is a close call for Mars. We could not rule out a collision for over six months. While this comet is small, it is moving relative to Mars at a speed of 200,000 kilometers/hour (125,000 mph, 56 km/sec). This small body packs a wallop. From high school science or intro college Physics, many of us know that the kinetic energy of an object increases by the square of the velocity. Double the velocity and the energy of the object goes up by 4, increase by 3 – energy increases by 9.

So the close shave for Mars is yet another wake up call for the “intelligent” space faring beings of the planet Earth. A wake up call because the close passage of a comet could have just as easily involved Earth. Astronomers would have warned the world of a comet heading straight for us, one that could wipe out 70% of all life as happened 65 million years ago to the dinosaurs. Replace dinosaur with humans and you have the full picture.

Time would have been of the essence. The space faring nations of the world — those of the EU, and Russia, the USA, Japan and others — would have gathered and attempted to conceive some spacecrafts with likely nuclear weapons that could be built and launched within a few months. Probably several vehicles with weapons would be launched at once, leaving Earth as soon as possible. Intercepting a comet or asteroid further out would give the impulse from the explosions more time to push the incoming body away from the Earth.

There is no way that humanity could sit on their collective hands and wait for astronomers to observe and measure for months until they could claim that it would just be a close call for Earth. We could imagine the panic it would cause. Recall the scenes from Carl Sagan’s movie Contact with people of every persuasion expressing at 120 decibels their hopes and fears. Even a small comet or asteroid, only a half kilometer – a third of a mile in diameter would be a cataclysmic event for Mars or Earth.

But yet, in the time that has since transpired from discovery of the comet Siding Spring (1/3/2013), the Chelyabinsk asteroid (~20 m/65 ft) exploded in an air burst that injured 1500 people in Russia. The telescope that discovered Comet Siding Spring was decommissioned in late 2013 and the Southern Near-Earth Object Survey was shutdown. This has left the southern skies without a dedicated telescope for finding near-Earth asteroids. And proposals such as the Sentinel project by the B612 Foundation remain underfunded.

We know of the dangers from small celestial bodies such as comets or asteroids. Government organizations in the United States and groups at the United Nations are discussing plans. There is plenty of time to find and protect the Earth but not necessarily time to waste.

Previous U.T. Siding Spring stories:
“What Comets, Parking Lots and Charcoal Have in Common“, Bob King, Sept 5, 2014
“MAVEN Mars Orbiter Ideally Poised to Uniquely Map Comet Siding Spring Composition
– Exclusive Interview with Principal Investigator Bruce Jakosky”, Ken Kremer“, Sept 5, 2014
“NASA Preps for Nail-biting Comet Flyby of Mars“, BoB King, July 26,2014

October 7, 2014December 23, 2015 by David Dickinson

REAL Images of Eclipses Seen From Space

That ‘amazing astro-shot that isn’t’ is making the rounds of ‘ye ole web again.

You know the one. “See an Amazing Image of an Eclipse… From SPACE!!!” screams the breathless headline, with the all-too-perfect image of totality over the limb of the Earth, with the Milky Way thrown in behind it for good measure.

As the old saying goes, if it looks too good to be true, it probably is. Sure, the pic is a fake, and it’s been debunked many, many times since it was first released into the wild a few years back. But never let reality get in the way of a good viral meme. As eclipse season 2 of 2 gets underway tonight with a total lunar eclipse followed by a partial solar eclipse on October 23rd both visible from North America, the image is once again making its rounds. But there’s a long history of authentic captures of eclipses from space that are just as compelling. We’ve compiled just such a roll call of real images of eclipses seen from space:

A partial solar eclipse as captured by SDO. Credit: NASA/SDO.

The Solar Dynamics Observatory:

Launched in 2010, The Solar Dynamics Observatory or SDO is NASA’s premier orbiting solar observatory. But unlike Sun-staring satellites based in low Earth orbit, SDO’s geosynchronous orbit assures that it tends to see a cycle of partial solar eclipses twice a year, roughly around the equinoxes. And like many satellites, SDO also passes into the Earth’s shadow as well, offering unique views of a solar eclipse by the limb of the Earth from its vantage point.

Hinode:

A joint mission between NASA and JAXA (the Japanese Aerospace Exploration Agency) launched in 2006, Hinode observes the Sun from low Earth orbit. As a consequence, it nearly has a similar vantage point as terrestrial viewers and frequently nabs passages of the Moon as solar eclipses occur. Such events, however, are fleeting; moving at about eight kilometres per second, such eclipses last only seconds in duration!

Catching the passage of the Moon during a brief partial eclipse. Credit: ESA.

Proba-2:

Like Hinode, Proba-2 is the European Space Agency’s flagship solar observing spacecraft based in low Earth orbit. It also catches sight of the occasional solar eclipse, and these fleeting passages of the Moon in front of the Earth happen in quick multiple cycles. Recent images from Proba-2 are available online.

Eclipses from the ISS:

The International Space Station isn’t equipped to observe the Sun per se, but astronauts and cosmonauts aboard have managed to catch views of solar eclipses in an unusual way, as the umbra of the Moon crosses the surface of the Earth. Such a view also takes the motion of the ISS in low Earth orbit into account. Cosmonauts aboard the late Mir space station also caught sight of the August 11^th, 1999, total solar eclipse over Europe.

NASA-GOES:

Weather satellites can, and do, occasionally catch sight of the inky black dot of the Moon’s penumbra crossing the disk of the Earth. GOES-West snapped the above image of the November 13^th, 2012, solar eclipse. The umbra of the Moon’s shadow races about 1700 kilometres per hour from west to east during an eclipse, and we can expect some interesting images in 2017 when the next total solar eclipse crosses the United States on August 21^st, 2017.

Apollo-Soyuz Test Project:

The final mission of Apollo program, the 1975 Apollo-Soyuz Test Project, also yielded an unusual and little known effort to observe the Sun. The idea was to use the Apollo command module as a “coronagraph” and have cosmonauts image the Sun from the Soyuz as the Apollo spacecraft blocked it out after undocking. Unfortunately, the Apollo thrusters smeared the exposure, and it became a less than iconic— though unusual — view from the space age.

Gemini XII and the first eclipse seen from space:

On November 12^th, 1966, a total solar eclipse graced South America. Astronauts James Lovell Jr. and Edwin “Buzz” Aldrin Jr. were also in orbit at the time, and managed to snap the first image of a solar eclipse from space. Gemini XII was the last flight of the program, and the astronauts initially thought they’d missed the eclipse after a short trajectory burn.

The 2012 transit of Venus as seen from the ISS. Credit: NASA/Don Pettit.

ISS Astronauts catch a transit of Venus:

We were fortunate that the International Space Station had its very own amateur astronomer in residence in 2012 to witness the historic transit of Venus from space. NASA astronaut Don Pettit knew that the transit would occur during his rotation, and packed a full-aperture white light solar filter for the occasion. Of course, a planetary transit meets the very loosest definition of a partial eclipse, but it’s a unique capture nonetheless.

Kaguya:

Japan’s SELENE-Kaguya spacecraft entered orbit around the Moon in 2007 and provided some outstanding imagery of our solitary natural neighbor. On February 10^th, 2009, it also managed to catch a high definition view of the Earth eclipsing the Sun as seen from lunar orbit. A rare catch, such an event occurs during every lunar eclipse as seen from the Earth.

Mars eclipse — Curiosity captures a misshapen eclipse from the surface of Mars. Credit: NASA/JPL.

An unusual eclipse… seen from Mars:

We’re fortunate to live in an epoch in time and space where total solar eclipses can occur as seen from the Earth. But bizarre eclipses and transits can also be seen from Mars. The Spirit and Opportunity rovers have witnessed brief transits of the Martian moons Phobos and Deimos across the face of the Sun, and in 2010, the Curiosity rover recorded the passage of Phobos in front of the Sun in a bizarre-potato shaped “annular eclipse”. But beyond just the “coolness” factor, the event also helped researchers refine our understanding of orbital path of the Martian moon.

The future: It’s also interesting to think of what sort of astronomical wonders await travelers as we venture out across the solar system. For example, no human has yet to stand on the Moon and witness a solar eclipse. Or how about a ring plane passage through Saturn’s rings, thus far only witnessed via the robotic eyes of Cassini? Of course, for the best views of Saturn’s rings, we recommend a vacation stay on Iapetus, the only major Saturnian moon whose orbit is inclined to the ring plane. And stick around ‘til November 10^th, 2084, and you can witness a transit of Earth, the Moon and Phobos as seen from the slopes of Elysium Mons on Mars:

Hopefully, they’ll have perfected that whole Futurama “head-in-a-jar” thing by then…

-Looking for eclipses in science fiction? Check out the author’s tales Exeligmos and Shadowfall.

October 7, 2014December 23, 2015 by Elizabeth Howell

How to Turn Your Phone Into A Cosmic Ray Detector

Artist's impression of cosmic rays striking Earth (Simon Swordy/University of Chicago, NASA)

Quick, do you have an Android phone in your pocket? A few small changes and you could help physicists probe more of the curious nature of cosmic rays, high-energy particles that emanate from outside our solar system.

Just download an app, cover up your phone’s camera with duct tape, then place it somewhere (running idle) with the screen facing up. If a particle “event” happens, the information will be logged in a central database.

The project (called Distributed Electronic Cosmic-ray Observatory or DECO) aims to record secondary particles called muons that occur when cosmic rays hit the Earth’s atmosphere. Scientists believe cosmic rays are created in black holes and supernovas, but more studies are needed.

Screenshot of an Android app developed at the University of Wisconsin-Madison that aims to capture cosmic rays. Credit: Justin Vandenbroucke

Researchers at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), led by Justin Vandenbroucke, note that there are things about cosmic rays that confuse physicists. Their paths in space change as they go across magnetic fields, and it makes searching for other astronomy events difficult. That’s where they hope the phone study will be useful.

“Smartphone cameras use silicon chips that work through what is called the photoelectric effect, in which particles of light, or photons, hit a silicon surface and release an electric charge,” the University of Wisconsin-Madison wrote in a press release.

“The same is true for muons. When a muon strikes the semiconductor that underpins a smartphone camera, it liberates an electric charge and creates a signature in pixels that can be logged, stored and analyzed.”

For more details on how to run and use the app, consult this page (it’s the second item).

Source: University of Wisconsin-Madison