An Unusually Close Comet

On Sunday, October 19 2014, humanity will experience its closest brush ever with a comet. Unfortunately, the comet will not be passing by the Earth on that date, but the planet Mars. While there will be no people on Mars to enjoy the sight, several human controlled spacecraft are there to give scientists – and us amateur science nerds – a ringside seat to observe this spectacle.


 Image credit  NASA/JPL-Caltech (click to enlarge)

Comet C/2013 A1, known also by its informal name Siding Spring (after the Australian observatory where it was discovered last year) will barnstorm Mars in a breathtakingly close passage. While its visibility from here on Earth can’t be estimated yet, the Mars science community who control spacecraft such as Mars Express, and the Curiosity and Opportunity rovers are already deep into preparations to observe its passage.

For perspective, the closest comet pass by the Earth in modern times (and for the purposes of this blog, I’ll define “modern” as post-telescope, e.g., >1609 CE), was Comet Lexell, which passed within 1.4 million miles of Earth on July 1, 1770. It had been discovered just two weeks earlier by none other than Charles Messier and was observed at its closest passage by many astronomers, when the apparent size of its coma reached over 2 degrees (4 times the width of the full moon). On the day of its closest approach to Earth, it was observed to cross 42 degrees of sky in just 24 hours! (Lexell, by the way, was named for Swedish astronomer Anders Johan Lexell, who computed its orbit).

In more modern times (e.g., our lifetimes), a notable close approach was Comet Hyakutake, which in March 1996 passed just under 9.5 million miles from Earth. It was recorded at a visible magnitude of about 0 and about a degree in angular diameter. For a short period of time, it was a big, bright comet.

By comparison, Siding Spring will pass Mars at a distance of just 85,000 miles. In astronomical terms, that’s astoundingly close! So close in fact, that the comet’s coma (its visible cloud of debris) will likely encompass the planet. Cometary comas are believed to be made up of particles that range from dust size up to a significant fraction of an inch. For the rovers on the surface, this means a high likelihood of a really good meteor shower to accompany the visual spectacle of the comet itself. For any spacecraft in Mars orbit however, this could spell significant danger.

Orbiting spacecraft, as we know from our experience with Earth-orbiting satellites, are vulnerable to hits from both natural and artificial orbital debris. At orbital speeds, an impact with an object the size of a speck of dust can be serious. When Mars and Siding Spring find themselves so close this coming October, their speed relative to one-another will be well over 100,000 miles per hour. At those speeds, an impact with even a speck of dust would likely be catastrophic.

Currently, there are three active spacecraft orbiting Mars, NASA’s Mars Reconnaissance Orbiter (MRO) and Mars Odyssey, and ESA’s Mars Express. Just before the encounter with the comet, two additional spacecraft, launched recently, will arrive in orbit (NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) and India’s Mars Orbiter Mission). Since missions like these cost anywhere from hundreds of millions to billions of dollars, you can imagine that the engineers are already busy brainstorming the best ways to protect their investments.

The comet encounter at Mars will be fun to watch. Interest from the science community will likely be high and news of the event will lead to lots of web coverage and perhaps some stories in the mainstream news outlets. It will also bring to the surface an ever present tension between the science and engineering teams that run spacecraft operations. The engineers, who are responsible for the safety and operation of missions like the Mars orbiters, will want to batten down the hatches and place the instruments in safe mode, put the covers on all the cameras, and angle the spacecraft so that sensitive instruments are protected as much as possible from the assault of debris. The scientists, naturally, will want to take advantage of this unique opportunity to gather as much data as possible. But you can’t have it both ways and in the end, the safety of these valuable assets will have to be protected for the future, and even the scientists will grudgingly admit that safe is better than sorry.

And, as we learned this past Thanksgiving with comet ISON, you never know what a comet will do. It could be a wondrous and unforgettable experience, or it could be a fizzle. Stay tuned to see.

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Over the Moon

Thierry Legault is an amateur astrophotographer whose work I have admired for a long time. This lunar photo of his will serve as a good example for those of you who have never heard of him or seen his work before.

The image above is the crater Clavius, one of the largest craters in the southern highlands of the moon. I encourage you to click the image to view it on Legault’s site and spend some time luxuriating in the sheer beauty and immensity of this picture. For those who don’t know, any type of astrophotography is hard to do well. Images of the moon in particular are very tough because achieving sharp focus is virtually impossible, and you’re constantly fighting against Earth’s boiling and roiling atmosphere. I just can’t stress enough how outstanding these photos are. They look as though they could have been taken from an orbiter, or from one of the lunar landers on descent.

The linked photo contains several other examples from Legault’s September lunar shoot and all are as amazing as this one. In his note, he says, “Best view of the images with full-HD screen in subdued surroundings.” In other words, turn the lights low and enjoy!

Shout out to Bad Astronomy for the original link.

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What’s That Glow?

What’s that glow?

Over the past several years, Mark Weller and I have collaborated on a project where we’ve been capturing the Milky Way over visually interesting landscapes in northern Wisconsin. For the past four years, this trek has taken us to the Apostle Island National Lakeshore in southwest Lake Superior.

The Lights of Outer Island, 2009
(click to view full size)

For the astro-photographically challenged among you, taking pictures of the sky is pretty hard work and involves knowing a lot about cameras, astronomy, a little luck, and being in the right place at the right time. Pictures like the Outer Island shot (above) are usually long exposures. We shoot digital so our exposures are generally between two and a-half to four minutes long. Back in the film days, it was not unusual for amateurs like us to require exposures of 20 to 30 minutes, so digital has definitely made things much easier.

The Lights of Sand Island, 2010
(click to view full size)

Above is the sand island shot we did in 2010. Note the vivid appearance of the milky way, but note also that there is something else: a diffuse pink glow that appears perpendicular to the axis of the milky way. There had been some faint auroral activity earlier this same evening. We had noticed the characteristic green glow far off on the northern horizon. There was no question about its nature – it was clearly a faint display of aurora borealis. The pinkish glow in the above photo was not visible to the naked eye and was in fact not noticed until we had a chance to examine the shots later. The exposure of this shot is 3 minutes so whatever the pinkish glow was, it was very faint. I finished processing the Sand shot and thought little more about the spurious glow until the following year.

July 2011 found us at Raspberry island, home to one of the most beautiful lighthouses in Lake Superior.

We again saw evidence of the spurious glow, this year appearing in some time lapse shots captured by my daughter Andrea.

Though the video is short, the greenish glow rippling wave-like through the several seconds of video reminded me strongly of the strange pinkish glow we had seen the year before at Sand Island.

Upon returning home from Raspberry Island, I began to do some research and found that the glow we had seen both at Sand and Raspberry islands was likely air glow, also called atmospheric air glow and sometimes banded air glow, due to the appearance of the characteristic wave-like behavior. Googling around the internet turned up several other examples of the same effect:

TWAN Video

Argentina Video

It’s not very well known, and not written about that much, but a determined search does turn up plenty of examples, and more than enough discussion of the science to establish that it’s a fairly well understood phenomenon, at least among atmospheric scientists. There are many more references available on the web, and enough discussion to satisfy most curious amateur scientists. And there the matter would have rested, until the summer of 2012.

This past July found Mark, Ian and myself back in the Apostles, this time at Devils Island, again attempting to get a shot of the milky way over the somewhat utilatarian Devils Island light. What we weren’t expecting was a display of airglow that absolutely left us speechless due to its unbelievable brightness. Indeed, it completely dominates the image:

The Lights of Devils Island
(click to view full size)

The sheer brilliance of the airglow in this shot stopped us in our tracks. In our quest to present images of the milky way to a new audience, we now had a problem: how would this image be received? Would people understand what they were looking at? The risk, of course, is that many would assume they’re looking at aurora borealis, which is a very good guess. The green color is very characteristic of aurora displays. But airglow is something entirely different, and very novel. We thought it was important to accurately describe for our audience and educate our public about what they were seeing. Here is the description that I finally settled on after reviewing all the applicable science and trying to boil it down for a general audience:

The spectacular green banding seen in the Devils Island photo at first glance look like aurora borealis (northern lights), but in fact is something different. It’s called banded air glow. 

 Even absent light from the stars or other celestial objects, the night sky is never completely dark. Earth’s atmosphere itself glows faintly all the time as atoms of oxygen, having been excited during daytime hours by UV radiation from the sun, emit faint light as they drop back to their less energized state.

 On the night we shot this photograph, this air glow display was unusually bright. To the unaided eye, it looks like a very thin cloud layer, and usually escapes notice altogether. Only with the exceptionally dark skies of the Lake Superior region and the long exposure capability of the camera did the color emerge. The banded structure is caused by atmospheric gravity waves, a common wave-like movement of air high in the thermosphere (more than 50 miles up). 

The Devils shot, and all the “lights of” island series, are available for purchase at the Friends of the Apostle Islands website. All proceeds from the sale of these images go directly to support the Apostle Islands National Lakeshore; Mark and I do not profit at all from these shots.

For more images from the island shoots, check out my pBase gallery page.

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Gear heads


NASA/JPL’s Mars rover Curiosity landed successfully on Mars early last month. Famously expensive and technologically sophisticated, a mission like this is a true marvel. One mission scientist, when challenged by a journalist to justify the staggering 2+ billion dollar price tag, reminded the writer that every penny of that budget was spent right here on Earth. All of that money was spent to support jobs, manufacturing, and research in the US and a few contributing international partners.

The video above tells the story of a small company in Rockford, Illinois who had a small but critical part in the construction of this wonderful machine. The pride and deep meaningfulness of their work is evident. This is a great story, and one that is told many times on the web. Other contributions of small businesses can be found here, here, and here.

Shout out to Kottke for first highlighting this story.

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WISE finds a bounty of black holes

Credit: NASA/JPL

Given all the excitement generated by a big NASA/JPL success story like the landing of MSL/Curiosity earlier this month, one could be forgiven for not having heard of some other stunning success stories in recent space exploration. This one caught my eye today. NASA/JPL’s Wide-field Infrared Survey Explorer (WISE) mission has been quietly photographing the universe since its launch in December of 2009. The infrared region of the electromagnetic spectrum is a stunningly useful and important area, giving WISE an unusually broad mission. It has assisted in the search for asteroids within our own solar system, and is invaluable for studying the most distant of galaxies.

The news release that just caught my eye is here:

In one study, astronomers used WISE to identify about 2.5 million actively feeding supermassive black holes across the full sky, stretching back to distances more than 10 billion light-years away. About two-thirds of these objects never had been detected before because dust blocks their visible light. WISE easily sees these monsters because their powerful, accreting black holes warm the dust, causing it to glow in infrared light.

You read that right: 2.5 million actively feeding supermassive black holes, most of which had never been observed before. Daniel Stern of JPL quipped “We’ve got the black holes cornered.” Stern is lead author of a paper just published on these and other WISE results.

Incredibly cool stuff. More on WISE here, here and here.

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One small step


Neil Armstrong died last night at age 82. The high water mark of the US space program was project Apollo from 1967-72 and undoubtedly, the high water mark of Apollo was Neil’s unforgettable step off the landing pad of the Eagle.

Including Apollo 11, a total of 12 men would walk on the surface of the moon. Though the program was entirely motivated by geopolitical interests embedded in the cold war, some great science was accomplished. Neil Armstrong was unique in that very few people in history have been thrust into such a landmark “first” role. Columbus exploring the new world and Lindbergh crossing the Atlantic come immediately to mind. Armstrong was forever uncomfortable with his historic role. Always a shy and unassuming man, he avoided the limelight and struggled his whole life to maintain his own privacy.

In an age when many astronauts were known for being hot-dogging test pilot jocks with egos to match, Armstrong was always a refreshing counter-story. He was a civilian pilot at the time of his selection to the astronaut corps. He was never embroiled in any controversies and managed to avoid entanglements in questionable business ventures in his later life. To most appearances, he continued being, well, just a pretty normal guy.

His death for many will mark the end of an age, and no doubt generate more editorials and discussions of the directions of the US space program. In his modesty and humility (and perhaps even more so because of it), he was an american hero.

Here is NASA’s announcement.

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