Last night was a Ray Bradbury kind of walk: sun setting purple and red amid gray clouds scattered like lost ships before a storm, deer walking their hooved shadows across silent roadways, tall corn whispering summer secrets to those who scamper furry and four-legged among knobbled roots, old wood frame houses with sepia light in the windows and someone running an honest-to-God player piano. I could almost hear the clink of ice in the tall glasses of lemonade. The fireworks were long over and the gunpowder smells had faded like a lost memory. Only the soft scent of grass clippings and pine trees herald this night. Summer is here and many an opportunity for a long evening stroll. And still not too late to pick up “Dandelion Wine.”
photo title: “Officer Painter Patrols Main Street., Stanley, Virginia. 1956” by Winston Link
I first learned of the potential threat of asteroids when I read Arthur C. Clarke’s Rendezvous with Rama. As with all of Sir Arthur’s novels it is a book full of hope, speculation, wonder, and hard science. We travel with the crew of the exploration vessel Endeavour as it encounters a massive space vehicle from parts unknown that is just passing through our solar system. It’s a fabulous book and I pick it up from time to time and re-read it. It’s a thoroughly enjoyable yarn.
The book begins on a bit of a grim note, however. It briefly mentions the Tunguska event of 30 June 1908 when a meteor or comet slammed into the Earth’s atmosphere and exploded with several megatons of energy high above the Siberian taiga. The airburst flattened millions of trees and devastated almost 2100 square kilometers of an unpopulated region.
Clarke goes on and describes a fictional event in the year 2077, when a large asteroid enters the atmosphere somewhere high above the Mediterranean Sea. Crossing the sky, it leaves a trail of devastation across southern Europe and northern Africa before it impacts northern Italy. I read this book in high school and the scenario left a deep impression on me. When the Chelyabinsk meteor and its shockwave struck in February of 2013 Clarke’s book immediately came to mind.
Clarke suggested that one of the remedies to avoid potential disaster was to use powerful arrays of optical telescopes and radars to catalog the many asteroids that cross Earth’s path. In the novel he called this observational campaign Project Spaceguard. It is one such telescope array that discovers the object Rama and drives the plot forward.
The Earth has been struck by asteroids many times. Evidence of this can be seen in places like Meteor Crater, Arizona. Earlier impacts include the devastating Chicxulub impact that wiped out the dinosaurs 65 million years ago. Perhaps lesser known is the Eltanin impact that struck the Pacific Ocean 2.5 million years ago. The Eltanin asteroid was 4 kilometers in diameter and left a crater 35 kilometers across on the ocean floor. It led to large tsunamis and was perhaps the trigger for an ice age. If an Eltanin happened tomorrow it would be a global catastrophe.
Since Clarke’s novel a number of efforts have been made to actively catalog near-Earth objects (NEOs). In a nod to Sir Arthur these efforts are collectively referred to as Project Spaceguard. Many scientists, amateur astronomers, and even governmental agencies around the world have become involved. This includes many notable writers, cosmonauts, astronauts, artists, and celebrities. Detection of a threatening asteroid would give us some lead time to prepare either for a disaster or, better yet, to put the energies and technologies of humanity forward to deflect a NEO. An asteroid strike is the only type of natural disaster that could potentially be prevented.
International Asteroid Day is an attempt to raise awareness of the hazard of NEOs. It also seeks to explore possible mitigation methods which could literally save the planet. Many activities related to the International Asteroid Day and Project Spaceguard are led by the B612 Foundation. One of the founders of the B612 Foundation is Apollo 9 astronaut Rusty Schweikart. He and Brian May…who is both a celebrated guitarist for Queen as well as a PhD astrophysicist…helped establish Asteroid Day. According to the B612 Foundation’s website there is a working group in place that has three primary goals:
1. Employ available technology to detect and track Near-Earth Asteroids that threaten human populations via governments and private and philanthropic organisations.
2. A rapid hundred-fold acceleration of the discovery and tracking of Near-Earth Asteroids to 100,000 per year within the next ten years.
3. Global adoption of Asteroid Day, heightening awareness of the asteroid hazard and our efforts to prevent impacts, on June 30 – with United Nations recognition.
Activity on these three tasks has been robust and the third action item has been achieved. There are many ongoing events and activities around the world today. There are also links and interesting interviews and videos at Asteroid Day.
It should be noted that in recent years various exploration craft have visited both asteroids and comets. This small armada includes the Deep Impact mission, the Rosetta orbiter and Philae lander, NEAR-Shoemaker, and the Dawn spacecraft that is currently orbiting Ceres. In addition, the OSIRIS-REX craft is on its way to asteroid Bennu. The spacecraft’s acronym stands for: Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer. That’s a mouthful!
The “Security” part of that title is based on the fact that this mission will extensively study the asteroid to learn about its composition and interaction with its surroundings, including the Yarkovsky Effect. Bennu was chosen in part due to the fact that it has a 1-in-1800 chance of impacting the Earth when it passes nearby in the year 2170.
In flight to a distant worldlet and on the hunt, OSIRIS-REX has used its camera systems to search for NEOs. It should arrive at Bennu in August of 2018. A sample probe will be returned to Earth by September of 2023. The samples could shed light on the composition of asteroids. It may also give us some idea as how to thwart an asteroid should we ever detect one on a path to hit us.
According to NASA’s JPL website other scientific objectives of the mission include:
Return and analyze a sample of pristine carbonaceous regolith in an amount sufficient to study the nature, history, and distribution of its constituent minerals and organic material.
Map the global properties, chemistry, and mineralogy of a primitive carbonaceous asteroid to characterize its geologic and dynamic history and provide context for the returned samples.
Document the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site in situ at scales down to millimeters.
Measure the Yarkovsky Effect on a potentially hazardous asteroid and constrain the asteroid properties that contribute to this effect.
Characterize the integrated global properties of a primitive carbonaceous asteroid to allow for direct comparison with ground-based telescopic data of the entire asteroid population.
The Yarkovsky Effect is of interest and definitely falls under the “Security” part of the OSIRIS-REX mission. First described in 1900 by Ivan Yarkovsky, the theory relates the thermal effects of sunlight falling on a rotating body in space to tiny forces that are generated on the object’s center of mass. Over time these tiny forces could nudge even a large asteroid into a different orbit. Scientists have studied the idea that by changing the areal coverage or location of sunlight on the surface of an asteroid its course could be adjusted. Given enough of a warning a spacecraft could be sent out to intercept the asteroid. A crew or robots (or both) could paint absorptive material onto an asteroid or deploy reflectors that might increase the level of solar radiation that strikes its surface. These alterations could change the asteroid’s orbit just enough for it to miss Earth.
This is not science fiction. The Deep Impact mission voyaged to the comet Tempel-1 and arrived in 2005. It launched an impactor into the comet. The impactor was a semi-autonomous vehicle that could maneuver and return telemetry and images to Earth. On July 4th 2005 it hit Tempel-1 at a high rate of speed and released the energy equivalent of 5 tons of dynamite. Careful study showed that the comet’s course was altered slightly, with a 10 centimeter adjustment to its perihelion, or closest point of its orbit to the Sun. Follow-on studies by NASA and other organizations have indicated that an impactor strike of this type is perhaps the most mature technology currently available to successfully deflect an inbound asteroid.
So we live in an amazing age. Rather than fearing this hazard, people around the globe are staring it in the face, pooling resources, and coming up with competent strategies. We even have an International Asteroid Day. I think Sir Arthur would approve.
The Sun passes through 12 constellations in its annual journey across the sky. These constellations are known to astronomers as the 12 signs of the zodiac. Libra is the only non-living entity represented by the twelve asterisms. By my count there are 7 animals (Leo, Cancer, Taurus, Aries, Pisces. Capricorn, and Scorpius) and 4 humans (Virgo, Gemini the Twins, Aquarius) among the famous constellations of the zodiac. Sagittarius is a centaur so I suppose that makes it 1/2 animal and 1/2 human. Given the wealth of animals among these constellation names it makes sense that zodiac has the same root as zoo.
As far back as 5000 years ago twelve was used to represent the number of months in a year, each dominated by one of the constellations. The sun follows a line called the ecliptic and in fact there is a 13th constellation in the zodiac. This one is called Ophiuchus the Serpent Holder. It is a very large constellation but a small portion of it drops down to the Sun’s path on the ecliptic. Indeed, the Serpent Holder places one foot between Scorpius and Sagittarius.
Another “intruder” in the ecliptic is the Moon. It will always be found within 5 degrees of the ecliptic. Generally speaking it follows the same path as the Sun across the sky. Both Sun and Moon appear to take up 1/2 a degree of arc in the sky when viewed from Earth. Use your thumb and you can block out both a full Moon and the Sun. This cosmic coincidence is what leads to some of the beautiful eclipses we experience on Earth: a 1/2 degree wide Moon just perfectly blocks out a 1/2 degree wide Sun. This summer North America will be treated to a solar eclipse. It will occur on August 21st. More about that later!
It’s interesting how a writer can on occasion transcend their own moment or place and create a sense of timelessness. The words on the page focus you in the moment and enthrall the reader. It’s a form of magic. This week I picked up The Adventures of Huckleberry Finn by Mark Twain. I haven’t read this book in about 10 years and I am thoroughly enjoying it. As an astronomer one passage was quite striking. Huck and Jim are adrift on the raft going down the Mississippi River and Twain captures the sense of wonder we so often feel when we look up at the night sky.
Twain wrote: Sometimes we’d have the whole river to ourselves for a long time. The riverbanks and the islands would all be far off in the distance. Sometimes you’d see a spark of light, which would be a candle in a cabin window. Or sometimes you’d see a spark or two on the water as a raft or scow or something passed by. Every now and then you’d hear the sounds of a fiddle or a song drifting out across the water from another boat. Then there was the sky, all speckled with stars. We used to lie on our backs and look up at them and discuss whether they were created or just came into being on their own. Jim thought they’d been made, but I thought they’d just happened. I figured it would have taken too long to make so many. Jim said the moon could have laid them like a chicken lays eggs. That sounded reasonable, so I didn’t argue with him. I’ve seen a frog lay a lot of eggs, so I knew it could be done. We used to watch the falling stars, too, as they streaked down. Jim thought they were falling because they’d spoiled and were being thrown out of the nest. It sure was nice to live on a raft. [Bantam Classics Edition, p115]
I’ve sat in observatories on many a night and shared such moments with other astronomers. And like Jim and Huck we too speculate about the nature of it all. May life always be good on this little raft called Earth.
The constellation Libra can be seen toward the southern horizon. It sits between the constellation Scorpius and the bright star Spica. Libra is a kite-shaped constellation and one of its dominant features is the Northern Claw and the Southern Claw. They are called claws because once upon a time the two stars were part of Scorpius, but the Romans changed that when they created a new constellation called The Scales, which was meant to represent Justice.
The Northern Claw’s recognized name is Zubeneschamali. Say that five times fast! It is the brightest star in Libra. Long ago the Greek astronomer Erastosthenes, who was the first to measure the diameter of the Earth, recorded the fact that Zubeneschamali was brighter than the star Antares which is in Scorpius. This is surprising because Antares, which sits some 500 light-years away, is a bright red first magnitude star. Even a casual viewer would note that on a summer evening Antares quite outshines the Northern Claw. So the question begs to be asked: has Zubeneschamali dimmed since the time of Erastosthenes? But rather than dimming it is possible that Antares has expanded and brightened over the course of the last 2300 years. The heart of Scorpius is well on its way to becoming a red super-giant.
The Southern Claw is called Zubenelgenubi. It is somewhat dimmer than the Northern Claw. That seems fitting as this difference in luminosity between the two stars would have been suggested an imbalance to the creative Roman who came up with the idea of The Scales. Looking carefully the two stars do appear out of balance.
The image above is taken from the EarthSky website (www.earthsky.org). The article on Libra indicated that Willian Tyler Olcott, a noted astronomer, was quoted in Burnham’s Celestial Handbook as having stated that the Northern Claw is “… the only naked-eye star that is green in color.” I’ve heard this before at a stargazing party in Bristol Springs, NY. Several of us looked through some large Dobsonian telescopes that were present and could not see the green tinge. To me it looked deep blue, so I can see how, under certain conditions, Zubeneschamali might take on a greenish tinge.
Stars populate a zoo of sizes and types, the most common and understood occupying what is called the main sequence. The main sequence can describe a “typical” star’s lifespan. The main sequence shows the phases that a star will go through across the billions of years of its lifespan. For astronomers it is a key to understanding stellar evolution.
It seems impossible that if a star were to move off the main sequence some combination of nuclear burn rate, scale, and pressure could lead, ever so briefly, to a star that looks green. This scenario turns up from time to time in science fiction. I’ll give the authors who create such stars a good deal of credit. They very cleverly explain such a star’s existence as being based on a set of freakish conditions that impact the burn ratio of elements in the core of a star. This leads, ever so briefly, to a green star. Could such a thing exist? Well, across an infinite amount of time and space, perhaps.
Is Zubeneschamali green? Go out on a clear summer night and look for yourself! Maybe you’ll solve the mystery of the green star.
I took a walk along the Genesee River at lunch today and came upon the Swinburne Rock. It is named for Thomas Thackeray Swinburne who attended the University of Rochester and was a member of the class of 1892. Although Swinburne took classes up until his senior year he did not complete his degree. Yet he was voted Class Poet by his cohort and made many literary contributions, including poems, articles, and editorial work in the student newspaper. Later, Swinburne was named City Poet during the city’s 1912 centennial celebration. At one gala that year he read a 30-stanza poem that featured a chat between the Genesee and the statue of Mercury that was atop a downtown building.
Swinburne owned a printing company and published many books including some that featured his own poems. One book was called Rochester Rhymes. Published in 1907 the book was dedicated to his sister Rose. Sadly, Rose passed away in 1926 and Swinburne, distraught by this loss, took his own life by jumping into the river’s icy waters in December of that year.
The Swinburne rock is a memorial to this poet. It features a large plaque with his poem The Genesee. The poem serves as the alma mater of the University of Rochester. It was later set to music by Herve Dwight Wilkins. The memorial plaque is affixed to a large glacial boulder. The plaque is made of bronze, now tinged green, with the words of The Genesee boldly inscribed. Overlooking the river next to the University’s Interfaith Chapel, the memorial has a timeless feeling. It is nice to take a moment, breathe the air, and read the words.