The bad thing about science is that it lets us know just how precarious our position is.  Our ancestors were blissfully ignorant, thinking they were living in a safe and unchanging world.  Now we know that this was only a misconception caused by lack of knowledge.  As we get smarter, we realize just how dangerous this universe is, and how quickly and completely our little corner of it could change.  All the bodies of the solar system, including Earth, are pockmarked with the prints of past impacts, and more of them are being discovered all the time.

There are many examples.  In 2004, for instance, a systems analyst in Buenos Aires, Max Rocca, was indulging his hobby of poring over Landsat images online, when he noticed something unusual.  There is a river in Colombia called the Vichada which travels through miles of dense jungle before finally reaching the Orinoco.  For most of its course, the Vichada travels in a very predictable way, following the natural shape of the land.  Max Rocca had some training as a geologist, and he could tell where the path of the Vichada River should be in that landscape.  For most of the river’s course, he was absolutely right.  Only at one point did it deviate from the expected course, and that was where it turned at almost a right angle, traced a perfect semicircle through the jungle, and then returned to its former path.

Apparently there was a semi-circular feature on the land at that point, which had never been found before because the jungle growth obscured its outline.  Rocca knew it shouldn’t be there.  There was nothing in the normal seismic and erosional forces shaping this landscape that should have made a perfectly round depression there.

Further investigation showed that the crook in the Vichada River was following a ridge along one side of a circular depression 50 kilometers wide.  A shallow depression surrounded by a ridge of hills is the classic signature of an impact crater, and this was the biggest one every found in South America, 50 kilometers wide.

While Mr. Rocca certainly deserves kudos for his discovery, such features are not rare.  One truly spectacular example is Vredefort Crater in South Africa, which at 300 kilometers wide, is the largest confirmed impact crater on Earth.  (The Wilkes Land Crater in Antarctica is even larger at 500 km., but has not yet been confirmed to be an impact crater.)   Luckily, this event occurred some two billion years ago.  If such an impact happened today, it would induce an “impact winter” effect that would disrupt agriculture on a global scale, resulting in widespread famine and the probable extinction of many of the lifeforms on the planet- especially big ones at the top of the food chain (that’s us).

Of course, the situation is much better now than it was back then, because many of the rocks that were whizzing around two billion years ago have already hit something, but there are still plenty of rocks flying around the sun that are big enough to cause vast destruction.  When you consider the consequences of a single event of the magnitude of Vredefort or even the Vichada impact, it is impossible to ignore the threat.

With this in mind, there has been a lot of very serious discussion in recent years about what we can do if an asteroid or comet is found to be on a collision course with Earth.

The issue is being addressed by various organizations around the world, some associated with specific national governments and others of an international nature.  In 1998, NASA established its Near-Earth Object Program and set a goal of locating at least 90 percent of the estimated 2,000 asteroids and comets larger than one kilometer that approach Earth by the end of the following decade.  Unfortunately, it is now 2010 and this goal has still not been reached, but it probably will be realized in the next few years (see the article on the WISE space probe at this site).

Despite the fact that it has had to revise its original timetable, the NEOP is still alive and well.  In a 2007 report to Congress, NASA refined the goal of the project to the mapping of all bodies larger than 140 meters across whose orbits pass within .05 AU of Earth’s orbit.  At that time, the date of completion was estimated to be 2020.

In its web page about the establishment of this organization, NASA points out that the detection of NEOs also has a possible good side.  We now know that comets and asteroids are rich in substances that will prove useful to future space exploration efforts.  One of the most important of these is water, which exists in frozen form on many of the small bodies of the solar system.  In addition to its obvious usefulness for human consumption, water can be processed to yield oxygen and hydrogen, which also have multiple uses.  Besides this, there may be metals and minerals on some of these bodies that can be mined by future explorers.

The United Nations started an organization in 2001 called Action Team-14, which is dedicated to international discussions of the NEO issue.

This is all good, but it does raise an obvious question: when we find a NEO that is clearly going to impact Earth, what can we do about it?  Bear in mind that if we just shoot a missile at the thing, it will only make matters worse by creating a multitude of smaller pieces, all of which would follow roughly the same path as the parent body.  That would be turning a cannonball into buckshot- not a good idea.

Recent scientific findings have shown just how likely such an outcome would be.  We now know that “rubble piles” are very common in the solar system- see the article at this site about Mars’ moon, Phobos.  These are groups of rocks that stick to each other because of their slight gravitation, but are not actually attached.  If nothing happens to separate these rocks, they might stay together for billions of years; but if something hits them and jostles them apart- say, a missile fired by foolish little germs on some nearby planet- then they could fly apart very easily, and the buckshot analogy would be quite appropriate.

In its 2007 report to Congress, NASA listed different techniques that might be used to deflect a NEO that is on a collision course with Earth, and assessed the potential effectiveness of each one.  Because of the rubble pile problem, they immediately dismissed any idea of detonating an explosive on or under the surface of the body.  However, the report did propose an alternative: bring a nuclear device close to the NEO- but not too close- and set it off.  The force of the blast would nudge the NEO into a different orbit, but if you positioned the explosion right, it might not blow the object to pieces.

What we do depends, to some extent, on how much time we have to get to know our intruder.  In a best-case scenario, we would spot the object some years before it was to make impact.  Then we would be able to send an unmanned probe to study the threatening object.  By transmitting a continuous radio signal during a flyby of the body, the probe would allow Earth-based scientists to measure the Doppler shift of the signal, and calculate the body’s mass.  This would give us a pretty good idea of whether we were dealing with a rubble pile or not.  (As we saw in our Phobos article, rubble pile objects tend to have very low gravity because so much of their interior is empty space.)  If it turns out that we are dealing with a solid body rather than a rubble pile, our troubles are over (almost).  NASA estimates that for such a body, the best approach would be to shoot a non-explosive impactor, or more likely a series of them, at the body and knock it into a new orbit like an oversized pool ball.

Various “slow push” techniques have been proposed.  One of these is to find another asteroid and modify its orbit so that it acts as a tugboat, pulling the threatening object into a new orbit.  Another idea is to put down a robot lander which would actually mine rock from the body and fire it off in high-velocity “bullets,” in effect turning the NEO into a rocket.  Another idea is to send a spacecraft to rendezvous with the NEO and spray-paint it with some coloring agent which would make one side brighter than the other, so that radiation from sun-heated material would provide a small thrust.

One particularly novel proposal has come from America’s Planetary Society: mirror bees.  These are small, unmanned craft that use mirrors to focus sunlight on the NEO, causing material to boil off and create jets which, if carefully positioned, could change its orbit.  Alternatively, they might use lasers rather than mirrors.

The 2007 Congressional report said that while slow push techniques would work in theory, they could only be used if we had plenty of warning, since they all involve getting spacecraft to the object and performing operations that would take some time to be effective.  If we only have short warning- which is likely, unfortunately- then a stand-off nuclear explosion is probably our best bet.

The report also pointed out that up to 80 percent of NEOs might be in orbits that could not be attained by current launch vehicles, which would mean that new launchers would need to be developed.  Even then, it would be necessary to use gravity-assist maneuvers to the fullest advantage to reach some of them.

So the bad news is, if it happens, we’re in big trouble.  The good news is, at least the governments and other institutions of the world are aware of the problem, and are trying to do something about it.  These discussions have yielded some good ideas, but now those ideas must be acted on.  Our planet has been pounded many times before, and each time, many species became extinct as a result.  If we are lucky, maybe it will be different next time.

Sources:

Lendroth, Susan: Press Release- “Saving Earth One Asteroid at a Time” at the website of the Planetary Society:  planetary.org/about/press/releases/2010/0212_Saving_Earth_One_Asteroid_at_a_Time.html

Alexander, Amir: “Project: Asteroids- the Potential Threat” at the website of the Planetary Society:  planetary.org/programs/projects/targetearth/20100213.html

Projects: “Mirror Bees: Planetary Defense” at the website of the Planetary Society:  planetary.org/programs/projects/mirrorbees/

Murrill, Mary Beth and Whalen, Mark: “JPL Will Establish Near-Earth boject Program Office for NASA” at the NASA website:  neo.jpl.nasa.gov/program/neo.html

“Near-Earth Object Survey and Deflection Analysis of Alternatives” (report to Congress, March 2007):  neo.jpl.nasa.gov/neo/report2007.html

Vredefort Crater entry at Wikipedia:  wikipedia.org/wiki/Vredefort_crater

The fortuitous combination of atmospheric gases that may life as we know it possible may have a decidedly extraterrestrial origin, stemming not from the actions of terrestrial volcanoes but from the appearance of comets.

Scientists have long been puzzled by the mixture of gases in the Earth’s atmosphere ”“ and by the origins of those gases. For years one of the most popular theories has been that the gases in the Earth’s atmosphere are the result of the eruption of volcanoes. As those gases bubbled up from those ancient volcanoes, the theory goes, they helped to create the atmosphere as we know it today.

But recently researchers at the University of Manchester in the UK came up with a different theory for the origins of the Earthly atmosphere, based on their findings after they collected samples of krypton gas hundreds of meters below New Mexico.

Researcher Greg Holland and his colleagues at the University of Manchester found that the area they studied was rich in heavier isotopes of krypton but poorer in lighter versions of the gas. In fact the composition of the samples closely resembled that found in meteorites, lending further credence to an exterritorial origin of the terrestrial atmosphere.

The comet theory supposes that the current atmosphere of the Earth has its origins not in volcanoes that spewed krypton and other gases into the air but in the bombardment of the earth by thousands icy comets. Specifically this emerging research is focused on the Kupier Belt, which formed when the solar system was born. The millions of icy bodies in the Kupier belt have been found to contain a noble gas signature very similar to that of the Earth’s present atmosphere.

Scientists already know that a shift in the orbit of gas giant Jupiter took place some 4.5 billion years ago, and that shift may have been enough to move the Kupier belt and release those comets on a collision course with Earth. It is an interesting theory, and one that is bound to gain additional attention as new evidence is discovered.

Deep Impact started out as a neat, straightforward mission.  The idea was to get close to a comet, hit it with a projectile, and observe the ensuing dust cloud for scientific data.  The spacecraft was launched on January 12, 2005, from Cape Canaveral.  After about seven months in flight, it reached its destination, the comet Tempel 1.  On July 2, Deep Impact released its “impactor,” which had its own power source and was designed to operate autonomously for just one day, long enough to move itself into the path of the comet and hit it.  About 24 hours later, the impactor successfully performed this maneuver, taking some spectacular pictures during the approach.  The actual moment of impact was recorded by the larger Deep Impact probe, which was watching from about 300 miles away.

The impact caused a brilliant flash of light, illuminating the side of the comet facing the probe: a battered little world covered with craters and other scars.  The cloud of debris was bright and larger than anticipated.  While planetary scientists were expecting the collision to throw up some liquid water with chunks of rock and ice, what they actually saw was more fine and powdery.  Because of this, it was not possible to see the resulting crater, and its exact size remained a mystery.

But it certainly made a nice plume, and this was observed by the Deep Impact probe itself and by the Spitzer Space Telescope, which is in an Earth-trailing solar orbit.  Scientists will be mining information out of this data for a long time, but already they have gotten some interesting facts.  Spitzer obtained spectrographic information, and analysis of this has revealed the signatures of a list of chemicals- they’re calling it “comet soup.”

Some of the ingredients are not surprising: silicates (sand) which were already known to be standard comet components.  But here’s a real head-scratcher: the plume from Tempel 1 also contained clay and carbonates.  What’s strange about them is that they are only supposed to form in water.

Commenting on this, Dr. Carey Lisse of Johns Hopkins University’s Applied Physics Laboratory said, “How did clay and carbonates form in frozen comets?  We don’t know, but their presence may imply that the primordial solar system was thoroughly mixed together, allowing material formed near the sun where water is liquid, and frozen material from out by Uranus and Neptune, to be included in the same body.”

This goes along with findings from the Stardust probe (featured in one of our earlier articles) which took samples of dust from comet Wild 2,  in which materials that could only have formed in extreme heat were found.  Since these particles were encased in the ice of the comet, it is obvious that the different components of the comet were formed in different places, and then somehow combined.

Spitzer also spotted some substances that have never been seen in a comet before, such as iron-bearing compounds and aromatic hydrocarbons, which can be found more commonly in car exhaust and barbecue pits.

We will certainly hear more from the ongoing analysis of that data, but meanwhile, Deep Impact is moving on to bigger and better things.

The probe is still operational, and NASA has big plans for it.  It has been renamed EPOXI, and is actually two missions combined: a search for extrasolar planets and another comet investigation.

In July 2007, NASA announced that the Deep Impact mission would be extended to include a second encounter, this time with the comet Boethin.  That would be an impressive accomplishment, but there might be a problem: the orbit of this comet was not known with absolute certainty.  It had only been seen twice ever, and the most recent sighting was more than twenty years ago.  To make the necessary course alteration, the probe was going to make a flyby of Earth and use the planet’s gravity to bend its path.  In order do this accurately, it would have to make its approach to Earth at exactly the right angle, so that it would emerge from the maneuver headed in the right direction.  The probe was in hibernation following its encounter with Tempel 1, and would only wake up when it was close to Earth.  The NASA scientists would have to find the comet quickly and calculate exactly what the angle of the flyby should be.

Unfortunately, it didn’t work.  When the probe came out of hibernation, the ground crew looked for comet Boethin, and it wasn’t there.  The approximate orbit of the comet had been calculated from the two sightings that had been made, but the calculations were obviously off.

Time was wasting; the flyby of Earth was approaching, and NASA couldn’t find its target.  A desperate decision was made: pick another comet, quick!

They picked a comet called Hartley 2.  This was actually a better target because it had been extensively observed, and its orbit was known accurately.  However, the new course would take two years more than the mission to Boethin would have, and the cost would be correspondingly higher.  That cost had not been taken into account when the original budget was drawn up, so the extension would require new funding.

There was no time for a budget meeting.  The mission team made the Earth flyby and sent the probe off toward Hartley 2, thus obligating NASA to pay for two more years of mission time.  Luckily, their bosses were understanding, and NASA increased the mission’s funding to include the extra expense.

That encounter will happen in November of this year.  Until then, EPOXI has its work cut out for it- and here we get into the other part of the extended mission.  In a complete departure from its original purpose, the probe is going to do some searching for planets around other stars.

It all came out of an earlier exercise in the Deep Impact itinerary.  When the probe was near Earth, it performed a series of observations of this planet.  As much as we know about our home world, there’s always room for more knowledge, and it was thought that Deep Impact might be able to yield some interesting science.

It certainly did.  The NASA scientists found that by analyzing the sunlight glinting off the Earth, they could tell what kind of terrain was passing by.  Not surprisingly, the oceans reflected a lot more sunlight than the land did, and water, soil, vegetation etc., all reflect different wavelengths.  By analyzing the light, it was possible to tell whether land or water was passing underneath the probe.  It was also easy to detect the presence of vegetation, as this caused a bright glow in the infrared just above the visible light range.

This was something new.  Reading the accounts at the NASA website, you get the feeling that the space boys were really surprised at the degree of detail and accuracy that they were able to achieve, and it suggested a whole new purpose for this mission.  On the way out to comet Hartley 2, EPOXI can stay busy by scanning stars and looking for glints of sunlight from them.  A brilliant gleam can only mean one thing: water.  In nature, only water, either in its solid or liquid form, is smooth and reflective enough to do that.  Even if we don’t see that, slight changes in the light reflecting from an extrasolar planet may tell us what kind of terrain it has, or maybe even reveal the presence of vegetation.

This research has already yielded some interesting results.  The probe has scanned seven stars, and while it hasn’t found the telltale glint of oceans, it has found a new planet.  It’s a “hot Neptune,” a planet roughly comparable to Neptune in size, but orbiting very close to its parent star.  While extrasolar planets aren’t the big news that they once were, there is always the chance that EPOXI will turn up something really big.  An extrasolar planet with water oceans would be a revolutionary discovery, and this could be the way we find one.

Considering the fact that this angle of research had not even been thought of when the mission started, the NASA folks certainly deserve high marks for resourcefulness and ingenuity.

Check back here for updates.  When EPOXI encounters Hartley 2 in November, we will cover it, of course.  Stick with us, and you won’t miss a thing.

Sources:
Deep Impact: MIssion to a Comet at NASA website:  nasa.gov/mission_pages/deepimpact/media/spitzer-di-090705.html

Mission news: NASA’s Deep Impact Films Earth as an Alien World at NASA website:  nasa.gov/topics/solarsystem/features/epoxi_transit.html

News Releases: NASA Gives Two Successful Spacecraft New Assignments at NASA website:  nasa.gov/home/hqnews/2007/jul/HQ_07147_Discovery_missions.html

Lakdawalla, Emily: Deep Impact Snaches Science Data From Earth-Moon Flyby at Planetary Society website:  planetary.org/blog/article/00001276/

Lakdawalla, Emily: DPS Meeting: Saturday: Studying Extrasolar Planets with Planetary Spacecraft at Planetary Society website:  planetary.org/blog/article/00001691/

Even before they were launched, these three missions were successes. Mars Express, Venus Express and Rosetta were all built using the same design and many of the same data-gathering instruments. The same facilities were used to assemble the probes, and even many of the same people worked on all three projects. By using this strategy, the ESA was able to greatly reduce the amount of time and expense required to launch the missions.

But at first, Rosetta had a troubled childhood. It was originally approved in November 1993, and the destination was to be the comet 46 P/Wirtanen- but the project ran into delays and was not able to make that destination. Preparations continued with a new goal: comet 67 P/Churyumov-Gerasimenko. The new itinerary was an ambitious 10-year journey that would include two asteroid flybys: 2867 Steins in 2008 and 21 Lutetia in 2010.

This was the mission that finally made it into space on March 2, 2004, launched on an Ariane-5G rocket from Kourou, French Guiana. After that, the probe spent almost four years modifying its orbit by making two passes near Earth, and one near Mars. This put it on course for its first destination, asteroid 2867 Steins.

This was our first chance to get a close-up look at a rare kind of asteroid, the E-type. These bodies are thought to be fragments of larger asteroids that fragmented. They are highly reflective, with a featureless flat spectrum, and are thought to be the source of a type of meteorite called Aubrites. They are greatly outnumbered by other types of asteroids, mainly the M-types. While other probes had obtained pictures of eight asteroids, none of them was an E-type. As Rosetta approached 2867 Steins, the planetary scientists were keenly anticipating their first peek at one of these rare bodies.

The flyby took place flawlessly on September 5, 2008. The closest approach was 800 kilometers, and the relative velocity was 8.62 km/sec. Rosetta immediately confirmed the calculations of ground-based astronomers by affirming that 2867 Steins rotates once every 6.05 hours. The probe took some beautiful, clear pictures of the asteroid, imaging about 60 per cent of its surface. While the pictures were in color, 2867 Steins still looked gray; there was no significant color variation over its surface. Rosetta measured the asteroid’s albedo (reflectivity) and found it to be .4, meaning that it reflected about 40 per cent of the sunlight hitting it. (This is about four times as reflective as Earth’s moon.)

Steins is shaped like a child’s top: rounded on “top,” pointed on the “bottom.” The rounded end is dominated by a huge impact crater, 2.1 kilometers in diameter. Running down the side of the asteroid is a row of seven circular indentations. While these look like impact craters, their similar size and shape, and the fact that they are in a row, would seem to indicate that there is a fracture along that line, and the indentations are actually collapsed pits where dust has settled into the crack. There is also a similar groove along the other side of the asteroid, which may be the same fracture running completely through the body.

The surface features of Steins can be used to make inferences about its history. Its surface is not saturated with impact craters; in other words, there is some empty space visible between them. But we know that the early solar system was a violent place, with many impacts occurring frequently, so we would expect that an asteroid would be completely covered with impact craters. If we find an asteroid that doesn’t look like that, we must assume that something happened to erase the older craters. When looking for a likely cause of this phenomenon on Steins, our attention is immediately drawn to that 2.1-kilometer crater on its top. This is a puzzle, because the impact was so great, it should have shattered a solid body. Normally, if you take a solid rock that’s about 6 km wide and hit it with another rock that’s also of considerable size, they should both split into lots of little fragments.

The conclusion is inescapable: 2867 Steins was never a solid body. It’s a “rock pile,” a collection of fragments held loosely together by their mutual gravitation. When the big impact happened, these fragments were shifted around; some of them probably even flew away and then came back and re-collided with the larger body. Since the asteroid itself was the greatest source of gravity nearby, all the pieces eventually settled back together. The crater from the big impact was so huge, it was still recognizable after the shift- but any smaller craters were completely obliterated. Except for that big crater, Steins got a completely fresh surface, and any smaller craters that we see on it now have occurred since then.

So now we have another portrait of an asteroid, and we know something about its past. Before now, this type of body was an abstraction that existed only on the pages of astronomy textbooks. Now it is a real object that we can see and study. ESA has posted a video of the approach to Steins, and the sight of this little jewel-like object spinning out of the darkness is truly inspiring.

And Rosetta hasn’t even reached its destination yet! This is a really ambitious project, and the hits just keep on coming. In November of 2009, Rosetta modified its course by flying past Earth one more time, which put it on course for the asteroid 21 Lutetia. That encounter will happen in July of this year, and we will gain another asteroid for our photo gallery. These encounters always give us some interesting science, and this one will certainly be no exception.

After this, the probe will go into a period of hibernation. When it wakes up, it will be at it final destination, the comet 67P/Churyumov-Gerasimenko. If all goes well, the probe will go into orbit around the comet and put down a lander, which will anchor itself by shooting harpoons into the comet’s surface. The lander and the probe will stay with the comet through its entire approach to the sun, observing the changes that occur as it heats up and begins to give off the gasses that form the comet’s “tail.” If this is successful, we will finally know in detail exactly what happens to a comet as it approaches the sun.

The show is just starting! Watch for updates at this website.

Sources:

Rosetta homepage at the website of the european Space Agency: sci.esa.int/science-e/www/area/index.cfm?fareaid=13

Space Topics: Rosetta at the website of the Planetary Society: planetary.org/explore/topics/rosetta/

Rosetta: the United States’ Contribution at the NASA website: search.nasa.gov/search/search.jsp?nasaInclude=rosetta+comet+mission

Many people may have missed the news but an asteroid was detected passing less than 9000 miles from the Earth on Friday 6 November and it was only 15 hours before this happened that the comet was actually detected. The asteroid was first picked up by researchers at the University of Arizona as part of their Catalina Sky Survey and following this was detected by the Minor Planet Centre in Cambridge Massachusetts. The asteroid was then picked up by the National Aeronautics and Space Administration (NASA) and its trajectory plotted.

The 23 foot wide asteroid has been christened 2009 VA and at its closest it was only 8700 miles from the Earth. This is 30 times closer than the Moon which lies approximately 250,000 miles from the Earth and it was the third closest approach of an asteroid ever recorded. However it is not considered that the asteroid would have made much of an impact and in actual fact it probably would have burned up in the Earth’s atmosphere long before it reached the ground.

However the more worrying aspect of the story is the fact that it was only detected 15 hours before it passed the Earth. This demonstrates that there are still objects out there that we know little about and shows how close they can approach before actually being detected. Although 2009 VA actually posed little threat, a larger asteroid could have potentially devastating consequences if it were to collide with planet Earth.

NASA was tasked by Congress with identifying at least 90% of the asteroids that are considered to pose a threat to our planet by 2020. They were assigned the task in 2005 and initially estimated there were around 20,000 dangerous comets and asteroids, with those that are 460 feet or greater in size being considered a risk. To date scientists have accurately located around 6000 of these and the scheme which is known as the Near-Earth Object Program continues.

However the passing of 2009 VA shows how difficult this task will be. For an asteroid to get so close to the Earth without being detected is not something that should be taken lightly. NASA monitored a 100 foot asteroid in March this year as it passed around 45,000 miles from the Earth. An asteroid of similar size crashed into planet Earth in 1908 although it landed in a remote part of Siberia. The impact however devastated an area 1,200 square miles in size and if such an object landed near an area of dense population there would be severe consequences.

The NASA project is therefore important and if an early warning of an imminent strike was given this could greatly reduce the human consequences involved. 2009 VA was a lesson that the task of identifying near earth comets and asteroids is not an easy one although the hunt will go on.

This meteor shower is one of the most showy and dazzling of them all in the northern hemisphere. For over a hundred and fifty years this event has been known to be very active displaying at least one streaking meteor every thirty seconds. In other past occurrences it created sixty meteors per hour. On the average, one hundred meteors per hour radiate throughout the sky. This is known as the Zenith Hourly Rate (ZHR).

The winter December sky will provide an excellent chance to experience the meteor event. Visibility will be enhanced by a new moon ensuring that zenith hour rate is seen. Originating from the Gemini constellation and scattering relatively slowly across the sky provides viewers a chance to see the trails with the unaided eye. These shooting star trails last a number of seconds and be seen in varying colors. In the northern latitudes it can be visible in the not-to-late evenings. This is perfect timing for star parties, astrophotography and even family viewing.
Discovery of the Geminids
Three astronomers all working independently in 1862 are credited for the discovery of the Geminids meteor shower. The first noted was R. P. Greg (England), secondly B. V. Marsh (United States.) and lastly A.C. Twining (United States). More sightings and reports came during 1863 and 1864.

It wasn’t until 1983 that the origin of the Geminids meteor shower was uncovered. Once again, three astronomers are given the credit. Two for identifying an asteroid and one for researching and associating the orbit to the meteor shower. Simon Green and John Davies identified the asteroid 3200 Phaethon. Fred Whipple noted the asteroid’s orbit and associated it to the meteor shower.

What is still a mystery about the Geminids meteor shower? Even though 3200 Phaethon has been identified as an asteroid, there is a possibility that it could be a dormant comet. The question arose when a photographic density study was conducted and the results proved to be less dense than asteroids.

Asteroid or comet, 3200 Phaethon has been officially linked to be the origin of the Geminids meteor shower. The meteor shower happens every December and this year gives us a great chance to watch.

The art/science of studying the stars was engaged by several ancient populations like Maya, Incas, Egyptians and Greeks, and soon grew in importance to the point where those who practiced it were highly regarded and respected in their own society. The reason for this is evident: this science could provide, even from its first, rudimentary structure, an explanation to phenomena strictly connected to their life, such as the alternating of day and night or the cycle of seasons, and provided an essential instrument for activities such as agriculture and navigation.

The history of Astronomy is in part — from its origins to the invention of the telescope by Galileo Galilei, in 1610 — also the history of astrology. In prehistoric ages, the most advanced tribes were familiar with the motion and trajectories of just a few, visible objects like the sun, the moon and some of the brightest stars. The most commonly cited example of such knowledge is the Stonehenge complex, residing in Great Britain, which is thought to have served as a monumental calendar.

Chinese astronomy was born before 2000 BC and is still cited nowadays for its great tradition of carefully, a-critic documentation. From the documents in our possession we know that in their time they were already aware of events such as the passage of comets, or even the explosion of a Supernova star.

A few civilizations in central America also reached astonishing results, but unfortunately they didn’t manage to share they knowledge with other populations. Maya and Inca tribes would often build pyramids and temples, which were devoted to the Gods of the Sky. Their religion was strictly related to the planet Venus and, based on estimations of its motions, they managed to create an incredibly precise astronomical calendar, finding out, among other things, that the planet would accomplish five complete orbital revolutions in the time span of exactly 584 days.

Babylonians soon showed exceptional knowledge in the matter of astronomy, which would later be inherited by Egyptians and Indians. In their case, the desire to perfect this science at all costs came, rather than an actual need, from skeptical reasons that linked the motion of stars and planets to good or bad luck (solar and lunar eclipses were thought to bring extremely bad luck, and this conception would persist until relatively recent times). Even lacking any sort of precise instrumentation, Babylonians managed to find out many things about the apparent motion of planets, basing their observation on the position of a few bright stars on the sky: they therefore discovered the orbital revolution time of many planets, among which Venus, Mars, Jupiter and Saturn, only mistaking by a few days, and reporting the results of their calculations on special tables, most of which are well-preserved and can still be seen now in astronomical museums.

Egyptians’ immense and astonishing knowledge regarding astronomy relies, once more, on their ability to forge precise calendars describing the motion of stars and planets. As their life cycle was strictly linked to that of the Nile river, astronomy was given a central role by this society from the very beginning. Around 3000 BC, Egyptians were already used to dividing their day and night time in regular intervals of 12 parts each: day time would be measured by sundials, while night time would be measured by observing the relative position of 24 bright stars. Measuring this way, their ‘hours’ would have a different duration depending on the season, but still averaging 60 minutes each.

It was only with Greek astronomy, though, that a stress was posed on developing theories that would explain the birth of the Universe and its mechanics: Anaximander thought the planet Earth was a cylinder at the center of the Universe, while the stars would rotate around it in all directions; Plato had at a first time a theory, extremely advanced for its time, that put the Sun at the center of the Universe, but he later withdrew it to favor an Earth-centric theory similar to that of Anaximander; Eudoxus of Cnidus, finally, advanced a theory that was later approved by Aristotle, according to which the Universe was made of concentric spheres, rotating one inside another, where the Earth would be in the center.

The Aristotle conception of the structure of the universe was meant to last, with minimal variations, until the year 1500 AD, when Nicolaus Copernicus — which many consider the father of modern astronomy — advanced a theory that put the Earth orbiting in perfect circles around the Sun, together with all the other planets: this approach could in fact solve many of the contradictions that those who supported Aristotle had to face. A few decades later, John Kepler refused yet another innovative model of the universe from his mentor Tycho Brahe, and later became famous for formulating the three laws of star mechanics that were named after him, which are considered valid still nowadays.

In 1610, Galileo Galilei invented the telescope, after a long period of research and experimentation. As soon as he pointed it at the stars, a never seen before universe appeared in front of his eyes: the Moon had a surface full of craters, Jupiter was surrounded by four satellites, while the Milky Way suddenly appeared as nothing but a huge mass of countless stars. In 1632, after publishing his book ‘Dialogo sopra i due massimi sistemi del mondo’ [On the main two models of the Universe] in which he was openly exposing the results of his observations, he was forced by the Catholic Church to abjure not having made those discoveries.

A few decades later, while researching innovative techniques to build more and more powerful telescopes, an important debate took place between the scientist Huygens and Newton over the nature of light: the first said it was a wave, while the second thought it was made of physical ‘atoms’ (photons). The debate that was destined to be solved once and for all just a few decades ago (light is, indeed, both a wave and a physical object). Huygens studied advanced optics as well, and managed to build a telescope that could noticeably minimize the chromatic aberration in observations, which led him to discover Saturn’s rings and its moon, Titanus.

Just a few years later, Cassini and Romer found out that phenomena such as solar eclipses would happen just several minutes after they were expected: this led them to think that light could actually travel at a finite although extremely high speed, rather than to an infinite speed: their estimation put the speed of light at 230,000 km per hour (the actual speed of light is 300,000 km/h).

Starting from the 19th century, following the Industrial Revolution, the continuous development of innovative techniques and instruments for the observation of the sky led to a series of discoveries that quickly contributed to our knowledge. Nowadays, the main purpose of astronomy is to study the life cycle of stars and galaxies, the origin and future of the Universe, obscure objects like pulsars and black holes, and methods to measure interstellar distances with increased precision.