The May 23-24 Camelopardalid meteor shower is created by the Comet 209P/LINEAR, seen here in a NASA telescope image.
Image: A series of photographs of comet Hartl
6 Intimate Comet Encounters
Feb. 14, 2011 will go down in history as the Valentine's Day when a comet was visited a second time. Comet Tempel 1 has now played host to two different NASA spacecraft; Deep Impact in 2005 and Stardust-NExT in 2011. This amazing scientific feat comes hot on the heels of another cometary encounter only a few months ago. The NASA mission called EPOXI flew past comet Hartley 2 on Nov. 4, 2010 coming within 700 kilometers (435 miles) of the icy body. Both Stardust-NExT and EPOXI (formerly known as Deep Impact) are recycled comet missions and both have seen Tempel 1 up-close. EPOXI and Stardust-NExT may be the first two missions to be recycled for two comet flybys, but they certainly are not the first mission to rendezvous with these mysterious "dirty snowballs." So far, with the help of our robotic space explorers, humanity has had a close-up look at six cometary nuclei in the aim of unraveling their secrets. Let's take a look at each encounter with imagery from other space probes.
Image: Giotto's view of Halley's nucleus (ESA
Unquestionably the most famous comet in history, Halley's Comet was a prime target for space agencies in 1986 during its 75- to 76-year orbit through the inner solar system. Comet science is still a developing field, but in 1986, very little was known about the composition of these interplanetary vagabonds. In October of that year, the 15-kilometer-long Halley's Comet was visited by the European Space Agency's Giotto mission. The half-ton probe came within 600 kilometers (373 miles) of the comet's nucleus, taking the first photographs of the outgassing vapor from discrete areas of the surface producing its tail and coma (the gas surrounding the nucleus). It was this mission that confirmed the "dirty snowball" theory of cometary composition: a mix of volatile ices and dust. However, Giotto was only able to get so close to the famous comet with the help of the "Halley Armada," a number of international spacecraft all tasked with observing this rare event. Giotto captured the closest imagery, but two Russia/France probes (Vega 1 and 2) and two Japanese craft (Suisei and Sakigake) observed from afar.
Image: Comet Borrelly just before Deep Space
At roughly half the size of Halley's comet, Comet Borrelly was found to have similar attributes to its famous cousin. The nucleus was also potato-shaped and blackened. Outgassing vapor was also observed coming from cracks in the nucleus crust where volatiles were exposed to sunlight, sublimating ices into space. NASA's Deep Space 1 probe flew past the comet with a close approach of 3,417 kilometers on Sept. 22, 2001.
Image: A Stardust image of Wild 2 during its
Comet Wild 2 -- pronounced "Vilt" after its Swiss discoverer Paul Wild who spotted it in 1978 -- underwent a dramatic alteration in 1974. It is calculated that due to a close pass of Jupiter in 1974, the 5 kilometer-wide comet now orbits the sun every 6 years as opposed to its leisurely 43 years before the gas giant bullied it. The orbital modification meant that Wild 2 was an ideal target for NASA's Stardust mission to lock onto. On Jan. 4, 2004, the Stardust probe gave chase, getting so close to the comet that it was able to collect particles from Wild 2's coma. This image was taken at a distance of less than 240 kilometers (149 miles). The Stardust sample return canister came back to Earth safely, landing in Utah on Jan. 15, 2006. The microscopic particles captured from the comet continue to provide a valuable insight into the organic compounds comets contain. Interestingly, the Stardust spacecraft has been granted a mission extension (dubbed New Exploration of Tempel 1 -- NExT). In 2011 it will rendezvous with comet Tempel 1 -- the scene of NASA's 2005 Deep Impact mission -- to analyze the crater that Deep Impact's impactor left behind on the cometary surface.
Image: The view from Deep Impact's impactor b
NASA's Deep Impact mission reached the eight-kilometer-wide (five-mile-wide) comet Tempel 1 in 2005. On July 4, the probe deliberately smashed its impactor into the comet's nucleus, producing a cloud of fine material. A crater -- 100 meters wide (328 feet) by 30 meters (98 feet) deep -- was left behind. A treasure trove of compounds were spotted by the Deep Impact spacecraft and the explosion could be observed from Earth. In 2011, the recycled Stardust-NExT mission visited comet Tempel 1 for the second time.
Image: A close-up of comet Hartley 2 (NASA)
The fifth space probe encounter with a comet happened on Nov. 4, 2010. NASA's recycled Deep Impact probe -- now the EPOXI mission -- visited comet Hartley 2, examining its strange-shaped nucleus. Described as a "peanut" or "chicken drumstick," this comet is an oddity. During its close approach of under 700 kilometers (435 miles), EPOXI photographed the comet's irregular topography: two rough lobes connected by a smooth center. Jets of gas could be seen being ejected from discrete locations. During the Hartley 2 flyby press conference at NASA's Jet Propulsion Laboratory (JPL), mission scientists expressed their surprise that these jets of vapor are being emitted from sun-facing
shaded regions on the comet surface. Needless to say, analysis of the Hartley 2 flyby data will keep scientists busy for some time to come. "This is an exploration moment," remarked Ed Weiler, NASA's Associate Administrator for the Science Mission Directorate, during the conference.
Image: Tempel 1 as seen by Stardust-NExT at c
Most recently, on Feb. 14, 2011, the veteran Stardust-NExT (New Exploration of Tempel) mission made history by visiting a comet for the second time. Comet Tempel 1 was first encountered by NASA's Deep Impact mission in 2005 after smashing the cometary nucleus with an impactor. This second encounter provides scientists with an unprecedented opportunity to study the same comet after six years of orbiting the sun. Preliminary findings suggest Tempel 1 has undergone some erosion during those six years in deep space. Also, the impact crater left behind by Deep Impact was imaged during the Stardust-NExT flyby and it appears to match the size and shape predicted after the 2005 impact. However, the crater appears to be smoother than expected, so further work will need to be done to analyze the 72 photographs taken by this most recent flyby to understand the processes shaping the comet's nucleus.
Meteor observation doesn't have to be rocket science: All you have to do is lie back in a comfortable place and look up at the sky with the naked eye. Every so often, a meteor will flit across the stars. You simply make a note on a clipboard or speak into a tape recorder.
On Friday night and early Saturday morning (May 23-24), Earth will plow through debris shed over the years by Comet 209P/LINEAR. The result likely will be a new meteor shower, and possibly a spectacular meteor storm of 1,000 or so shooting stars per hour, experts say.
Even if you can't watch the meteor shower in person, you can catch the celestial showcase live online via a few webcasts. The Slooh community is hosting live views of the shower beginning at 11 p.m. EDT (0300 May 24 GMT), and they will also stream a webcast about Comet 209P/LINEAR before that at 6 p.m. EDT (2200 GMT). Watch the webcasts directly through Slooh.com, or catch the Slooh meteor shower feed on Space.com. The Virtual Telescope Project will also host a meteor shower webcast. (See maps and pictures about the new meteor shower)
No two observers prepare for a meteor vigil the same way. It will help if you can take a late-afternoon nap and a shower, and wear all fresh clothing. The ground can get cold, so heavy blankets, sleeping bags, cushions and even pillows are all essential. Sleeping bags provide some mosquito protection, but don't forget the insect repellent!
A long, reclining lawn chair makes a good observation platform because it's comfortable, portable and, in most cases, relatively inexpensive. It also allows you to move your head toward any section of the sky. A Thermos of hot coffee, tea or juice is a welcome comfort. Avoid alcohol; it impairs night vision.
Find a safe observing site that provides a wide-open view of the sky. Once you arrive, allow 20 minutes for your eyes to become fully adapted to the dark. You can use a flashlight, but only after you make some key modifications: Cover the lens with a sheet of dark-red cellophane, since dim red light affects your eyes far less than lamplight.
A new meteor shower, the Camelopardalids, will make their first night sky appearance on May 23 and 24, 2014. Created by the Comet 209P/LINEAR, the meteors will appear to radiate out from the constellation Camelopardalis (center, giraffe shape).Science@NASA
Complete darkness is best for observing meteors. With light pollution so widespread, it's getting harder to find a truly dark sky. Use the bowl of the Little Dipper to help determine how dark the sky in your area is. The brightest star in the Little Dipper is Kochab, a second-magnitude star. The next brightest is Pherkad, at third magnitude. The next brightest star is fourth-magnitude, and the next brightest is fifth-magnitude. So, if you can see all four stars in the bowl, you're in a pretty dark observing site. Keep in mind that for an increasing number of locations, only Kochab and Pherkad are visible, meaning you're likely to miss many of the fainter streaks.
It really doesn't make much of a difference in which direction you face. You just don't want trees, buildings or sky glow blocking your field of view. Gazing directly overhead (at the zenith) might be best. Your clenched fist held at arm's length measures roughly 10 degrees; some groups recommend looking about 60 degrees up in the direction of the radiant; the radiant for the Comet 209P/LINEAR meteors is in the dim constellation of Camelopardalis, which will be located about one-third up in the sky from the north-northwest horizon.
Use a portable radio to stay updated on the weather. Before changing to what might be a better site, however, note whether the cloudiness is spotty. Sometimes, there are lengthy intervals when few meteors can be seen. Of course, hourly counts mean little if your sky is not entirely clear. (How to Pronounce the Camelopardalids (Video))
If you just want to wait for the occasional shooting star, that's fine. But it's much more fun and interesting to make a useful meteor count that can be reported to the International Meteor Organization (IMO) and the American Meteor Society (AMS) to be compared with other people's results. You'll need a watch or a clock, a notepad, a pen or pencil, a red-covered flashlight and, if you have it, a tape recorder so you can dictate notes without taking your eyes off the sky.
The May 23-24 Camelopardalid meteor shower is created by the Comet 209P/LINEAR, seen here in a NASA telescope image.Science@NASA
Meteors have a way of coming in bunches that defy counting, magnitude estimating and plotting all at the same time. Often, people notice what some call the "clumping effect" — meteors arrive in groups of two or three, and will fall within a matter of seconds, followed by a lull period of several minutes or more before the sky again bears fruit. Some observers say this is an illusion; if you are observing alone, just make hourly counts and estimate magnitudes. It's helpful to use a hand counter to click off the number of meteors you see.
Meteor observing can also be a fun social affair. But if you observe in a group, do not combine results! Group counts are worthless. If you're in a group, assign each observer a limited program. Every person should observe as if alone, preferably watching a different section of the sky. Try not to be influenced by somebody who might yell out something like, "Whoa, look at that!"
The simplest method is to just count the meteors you see. If a few obstructions intrude, they should block no more than 20 percent of your view, and you must note the percentage of the view they're covering. The same applies to clouds.
If you take any breaks, note the times each begins and ends. Your vigil should total at least an hour, not counting breaks, and preferably longer. Ever hour, separate your observing records with a time annotation.
More from SPACE.com:
Amazing Night Sky Photos for May 2014 (Stargazing Gallery)
How Do You Pronounce Camelopardalids? | Video
Best Meteor Storm of 2014 Coming? 'Camelopardalids' | Video
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