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Sunlight Puts the Spin on Asteroids.


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Asteroid 2000 PH5.
asteroid 2000 PH5. Image credit: ESO.

Astronomers have theorized that light from the Sun influences the speed at which asteroids spin, and now they've gathered the evidence to back it up.

The 'Yarkovsky-O'Keefe-Radzievskii-Paddack' (YORP) effect proposed that when sunlight strikes an asteroid's surface, it warms the region up slightly. As the heat is radiated away, there's a recoil effect that causes the asteroid to spin. It's not a lot, but added up over millions of years, it can really set an asteroid spinning.

Now Astronomers have found this effect in action on nearby asteroid 2000 PH5. They watched the asteroid using a variety of instruments across the Earth over the course of 4 years. During this period, they were able to measure an increase in its rotation speed. Although it takes 12 minutes to complete one rotation, that period is decreasing by 1 millisecond a year.

They calculated that over the next 35 million years, the rotation period will drop to 20 seconds, and it might end up spinning so fast that it reshapes itself or breaks apart.

Original Source: ESO News Release

Is Pluto a Planet?

Is Pluto a Planet?.
March 5th, 2007: Is Pluto a Planet? by Mark Mortimer.

Pluto has been in the news of late. One occasion saw its status as a planet come up for debate. Another concerns the New Horizons probe which is well on its way to meet our outermost planet.. Perhaps in preparation for the later, David Weintraub prepares us by addressing the former in his book, Is Pluto a Planet? ' A Historical Journey through the Solar System. For though Pluto is a remote wanderer it has many interesting points even if we're not sure what to call it.

Pluto has a recent and rich history. Following clues and deductions, Astronomers raced to find something orbiting past Neptune. More by perseverance than design, Pluto was found distantly floating along the cold edges of our system. However, Pluto was less than expected. It was too small, had an odd orbit and showed little resemblance to Neptune. Thus, though popular media jumped on using the word 'planet' for it, there was little rationale for this nomenclature.

Weintraub's book considers this rationale. He's got a bone to pick with the English language and presents a rich review of his consternation. He starts with our glorious Greeks predecessors who spent much time thinking about life, the universe and everything. It was from them that everything in the skies were perfect; revolving in perfect paths about stationary Earth. Their geocentric notion, and minimal eyesight, saw tiny stars and seven 'others' that followed regular paths through the sky. These others were given the name planet. This, to Weintraub, is rationale.

However, Weintraub then shows how we changed our understanding of the universe and thus changed our consideration of planets. He proceeds through the historical route of the Copernican upheaval, the Galileo teachings, and the Kepler refinements. Through these, he shows how many more descriptors were needed to define the objects we see at night. He continues on with the consideration of comets, asteroids, and other moons. For as he shows, while our vision improved, so did our appreciation of the complexity of the universe.

Bringing his work toward conclusion, Weintraub brings the reader up to date with our solar system. He considers Kuiper belt Objects and the Oort cloud. There's 2003 UB313 and Quaoar. Some objects are big. Some are small. Some have nice orbits. Some are very eccentric. Some are metal-ice. Some aren't. He even brings in Brown Dwarfs, other speculative objects that might orbit fusion reactors, and, potential oddities floating in isolation amongst the emptiness of space. From this, he does have, and solidly presents, his opinion on whether Pluto is a planet.

To make his argument accessible, Weintraub does away with almost all technical verbosity and keeps his language toned for the average reader. His sections on the historical aspects are well researched and enjoyable to read in their own right. He comfortably associates astronomy to general science to show how astronomy initiated predictive science as well as international collaboration. Many clear black and white photographs amongst the text show distant moons and 'planets', as well as some of the principle researchers. In all, it's very enjoyable reading that imparts lots of information in a manner that misleads the reader into learning more than they might have expected. By the end of the book, the reader should be very comfortable in taking up either of the sides of whether Pluto is a planet..

The main problem with Weintraub's book is his apparent assumption that the English language must be precise. Science is precise. Math is even more precise. However, the English language has to accommodate passion. Love and fear are not precise. Books are written trying to define these and still nothing is definitive. As such, if the reader wants a good rationale argument on the definition of a planet, this book is perfect. However, if you're more interested in enjoying the pretty lights at night because they make such a wonderful display, then this very objective book is not for you.

With humanity's vision getting stronger, we need new ways to express what we see. Pluto is far out there, but other stranger fare are farther. These may be planets. These may be planetoids. David Weintraub in his book Is Pluto a Planet? gives the sound scientific reasoning for his own resolution. And with it, he provides a fine summary of the astronomical beauties floating within our solar system.

Read more reviews, or purchase a copy online from Amazon.com.

Universe: What's Up this Week: March 5 - March 11, 2007

M50. Image credit: NOAO/AURA/NSF.
March 5th, 2007: M50. Image credit: NOAO/AURA/NSF.

Monday, March 5 - Today is the birthday of Gerardus Mercator, famed mapmaker, who started his life in 1512. Mercator's time was a rough one for astronomy, but despite a prison sentence and the threat of torture and death for his 'beliefs,' he went on to design a celestial globe in the year 1551.

Tonight we'll use both Sirius and Beta Monocerotis as our guides to have a look at one fantastic galactic cluster for any optical aid - M50. Hop about a fistwidth east-southeast of Beta, or northeast of Sirius'and be prepared!

Perhaps discovered as early as 1711 by G. D. Cassini, it was relocated by Messier in 1772 and confirmed by J. E. Bode in 1774. Containing perhaps as many as 200 members, this colorful old cluster resides almost 3000 light-years away. The light of the stars you are looking at tonight left this cluster at a time when iron was first being smelted and used in tools. The Mayan culture was just beginning to develop, while the Hebrews and Phoenicians were creating an alphabet. Do you wonder if it looked the same then as it does now?

In binoculars you will see an almost heart-shaped collection of stars, while Telescopes will begin to resolve out color and many fainter members - with a very notable red one in its midst. Enjoy this worthy cluster and make a note that you've captured another Messier object!

Tuesday, March 6 - If you get a chance to see sunshine today, then celebrate the birthday of Joseph Fraunhofer, who was born in 1787. As a German scientist, Fraunhofer was truly a 'trailblazer' in terms of modern astronomy. His field? Spectroscopy!

After having served his apprenticeship as a lens and mirror maker, Fraunhofer went on to develop scientific instruments, specializing in applied optics. While designing the achromatic objective lens for the telescope, he was watching the spectrum of solar light passing through a thin slit and saw the dark lines which make up the 'rainbow bar code.' Fraunhofer knew that some of these lines could be used as a wavelength standard so he began measuring. The most prominent of the lines he labeled with letters that are still in use today!

His skill in optics, mathematics and physics led Fraunhofer to design and build the very first diffraction grating which was capable of measuring the wavelengths of specific colors and dark lines in the solar spectrum. Did his telescope designs succeed? Of course! His work with the achromatic objective lens is the design still used in modern telescopes!

In 1986, the first of eight consecutive days of flybys began as VEGA 1 and Giotto became the very first spacecraft to reach Halley's Comet. Although there may not be a bright Comet for us to observe tonight, we can have a look at a wonderful comet-shaped object that displays all the 'blues' of Fraunhofer's work. You'll find it about 3 fingerwidths northeast of Epsilon, about 2 degrees northeast of star 13 in Monoceros.

NGC 2261 is more commonly known as 'Hubble's Variable Nebula.' Named for Edwin Hubble, this 10th magnitude object can be seen in smaller Telescopes and is very blue in appearance to larger apertures. Its cometary shape isn't what's so unusual, but the variability of the nebula itself. The illuminating star - R Monocerotis does not display normal stellar spectrum and may be a protoplanetary system. R is usually lost in the high surface brightness of the structure of the nebula, yet the whole thing varies with no predictable timetable - perhaps due to dark masses shadowing the star.

Wednesday, March 7 - Today the only child of William Herschel (the discoverer of Uranus) was born in 1792 - John Herschel. He became the first Astronomer to thoroughly survey the southern hemisphere's sky, and he was discoverer of photographic fixer. Also born on this day, but in 1837, was Henry Draper - the man who made the first photograph of a stellar spectrum.

Before we leave the constellation of Monoceros, let's head about 5 degrees east-southeast of Alpha and pick up another Herschel 400 study object - NGC 2506. On a dark night, this is perhaps one of the most impressive of the Monoceros open clusters. Caught in a chain of stars, it displays a rich concentration, so it has been used to study old, metal poor galactic clusters. Its evolution has enriched its iron content, and despite its extreme age - it is still a beauty!

Take the time tonight to have a look at Delta Monocerotis with binoculars. Although it is not a difficult double star, it is faint enough to require some optical aid. If you are using a telescope, hop to Epsilon. It's a lovely yellow and blue system that's perfect for small apertures.

Tonight our Moon is at apogee and bright Spica will accompany it as it rises. For many observers, this could be an occultation, so be sure to check IOTA information.

Thursday, March 8 - On this day in 1977, the NASA airborne occultation observatory made a unique discovery - Uranus had rings!

Tonight let's head towards the upside-down Y of the constellation of Canis Major and pick up some studies while dark skies are in our favor. Our first destination lies about three fingerwidths south of brilliant Sirius and is viewable with any optical aid - and even without under dark skies!

Messier object 41 was recorded as far back as Aristotle's time in 325 BC. Since it resides at a distance of around 2350 light-years - the light you see tonight in fact came from the time of Aristotle! Hosting around 100 true members of various magnitudes, this open cluster is very bright and totally resolved to larger telescopes. Its central star is a K-type red giant and many blue giants can also be seen.

For the large telescope, head north about another three degrees to spot NGC 2283. This small, faint spiral Galaxy has a bright nucleus and is very difficult to spot because it's involved with a small field of stars. Because Sirius is slightly more than a degree north, very good sky conditions are needed to spot this tough Herschel object!

Friday, March 9 - Today is also the anniversary of the Sputnik 9 launch in 1966 which carried a dog named Chernushka (Blackie). Also today we recognize the birth of David Fabricius. Born in 1564, Fabricus was the discoverer of the first variable star - Mira. Tonight let's start with an unusual variable star as we look at Beta Canis Majoris - better known as Murzim.

Located about three fingerwidths west-southwest of Sirius, Beta is a member of a group of stars known as quasi-Cepheids - stars which have very short term and small brightness changes. First noted in 1928, Beta changes no more than.03 in magnitude, and its spectral lines will widen in cycles longer than those of its pulsations.

When you've had a look at Beta, hop another fingerwidth west-southwest for open cluster NGC 2204. Chances are, this small collection of stars was discovered by Caroline Herschel in 1783, but it was added to William's list. This challenging object is a tough call for even large binoculars and small telescopes, since only around a handful of its dim members can be resolved. To the larger scope, a small round concentration can be seen, making this Herschel study one of the more challenging. While it might not seem like it's worth the trouble, this is one of the oldest of galactic clusters residing in the Halo and has been a study for 'blue straggler' stars.

Saturday, March 10 - Since this is a weekend night, why not break out the big telescope and do a little Galaxy hopping in the region south of Beta Canis Majoris.

Our first mark will be NGC 2207 - a 12.3 magnitude pair of interacting galaxies. Located some 114 million light-years away, this pair is locked in a gravitational tug of war. The larger of the pair is NGC 2207, and it is estimated the encounter began with the Milky Way-sized IC 2163 about 40 million years ago. Like the M81 and M82 pair, NGC 2207 will cannibalize the smaller Galaxy - yet the true space between the stars is so far apart that actual collisions may never occur. While our eyes may never see as grandly as a photograph, a mid-sized telescope will make out the signature of two galactic cores with intertwining material. Enjoy this great pair!

Now shift further southeast for NGC 2223. Slightly fainter and smaller than the previous pair, this round, low surface brightness Galaxy shows a slightly brighter nucleus area and a small star caught on its southern edge. While it seems a bit more boring, it did have a supernova event as recently as 1993!

Sunday, March 11 - If you're up before dawn this morning, be sure to have a look at the Moon. Beautiful, red Antares is less than a degree away and this could be an occultation event in your area! Today is also the birthday of Urbain Leverrier. Born in 1811, Leverrier predicted the existence of Neptune, leading to its discovery. While you're waiting for the occultation you can have a look at the lunar feature named for him. No feature on the Moon will be more prominent than the 'C' of Sinus Iridium, and just outside in Mare Imbrium even small Telescopes can resolve Helicon to the north and Leverrier to the southeast.

Tonight let's return to Canis Major with binoculars and have a look at Omicron 1, the western-most star in the central Omicron pair. While this bright, colorful gathering of stars is not a true cluster, it is certainly an interesting group.

For larger binoculars and telescopes, hop on to Tau northeast of Delta and the open cluster NGC 2362. At a distance of about 4600 light-years, this rich little cluster contains about 40 members and is one of the youngest of all known star clusters. Many of the stars you can resolve have not even reached main sequence yet! Still gathering themselves together, it is estimated this stellar collection is less than a million years old. Its central star, Tau, is believed to be a true cluster member and one of the most luminous stars known. Put as much magnification on this one as skies will allow - it's a beauty!




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