Monday, 31 August 2009

Not all those who wander are lost (Camera Obscura)

Camera Obscura are a Scottish indie band currently signed up with legendary record label 4AD. Comparisons with compatriots Belle and Sebastian are probably tired and irrelevant by now. Cambell's husky voice and compelling lyrics tie the music together and create a fast paced, quasi-psychedelic reverb landscape that is rather quirky but all too pleasant.

Here is "If looks could Kill" from the album "Let's Get Out Of This Country".

Thursday, 27 August 2009

Mars as large as the Moon?

This popular urban legend is also known as Two Moons.

The brief answer is, no, Mars will not look as big as the Moon.

Every year astronomers, including the one writing this article, get this question; and every year we have to debunk it. People's memories are short while the orbit of Mars is pretty stable.

Apparently this strange hoax first surfaced on the Internet back in 2003. The relevant e-mail went something like this:

The Red Planet is about to be spectacular! This month and next, Earth is catching up with Mars in an encounter that will culminate in the closest approach between the two planets in recorded history. The next time Mars may come this close is in 2287. Due to the way Jupiter's gravity tugs on Mars and perturbs its orbit, astronomers can only be certain that Mars has not come this close to Earth in the Last 5,000 years, but it may be as long as 60,000 years before it happens again.

The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of -2.9 and will appear 25.11 arc seconds wide. At a modest 75-power magnification

Mars will look as large as the full moon to the naked eye. By the end of August when the two planets are closest, Mars will rise at nightfall and reach its highest point in the sky at 12:30 a.m. That's pretty convenient to see something that no human being has seen in recorded history. So, mark your calendar at the beginning of August to see Mars grow progressively brighter and brighter throughout the month. Share this with your children and grandchildren. NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN

Or the Greek version (which actually gives an incorrect year - the original doesn't):

Αυτό γίνεται μόνο μια φορά στην ζωή μας
Την 27η Αυγούστου 2009, 30 λεπτά μετά τα μεσάνυκτα, κοιτάξτε στον ουρανό.
Ο πλανήτης Άρης θα είναι πολύ λαμπερός μέσα στον ουρανό
Θα είναι το ίδιο μεγάλος όπως και το φεγγάρι παρόλο που ο πλανήτης Άρης θα είναι 34,65 εκατομμύρια μίλια μακριά από την Γή.
Προσπαθήστε λοιπόν να μην χάσετε αυτό το γεγονός
Θα το βλέπουμε με γυμνό μάτι σαν να και η γη έχει δύο φεγγάρια!
Η επόμενη φορά που θα λάβει χώρα αυτό το γεγονός θα είναι το έτος 2287.
Μοιραστείτε αυτή την πληροφορία με όλους τους φίλους σας γιατί κανένας ζωντανός δεν θα μπορέσει να το δει για δεύτερη φορά...

This is plainly wrong. Mars isn't going to be making a close approach on August 27. The close approach this e-mail is alluding to happened back in 2003. It did indeed get closer than it had in at least 50,000 years, but this was a very small amount. On August 27th, 2003, Mars closed to a distance of only 55,758,006 kilometers (34,646,418 miles). The Moon, by comparison, orbits the Earth at a distance of only 385,000 kilometers (240,000 miles). Mars was close, but it was still 144 times further away than the Moon. The Moon's diameter is 3474 kilometres (2159 miles), a little more than a quarter of that of the Earth while that of Mars is 6,800 km, about half that of the earth.

[Here is a little experiment you can do. Put an orange 114 meters away from you and a golf ball at your feet, lie down and look at them. Do they look about the same size?]

So what happened was this: Instead of appearing like a huge red orb in the sky, Mars looked like a bright red star. Amateur astronomers around the world set up their telescopes, and had a look at this close encounter. But you still needed a telescope and it really didn't look that much different. And everyone was happy; because if Mars did actually come close enough to rival the Moon, its gravity would alter the Earth's orbit and raise terrible tides.

See what NASA has to say about this hoax.

Sunday, 23 August 2009

What is a radio image?

One of the great discoveries of the Renaissance was the theory of perspective. At the core of the theory is the realisation that a picture is a map of the directions from which light is coming as seen from a particular viewpoint. So every point on the canvas corresponds to a particular direction in space. The hue at each spot represents in colour and intensity the light arriving from the corresponding direction.

Now, colour is the eye's way of describing the spectrum of light; for instance, the colour blue tells us that the light coming from that direction contains a range of wavelengths in the visible band but is relatively strong at around 450 nm. Colour is actually a rather inaccurate measure of the spectrum; for instance, it is hard to tell a mixture of red and blue light (i.e. purple) from the very deep blue (i.e. violet). For technical work astronomers prefer to obtain a series of monochrome images through the use of coloured filters, much like the ones used in ordinary photography, so that each is a record of light with wavelengths within a specific narow band.

The astronomical B, V and R bands correspond roughly to the three basic colours, blue, green and red.
Combining the images in the different filters then allows astronomers to reconstruct a "false-colour" image of the observed object.Our images are then abstracted a futher step: the intensity of white light from our print (or computer monitor) is telling us about the insnsity of the red light on the sky.

There is no reason to restrict the wavelengths used to the tiny range that the human eye can detect. Visible light is just a tiny segment of the electromagnetic spectrum and with the appropriate technology we can make images, maps of "light" in a more general sense, at wavelengths far outside this familiar band; You are probably already familiar with such "invisible" colours like X-rays, ultraviolet, infrared and radio. In fact, the range of colours used by radio-astronomers would correspond to about twenty new colours (or bands) if we say that there are three basic ones in visible light! Fortunately, just as with monochrome images, we can use ordinary visible gray-scales to display these images of "invisible" light.

These composite images show M84, a massive elliptical galaxy in the Virgo Cluster, about 55 million light years from Earth. Radio data from the Very Large Array is shown in red. A background image from the Sloan Digital Sky Survey is shown in yellow and white.
(Credit: Radio (NSF/NRAO/VLA/ESO/R.A.Laing et al); Optical (SDSS))

The leftmost image is in radio wavelengths, the middle one in optical and the rightmost a combination of the two.

Friday, 21 August 2009

The Origin of Zero

The number zero as we know it arrived in the West circa 1200, most famously delivered by Italian mathematician Fibonacci (aka Leonardo of Pisa), who brought it, along with the rest of the Arabic numerals, back from his travels to north Africa. But the history of zero, both as a concept and a number, stretches far deeper into history—so deep, in fact, that its provenance is difficult to nail down.

"There are at least two discoveries, or inventions, of zero," says Charles Seife, author of Zero: The Biography of a Dangerous Idea (Viking, 2000). "The one that we got the zero from came from the Fertile Crescent." It first came to be between 400 and 300 B.C. in Babylon, Seife says, before developing in India, wending its way through northern Africa and, in Fibonacci's hands, crossing into Europe via Italy.

Initially, zero functioned as a mere placeholder—a way to tell 1 from 10 from 100, to give an example using Arabic numerals. "That's not a full zero," Seife says. "A full zero is a number on its own; it's the average of –1 and 1."

It began to take shape as a number, rather than a punctuation mark between numbers, in India in the fifth century A.D., says Robert Kaplan, author of The Nothing That Is: A Natural History of Zero (Oxford University Press, 2000). "It isn't until then, and not even fully then, that zero gets full citizenship in the republic of numbers," Kaplan says. Some cultures were slow to accept the idea of zero, which for many carried darkly magical connotations.

The second appearance of zero occurred independently in the New World, in Mayan culture, likely in the first few centuries A.D. "That, I suppose, is the most striking example of the zero being devised wholly from scratch," Kaplan says.

Kaplan pinpoints an even earlier emergence of a placeholder zero, a pair of angled wedges used by the Sumerians to denote an empty number column some 4,000 to 5,000 years ago.

But Seife is not certain that even a placeholder zero was in use so early in history. "I'm not entirely convinced," he says, "but it just shows it's not a clear-cut answer." He notes that the history of zero is too nebulous to clearly identify a lone progenitor. "In all the references I've read, there's always kind of an assumption that zero is already there," Seife says. "They're delving into it a little bit and maybe explaining the properties of this number, but they never claim to say, 'This is a concept that I'm bringing forth.'"

Kaplan's exploration of zero's genesis turned up a similarly blurred web of discovery and improvement. "I think there's no question that one can't claim it had a single origin," Kaplan says. "Wherever you're going to get placeholder notation, it's inevitable that you're going to need some way to denote absence of a number."

This article is by John Matson and appeared in the Scientific American (August 21, 2009)

Thursday, 13 August 2009

Scientists Detect "Wrong-Way" Planet

The Planetary Society
Article By Amir Alexander
August 12, 2009

An international team of scientists has detected the first extrasolar planet orbiting in the "wrong" direction. This means that the planet, designated WASP-17, is circling its star in a direction opposite to the rotation of the star itself. Such a motion, known as a "retrograde orbit," is very unusual since the motions of both star and planet were acquired from the swirling cloud of gas and dust that formed them both. As a result, the planets orbiting the same star almost always move in the same direction, which is the same as the rotation of the star itself.

A retrograde orbit is almost certainly a legacy of a planet's violent past, most likely dating to the planetary system's early days. "Newly formed solar systems can be violent places" explained graduate student David Anderson of Keele University, who is a member of the team that made the discovery. "A near-collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit."

WASP-17 was first detected through the transit photometry technique by the Wide Area Search for Planets (WASP) consortium of British universities, using the WASP-South camera array in South Africa. But in order to detect its retrograde motion the WASP team needed an assist from planet hunters at the Geneva Observatory, who specialize in radial velocity measurements.

According to Darin Ragozzine of the Harvard-Smithsonian Center for Astrophysics astronomers can identify the direction of a planet's orbit because of slight discrepancies in the radial velocity data when a planet transits a star. Because a star is rotating, one side of it is moving towards (or away) from Earth faster than the other side. During a transit, the planet covers first one side of the star and then the other, causing a slight but measurable shift in the radial velocity readings. If during the transit the star first appears to be moving relatively slowly towards the Earth, but then faster as the transit progresses, then the planet is orbiting in the same direction as the star's rotation. But if the reverse is the case – as it is for WASP-17 – then the planet is in a retrograde orbit.

WASP-17 is located about 1000 light years from Earth, and is unusual not only because of the direction of its orbit but also because of its size and low density. Although its mass is only half that of Jupiter, its diameter is nearly twice that of our giant neighbor, which makes WASP-17 the largest known planet. The reason, according to Coel Hellier of Keele University, is related to the planet's unusual orbit. Retrograde motion coupled with a highly eccentric orbit subject the planet to intense tidal forces. Such tidal compression and stretching would have the effect of heating up the planet, causing it to expand to its current bloated dimensions. As a result, Hellier noted, the density of WASP-17 is only one seventieth (1/70) of the density of Earth.

Just as there are moons in retrograde orbits in our solar system, it stands to reason that there are also planets in retrograde orbits, and the discovery of WASP-17 did not therefore come as a complete surprise to planetary scientists. Nevertheless, this highly unusual planet does contribute to our understanding of the birth and life of planets, and adds one more member to the menagerie of strange and wonderful worlds astronomers are uncovering in the depths of space.

Monday, 3 August 2009

Sigur Ros - Glósóli

"Glósóli" (Icelandic for "Glowing Sole") is a song by Sigur Rós, released as part of their 2005 album Takk.

The name is a combination of gló- from the verb að glóa meaning "to glow, shine, glitter" and sóli meaning "sole." The second element of the name, sóli, shares its grammatical stem with the word "sól", meaning "sun". In combination "glósóli" can be understood as a childish way of saying "glowing sun".

The song is also praised for its artistic and highly cinematographic music video which consists of children dressed in old-fashioned Icelandic clothing, "migrating" towards an unknown destination.