Friday, 8 November 2013

Who Is the Best Scientist of All Time?

An online ranking that compares the performance of academics across all fields found that Karl Marx is the most influential scholar and Edward Witten is the most influential scientist Is theoretical physicist Ed Witten more influential in his field than the biologist Solomon Snyder is among life scientists? And how do their records of scholarly impact measure up against those of past greats such as Karl Marx among historians and economists, or Sigmund Freud among psychologists? Performance metrics based on values such as citation rates are heavily biased by field, so most measurement experts shy away from interdisciplinary comparisons. The average biochemist, for example, will always score more highly than the average mathematician, because biochemistry attracts more citations.

But researchers at IUB (Indiana University Bloomington) think that they have worked out the best way of correcting this disciplinary bias. And they are publishing their scores online, for the first time letting academics compare rankings across all fields.Their provisional (and constantly updated) ranking of nearly 35,000 researchers relies on queries made through Google Scholar to normalize the popular metric known as the h-index (a scientist with an h-index of 20 has published at least 20 papers with at least 20 citations each, so the measure takes into account quantity and popularity of research). It found that as of 5 November, the most influential scholar was Karl Marx in history, ahead of Sigmund Freud in psychology. Number three was Edward Witten, a physicist at the Institute for Advanced Study in Princeton, New Jersey. The ranking appears on the website Scholarometer, developed by Filippo Menczer, an informatician at Indiana University Bloomington, and his colleagues Jasleen Kaur and Filippo Radicchi.Universal metrics “We think there is a hunger for this. Our colleagues use Google Scholar all the time, and yet it only shows the h-index," says Menczer. "We are constantly asking ‘how do we evaluate people in a discipline we don’t understand?’”

In October, Menczer's team published a paper arguing that the best statistical way to remove disciplinary bias is to divide a researcher’s h-index by the average of their scholarly field. Using this correction, Marx scores more than 22 times the average h-index of other scholars in history (but 11 times that of the average economist). Witten has more than 13 times the average physicist, and so on. The effect is to ensure that those in, say, the top 5% of their discipline also appear in the top 5% of all scholars. The idea is not new. Metrics experts have invented numerous methods to solve bias, often using averages based on age, journal and scholarly field. Normalized measures are available from commercial information firms such as Thomson Reuters.

First time for everything
But Scholarometer pushes boundaries in two ways. Most importantly, its normalized scores are freely accessible, unlike those of most sites. Thomson Reuters analyses are based on proprietary databases and cannot be made public. Another site, Publish or Perish, does return a variety of age and field-normalized metrics from public queries to Google Scholar — but only to one individual at a time. The problem is that Google Scholar blocks automated computer programs that hit it with multiple queries, making it impossible to collate scores.

The Indiana team’s solution is to create an automated program that does not query Google Scholar itself, but rather scrapes the results of individual Google Scholar queries placed through a Scholarometer browser extension. Over years, they have built up a dynamic public database, with h-indices constantly revised as new Google Scholar queries come in. Menczer says that an age-corrected h-index that allows comparison of scholars at different career stages may follow.

Karl Marx is the most influential scholar ever, according to a discipline-corrected ranking system
Original Article At

Sunday, 3 November 2013

Sunday's Solar Eclipse To Be Rare, Dramatic 'Hybrid' Event

A slice of eastern North America will undergo a weird and dramatic event early Sunday (Nov. 3) morning: a partial eclipse of the sun.

For most North American observers, the partial eclipse will coincide with sunrise. But within a very narrow corridor that extends for 8,345 miles (13,430 kilometers) across the planet, the disks of the sun and the moon will appear to exactly coincide, providing an example of the most unusual type of eclipse: a "hybrid" or "annular-total eclipse."

During annular solar eclipse, the sun looks like a "ring of fire," while the moon and sun line up perfectly during a total eclipse. Throughout a hybrid eclipse, however, the celestial sight transitions from annular to total.This overview map of the Nov. 3, 2013 annular and total solar eclipse, a hybrid solar eclipse, shows the path of the event. Cartographer Michael Zeiler of created this map.

If you don't have a chance to see the eclipse from your part of the world, you can watch the cosmic rarity live on courtesy of the online community observatory The eclipse event begins at 6:45 a.m. EST (1515 GMT) and will run throughout the entirety of the eclipse.A Rare Occurrence

During the 21st century approximately 4.9 percent of all central solar eclipses — those eclipses where the moon crosses directly in front of the disk of the sun — fall into the hybrid classification.

In most cases, an annular-total eclipse starts as an annular, or "ring of fire" eclipse, because the tip of the moon's dark shadow cone — the umbra — falls just short of making contact with the Earth; so the moon appears slightly smaller than the sun producing the same effect as placing a penny atop a nickel leaving a ring of sunlight shining around the moon's edge.

Then the solar eclipse transitions to total, because the roundness of the Earth reaches up and intercepts the shadow tip near the middle of the path, then finally it reverts back to annular toward the end of the path.

However, as pointed out by the renowned Belgian eclipse calculator, Jean Meeus, the hybrid eclipse of Nov. 3 will be a special case: here the eclipse starts out as annular, then after only 15-seconds it will transition to a total eclipse, and then it remains total up to the very end of the eclipse path. The last time this happened was on Nov. 20, 1854 and the next such case after 2013 will occur on Oct. 17, 2172.

Diamond necklace, then totality

At the very beginning of this eclipse track, the tip of the umbra is literally scratching at the surface of the Earth; sitting on the borderline between annular and total it is, for all intents and purposes, a total eclipse with zero duration or ever-so-slightly more after the first 15-seconds of its interaction with our planet. And yet, whether the umbra touches the Earth's surface at the very beginning of the eclipse track – or barely misses — is somewhat irrelevant. Because the silhouette of the moon is not a perfect circle, but rather slightly prickly with mountains, so just before the transition from annular to total, the eclipse will become something neither annular nor total: for a few precious seconds it will be a broken annular.

As lunar mountains protrude onto the hairline-thin ring of the sun, it will be seen not as an unbroken ring but an irregular, changing, sparkling sequence of arcs, beads and diamonds very briefly encircling the moon: a "diamond necklace" effect!

One might witness this highly unusual sight from a particular spot in the Atlantic Ocean — probably measuring less than a mile or two in width — some 405 miles (650 km) southwest of Bermuda. At least one group of ardent eclipse watchers from Germany hope to fly above any possible ocean cloudiness to experience this event.

Sweeping rapidly southeast, the eclipse will rapidly transition to a total eclipse; the totality path will slowly widen and the duration of totality will gradually increase, although the shadow will remain out over open ocean water for 165 minutes before finally making its first landfall at Gabon. Along the way, the point of greatest eclipse is reached at 12:46:28 UT over the tropical eastern Atlantic, at a point 204 miles (328 km) southwest of Monrovia, Liberia. At maximum at mid-path, totality lasts 1 minute 39.6 seconds and the path is 36 miles (57.5 km) wide. The umbra's first landfall comes at 13:50:21 UT at the remote Wonga-Wongue Presidential Reserve, a tract of rain forest on the coast of the central African nation of Gabon. Here, on the center line, the total eclipse will last 1 min 08 sec, with the sun standing 47 degrees high in the southwest sky.

During the next 37 minutes, the path continues out across equatorial Africa as its width and central duration again dwindle. Sliding east-northeast, it will cut through six more African nations. The first two are The Congo and the Democratic Republic of the Congo (known between 1971 and 1997 as the Republic of Zaire).

The path then cuts across a small slice of sparsely populated northern Uganda and northern Kenya and as it is nearing its end, crosses over into southern Ethiopia. Finally, just before the umbra leaves the Earth at sunset over west-central Somalia at 14:27 UT, an exceedingly short total phase predicted to last for less than a second! As was the case at the sunrise part of the path three hours and 22 minutes earlier, fortuitous observers who might have access to a clear horizon toward the west-southwest might witness the setting sun again taking on the appearance of "a diamond tiara."

Detail on the Partial Eclipse

As was noted earlier, only a slice of eastern North America will see a partial solar eclipse, while most of the rest of the continent will see nothing of this event. If you have an atlas, draw a line starting from a point at Sudbury, Ontario south to Port St. Joe, Florida. All places to the left (or west) of this line will not have any view of the eclipse. Meanwhile, those localities to the right (or east) of the line will be able to see at least a part of this eclipse at sunrise, although for those places in the immediate vicinity of this line, the moon's "bite" out of the lower edge of the sun will be tantalizingly small.

For example, while the eclipse will not be visible from Detroit, only about 100 miles to the southeast at Cleveland, the edge of the moon's dark silhouette will be evident on the sun's lower limb as it rises above the east-southeast horizon at 7 a.m. EST (1100 GMT); the moon will obscure only about 15 percent of the sun's diameter, or just about 7 percent of the total disk area of the sun. The "eclipse" -- if we can charitably call it that – will come to an end just nine minutes later.As one heads farther east, the eclipse will last longer and this slight dent will evolve into a more noticeable scallop out of the sun's lower rim. From Pittsburgh, the eclipse will last 29 minutes from the time of local sunrise (6:51 a.m. EST), with about 29 percent of the sun's diameter darkened when it first emerges from above the horizon.

From New England, Sunday's eclipse will mark the end of a nearly 13-year long solar eclipse drought; the last time a solar eclipse was visible from this part of the U.S. was on Christmas Day in the year 2000. From Boston, weather permitting, a most unusual sunrise will occur at 6:22 a.m. EST, with nearly 63 percent of the sun's diameter hidden behind the moon; the sun's lower right portion will be covered. Fifty two minutes later, the last trace of the moon will disappear at the bottom of the solar disk.

From Hamilton, Bermuda, nearly 90 percent of the sun's diameter will be eclipsed, maximum eclipse coming at 7:07 a.m. AST. San Juan, Puerto Rico will see 69 percent coverage at 7:04 a.m. AST.

Full prediction details for many cities are available through NASA.

This information, courtesy of NASA astronomer, Fred Espenak, is given in Universal Time. The sun's altitude and azimuth, the eclipse magnitude (fraction of the sun's diameter occulted by the Moon), and obscuration (fraction of the sun's area occulted by the Moon) are all given for the instant of maximum eclipse.

Remember that Daylight Saving Time ends at 2 a.m. on Sunday morning! You must set your clocks back one hour to return to standard time. If you fail to do this, you'll be too early by one hour for viewing the eclipse.

A Google map shows the path of the eclipse and you can zoom into it and click at any location to see your local circumstances.

Be Careful!

Once again it needs repeating: to look at the sun without proper eye protection is dangerous.

If you live in the zone where it will be visible, no doubt early on Sunday morning the eclipse will top the local news, followed of course by the usual dire warnings to the public not to risk blindness by carelessly looking at it. This has given most people the idea that eclipses are dangerous. Not so. It's the sun that's dangerous — all the time. Ordinarily, we have no reason to gaze at it. An eclipse gives us a reason, but we shouldn't.