Obama takes super-delegate lead

Democratic presidential candidate Barack Obama has overtaken his rival Hillary Clinton for the first time in endorsements from super-delegates.

Four super-delegates - party and elected officials - pledged to support Mr Obama, including two who previously supported Mrs Clinton.

Mr Obama also has a strong lead in delegates won in state primary and caucus votes.

The Democratic super-delegates look set to decide who wins the nomination.

Added to the nine who came out in support of Barack Obama on Friday, he now has 275 super-delegates to Mrs Clinton's 271.

'Likely nominee'

Mr Obama won a convincing victory in Tuesday's North Carolina primary; while Mrs Clinton narrowly won in Indiana.

Six more states hold primaries before the Democratic Party officially declares at its nominating convention in August who will take on presumptive Republican candidate John McCain.

The nearly 800 super-delegates automatically attend the Denver convention and can vote for whomever they choose.

Mrs Clinton held a massive lead in super-delegate support before the party's first primary in Iowa in January.

But a string of wins for Mr Obama has convinced many of them to come out in his favour.

Unity stressed

On Friday, former Democratic US presidential hopeful John Edwards said that Mr Obama is now the party's "likely presidential nominee".

But he stopped short of actually endorsing Mr Obama.

With fears mounting that the long, indecisive campaign may be fatally dividing the party, both candidates have been careful to say that they will work to unify Democrats before November's election.

"I want to go into the general election... with the party unified and ready to take on what I think is a wrong-headed vision of where the country should go," said Mr Obama from Bend, Oregon.

Although Mrs Clinton has said the nominating race is not over, she also said Democrats would come together against the Republicans no matter who wins.

"What I hear and what I see is all about how we're going to finish this nominating contest which we will do," she said at a New York fund-raiser.

"Then we will have a nominee, and we will have a unified democratic party, and we will stand together and we will defeat John McCain in November and go on to the White House."

Mrs Clinton is favoured to win the next primary in West Virginia on Tuesday. Then Oregon and Kentucky vote on 20 May.

All About Supernovas

A supernova is essentially the explosion of a star in outer space. During a supernova occurrence, a star’s luminosity is increased by as much 20 times as the bulk of the star’s mass is blown away at an extremely high velocity. Supernova remnants, including the signature bright light they leave behind, can often be seen in the night sky by the naked eye for several weeks as it gradually diminishes.

There are several different kinds of supernovae, which are believed to be caused by two distinct sources. One possible cause for Supernova occurrences results from a star halting its generation of fusion energy from fusing the nuclei of atoms in its core, causing it to collapse under the force of its own gravity. Another possible source occurs when a white dwarf star accumulates material from another nearby star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, ultimately leading to its destruction.

Supernovas are generally classified according to the lines of different chemical elements that appear in their spectra, the first of which is hydrogen. If a supernova's spectrum contains a hydrogen line, it is classified as Type II, if this line of hydrogen is not present the Supernova is Type I. Within the Type I and Type II classifications are five sub-classifications that include Type Ia, Type Ib, Type Ic, Type II-P and Type II-L, each having its own distinct chemical and physical characteristics.

Latest Sun Flare Put at X28, Strongest on Record

NOAA's Space Environment Center (SEC) has classified this flare as an X28, making it in fact the strongest ever recorded. A source told SPACE.com that the SEC is aware other scientists still think the flare was even stronger. The article below remains as it originally appeared. - RRB

A flare released by the Sun on Tuesday could be the most powerful ever witnessed, a monster X-ray eruption twice as strong as anything detected since satellites were capable of spotting them starting in the mid-1970s

The strongest flares on record, in 1989 and 2001, were rated at X20. This one is at least that powerful, scientists say. But because it saturated the X-ray detector aboard NOAA's GOES satellite that monitors the Sun, a full analysis has not been done.

The satellite was blinded for 11 minutes.

Craig DeForest, a solar physicist at the Southwest Research Institute, said others in his field are discussing the possibility that Tuesday's flare was an X40.

"I'd take a stand and say it appears to be about X40 based on extrapolation of the X-ray flux into the saturated period," DeForest told SPACE.com.

That estimate may even be conservative, he said.

The flare leapt from a sunspot that is rotating off the visible face of the Sun, so its effects were not directed squarely at Earth. Nonetheless, a radio blackout occurred at many wavelengths as the storm's initial radiation arrived just minutes after the eruption. Radio blackouts are ranked from R1 to R5 by NOAA's Space Environment Center, the space counterpart to the National Weather Service.

"This is an R-5 extreme event," said SEC forecaster Bill Murtagh. "They don't get much bigger than this."

Paal Brekke, deputy project scientist for the SOHO spacecraft, which monitors the Sun, also told SPACE.com the outburst could be as strong as X20 "or much higher."

At least X20

The SEC is still evaluating the flare's ranking. For now, they are calling it an X20+, indicating that it is indeed the most powerful on record. The only known event that might outrank it is an 1859 solar storm that zapped telegraph lines in an era when solar monitoring could not provide an evaluation of a flare's strength.

The radiation flare was accompanied by a coronal mass ejection (CME), an expanding cloud of charged particles -- actual matter that moves at supersonic speeds but not as fast as light. Had this CME been aimed at Earth, scientists would have feared a potential space storm unlike anything seen in the Space Age.

As it is, the expanding cloud is expected to provide a glancing blow sometime Thursday.

The storm, if it arrives, will not likely be major, forecasters say. But as with all space weather, satellites and communication systems will be at risk of disruption or damage. Colorful sky lights called auroras may be active at high latitudes and possibly into northern U.S. states and Europe.

More to come?

Tuesday's flare was generated by Sunspot 486, which is about 15 times the size of Earth.

Sunspots are dark, cooler regions of the solar surface, areas of pent-up magnetic activity. They're a bit like caps on a shaken soda bottle, and upwelling matter and energy can blow at any moment. Scientists cannot predict when a flare will occur.

During the past two weeks, number 486 and two other large sunspots set off nine other major flares. It was one of the stormiest periods of activity ever witnessed, all experts agree. The number of intense flares, some shooting out within a day of another, was unprecedented. Auroras were seen as far south as Texas and Florida.

The second strongest flare in this historic two-week series was an X17 event on Oct. 28. It was aimed at Earth and generated severe geomagnetic storming when it blew past the planet less than 24 hours later.

A period of relative calm is now expected on the solar surface. But another round is possible.

The Sun spins once on its axis once every 25 days at its equator, carrying sunspots around. Sunspots can last days or weeks. Any of the three that have rotated off the right side of the Sun could return in about two weeks on the left side and, possibly, send more major storms toward Earth.