गामा किरण विस्फोट के निशाने पर थी धरती

विभिन्न उपग्रहों और दुनिया भर की वेधशालाओं से प्राप्त आंकड़ों से संकेत मिला है किहमारी धरती इस वर्ष 19 मार्च 2009 को शक्तिशाली तारकीय विस्फोट के निशाने परथी। इस खगोलीय घटना को 'गामा किरण विस्फोट' के नाम से जाना जाता है। 'जीआरबी 080319बी' नामक नासा के स्विफ्ट उपग्रह ने इस विस्फोट का पता लगायाथा। इस उपग्रह के आंकड़ों से इस खगोलीय घटना की वास्तविक स्थिति की जानकारीभी मिली थी। समाचार एजेंसी 'शिन्हुआ' के मुताबिक इस घटना के अवलोकन सेखगोलविदें को गामा किरणों के फटने की जितने विस्तृत चित्र मिले उतने पहले कभी नहीं मिल पाए थे। जिस क्षणस्विफ्ट उपग्रह गामा किरण विस्फोट का चित्र भेज रहा था उसी क्षण नासा के पवन उपग्रह पर स्थित रूस केकोनस' यंत्र ने गामा किरणों के व्यापक ढांचे का विस्तृत ब्यौरा उपलब्ध कराया। ''पाई आफ द स्काई' नामकरोबोटिक ऑप्टिकल कैमरे ने गामा किरणों में विस्फोट का पहला दृश्य प्रकाश का चित्र लिया। इसके 15 सेकेंड बादविस्फोट की चमक इतनी बढ़ गई कि उसे काले आसमान में साफ देखा जा सकता था।

Brightest Star

The Peony nebula (reddish cloud around white circle) near the galactic centre is home to a star that rivals the stellar powerhouse Eta Carinae in brightness
(Image: NASA/JPL-Caltech/Potsdam Univ)

The star had been discovered previously in the Peony nebula near the galaxy's dusty centre is Milky Way's brightest star. But infrared observations taken from the ground and with NASA's Spitzer Space Telescope have pierced the dust to reveal just how bright the star is.

It boasts a wattage of about 3.2 million Suns. That is close to the output of Eta Carinae, the current record holder, which shines with the light of about 4.7 million Suns. However, measuring stellar brightness is not an exact science, and the stars may actually radiate similar amounts of light.

It's possible that the galaxy's brightest star has not even been discovered yet. Both Eta Carinae and the Peony nebula star are evolved blue giants known as "Wolf-Rayet" stars, which have masses of 100 to 200 Suns.The Peony nebula star lies about 26,000 light years away and Eta Carinae about 7500 light years away.

Journal reference: Astronomy & Astrophysics (forthcoming)

http://space.newscientist.com/article/dn14328-whos-the-brightest-star-of-all.html

Biggest Stars

The Pistol Star appears as the bright white dot in the center of the image shown left.

The largest star measured in solar diameters is either VV Cephei or VY Canis Majoris (right image)

"What's the Biggest Star in the Universe"? Generally students ask this question.

I may give an easy answer, the Universe is a big place, and there's no way we can possibly know what the biggest star is. That didn't go over so well.

However the question may be refined:- What's the biggest star that we know of ?

Pistol Star: The largest known star, in terms of mass and brightness is called the Pistol Star. It is believed to be 100 times as massive as our Sun, and 10,000,000 times as bright! In 1990, a star named the Pistol Star was known to lie at the center of the Pistol Nebula in the Milky Way Galaxy. Observations from the Hubble Space Telescope in 1997 confirmed the relationship between the star and the nebula.

Eta Carinae: One huge, famous star in our galaxy is the monster Eta Carinae, located approximately 7,500 light years away, and weighing in at 100 solar masses. It's 4 million times as bright as the Sun. Most stars blow with a solar wind, losing mass over time. But Eta Carinae is so large that it casts off 500 times the mass of the Earth every year. With so much mass lost, it's very difficult for astronomers to accurately measure where the star ends, and its stellar wind begins.

So the best answer astronomers have right now is that Eta Carinae's radius is 400 times the size of the Sun. Eta Carinae should explode pretty soon as one of the most spectacular supernovae humans have ever seen.

VY Canis Majoris: The largest known star is VY Canis Majoris; a red hypergiant star in the constellation Canis Major, located about 5,000 light-years from Earth. University of Minnesota professor Roberta Humphreys recently calculated its upper size at more than 2,100 times the size of the Sun. Placed in our Solar System, its surface would extend out past the orbit of Saturn. Light takes more than 8 hours to cross its circumference!

Some astronomers disagree, and think that VY Canis Majoris might be smaller; merely 600 times the size of the Sun, extending past the orbit of Mars.

That's the biggest star that we know of, but the Milky way probably has dozens of stars that are even larger, obscured by gas and dust so we can't see them.

But let's see if we can work out the original question, what's the biggest star in the Universe?

Obviously, it's impossible for us to actually find it - the Universe is a big place, and there's no way we can peer into every corner. The largest stars are the coolest. So even though Eta Carinae is the most luminous star we know of, it's extremely hot - 25,000 Kelvin - and so only a mere 400 solar radii.

The largest stars will be the cool supergiants. For example, VY Canis Majoris is only 3,500 Kelvin. A really big star would be even cooler. At 3,000 Kelvin, a cool supergiant would be 2,600 times the size of the Sun.

Whatsoever,

Lots of half-truths and old information are being recycled partly because people don't read the question. The largest star measured in solar diameters is either VV Cephei or VY Canis Majoris,

As the table below makes clear,

LIST OF THE LARGEST KNOWN STARS
Star name / solar diameter (Sun = 1)

1st VY Canis Majoris (Humphreys Model) 1800-2100
2nd VV Cephei 1600-1900
3rd V354 Cephei 1520
4th KW Sagitarii 1460
5th KY Cygni 1420
6th Mu Cephei (Herschel's "Garnet Star") 1420
7th V509 Cassiopeiae 910
8th V838 Monocerotis 800
9th V382 Carinae 747
10th Antares (Alpha Scorpii) 700
11th Betelgeuse (Alpha Orionis) 650

or 11th VY Canis Majoris (Massey-Levesque-Plez Model) 600

(in which case the rest are all one place higher)

Other candidates mentioned by other contributors are:

24th Eta Carinae 400
28th The Pistol Star 340
30th Deneb 220

Source(s):

http://uk.answers.yahoo.com/question/index?qid=20070709120433AAmaZHk

http://en.wikipedia.org/wiki/List_of_lar...
http://en.wikipedia.org/wiki/VY_Canis_Ma...

Phoenix Spacecraft Confirms Water on Mars

Scientists working on NASA's Phoenix Mars lander have confirmed that there is water ice on the Red Planet. But they still have not found any evidence of life on Mars.

Phoenix's telescoping arm scoops up soil samples

The Phoenix Mars Mission was launched a year ago to look for water and the complex organic molecules that could be signs that life once existed on Mars.

Water had already been identified from a distance, by the Mars-orbiting Odyssey spacecraft, and Phoenix had photographed what was presumed to be melting ice at the landing site.

Phoenix landed on Mars two months ago. It is equipped with a telescoping arm to enable it to scoop up soil samples so they can be analyzed by the spacecraft's onboard instruments.

Although Phoenix is apparently sitting on top of a layer of ice just a few centimeters below the surface, the clumpy quality of the Martian soil made it difficult to retrieve a sample.

Finally, though, on 30 June, 2008, Phoenix scientist William Boyton said they were able to analyze a soil sample and confirmed that it contained frozen water. "Finally it has been touched and tasted. That's one thing that hasn't been done before.

Scientists found more than just water, they are also finding nutrients - sodium, potassium, magnesium. However, they are yet to discover organic materials. Future Mars missions will determine whether life has ever existed on Mars. In the meantime, NASA has extended the Phoenix mission for another month, through the end of September.

Cassini ends one mission, begins another

Cassini is a cooperative project of NASA and the European and Italian space agencies. Cassini was launched Oct. 15, 1997, on a seven-year 2.2 billion-mile journey. The spacecraft entered Saturn's orbit June 30, 2004.

U.S. space agency's Cassini spacecraft is ending its first mission at Saturn and starting a two-year task to focus on Saturn's moons Titan and Enceladus.

Cassini completed its four-year primary mission on 30th June, 2008, beginning the extended mission. Among other things, Cassini revealed the Earth-like world of Saturn's moon Titan and showed the potential habitability of another moon, Enceladus.

These two worlds are primary targets in the two-year extended mission, dubbed the Cassini Equinox Mission. This time period also will allow for monitoring seasonal effects on Titan and Saturn, exploring new places within Saturn's magnetosphere, and observing the unique ring geometry of the Saturn equinox in August of 2009, when sunlight will pass directly through the plane of the rings.

NASA said data from Cassini's could lay the groundwork for possible future missions to Saturn, Titan or Enceladus.

"Plutoid" as a name for dwarf planets like Pluto

The International Astronomical Union has decided on the term "plutoid" as a name for dwarf planets like Pluto.

The name plutoid was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III and by the IAU Working Group for Planetary System Nomenclature (WGPSN), and approved by the IAU Executive Committee at its recent meeting in Oslo, according to a statement released on 11th June, 2008.

Here's the official new definition:

"Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit."

In short:

small round things beyond Neptune that orbit the sun and have lots of rocky neighbors.

The two known and named plutoids are Pluto and Eris. The organization expects more plutoids will be found.

The dwarf planet Ceres is not a plutoid as it is located in the asteroid belt between Mars and Jupiter, according to the IAU. Current scientific knowledge lends credence to the belief that Ceres is the only object of its kind, the IAU stated. Therefore, a separate category of Ceres-like dwarf planets will not be proposed at this time, the reasoning goes.

The term plutoid joins a host of other odd words -- plutinos, centaurs, cubewanos and EKOs -- that astronomers use to define objects in the outer solar system.