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ries a year鈥攏ot a huge payoff for hundreds of nights of peering andpeering。 once he found three in fifteen days； but another time he went three years withoutfinding any at all。
鈥渢here is actually a certain value in not finding anything；鈥潯e said。 鈥渋t helps cosmologists towork out the rate at which galaxies are evolving。 it鈥檚 one of those rare areas where theabsence of evidenceis evidence。鈥�
on a table beside the telescope were stacks of photos and papers relevant to his pursuits；and he showed me some of them now。 if you have ever looked through popular astronomicalpublications； and at some time you must have； you will know that they are generally full ofrichly luminous color photos of distant nebulae and the like鈥攆airy…lit clouds of celestial lightof the most delicate and moving splendor。 evans鈥檚 working images are nothing like that。 theyare just blurry black…and…white photos with little points of haloed brightness。 one he showedme depicted a swarm of stars with a trifling flare that i had to put close to my face to see。
this； evans told me； was a star in a constellation called fornax from a galaxy known toastronomy as ngc1365。 （ngc stands for new general catalogue； where these things arerecorded。 once it was a heavy book on someone鈥檚 desk in dublin； today； needless to say； it鈥檚a database。） for sixty million silent years； the light from the star鈥檚 spectacular demise traveledunceasingly through space until one night in august of 2001 it arrived at earth in the form ofa puff of radiance； the tiniest brightening； in the night sky。 it was of course robert evans onhis eucalypt…scented hillside who spotted it。
鈥渢here鈥檚 something satisfying； i think；鈥潯vans said； 鈥渁bout the idea of light traveling formillions of years through space and just at the right moment as it reaches earth someonelooks at the right bit of sky and sees it。 it just seems right that an event of that magnitudeshould be witnessed。鈥�
supernovae do much more than simply impart a sense of wonder。 they e in severaltypes （one of them discovered by evans） and of these one in particular； known as a iasupernova； is important to astronomy because it always explodes in the same way； with thesame critical mass。 for this reason it can be used as a standard candle to measure theexpansion rate of the universe。
in 1987 saul perlmutter at the lawrence berkeley lab in california； needing more iasupernovae than visual sightings were providing； set out to find a more systematic method ofsearching for them。 perlmutter devised a nifty system using sophisticated puters andcharge…coupled devices鈥攊n essence； really good digital cameras。 it automated supernovahunting。 telescopes could now take thousands of pictures and let a puter detect thetelltale bright spots that marked a supernova explosion。 in five years； with the new technique；perlmutter and his colleagues at berkeley found forty…two supernovae。 now even amateursare finding supernovae with charge…coupled devices。 鈥渨ith ccds you can aim a telescope atthe sky and go watch television；鈥潯vans said with a touch of dismay。 鈥渋t took all the romanceout of it。鈥�
i asked him if he was tempted to adopt the new technology。 鈥渙h； no；鈥潯e said； 鈥渋 enjoy myway too much。 besides鈥濃�攈e gave a nod at the photo of his latest supernova and smiled鈥斺�渋can still beat them sometimes。鈥�
the question that naturally occurs is 鈥渨hat would it be like if a star exploded nearby？鈥潯urnearest stellar neighbor； as we have seen； is alpha centauri； 4。3 light…years away。 i hadimagined that if there were an explosion there we would have 4。3 years to watch the light ofthis magnificent event spreading across the sky； as if tipped from a giant can。 what would itbe like if we had four years and four months to watch an inescapable doom advancing towardus； knowing that when it finally arrived it would blow the skin right off our bones？ wouldpeople still go to work？ would farmers plant crops？ would anyone deliver them to the stores？
weeks later； back in the town in new hampshire where i live； i put these questions to johnthorstensen； an astronomer at dartmouth college。 鈥渙h no；鈥潯e said； laughing。 鈥渢he news ofsuch an event travels out at the speed of light； but so does the destructiveness； so you鈥檇 learnabout it and die from it in the same instant。 but don鈥檛 worry because it鈥檚 not going to happen。鈥�
for the blast of a supernova explosion to kill you； he explained； you would have to be鈥渞idiculously close鈥濃�攑robably within ten light…years or so。 鈥渢he danger would be varioustypes of radiation鈥攃osmic rays and so on。鈥潯hese would produce fabulous auroras；shimmering curtains of spooky light that would fill the whole sky。 this would not be a goodthing。 anything potent enough to put on such a show could well blow away themagnetosphere； the magnetic zone high above the earth that normally protects us fromultraviolet rays and other cosmic assaults。 without the magnetosphere anyone unfortunateenough to step into sunlight would pretty quickly take on the appearance of； let us say； anovercooked pizza。
the reason we can be reasonably confident that such an event won鈥檛 happen in our cornerof the galaxy； thorstensen said； is that it takes a particular kind of star to make a supernova inthe first place。 a candidate star must be ten to twenty times as massive as our own sun and鈥渨e don鈥檛 have anything of the requisite size that鈥檚 that close。 the universe is a mercifully bigplace。鈥潯he nearest likely candidate he added； is betelgeuse； whose various sputterings havefor years suggested that something interestingly unstable is going on there。 but betelgeuse isfifty thousand light…years away。
only half a dozen times in recorded history have supernovae been close enough to bevisible to the naked eye。 one was a blast in 1054 that created the crab nebula。 another； in1604； made a star bright enough to be seen during the day for over three weeks。 the mostrecent was in 1987； when a supernova flared in a zone of the cosmos known as the largemagellanic cloud； but that was only barely visible and only in the southern hemisphere鈥攁ndit was a fortably safe 169；000 light…years away。
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