Stunning Time-lapse of Lasers at the Mauna Kea Observatories in Hawaii

Sean Goebel, a grad­u­ate stu­dent in astron­o­my at the Uni­ver­si­ty of Hawaii, has made this beau­ti­ful and fas­ci­nat­ing time-lapse film of the obser­va­to­ries on Mau­na Kea shoot­ing laser beams into the night sky over the Big Island of Hawaii.

The lasers are part of the obser­va­to­ries’ adap­tive optics sys­tems, which com­pen­sate for dis­tor­tions in light trav­el­ing through the Earth­’s atmos­phere. “Just as waves of heat com­ing off pave­ment blur out the detail of far­away objects,” explains Goebel on his Web site, “winds in the atmos­phere blur out fine detail in the stars/galaxies/whatever is being observed. This is the rea­son that stars twin­kle. The laser is used to track this atmos­pher­ic tur­bu­lence, and one of the mir­rors in the tele­scope bends hun­dreds of times per sec­ond in order to can­cel out the blur­ring.”

Adap­tive optics make use of a guide star in the area of the sky near the object being observed. As light arriv­ing from the guide star shifts, elec­tron­ic cir­cuits in the sys­tem auto­mat­i­cal­ly com­pute the minute adjust­ments to the deformable tele­scope mir­ror that are need­ed to can­cel out the dis­tor­tion.

There are, how­ev­er, places in the sky where a nat­ur­al guide star does­n’t exist close enough to the object astronomers want to observe. To solve this prob­lem, the sci­en­tists cre­ate arti­fi­cial guide stars using laser beams. For exam­ple, sev­er­al of the obser­va­to­ries on Mau­na Kea shine sodi­um laser beams into the upper atmos­phere, where they inter­act with a nat­u­ral­ly occur­ring lay­er of sodi­um atoms. The excit­ed atoms give off light, cre­at­ing a point source for the adap­tive optics sys­tem to focus on. The pow­er­ful lasers must be used very care­ful­ly, says Goebel:

A typ­i­cal laser point­er that you might use to point at stuff/exercise your cat is about 5 mW. That’s five one-thou­sandths of a watt. Not a whole lot of pow­er. And yet it’s enough to blind air­plane pilots. The lasers on the tele­scopes are in the range of 15–40 watts. The FAA calls a no-fly zone over the area when a laser is in use, and two peo­ple have to stand around out­side in the freez­ing tem­per­a­tures and watch for air­planes. Each of them has a kill switch to turn off the laser in case an air­plane comes near. Addi­tion­al­ly, the tele­scope has to send its tar­get list to Space Com­mand ahead of time. Space Com­mand then tells them not to use the laser at spe­cif­ic times, osten­si­bly to avoid blind­ing spy satel­lites. How­ev­er, you could cal­cu­late the spy satel­lite orbits if you knew where they were at spe­cif­ic times, so Space Com­mand also tells the tele­scope to not use the laser at ran­dom times when no satel­lites are over­head.

Goebel cap­tured the images for his time-lapse mon­tage over a peri­od of sev­en nights this past spring and sum­mer. Con­di­tions atop Mau­na Kea, which ris­es to an alti­tude of over 13,000 feet above sea lev­el, pre­sent­ed a chal­lenge. Goebel had to con­tend with high winds, freez­ing tem­per­a­tures and low oxy­gen. “Essen­tial­ly every­one suf­fers from alti­tude sick­ness” on Mau­na Kea, he says. “It’s not uncom­mon for tourists to step out of their vehi­cles and imme­di­ate­ly pass out. Going from sea lev­el to 14,000 feet in the span of a cou­ple of hours will do that to you.”

For more on Goebel and his work, includ­ing tech­ni­cal spec­i­fi­ca­tions and exam­ples of oth­er work, vis­it his Web site.

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