A Venus transit drew hundreds of viewers in Anchorage Tuesday, as the solar system's second-closest planet to the sun passed across its face in a once-in-a-lifetime celestial event.
The University of Alaska Anchorage opened the the third floor of its parking garage near the ConocoPhillips Integrated Science Building to viewers, converting the garage's first two floors to free parking for the day. Inside the science building, free shows at UAA's planetarium explained the event, which won't happen again until the year 2117.
In astronomical terms, a transit occurs when a planet passes between Earth and the sun -- casting its shadow on Earth.
Beginning shortly after 2 p.m., the black dot of Venus appeared in the upper-left quadrant of the sun. It then spent the afternoon and early evening slowly moving across the much larger star.
To viewers at UAA Tuesday, Venus looked tiny -- maybe a bit larger than the period at the end of this sentence. It took up only one-thirtieth of the sun's disc, but its slow dance once revealed to astronomers the size of the solar system.
In 1769 then-Lt. James Cook, an officer in the British Navy, shipped off to Tahiti to watch a Venus transit.
Cook was in the Southern Hemisphere, about as far away from his home port in England as it was possible to get and still be able to observe the Venus transit while London-based astronomers in Great Britain were observing it.
The separation between Tahiti and London gave Cook thousands of miles of parallax -- a difference in the apparent position of Venus based on the two viewpoints, much the same way a pencil shifts position if you hold it at arm's length then look at with your left or right eye closed.
That slight angle made Venus appear to shift position against the disk of the sun, and measuring it gave astronomers the true size of the solar system. For the first time it was clear that Earth was 93 million miles from the sun -- and that the solar system was 50 percent larger than previous estimates had indicated.
In Alaska, Cook may be famous for naming Turnagain Arm and for having Cook Inlet named after him. But though he was a voyager of the sea, he helped give everyone on the planet earth a truer perspective of their place in the solar system.
Tuesday's intrepid astronomers, who turned out at UAA, were following in Cook's footsteps.
Astronomers say the transit will remain visible until 8:47 p.m., but NASA advises people to NOT stare at the sun because Venus will only cover a part of the solar disc. It suggests people use a type of solar filter or No. 14 welder’s glasses.
NASA also notes that your sunglasses do not have sufficient protection from the blinding glare.
If you take photos of the transit of Venus from Alaska, email us at firstname.lastname@example.org.
Email Dan Fiorucci