Venus, like all the stars and all the other planets, can usually be seen only at night. In the daytime, the sun’s brilliance makes them invisible. A spectacular exception will occur on Tuesday, June 8, when the sun, Venus and Earth will form points along a straight line. Venus will cross in front of the sun, looking about like a black fly crawling across an orange.

The phenomenon is a rare opportunity. No one alive saw it the last time it happened, in 1882. But it also presents a dangerous hazard. If you look directly at the sun, even through ordinary dark glasses, you could seriously damage your eyes.

The transit, as it is called, will take about seven hours, but here in Maine, much of that time will be before sunup. Neil Comins, professor of astronomy at the University of Maine, says that people around here can see it – assuming no clouds are in the way – from sunrise at 4:50 a.m. until the transit ends at 7:25 a.m.

Professor Comins emphasizes the warning against looking straight at the sun without special protective glasses, which aren’t available here. He got his from a Texas company, Rainbow Symphony Inc. They are called Eclipse Shades. They sell for $1 apiece but the minimum order is 10.

A cheaper way to see the transit is to make a pinhole camera. Take a long box, cut a hole in one end and paste a piece of aluminum foil over it. Make a pinhole in the foil. Paste a white sheet of paper inside the other end. Leave one side of the box open so you can see the yellow sphere with the little round black dot crawling across it. The image of Venus will be 1/32 of the sun’s diameter. The longer the box, the bigger the image will be.

If you miss this rare sight, you will get another chance in eight years, just before sunset on June 6, 2012. If you miss that one, tough luck. The next transit will be on Dec. 11, 2117.