But we're about to get a rare and spectacular view of the tiny world as it sails across the sun in an event known as a transit. The next one isn't until 2032, so this is the last chance to see the tiny dot of Mercury traversing the sun. Transits of Venus occur in pairs separated by 121.5 or 105.5 years, with eight years separating each transit; the next transit of Venus will occur in the year 2117. But the transit isn't just an awe-inspiring spectacle; it has scientific importance, too.
The transit of Mercury will be partly or fully visible across much of the globe.
Do not try to observe this event directly with your naked eye, or through exposed film negatives, smoked glass, mylar, or multiple sunglasses - they will pass infrared radiation which will damage your vision. The best and safest way to see transits is to project a solar image through telescopes or binoculars onto a flat white surface.
It'll be visible from Minnesota as the sun rises Monday, continuing through about noon.
Mercury's trek across the Sun begins at 4:35 a.m. PST (7:35 a.m. EST), meaning viewers on the East Coast of the USA can experience the entire event, as the Sun will have already risen before the transit begins. Pinhole projection or eclipse glasses will be inadequate. Kepler didn't survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury. Edmund Halley used a transit of Venus in 1761 and 1769 to determine the absolute distance to the sun. Unfortunately, our atmosphere and optical diffraction effects limited the accuracy of this method. Because the planet is so tiny and so close to the sun, it doesn't block the sun's light, as the moon does during an eclipse.
It happens only 13 times per century, and the next one isn't set to happen until 2049. But the transits of Mercury and Venus still provide scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets. Considering how rare these events really are, it's clear that our galaxy is teeming with planets.
Numerous thousands of exoplanets we've been finding around other stars were discovered when they transited the face of their suns, mostly by the Kepler spacecraft.