The wait is finally over. Scientists are watching a rare Mercury transit of the sun on Monday. The tiny planet’s passage across the sun’s face has got astronomers and skywatchers excited alike. It should provide crucial data about Mercury’s thin atmosphere. From the Earth’s perspective, the rocky planet crosses the disc of the sun just 13 times per century.

Mercury Transit Of Sun An Event Scientists Have Been Waiting For

Only 13 times in a century

The last Mercury transit occurred in 2006, and the next one will take place in 2019. Planetary geoscientist David Rothery told Space.com that currently the transits occur in either May or November, with spring transits taking place only about a third of the time. It changes over the course of hundreds of years, though. Mercury is closer to Earth during the May transit, so it appears bigger than in November, Rothery said. It allows astronomers to make more precise measurements in May.

Monday’s 7.5-hour transit gives researchers an opportunity to use the New Solar Telescope to catch a glimpse of sodium in Mercury’s thin atmosphere. The sunlight will illuminate the atmosphere when the planet crosses in front of the sun. NASA is using its Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory(SDO) to study the event.

How to watch the Mercury transit

Mercury should appear black while crossing in front of the sun. But it appears illuminated due to scattered light from scientific instruments. You can watch the event first-hand through a telescope if you have the proper solar filters. You shouldn’t look directly at the sun without adequate protective equipment as it may damage your eyes or even cause blindness. If you don’t have the necessary equipment, there are other ways to watch it.

NASA is broadcasting near-live images of the Mercury transit from the Solar Dynamics Observatory (SDO). The Slooh Community Observatory has also hosted a free, live webcast of the event. You can also watch it live on Space.com. Don’t miss it.