On Monday, May 9, 2016, people around the globe will be able to watch the transit of Mercury online – an astronomical event when Mercury passes between the Earth and the Sun.The transit of Mercury only happens around 13 times every 100 years. The last time it occurred was in 2006 and the next time will be in 2019. The May 9, 2016 Mercury transit will occur between about 7:12 a.m. and 2:42 p.m. EDT. Mercury will be at the mid-point of the Sun around 10:47 a.m.
Scientists will use the transit to study Mercury
NASA scientist Rosemary Killen and her colleagues plan to use the transit to study Mercury’s ultra-thin atmosphere or exosphere. The atoms in Mercury’s exosphere come from the surface of Mercury itself. They are blasted into space by solar radiation, solar wind bombardment and meteoroids. This gives Mercury a comet-like tail stretched out as long as 1.2 million miles. You cannot see this tail during the transit, however.
“When Mercury is in front of the sun, we can study the exosphere close to the planet. Sodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption we can learn about the density of gas there,” said Killen.