Today, in a rare treat for us, Mercury will pass directly in front of the Sun for a few hours. According to NASA, the event is called a transit, and for Mercury, they happen only about 13 times in a century. The event will last about five and a half hours, during which Mercury's path will take it right across the middle of the Sun's disk.
For observers in the Eastern US, the transit will begin after sunrise at 7:35 AM (5:25 PM IST), meaning you will be able to view the entire thing. For the central and western US, the transit begins before sunrise, but there's enough time left as the Sun climbs up the sky for you to catch a glimpse before Mercury makes its exit.
In Europe and western Asia, the transit will occur during sunset. For the Pacific Coast, it’s a sunset transit. Australia, the Maritime Continent, Southeast Asia, much of China and the Koreas will miss out on the event entirely.
Mercury transits occur 13 times per century, and the next one is slated for November 13, 2032. Mercury transits typically happen in May or November. That's mainly because of how Earth aligns with Mercury's orbit.
In 2004 and 2012, Earth was treated to some rather spectacular transits of Venus. Our second planet from the sun, which is much larger and closer, appeared more noticeably on the solar disk. The next transit of Venus isn't until 2117.
The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon. From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.