Today, Mercury will pass across the Sun and it can be seen around the world, except for Australia, most of Asia and Alaska, with weather permitting, binoculars or a telescope, and of course a sun filter.
Mercury is the smallest planet in our solar system, also it's the closest one to the sun. It occasionally crosses the Sun's bright disk and it can be seen from Earth. The last time this happened was in 2016, but it won't happen again until 2032, so we'll have to wait for 13 years for this event. Also, the transits of Mercury only happen about 13 times per century, so you shouldn't miss this magical event, of course by using the required safety equipment.
You'll see a tiny dark spot passing across the Sun's face, of course since Mercury is really small, you need binoculars or a telescope with a Sun filter.
The transit will start today at 7:35 a.m. EST, it'll take around 5.5 hours and it'll end at 1:04 p.m. EST. It means that people on the East Coast of the U.S.A can watch the entire transit since Sun will already rise before the transit begins. For the West Coast of the U.S.A, by the time the Sun rises, Mercury will have been transiting for 2 hours, but since it'll take around 5.5 hours to complete the transit, people in West Coast can witness the event too.
When Mercury transits the Sun, the brightness of the Sun lowers a little since Mercury blocks a tiny portion of the Sunlight.
However, you shouldn't look at the Sun directly since it can cause serious and permanent damage in your eyes.