Watch Rare Transit of Mercury Live as Planet Passes in Front of the Sun

Today, a rare celestial event which only happens around 13 times a century will be visible in the sky as Mercury passes directly between the Earth and the sun in what astronomers call a "transit."

The transit will begin at 7:35 a.m. EDT (4:35 a.m. PST) and will last for about five-and-a-half hours, according to NASA. As Mercury—the smallest planet in the solar system and the closest to the sun—passes in front of our star, it will appear as a tiny black dot, blocking a small amount of sunlight.

The transit will be visible when the sun is in the sky—weather permitting of course—although you will need a telescope or binoculars because the planet is too small to see with the naked eye. However, you MUST use a certified solar filter when looking at the sun to avoid eye damage.

"WARNING! Looking at the Sun directly or through a telescope without proper protection can lead to serious and permanent vision damage. Do not look directly at the Sun without a certified solar filter," NASA said in a statement.

The transit will be visible across North America with viewers on the east coast able to watch the entire event. However, people living in western and central areas of the continent will miss the start. This is because the transit will already be in progress by the time the sun rises in these areas.

You will also be able to watch the entire event online with several organisations live-streaming the transit, including the Griffith Observatory in Los Angeles, The Virtual Telescope Project and Slooh.

NASA will also be sharing near-real-time images of the sun during the transit, captured by the Solar Dynamics Observatory.

Be sure to catch a glimpse of the transit if you can because another one won't be visible in the continental United States until the year 2049, according to NASA.

Prior to the year 1585, Mercury transits took place in the months of April and October. However, they have gradually shifted to later in the year over time. Now, they occur in either May or November.

Transits only take place in these two windows because the orbits of Mercury and Earth around the sun are slightly tilted relative to one another, only overlapping at two points, known as nodes, reported.

transit of mercury
The transit of Mercury on November 11, 2019, begins at 7:35 a.m. EST but it won’t be visible to West Coast viewers until after sunrise. Luckily, viewers will have several more hours to take in the stellar show, which lasts until 10:04 a.m. PST (1:04 p.m. EST). NASA/JPL-Caltech

These two nodes are located at points in Earth's orbit where transits could be possible in May or November. However, because the Earth and Mercury take different amounts of time to complete a full circle around the sun, we don't see transits every year.

For a transit to be possible, the Earth and Mercury both need to arrive at the nodes at precisely the same time. In May, Mercury is further away from the sun and closer to Earth, meaning it appears to be a fraction larger from our perspective during these transits compared to those which take place in November.

The only planets that we can see transiting from our perspective are Mercury and Venus because they are the only two that are within the Earth's own orbit. Transits of Venus are even rarer than those of Mercury, with the next one scheduled to take place in 2117.