A special event is currently underway in the skies, as the solar system's smallest planet of Mercury makes a rare, visible transit across the sun.

From 7:12 a.m. until approximately 2:45 p.m. ET, stargazers will be able to see Mercury as a small black dot silhouetted against the sun.

The reason why the event is rare comes down to gravity and elliptical orbits. A solar year lasts only 88 days for Mercury, but because the planet’s orbit is inclined several degrees differently from Earth, it's not every day that the sun, Mercury, and Earth line up perfectly.

In fact, says York University astronomy professor Paul Delaney, this is the first visible Mercury transit in almost a decade.

“This is a relatively rare event; it takes place only about 12 times a century,” he told CTV’s Canada AM Monday.

“There will be another one in 2019, but after that, here on Canadian soil, you won’t actually be able to observe one again until 2049.”

While the transit may not appear that exciting as just a black spot against the sun, Delaney says what’s mind-boggling is how fast the planet will be moving as it streaks past a sun that measures nearly 1.4 million kilometres across.

For astronomers, the event will allow them to learn a little bit more about Mercury, because even though stargazers have been watching Mercury and Venus transits for 400 years, there’s still much to learn.

“Strange as it might sound, we’re still fine-tuning the orbit (calculations) of all the planets and objects in our solar system,” he said.

Scientists for the Solar and Heliospheric Observatory, which is jointly operated by NASA and the European Space Agency, and NASA’s Solar Dynamics Observatory, or SDO, will work in tandem to study the transit. Louis Mayo, program manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a news release that, as celestial events go, this one is pretty fascinating.

“Astronomers get excited when any two things come close to each other in the heavens,” he said.

To catch a glimpse of the event, don’t even think about staring at the sun without eye protection. Not only will it damage your eyes, you won’t be able to spot tiny Mercury anyway. Instead, what’s needed is a telescope or binoculars fitted with protective solar filters.

For stargazers who don’t have access to such tools, the astronomy departments of many of the country's large universities will be hosting events, with some making telescopes available for use. Mercury's journey can also be seen on several live web streams, including off NASA's website.

The forecast is good in most parts of Canada with clear skies unimpeded by clouds, says Delaney, so it’s an ideal day for sun gazing.

“Grab it now, while you can,” he said.