Mercury's journey across the sun happened on November 11th and if you missed it, you will have to wait another 13 years before this event occurs again. Mercury's next journey across the sun will not take place until November 13, 2031. If you think this is a long wait, consider Venus who will travel 93 years from now!
Phenomenal events like this only happen when there is a set alignment on planet orbits. Just like all the planets in our solar system, Mercury and Venus circle the sun in a plane, similar to a pancake but it's not perfectly flat because each planet has a tilt in its orbit.
Take Mercury's path, there is an incline of 7° to the plane in which the planet, on average, orbits in the sky. From the perspective of our planet Earth, Mercury passes above or below the sun almost all the time, only crossing the sun 13 or 14 times in one century.
With Venus, this phenomenon is much rarer. It happens in transit pairs separated by 8 years and each pairing only happens about a century apart from each other.
Also, only Mercury and Venus can cross the sun since they are on the inner side of the solar system, unlike Earth. Transits of Mercury seem to happen around the same time of year, either in November or May while Venus' is more scattered.
According to NASA, if you missed this last transit of Mercury, you will have to wait a really long time. The next 2 transits will happen in 2032 and 2039 but will not be visible from North America. Skywatchers in the U.S will have to wait until 2049 and from the West Coast in 2052.
Regarding Venus, you should mark it on your calendar and even consider if you will still be around. According to NASA, from December 10 to 11, 2117 it will be visible in southern and western North America and other locations.
As of December 8, 2125, it will be visible for half its journey in the U.S. The next pairing will not occur until 2247 and 2255.
If all of this seems too far in advance for you to even consider, have peace of mind, you will have plenty of chances to watch the moon travel across the sun during a solar eclipse or to watch the moon pass into Earth's shadow during the lunar eclipse.
Eclipses take place every few months but visibility varies considerably, especially for solar eclipses.
If you were fortunate enough to capture the Mercury event, share it on your social media so the rest of us can enjoy the moment!