A transit is a rare alignment of the sun, the earth, and a planet in which the planet appears in front of the disk of the sun. In the solar system, only the planets inside the earth's orbit, namely Mercury and Venus can produce a transit.

Viewing a transit

When a transit appears, it is visible almost everywhere that the sun is visible. In spite of this wide region of visibility, there are obstacles to observing transits. Venus and Mercury are very small compared to the size of the sun and their disks cannot be discerned against with the naked eye without magnification. In addition, it is unsafe to look at the sun through binoculars or a telescope without appropriate filtering. Accordingly, some special viewing techniques must be used. It is possible to use a telescope or binoculars to project an image of the transit onto a white surface. This article from space.com describes the care needed to observe a transit and describes several techniques for viewing a transit.

Transits of Mercury

Currently, transits of Mercury occur only in the months of May or November. The last transit of Mercury occurred on November 19, 2019. The next transit will occur on November 13, 2032. As a result, many of us will have an opportunity to see that one if we are willing to travel.

Transits of Venus

All transits of Venus occur during either June or December. The last transit of Venus took place on June 6, 2012. The next transit of Venus will not occur until December 11, 2117. Accordingly, it is unlikely that anyone reading this will see a transit of Venus from the earth during their lifetime.