Monday, December 7, 2015

Today's Occultation of Venus and the 2016 Mercury Transit Across the Sun

Today Venus will disappear behind the Moon at varying times across the United States. It will not be visible from SDO as we do not have a lunar transit today. Please see the front page of SpaceWeather.com for details on when to watch this occultation. You will need a pair of binoculars for the best view. Just find the Moon (a little ahead of the Sun in the sky) and watch as the bright dot of Venus goes behind it at about 12:30 p.m. ET.

But that brings up occultations that SDO will see. Next year we will see a transit of Mercury across the disk of the Sun on May 9, 2016. Here is a movie of the transit (using our predicted ephemeris, but it should be fairly close.)

video
The 2016 Mercury transit will last 7.5 hours. Mercury will touch the edge of the Sun at 1112 UTC (7:12 a.m. ET, called first contact), move completely into the disk at 1115 UTC, cross the center of the Sun at 1457 UTC, touch the far edge of the Sun at 1839 UTC, and leave the disk at 1842 UTC (2:42 p.m. ET, fourth contact). Unlike the 2012 Venus Transit, which was only visible in Alaska and Hawai'i, this transit will be visible throughout North America. People in the USA will be able to see most, if not all, of this transit.

Mercury is smaller and further from the Earth, so, compared to the transit of Venus in 2012, it will be a smaller disk as it passes between SDO and the Sun. Due to the shorter orbital period, transits of Mercury are more common than transits of Venus.

Johannes Kepler predicted a transit of Mercury would occur in November 1631. The first observed transit of Mercury was on November 7, 1631 by Pierre Gassendi. This was the first observed planet transit and showed that Kepler's equations of planetary motion could be used to predict the positions of planets.

SDO will provide near-realtime pictures of the Mercury Transit at a dedicated webpage. More details as the time approaches.

While you are waiting, grab your binoculars and go watch Venus disappear behind the Moon!