2019 Mercury Transit

   On Monday November 11th the innermost planet Mercury will transit the Sun in an event that will be visible across the continental U.S.A. as the Sun rises. Depending on the viewing location the transit may already be in progress, with the entire transit visible from the east coast, and further west the transit will be in progress as the Sun rises.

   The video is cropped from the original 2-minute video showing many more views of the transit using different filters.

   As we view from Earth Mercury will pass in between the Earth and the Sun much like our Moon during a solar eclipse. In both situations the transit or eclipse occurs when there is a node crossing at inferior conjunction for either Mercury or Venus, or at a new Moon phase. A node crossing involves two orbits and where the orbits intersect. The Earth’s orbit around the Sun is used as the reference, and typically the Earth’s orbit is referred to as the ecliptic, or the plane of the ecliptic. Any other object orbiting the Sun with its respective orbital path inclined or tilted away from the Earth’s orbit, the ecliptic, will have a node crossing at the point where that orbit intersects the Earth’s orbit. Mercury for example has an inclination of around 7o. There are two node crossings, an ascending node and a descending node. The closer the timing of the node crossing is to the time for an inferior conjunction the greater the duration of transit time.

First or Ingress   First contact or ingress will be at 12:35 UT (6:35 am CST) as the leading edge of Mercury makes contact with the edge of the Sun.

   Transits of the inner planets are somewhat rare occurrences with approximately 13 Mercury transits each century and only in either May or November. The most recent Mercury transit was during May 2016 and after this year the next Mercury transit will not be until May 2032. On the other hand, Venus transits are even more rare with the Venus transits occurring as pairs of transits in June or December but are separated by 8 years. Each pair of Venus transits happen every 115 or 121 years. The most recent pair of Venus transits were 2004 and 2012, and the next pair will not be until next century during December of 2117 and 2125.


    What does a transit of the Sun look like? With proper viewing equipment the planet will appear as a small dot moving from left to right across the Sun’s disk. This animated graphic is made from pictures of the Mercury transit on May 8th 2003. As you can see Mercury appears as a small dot against the Sun’s disk. That is a sunspot toward the picture center.


mercury-transit-stages-ani   A transit consists of four stages starting with (I) when the leading edge of Mercury’s disk makes contact with the edge of the Sun’s disk. The 2nd stage (II) is when the trailing edge of Mercury disk is within the the Sun’s disk. (max) is when Mercury is as ‘deep’ into the Sun’s disk as it will be for this transit. Stage 3 (III) is when the leading edge of Mercury’s disk makes contact with the opposite side of the Sun’s disk. The transit is over at stage 4 (IV) when the trailing edge of Mercury’s disk leaves the Sun’s disk.

    How much of the transit you will see first depends on the weather. Otherwise it is a matter of timing. At my longitude of 94o west (Central Standard Time UT-6) sunrise is at 6:55 am CST meaning that the transit will already be in progress, however the rest of the transit through its conclusion will be visible.


   Transit Event Times for my Location as calculated with the Mercury Transit Calculator.

   Explore the Transit view path across the planet and where it will be visible or not visible on an interactive Google map.


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