Mercury Transit: 9 May 2016

   A transit of the Sun involves only the two inner planets and occurs when either Mercury or Venus reaches inferior conjunction, between the Earth and the Sun, and the inner planet is crossing the plane of the ecliptic. This is a node crossing and the inner planet could either be at the descending or ascending node. Since both the Earth and Mercury orbit the Sun at different inclinations (Earth 0o, Mercury 7o) a transit does not occur at every inferior conjunction. (This is also the same reason why we do not have a solar eclipse every month – the Moon is inclined about 6o from the Earth’s orbit.)
   There is an interesting dynamic involving the orbital periods and distance from the Sun that sort of locks Mercury into a specific pattern for transits. A Mercury transit happens 13-14 times each century and only occurs in May around the 8th, when the planet is the furthest from the Sun, aphelion, and at the descending node, or at November around the 10th. November transits happen when Mercury is closest to the Sun, perihelion, and at the ascending node. Mercury transits during May happen every 13 and 33 years, while November Mercury transits happen every 7, 13, or 33 years.

NEVER LOOK AT THE SUN WITHOUT PROPER VIEWING EQUIPMENT
The next Mercury transit of the Sun visible from the United States after the May 9th transit is on November 11th 2019, and then not again until 2049. There are, however two other Mercury transits during those years, but not visible from the United States.
NEVER LOOK AT THE SUN WITHOUT PROPER VIEWING EQUIPMENT

NASA will broadcast the Mercury Transit.

    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.
On the day of the 2016 transit Mercury will have an apparent diameter that is approximately 1/158th that of the Sun’s apparent diameter. The Sun will have an apparent diameter of approximately 1900 arc seconds compared with the 12 arc second apparent diameter for Mercury.
Here is a video of the Venus transit on June 5th 2012. It features the activity surrounding viewing the transit with a small group of folks (myself included). We had access to a 30 cm telescope and other equipment including what we each had brought along. Click here to see some pictures of the Venus transit of 2012.

Use this web site, the Mercury Transit Calculator, to determine the specifics of the transit for your location.

Use this interactive Google Map to see where the transit will be visible.

To learn more about solar transits by Mercury and Venus go to the NASA eclipse web site.

NEVER LOOK AT THE SUN WITHOUT PROPER VIEWING EQUIPMENT
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 Daylight Time UT-5) sunrise is at 6:08 am CDT meaning that the transit will already be in progress, however the rest of the transit through its conclusion will be visible.

NEVER LOOK AT THE SUN WITHOUT PROPER VIEWING EQUIPMENT
Transit Event Times for my Location as calculated with the Mercury Transit Calculator.

Click here to download an Excel spreadsheet for Mercury transits from 1901 CE to 2300 CE. With this spreadsheet you enter your local coordinates to get the viewing information for your location.
NEVER LOOK AT THE SUN WITHOUT PROPER VIEWING EQUIPMENT

infographic-aniDownload a 2-page Infographic (PDF 8MB)

lws

Visit NASA’s Living with a Star web site for information about our star, the Sun.