Mercury Transit on May 9, 2016

Between 1120 and 1845 UTC (7:20 am and 2:45 pm ET) on May 9, 2016, SDO will watch a small black dot move across the Sun. The black dot won’t be a sunspot, it’s the planet Mercury making a rare transit of the Sun. The top image shows Mercury’s position during the transit plotted on an HMI continuum image from April 9, 2016. The black circles are about the size of Mercury and are spaced 30 minutes apart.

We will be providing a near-live feed of the SDO images of the transit on the special website http://mercurytransit.gsfc.nasa.gov. Our feed is delayed a few minutes by the data delivery method, but our website will display the data in a self-updating movie format. The stream from the spacecraft will include a visible channel and most of the EUV wavelengths.

Compared to people on the Earth, the orbit of SDO causes the transit to start and end at different times as seen at SDO. The transit starts when SDO is behind and ahead of the Earth and ends with SDO in front of and close to the Sun-Earth line.

While Mercury moves across the face of the Sun we will provide several ways to look at the data. Along with the full-disk view of the Sun we will provide several zoomed views. The second picture shows the boxes where small movies will be published on an AIA 193 image from April 9, 2016. The top part of the image will be cutoff so that no compression is needed to send the images to the ground. You can also see that the EUV telescopes will see Mercury blocking the corona about an hour before it moves onto the disk.

• Full-disk images
• The ingress box will show the data when Mercury moves over the edge of the Sun
• The tracking box will show Mercury moving across the disk
• The egress box images will show the data when Mercury moves into that box as it exits the Sun
• The “Complete Transit box” will be updated throughout the transit so that you can watch the entire path of Mercury across the Sun

Images will be shown as short movies in your browser that update every minute or so to include the latest data from the satellite.

We will see the disk of Mercury against the corona in the EUV channels about 1 hour before Mercury gets to the edge of the Sun.

SDO scientists will use the Mercury transit to study how the Sun is oriented on the cameras. It will also be used as a test of the computer programs used to clean up stray light in the images. This stray light caused ghost images to appear inside of Venus during the 2012 Venus transit. The disk became black when the computer programs were used to analyze the images. Mercury’s disk appears smaller and it is a better test of the programs.

A Mercury transit was the first seen in history. The heliocentric theory of the solar system allowed the orbits of planets to be more accurately calculated and Johannes Kepler determined that a transit of Mercury was possible in 1631. Pierre Gassendi saw that transit on November 7, 1631.

Transits of Mercury across the solar disk are more frequent than transits of Venus. This is because Mercury’s orbital period is 40% of Venus. But Mercury is farther from the Earth during a transit and the shift of the transit path for observers at different latitudes is smaller than for Venus. This made the less frequent Venus transits a better source of data for measuring the distance from the Earth to the Sun (1 AU).

Mercury is smaller in radius than Venus and further away from the Earth. That makes the disk of Mercury smaller on the Sun and more difficult to see as it enters and leaves the solar disk. The times of these contacts are needed for measuring the size of 1 AU. Again the Venus transits are a better measurement of 1 AU.

Even though the Mercury transits were less useful for measuring the size of the solar system, they are fun to watch. You can also compare how the different telescopes on the ground and in space see the black dot of Mercury move across the Sun.

Never look at the uneclipsed Sun with unprotected eyes! Always use sun-safe optics to look at the Sun.

You can watch the transit at our special website. My thanks to the SDO scientists, engineers, and web programmers that make this SDO Data Event possible.

Enjoy!

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.)

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!

A "Jovial" Transit of Venus

If you lived on Jupiter you would be able to see a transit of Venus tomorrow. It might look something like the one we saw in June. Here is an example in SDO AIA 171, a time-lapse still of the black disk of Venus moving across the Sun. Even though the transit can't be seen from Earth, the Hubble Space Telescope may be able to see the small decrease in sunlight reflected off Jupiter toward Earth during the transit. SDO will help by telling the scientists how the Sun's brightness changes during the transit. Given how quiet the Sun has been of late, that should be pretty easy for us to do. Jupiter is ahead of the Earth in its orbit around the Sun, so the quiet side is rotating to face Jupiter, even as a new active region rotates into the view of the Earth.
First contact is at 0456 UTC, mid-transit is 0953 UTC and 4th contact is 1451 UTC (all September 20 UTC). That means the transit at Jupiter lasts almost 10 hours (compared to about 7.5 hours for the June 2012 Venus transit at Earth).
It's all part of our search for Earth-like planets around other stars. We see a lot of planets in the Kepler data; how can we determine which ones have water and oxygen?

Venus Transit is Over, Site is Online

The Venus Transit ended early last Wednesday morning. Here is an image of Venus exiting the solar corona in AIA 193. Many thanks to the people who made the data display possible, especially to our Data Meister Phil Scherrer at Stanford University.
The VenusTransit.gsfc.nasa.gov website is a permanent source of images of the 2012 transit of Venus. Although it was briefly offline this weekend, we have re-enabled the website and you can once again look at the images and movies.
Next goal is a posting about how the diffraction pattern of AIA created the ghosts in the EUV images during the transit.

Venus as you've never seen it before!!

 Watch SDO movies of Venus at http://venustransit.gsfc.nasa.gov and catch a NASA webcast at http://sunearthday.nasa.gov/transitofvenus/

Venus Is In LASCO C2!

Venus is getting ever closer to the Sun as it moves towards tomorrows transit. Here is the view as it enters images from SoHO's LASCO C2 coronagraph. The type of science we will do with SDO during the transit is a story at the NASA SDO webpage.
SDO images of the transit will be available at our dedicated website.

The Venus Transit is Getting Closer

You can see Venus just coming into view on the left of this LASCO image from May 31. Over the next 5 days Venus will approach and disappear behind the occulter disk. On June 5 we will watch Venus move across the Sun in the telescopes of SDO. Watch the SDO images at VenusTransit.gsfc.nasa.gov, starting at 2100 UTC (5 pm ET). The bright dot between Venus and the Sun is Mercury.

SDO Venus Transit Website is Looking Good

Next Tuesday SDO will witness a transit of Venus across the disk of the Sun. We will be producing a special set of data during the transit that allow us to check out the instruments on SDO, look at the Black Drop effect is several wavelengths, and see the atmosphere of Venus. AIA, the EUV telescopes on SDO, will see Venus against the corona about an hour before it touches the limb of the Sun.

We have started showing test data on the SDO Venus Transit website. There is no disk in the test data but you can see what the movies will look like. Use your imagination to see the disk! Then come back next Tuesday (June 5) at 2100 UTC (5 pm ET) to see the real transit.

Venus Transit Testing Today

Starting at 1700 UTC (1 pm ET) today and lasting until 0300 UTC tomorrow (May 25, which is 11 pm ET May 24), we will be running a simulation of the observations to be taken during the Venus transit on June 5. AIA will be switching modes to take different sequences of images to allow the scientists to study the instrument and Venus. HMI will try out its transit mode as well but will return to normal operations after about an hour of special mode.

Partial Image in 193

AIA will be taking three types of images during the test and transit. Every 96 seconds it will take a set of full-disk images. In between it will provide partial images (cropping out the southern polar region) at the usual cadences and striped images at extremely high cadences. Examples of these images are at left that were taken during a shorter test held May 23 between 1900 and 2015 UTC.

Striped Image in 193

During the transit we will be providing movies of images taken during the transit at http://VenusTransit.gsfc.nasa.gov.
Enjoy the show!