Sunday, November 17, 2019

200 Millionth Image from AIA

In all the hype about the Mercury transit last Monday, we overlooked another milestone in the SDO mission. On November 5, 2019, the AIA instrument returned its 200 millionth image. Here it is and it's a beauty in the AIA 171 Å passband!
The Sun looks like it is in solar minimum, with large polar coronal holes over the North and South poles. Hope for the future can be seen in the area with the black line drawn around it. That's active region 12750, a small bi-polar region that has the polarity of Solar Cycle 25 and an appropriately high latitude of 28°S. Other SC25 regions have been seen and they will become more frequent as SC25 starts its rise to maximum.

Mark Cheung, PI of AIA, made a movie to celebrate this milestone.

Congratulations to the AIA team for building a robust instrument that has returned excellent data for almost 10 years.

Wednesday, November 13, 2019

Extraordinary Pictures of the 2019 Mercury Transit

Here are composite views of Monday's transit (top) and the transit in 2016 (bottom). They were produced by Monica Bobra at Stanford University. What can we learn about Mercury's orbit from these pictures?

First, the images of Mercury (the black dots) are 21 minutes apart in both images. The 2019 dots are further apart than the 2016 dots. This means Mercury was moving faster across the Sun in 2019. If we check the orbit of Mercury at AstroPixels, we find that Mercury was closest to the Sun (at perihelion) on November 16, 2019. A planet's velocity is greatest near perihelion and least near aphelion (the furthest point from the Sun). So Mercury was moving at almost its maximum speed on Monday. The 2016 Mercury ephemeris shows that aphelion was May 20, 2016, only 11 days after the transit that year. That means Mercury was moving at almost its slowest speed during the 2016 transit. The spacing of the dots agrees with the orbit of Mercury.

We can also look at the size of Mercury on the disk. The dots are smaller in 2019, showing that Mercury was further from the Earth during this transit. If we look at Mercury's elliptical orbit from the Earth, Mercury is closest to the Earth when it is furthest from the Sun (aphelion) and farthest from the Earth when it is closest to the Sun (perihelion). Again, this agrees with the transit pictures and orbit.

The different tilts of the two paths show that Mercury's orbit is tilted away from the Earth's orbit (called the ecliptic) and the Sun's equator. Whenever Mercury's orbit crosses the ecliptic we have a chance to see a transit, but most crossings take place when the Earth and Mercury are not aligned. SDO images are usually aligned with the Sun's North Pole at the top of the image. So the interpretation of the tilts in a little more complicated.

We can see sunspots in the 2016 images but not in the 2019 image. The Sun has become very quiet in the last three years. Over the next year or so we should start seeing Solar Cycle 25 activity. But on Monday the Sun was blank in visible light, providing beautiful back-lighting for us to see Mercury.

The sunspots in the 2016 image are nice and sharp. Bobra's program does not use a simple average to make the image. You can check out the actual Python code (with the transit pictures) at her Planetary Transit githib site. Be ready for the 2032 transit!

Check out the 2019 transit in other wavelengths of light at the SDO website.

Many thanks to Dr. Bobra for producing these extraordinary images.

Thursday, November 7, 2019

Mercury Transit this Monday!

We will see a transit of Mercury across the disk of the Sun on Monday, November 11, 2019. You can watch the transit using SDO data at

Here is a movie of the transit (from our flight dynamics team.)

The 2019 Mercury transit will last about 5.5 hours in visible light. Mercury will touch the edge of the Sun in HMI at 1241 UTC (7:41 a.m. ET, called first contact) and leave the HMI disk at 1805 UTC (1:05 p.m. ET, fourth contact). Mercury will be visible in some of the AIA channels throughout the SDO Data Event, which starts at 1200 UTC (7:00 pm ET) and ends at 1845 UTC (1:45 pm ET).

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 its 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 accurately predict the positions of planets.

From the ground the transit starts at 1235 UTC (7:35 am ET, first contact) and ends at 1804 UTC (1:04 pm ET, fourth contact. Parts of this transit will be visible throughout North America. People in the eastern USA will be able to see most, if not all, of this transit. People in the western USA will see the Sun rise with Mercury already on the disk.

SDO will provide near-realtime pictures of the Mercury Transit at


Wednesday, October 23, 2019

Mercury transit, November 11, 2019

Starting around 1200 UTC (7:00 am ET) November 11, 2019, we will begin watching Mercury move into view against the corona of the Sun. This is about 45 minutes before it is visible against the Sun from the ground. We have created to let you watch this transit as short movies in almost real time. The transit lasts a little over 5.5 hours, ending as Mercury leaves the disk of the Sun about 1806 UTC but continues moving out through the corona for another 30 minutes.
The image shows the predicted positions of Mercury against an AIA 1600 Å image from 1803 UTC October 23, 2019. The blue circles are about the size of Mercury and are spaced 30 minutes apart. There are no sunspots along the path of Mercury and the Sun shows very few signs of magnetic activity. The corona is also smaller than it has been, meaning Mercury will come into view in the EUV images less than an hour before 1st contact. Although we will be taking images all the time, the special modes will start 45 minutes before 1st contact and end 45 minutes after 4th contact.

Along with the full-disk view of the Sun we will provide several zoomed views. These views are shown by the boxes that are drawn on the image. You can also see that the EUV telescopes will see Mercury blocking the corona before it moves onto the disk. All of the boxes are built in a 16x9 ratio that nicely fits into an 1080p screen.

  • The Ingress box will show the images from when Mercury moves over the edge of the Sun at the beginning of the transit. This includes 1st and 2nd contact (when Mercury first touches the edge of the Sun and when Mercury moves completely onto the Sun in visible light.) It will also show Mercury against the corona of the Sun before 1st contact in the EUV channels;
  • The Tracking box will follow Mercury as it moves across the disk;
  • The Egress box images will show the data when Mercury moves into that box as it exits the Sun. It will not be available until about 1715 UTC. This box will show 3rd and 4th contact (when Mercury starts leaving the disk of the of Sun and the last instant it touches the edge of the Sun, again in visible light);
  • The Full Passage box will be updated throughout the transit so that you can watch the entire path of Mercury across the Sun.

Each view is available as a self-updating movie, by clicking on the picture shown on the website, and as an mp4 movie, which can be seen by clicking on the View/Download mp4 button below the image. Depending on its settings, your browser will either show the movie or download it. The mp4 movies will also be regularly updated as new images arrive, but are not automatically updated on your browser.

Transits were important for two developments in astronomy, that Kepler's theory using ellipses for planetary orbits was better than the Ptolemaic theory and fixing the size of the solar system. Transits of Mercury and Venus can happen because they are the only planets that orbit between the Earth and the Sun. By using ellipses to describe the orbits of the planets Kepler was able to predict when transits would occur. The Ptolemaic theory that used circular orbits did not have the accuracy needed to do predict these events, even after epicycles and equants were introduced. In 1627, Kepler predicted that a transit of Mercury would occur on November 7, 1631. Pierre Gassendi watched from his Paris observatory and saw a small black dot move across the face of the Sun on that day. A real triumph for the Kepler calculations!

Later transits, especially of Venus, would be used to measure the distance between the Earth and the Sun — the astronomical unit that we now know is 149,597,870,700 meters (or 92.75 million miles).

But on November 11, 2019, we celebrate the success of Kepler's ideas. As we watch Mercury move across the Sun, you could also remember our successes in using Kepler's ideas to slingshot the Voyager spacecraft through a Grand Tour of the outer planets, or to use Venus to send the Parker Solar Probe ever closer to the Sun, or even the incredible accuracy of GPS positions we take for granted as we move about in our everyday lives.

Never look at the uneclipsed Sun with unprotected eyes!

You can safely watch the transit at

My thanks to the SDO scientists, engineers, and web programmers that made this SDO Data Event possible.


Testing of AIA Today, 1800-1900 UTC

Today from 1800-1900 UTC (2-3 pm ET), AIA will record some test images. This will exercise the ability to command AIA to produce partial (cropped) and uncompressed images. Other instruments will be unaffected. The actual testing is scheduled to last approximately 10 minutes. Test images will be in focus but may be missing a part of the Sun.

Calibration Maneuvers on October 9, 2019

SDO executed the EVE Field of View and HMI Flatfield calibration maneuvers on October 9, 2019. During these maneuvers the science data may be blurry or mission.

Friday, October 11, 2019

Website Outage - 2019-10-11

Today, October 11, 2019, there will be a brief website outage due to maintenance. The start time for this outage is approximately 12 noon. We are sorry for any inconvenience this may cause.

Friday, September 13, 2019

Lunar Transit on September 28, 2019

SDO will experience a lunar transit on September 28, 2019. Here is a movie from the Flight Operations Team that shows SDO, the Sun, and the Moon during the transit. This transit lasts from 2044-2115 UTC (4:24-5:16 pm ET) and covers at most about 7% of SDO's view of the Sun.
The Moon moves from left to right during this transit. That makes it an SDO-overtake transit.

During the transit SDO will be in inertial mode with the fine-guidance system turned off. Images may jiggle around a little bit, but will continue to be observed and recorded.
Although you can see the Moon throughout the movie SDO's instruments cannot see the Moon when it is not covering the Sun. The little white flash seen in the Moon is the word "Moon" being written by the software and then quickly covered. The boxes drawn around and on the Sun help the FOT run the spacecraft. The time is displayed in the lower left corner of the movie. The first seven numbers are the year (2019) and the day of year (271). The six numbers after the period are the hour, minutes, and second of UTC (2 numbers each).
The next SDO Transit will be the Mercury Transit on November 11, 2019. We will have a webpage dedicated to the transit.

Wednesday, August 28, 2019

Station Keeping Maneuver #19 Today

SDO will execute Station Keeping Maneuver #19 today at 2222 UTC (6:22 p.m. ET). From 2200 to 2245 UTC (6:00-6:45 p.m. ET) science data may be missing or blurred. Station-keeping maneuvers are designed to keep SDO’s orbit in the right place when the spacecraft travels through the geostationary belt twice each day.

Wednesday, August 14, 2019

Momentum Management Maneuver #35 Today

SDO will execute Momentum Management Maneuver #35 today at 1911 UTC (3:11 p. ET). From 1830 to 1930 (UTC) science data may be missing or blurred.

Eclipse season started on 08 Aug 2019 and continues until 01 Sept 2019. Each day around midnight Mountain Standard Time (0700 UTC) the Earth passes between SDO and the Sun. This is a normal part of our geosynchronous orbit.

Wednesday, July 24, 2019

Today's Maneuver is the EVE Cruciform

SDO is executing the EVE Cruciform calibration maneuver today. Between 1100 and 1600 UTC (7:00 am--12 noon ET), science data and images may be blurry or absent.

Wednesday, July 17, 2019

Today's Maneuver and Website Upgrade

Today between 1500 and 2200 UTC (11:00 am-6 pm ET) SDO will execute the HMI roll maneuver. During this maneuver science may be missing or blurry.

The SDO website upgrade will be happening today and tomorrow. There will be times when the website is unavailable while the new servers are brought on-line and services restarted.

Wednesday, July 3, 2019

Today's Maneuver

SDO is running the EVE Field of View and HMI/AIA Flatfield maneuvers today. During these maneuvers the science data may be blurry or absent.

New Features on Website

The SDO website ( has two new features. If you follow the "Sun Now" link to, you will see two new selections. One is the ability to access the various images through the "Data Links" menu under each image. Clicking on that link will show a menu of image size and other options.

The other is the ability to jump to earlier versions of the Sun Now page through the "Browse Daily Images" in the left column. You can enter a date and Jump to that day's images or Jump one day at a time.

These features were added due to feedback we received from users of the website.


Friday, June 21, 2019

Happy Summer Solstice and Congratulations to Phil Scherrer!

Today at 1554 UTC (11:54 a.m. ET) the Sun reached its most northerly point in the year. As a result, we have the most daylight hours in the northern hemisphere and the Southern Hemisphere has the most dark hours. At the solstice the Sun appears to stall and turn around, heading towards the south and northern winter. It's the official beginning of summer and all because the Earth's rotation axis is tilted 23° from the plane of its orbit. Here's an AIA 193 Å to celebrate.

But today is also a day to congratulate Phil Scherrer of Stanford University who is also the HMI PI and the person who watches over the JSOC with the HMI and AIA data. Dr. Scherrer was awarded the Solar Physics Division's Hale Prize last week at the 234th Meeting of the AAS. The Hale Prize is awarded annually to a scientist for outstanding contributions to the field of solar astronomy.

Dr. Scherrer has certainly made contributions to solar physics. He has measured and studied the Sun's magnetic field for 50 years. As important, he has encouraged others to use his data as well. He has also worked in helioseismology, both measuring the velocities of the Sun's surface and the theory of ow those measurements tell us something about the Sun. It is hard to know what our field would look like if he hadn't been around.

Congratulations Phil!

Friday, June 14, 2019

Listening to the Sun

Ever wish you could listen to SDO data? We have developed new ways to do just that!

This week the American Astronomical Society and the AAS Solar Physics Division had a joint meeting in St Louis. Astronomers and solar physicists got together to discuss our latest papers on understanding the Sun and universe.

Two of those papers were "Listening to the Sun" (by Kyle Ingram-Johnson, W. Dean Pesnell, and Kevin Addison) and "Listening to the Sun: the Sonification of Solar Harmonics Project" (by tim larson, Seth Shafer, and Elaine diFalco). Both papers allow you hear different kinds of SDO data. They were presented as iPosters, so they are available at the links below for others to read through and enjoy.

This paper converts several solar indices to sound before sonifying AIA images in three ways. You can listen to the entire image, small subsets of the image, and a series of images that shows a filament liftoff. We used a special math curve called a Hilbert curve to walk around the image and convert the pixels values into a set that can be then converted to sound. You should listen to the difference between the full image sonified with a Hilbert curve and sonified with a left-right scan. You will see a big difference.

The next paper shifts HMI sound waves from their very low frequency of about 3 mHz to about 3 kHz so you can hear the tones.

You are working to allow you to sonify images, both the entire image and as subsets, on the SDO website. Look for that new feature in the future.

Until then, please enjoy listening to the Sun!

Wednesday, May 1, 2019

Momentum Management Maneuver #34 Today

SDO will execute Momentum Management Maneuver #34 (MM#34) today from 1845-1915 UTC (2:45-3:15 pm ET). During a maneuver the science data may be unavailable or blurred.

Wednesday, April 24, 2019

SDO Maneuvers Today

SDO will execute two calibration maneuvers today. The EVE Field of View maneuver will run from 1315-1600 UTC (9:15 am-12 noon ET). The HMI/AIA Flatfield maneuver will then run from 1630-1907 UTC (12:30 pm-3 pm ET). During the maneuvers images may be blurred or absent. These maneuvers were delayed to provide data during the perihelion passage of the Parker Solar Probe earlier this month.

Thursday, April 4, 2019

SDO Plans for the Next Eight Months

Significant events in SDO's timeline are below. Calibration maneuvers are still being scheduled as we await the launch of CLASP-2 at White Sands and for the completion of the second perihelion pass of Parker Solar Probe.
  • 01 May 2019 @1845 UTC (1445 ET) – Momentum Management Maneuver #34
  • 19 Jul 2019 @0443 UTC (0043 ET) – First Handover Begins and Handover Season Starts (-Z HGA Active Prior)
  • 08 Aug 2019 @0709 UTC (0309 ET) – Fall Eclipse Season Starts
  • 12 Aug 20194 @TBD – Momentum Management Maneuver #35 (Tentative Date)
  • 28 Aug 2019 @2222 UTC (1822 ET) – Station Keeping Maneuver #19 (Tentative Date)
  • 01 Sep 2019 @0659 UTC (0259 ET) – Fall Eclipse Season Ends
  • 12 Sep 2019 @0515 UTC (0115 ET) – Last Handover Completes and Handover Season Ends (+Z HGA Active After)
  • 28 Sep 2019 @2043-2116 UTC (1643-1717 ET) – Lunar Transit - Video to follow
  • 11 Nov 2019 @1236-1802 UTC (0736-1302 ET) – Mercury Transit - Video to follow

Thursday, March 7, 2019

That's a Transit!

The long lunar transit SDO saw last night was quite a show. Here's a movie in AIA 171 Å from March 6, 2000 UTC, to March 7, 0400 UTC (March 6, 3:00-11:00 pm ET) showing the entire transit. The Moon touched the limb of the Sun at 2200 UTC and finally left the solar disk at 0207 UTC). During the transit the Sun moves in the frame as the spacecraft and telescopes cool and shiver in the lunar shadow.
Congratulations to the flight dynamics team for predicting a beautiful display of orbital mechanics.

Wednesday, February 27, 2019

Station Keeping Maneuver #18 Today

SDO will perform station keeping maneuver #18 (SK#18) today from 2225-2300 UTC (5:25-6:00 pm ET). During this time SDO data may be blurry or missing. These maneuvers are performed to keep SDO within the longitude limits assigned to our geosynchronous orbit. I'm sure our neighbors appreciate us staying inside the box!

Tuesday, February 19, 2019

Another Nifty Lunar Transit from SDO

The previously scheduled station-keeping maneuver is delayed until next week (February 27). It's time to talk the lunar transit of March 6-7, 2019.

From 2200 UTC on March 6,2019, until 0207 UTC on March 7 (5:00-9:07 pm ET, March 6) SDO will experience a lunar transit. The Moon will cover up to 82% of SDO's view of the Sun. This four-hour transit looks similar to the double transit of September 9-10, 2018, except that the shadow of the Moon is visible through the entire transit. Here is a movie from the Flight Operations Team that shows SDO, the Sun, and the Moon during the transit.

The Moon moves from lower left to upper right in the images during the first half of the transit and upper right to lower left for the second half. The first part of the transit is caused by SDO overtaking the Moon as SDO moves in the afternoon part of its orbit. (SDO orbits over the Mountain Time Zone of the USA so the transit happens from 3:00-7:06 MT.) SDO's velocity of about 3 km/s is faster than the Moon's of 1 km/s and SDO overtakes and moves past the Moon-Sun line. The second part of the transit happens as SDO moves into the dusk part of SDO's orbit around the Earth and is now moving mostly away from the Moon. The Moon's velocity takes it past SDO and the shadow appears to move from right to left across the Sun.
When I first saw this movie I thought we were going to talk about retrograde motion. Other planets, notably Mars, move in retrograde when the Earth moves between them and the Sun with our faster orbital velocity. But it isn't just that. The first part of the transit is like retrograde motion as SDO passes by the Moon-Sun line with its faster velocity and the Moon appears to move backwards. But the second part of the transit happens because SDO is moving mostly away from and even a little in the opposite direction of the Moon.
I created two videos to help understand what’s happening. The first shows why Mars appears to have retrograde motion and the second explains the extended lunar transits seen in September 2018 and March 2019.

Retrograde motion is the apparent backwards motion of an outer planet among the stars as the Earth moves past the line connecting the Sun and the outer planet. In this movie Mars is a red disk and the Earth is a blue disk moving in their orbits around the yellow disk of the Sun. A line is drawn connecting the Earth and Mars and extended out into space. A colored dot is drawn where an observer on the Earth will see Mars against the distant stars. The color of that dot then changes from red to blue as the Earth overtakes Mars in it's orbit. Those dots show that the path of Mars seen from Earth traces out a lazy Z in the stars. In this example the Z is centered about the time the Sun, Earth, and Mars are lined up.

The other video shows the situation for SDO's lunar transit on March 6. There is no line connecting SDO and the Moon, only the shadow of the Moon. SDO and the Moon are started at about the right times in their orbits and you can see the shadow line hits the grey disk of SDO as the satellite moves through the afternoon and dusk parts of the orbit. In the first part of the transit SDO moves across the black line from left to right across the Sun (so the Moon appears to move from left to right across the Sun.) During the second part of the transit SDO moves across the black line from right to left and the Moon moves in the opposite direction from the first.
During the total solar eclipse in August 2017 the Moon's shadow moved from the West coast of the US towards the East. This is because the speed of the rotation of the Earth (less than 0.5 km/s) is slower than the speed of the Moon. So the Moon overtakes the people on the rotating Earth. The shadow follows the Moon and moves from West to East, like the second part of the transit.
Although you can see the Moon throughout the movie SDO's instruments cannot see the Moon when it is not covering the Sun. The little white flash seen in the Moon is the word &ldquot;Moon&rdquot; being written by the software and then quickly covered. The boxes drawn on and around the Sun help the FOT run the spacecraft. The time is displayed in the lower left corner of the movie. The first seven numbers are the year (2019) and the day of year (065 and 066). The six numbers after the period are the hour, minutes, and second of UTC (2 numbers each).
One detail was left out of the discussion. A transit can only if the Sun, Moon, and SDO are in a line. The Moon's shadow has a small angle rather than the straight line in the movie. This means the model shown here is too simple, but it still explains why we see the long lunar transits with the Moon changing direction. Look at the FOT movie for a better simulation.

Once again, a lunar transit shows how complicated the motions of objects can appear even as they move along simple orbits.


Monday, February 11, 2019

Happy 9th Anniversary SDO!

Nine years ago today, at 10:23 am ET, SDO rose into the sky atop an Atlas V 401 launch vehicle. Since that day SDO has returned over 350 million images of the Sun, produced over 3000 scientific articles, and allowed millions to enjoy the Sun. Solar Cycle 24 was just starting in 2010. SDO watched it grow to maximum in 2014 and now the Sun is often spotless.

Here is a summary slide of what SDO saw. The AIA 193 Å shows the lower corona and the HMI magnetogram shows the surface magnetic field. We try to understand the Sun by watching what happens at the poles. The dark areas near the North and South poles in the October 2010 and February 2019 193 Å images are the polar coronal holes. They have disappeared by solar maximum (the February 2014 images). The magnetograms show how the Sun's magnetic field gets more complicated at maximum and quite simple at minimum. What happens in the poles at solar minimum seems to be one of our best predictors of future solar activity.

SDO data is the basis of accurate models of the solar corona. Machine Learning algorithms are being used to squeeze even more information out of our 12 PB of data. We are looking forward to another lengthy lunar transit next month and the Mercury transit in November.

You can make your own SDO Anniversary movie at our website or the Helioviewer website.

Happy Anniversary SDO!

Tuesday, February 5, 2019

Welcome to 2019!

The replacement of the computers serving have arrived at Goddard! The system will be replaced and the data moved to the new drives over the next few weeks. We will be ready to serve the near-realtime images during the Mercury transit on November 11, 2019.
The highlights of SDO's maneuvers for the first 2/3's of 2019 are:
  1. 01/31 @ 0506 UTC (00:06 am ET) - Spring Handover Season Starts
  2. 02/06 @ 0723 UTC (02:23 am ET) - Spring Eclipse Season Starts
  3. 02/20 @ 2210 UTC (10:10 pm ET) - Station Keeping maneuver #18
  4. 03/01 @ 0713 UTC (02:13 am ET) - Spring Eclipse Season Ends
  5. 03/06 2200 UTC to 03/07 0206 UTC (03/06, 05:00 to 09:06 pm ET) - Lunar Transit (movie released next week)
  6. 03/27 @ 0310 UTC (10:10 pm ET) - Spring Handover Season Ends
  7. 05/01 @ TBD - Momentum Management maneuver #34 (Tentative Date)
  8. 07/17 @ 0445 UTC (12:45 am ET) – Fall Handover Season Begins
  9. 07/24 @ TBD - Station Keeping maneuver #19 (Tentative)
  10. 08/08 @ 0709 UTC (03:09 am ET) – Fall Eclipse Season Starts
  11. 09/01 @ 0658 UTC (02:58 am ET) – Fall Eclipse Season Ends