Wednesday, December 20, 2017

Momentum Management Maneuver #31

SDO will perform Momentum Management Maneuver (Delta-H) #31 between 1919 and 1953 UTC (2:19-2:53 pm ET) today. We will fire the thrusters to bring the reaction wheels to their planned speeds. Science data may be unavailable or blurry during the maneuver.

Monday, November 20, 2017

Why Look at the Sun from Space?

SDO is one of fleet of satellites watching the Sun and recording the data that we use to study the solar magnetic field. The Sun was one of the first objects observed from above the Earth's atmosphere. One reason is the Sun's brightness — it was easy to see in the cameras. A more important reason was the ability to see wavelengths of light that are absorbed by the Earth's atmosphere. Although these wavelengths of light produce the ozone layer, which absorbs another wavelength, and the ionosphere, they are very useful to solar scientists. For example, the total solar irradiance measurements described in a previous post can only be made from a satellite.

What other satellites can you use to study the Sun?

Here are two sources (from many I could list) that can tell you about solar satellites from the dawn of space flight to today.

The first is Solar Satellites by Drs. Brian Dennis and Ryan Milligan. It is a web article on Scholarpedia with a list of 86 solar research satellites starting with the SOLRAD series that had its first launch in 1960. Dennis and Milligan also describe the instruments and observations on more modern satellites.

Another source is Watching the Sun from Space, which is available as a free download from the linked AJP website. This article starts with Skylab and traces the ways we observe the Sun from space. Links are provided for 27 solar missions, with data available for about 21. It also describes some orbits we haven't yet used to observe the Sun but could in the future.

Since the dawn of the Space Age during the decline of Solar Cycle 19, data from solar missions have been crucial in helping us understand the solar magnetic field and solar activity. Solar observatories in space continue to provide useful solar data and will as long as they keep flying and observing the Sun.

SDO should be around to watch Solar Cycle 25.

Wednesday, November 1, 2017

Is the Sun Getting Brighter?

I was asked whether SDO measures the total output of the Sun and whether an increase in that output could be causing the temperature of the Earth to increase?

SDO was built to study how the magnetic fields of the Sun are created and destroyed. AIA and EVE look at wavelengths of light that tell us a lot about those magnetic fields but are absorbed by our atmosphere and can’t be measured at the surface. HMI is designed to measure the velocity and magnetic field at the surface, not the total output of the Sun.

Other satellites in NASA’s fleet do measure the total output of the Sun, which we call the Total Solar Irradiance or TSI. One instrument on SoHO called VIRGO has measured TSI since 1996. Another instrument is TIM on NASA’s SORCE that is operated by the same group that built EVE. SORCE was very carefully calibrated and used to establish the baseline of TSI. VIRGO and other earlier satellites then provide the data since 1978.

Combining these data into a single measurement has been a challenge, but the people at LASP and the Physikalisch-Meteorologisches Observatorium Davos (PMOD) in Switzerland have risen to the task. The result is this figure. It shows the measured value of TSI from many satellites, spliced together into a single data set.

In the top plot, we drew the daily average of measured points in red (so there are a lot of points, 14187 to be precise). On the left is a red vertical bar showing a 0.3% change in TSI. The black curve is the average of TSI over each year. The dashed horizontal line shows the minimum value of year-averaged TSI data. The vertical black bar shows the 0.09% variation we see in that average. The bottom plot shows the annual sunspot number from the SIDC in Belgium in blue.

What do we learn from these plots? First, TSI does change! That’s why we stopped calling it the solar constant. Second, as the sunspot number increases, so does TSI. But the converse is also true. As the sunspot number decreases so does TSI. We have watched this happen for four sunspot cycles. This waxing and waning of TSI with sunspot number is understood as a combination of dark sunspots reducing TSI below the dashed line and long-lived magnetic features increasing TSI. SORCE has even observed flares in TSI.

Third, the horizontal dashed line is not an average, it is drawn at the lowest value in the year-averaged TSI data (that happened in 2009). When there are no sunspots the Sun’s brightness should be that of the hot, glowing object we always imagined it to be. We would expect TSI to be the same at every solar minimum. There is much discussion over whether the value of TSI at solar minimum is getting smaller with time, but it is not getting larger.

These data show us that the Sun is not getting brighter with time. The brightness does follow the sunspot cycle, but the level of solar activity has been decreasing the last 35 years. The value at minimum may be decreasing as well, although that is far more difficult to prove. Perhaps the upcoming solar minimum in 2020 will help answer that question.

To answer the question: No, we do not measure an increase in the output of the Sun that would cause the Earth to warm.

More information about the VIRGO instrument and how the composite (“spliced”) data is generated from the many measurements is at the PMOD website. The data I used was downloaded from

I highly recommend looking at the SORCE website for their data, which is how the absolute value of the composite was determined

The sunspot data is from You can download the sunspot number is several formats for your analysis.

Note: Both data sets mark days where a measurement was not made with a negative number. These points were ignored when doing the averages.

Thursday, October 19, 2017

Today's Lunar Transit

It was a lovely fall day in Maryland. A perfect day for a lunar transit! Here's an AIA 171 Å image showing the Moon blocking a slice of the Sun.

Wednesday, October 4, 2017

EVE Field of View and AIA/HMI Flatfield Maneuvers today

The wobbling images tell us that another round of calibration maneuvers has started. Today we have the EVE Field of View and AIA/HMI flatfield maneuvers from 1315-1910 UTC (9:15 a.m.-3:10 p.m. ET).
Next Wednesday SDO will perform the EVE cruciform.
On October 19 we will have another lunar transit. A little deeper than the one on August 21, but still not a total eclipse. Here is the movie showing what it will look like.

Wednesday, July 26, 2017

Momentum Management Maneuver #30 today, 1925-2000 UTC

SDO will perform Momentum Management (Delta-H) Maneuver #30 today. From 1925-2000 UTC (3:25-4:00 pm ET), SDO science data may be missing or incomplete. These maneuvers are used to manage the reaction wheel speeds on the spacecraft and are a normal part of our operations.

Thursday, July 6, 2017

Remainder of 2017 Maneuvers and two Lunar Transits

The next set of SDO maneuvers and other niceties has been released.
  • July 5, 1818 UTC 1320-1920 UTC (10:20 am ET - 3:30 pm ET) - EVE FOV and HMI/AIA Flatfield
  • July 12 - HMI Roll Maneuver
  • July 19 - EVE Cruciform Maneuver
  • July 23, 1818 UTC (2:18 pm ET) - Handover Season Starts (HGA +Z slew from storage)
  • July 24, 0449 UTC (00:49 am ET) - First Handover Begins
  • July 26, 1940 UTC (3:40 pm ET) - Momentum Management Maneuver #30
  • August 16, 0709 UTC (3:09 am ET) - Eclipse Season Starts
  • August 21, 1927-1955 UTC (3:27-3:55 pm ET) - Lunar Transit
  • August 30, 2241 UTC (6:41 pm ET) - Station Keeping Maneuver #15
  • September 9, 0650 UTC (2:50 am ET) - Eclipse Season Ends
  • September 25, 1942 UTC (3:42 pm ET) - Handover Season Ends (HGA -Z slew to storage, +Z Active)
  • October 19, 1941-2025 UTC (3:41-4:25 pm ET) - Lunar Transit (26% coverage)
  • December 20, Momentum Management Maneuver #31 (tentative)
The movie for the lunar transit has been updated. It isn't changed very much, but it's a nice finale to the Great American Eclipse taking place across the United States that day. From 1927-1955 UTC (3:37-3:55 pm ET) on August 21 the Moon will block up to 14% of the Sun.

Thursday, June 15, 2017

Measuring the International Sunspot Number

I was in Brussels visiting the Royal Observatory Belgium to talk about improving the accuracy of the International Sunspot Number. The ISN is the most important way we have to judge the Sun’s activity. Measurements from over 200 years ago have recently been found in several observatories and we would like to include them in the sunspot number. We are also looking at new ways to combine the data from the many observers who looked at the Sun since 1610. This would make the sunspot number record more accurate and help us understand the solar cycle.

While at ROB I saw how the ISN is measured. The Solar Influences Data Analysis Center (SIDC) at ROB is the World Data Center for the sunspot number and also measures the ISN as often as possible. Under a white dome sits several telescopes designed to look at the Sun. Every clear day an observer walks up the circular staircase to the floor of the observatory.

The long grey telescope projects a large image of the Sun onto a little table behind the telescope with four little spikes. The other telescopes are also used to study the Sun.

The observer secures a piece of paper on the spikes and draw what they see. There isn’t a lot of space and the back of your head can get very warm when it blocks the light of the Sun.

Here is a picture of what the paper looks like on the table. You can see the only sunspot group near the edge of the Sun by the upper right spike. It is quite small but has three spots in the group. (I was in the dome after the drawing for that day was finished and the telescopes are not centered on the Sun.)

Here is a picture of the actual drawing from that day. There is one small spot group with three visible spots. That makes the ISN, which is 10*number of groups + number of spots, 13 for 14-Jun-2017. This may change a little as other stations report, but the decline of Solar Cycle 24 is continuing.

My thanks to the people at the SIDC for both hosting our meeting and giving me at backstage look at the solar observatory. You can get more information, including more drawings and pictures of the Sun, are the SIDC website.

Thursday, May 25, 2017

Today's Lunar Transit

SDO had another visit from the Moon today, as it passed between SDO and Sun.
Here are two AIA 193 images showing the Moon moving onto and roughly maximum coverage.

Always nice to see another member of the solar system paying a visit. See you again in August!

Tuesday, May 2, 2017

Seven Years of SDO Data!

May 1, 2017 is SDO's 7th birthday of data collection. We launched on February 11, 2010, reached our final orbit, checked out the instruments and spacecraft, and began returning science data on My thanks to the SDO Team for their great work on this mission. My congratulations to the SDO Team for winning a NASA Honor Award for Group Achievement! This award reflects the effort and care the SDO Team has put into the mission.
We have updated a few things on the SDO Website. The kiosk movies will be turned off on May 31. Please migrate to the SDO Dashboard at, which has a lot more flexibility in setting up the 48-hour loop movies. As an added attraction, we have added some higher cadence channels (such as the AIA 171 Å channel shown here). This channel has also been produced with a radial gradient filter that enhances the corona around the edge of the Sun.
Update May 3, 2017: Here's an example of how to embed these html5 videos in a website using the high-cadence AIA 171 Å channel.


Wednesday, April 26, 2017

Server Maintenance - April 26, 2017

Notice. The SDO webserver will be down for maintenance today, April 26, 2017 at approximately 2:15pm. The outage for last for approximately one hour. We apologize for any inconvenience this may cause.

Today's Momentum Management Maneuver #29

Today between 1820 and 1845 UTC (2:20-2:45 pm ET) SDO will perform Momentum Management Maneuver #29. This thruster firing is used to keep the speeds of our reaction wheels within safe limits. As the wheel speeds are adjusted by their motors the thrusters fire to keep SDO pointed towards the Sun.

During this maneuver the science data from SDO may be interrupted or contain blurry images.

Tuesday, April 18, 2017

A Movie of the August 21, 2017, Lunar Transit

Here is a video showing the lunar transit SDO will see on August 21, 2017. While some in the United States will see a Total Solar Eclipse, SDO will see only a glancing transit an hour after the Moon's shadow leaves the US and goes over the Atlantic Ocean.

Monday, April 17, 2017

Today's EVE Cruciform and the Next Few Months

Today SDO is performing the EVE Cruciform. Images may be missing or blurry due to the motion of SDO. The 2017-094 SDO FDS Quarterly (LongSet) Predicts have been delivered. They extend through 2017 DOY 338. The highlights include:
  • 2017/109 (04/19) EVE FOV/ HMI/AIA Flatfield Calibration
  • 2017/116 @ 1825z (04/26 @ 1425L) - Momentum Management Maneuver (Delta-H) MM #29
  • 2017/145 @ 1824 to 1917z (05/25 @ 1424 to 1517L) - Lunar Transit
  • 2017/207 @ TBD (07/26 @ TBD) - Momentum Management Maneuver (Delta-H)MM #30 (tentative)
  • 2017/228 @ 0709z (08/16 @ 0309L) - Eclipse Season Starts
  • 2017/233 @ 1927 to 1955z (08/21 @ 1527 to 1555L) - Lunar Transit (LunTran_2017233_2dc_14pshdw)
  • 2017/242 @ TBD (08/30 @ TBD) - Stationkeeping Maneuver (Delta-V) SK #15 (tentative)
  • 2017/252 @ 0650z (09/09 @ 0250L) - Eclipse Season Ends
  • 2017/292 @ 1941 to 2025z (10/19 @ 1541 to 1625L) - Lunar Transit (LunTran_2017292_2dc_26pshdw)
With these new predicts we now think SDO will see a brief lunar transit on August 21, 2017, 1927-1955 UTC (3:27 pm ET to 3:55 pm ET). Although the Total Solar Eclipse passes over the continental US, SDO sees a brief transit 45 minutes after the Moon's shadow has moved off the coast into the Atlantic Ocean. More about this when the eclipse draws closer.

Tuesday, April 11, 2017

Website Update

Notice of upcoming change: The kiosk movies currently offered on the SDO website are being discontinued. We are launching a replacement called SDO Dashboard. Support for the kiosk product will end on April 30, 2017. The kiosk movies will be available until May 31, 2017. We are encouraging people to use our new product.

The dashboard product is located at: and is available for testing and use. The new product is similar in that is displays a looping movie of the most recent browse images. However, we are utilizing html5 video technology instead of the javascript slideshow used in the kiosks. This allows you to build your display in a drag-and-drop environment rather than a static html reference.

We are moving to html5 to satisfy website security requirements and to provide a better product. Some users have reported a noticeable flicker with the current kiosk javascript slideshow. Although we were unable to reproduce this flaw, wet concluded that it could be caused by several reasons including browser idiosyncrasies. The javascript solution also had a small memory leak. This necessitated a periodic browser refresh. Our new solution solves these issues and we are excited for the transition.

Monday, March 6, 2017

Planned Outage for the SDO website

A planned outage is scheduled for Tuesday, March 7, 2017. The outage will begin at approximately 8AM and will last until approximately 3PM. The website and all browse image products, movies, and RSS feeds will be taken off line for the duration.

Thursday, February 9, 2017

Happy Launch-versary SDO!

Seven years ago Saturday the Solar Dynamics Observatory rose into the Florida skies atop an Atlas V rocket. It was a spectacular sight that put a spectacular mission into orbit. To celebrate, here are some pictures of the models in my office with a solar spectrum lighting them up. (A prism in the window creates the spectrum. It's fun to watch people's reactions when it is displayed on the wall across the hall.)

On the left is the booster model and the right is a little display model of SDO. You can see more of the spectrum around the shadow of the nosecone. I think the rainbow looks pretty good on them. Reminds me of the sundog we saw during launch all those years ago.

SDO has helped to create over 2600 scientific papers since we began producing science data in May 2010. We are very happy that many young scientists are able to “cut their research teeth” in one of the 49 PhD dissertations that have been written using SDO data and science. People keep using helioviewer to look through the images and make movies.

Thanks for using our data. Many thanks to the science teams that keep SDO running.

Happy Launch-versary SDO!

Wednesday, January 11, 2017

January 2017 Maneuvers

Today SDO will perform the EVE Field-of-View calibration maneuver between 1315-1600 UTC (8:15-11:00 A.M. ET) and the HMI Offpoint calibration maneuver between 1630-1907 UTC (11:30 a.m.- 2:07 p.m. ET). During calibration maneuvers HMI magneto grams and Dopplergrams will not be available and AIA images will not be centered and may be blurry.

Last Wednesday, January 4, 2017, SDO successfully executed Momentum Management burn #28. Science data is not available during the 30 minutes of the burn.

The EVE Cruciform calibration maneuver will take place next Wednesday at 1700 UCT (noon ET) and the HMI Roll on January 25, 2017, at 1500 UTC (10:00 a.m. ET).