A Station Keeping Maneuver in the Spring 2016 Eclipse Season

SDO's Spring 2016 Eclipse Season started on February 19, 2016, with the Earth passing between SDO and the Sun at 0712 UTC that day. The top picture shows the Earth moving across the Sun in an AIA 171 Å image while the bottom picture shows the Earth almost covering the Sun 15 minutes later. Eclipse season runs through March 12, 2016.

On Wednesday, March 2, 2016, SDO will execute stationkeeping maneuver #12 at 2250 UTC (5:50 p.m. ET). Science data will be unavailable for about 45 minutes starting 2235 UTC. These maneuvers are used to help SDO be a good neighbor in the geostationary belt that we pass though twice each day.

Movies of the Alignment at NASA

NASA has posted a feature about the alignment yesterday morning. It looks great!
http://www.nasa.gov/feature/goddard/nasas-sdo-catches-a-double-photobomb
Check it Out!

I made a short video from the AIA jpeg2000 images. You can also make these movies at HelioViewer. The motion of the Sun is caused by the telescope heating up as the Sun rises. SDO cannot run its fine guidance system without seeing the entire Sun. During an eclipse the fine guidance system is turned off and a little while after the eclipse it is turned back on.

An Alignment of the Four Most Important Objects in the Solar System

Sunday morning, September 13, 2015, we will have an alignment of the four most important objects in the solar system. SDO, the Earth, the Moon, and the Sun will form a line in space. From 0614 UTC (2:14 a.m. ET), when the Earth's edge touches the edge of the Sun, until 0721 UTC (3:21 a.m. ET), when the Moon's edge leaves the Sun, SDO's field of view will be blocked by either the Earth or Moon. The attached movie was produced by the SDO flight operations team to show how the eclipse and lunar transit will look from SDO. This is the first time an eclipse by the Earth and a lunar transit will be seen by SDO. (Although we can see features on the Earth and Moon in the video, we cannot see them in the SDO cameras.)

But that's not all! At 0655 UTC (2:55 a.m. ET) a partial solar eclipse will be visible in Antarctica. The path of the solar eclipse starts in southwestern Africa and goes almost over the South Pole. On the left is a picture from NASA's Eclipse webpage showing the path of the solar eclipse. This is the first time a solar eclipse was visible on the Earth during an SDO lunar transit. SDO cannot see the entire solar eclipse because the Earth gets in the way. The Moon was at perigee (closest point to the Earth) for the Full Moon two weeks ago. That means it is at apogee (furthest point from the Earth) for the New Moon on Sunday. The Moon will appear to be a little smaller than average so a total solar eclipse is not possible this month.

On September 28, 2015 a total lunar eclipse will be visible from most of the United States, Europe, South America and Africa. SDO does not see lunar eclipses because we look the other way. Not to worry, SDO will see another Lunar Transit on October 12, 2015 from 1718 – 1733 UTC (1:18 – 1:33 p.m. ET). It will be a grazing transit. Because SDO will not be near midnight Mountain Time, this transit will not be seen at the surface.

I hope you enjoy the Alignment of the Four Most Important Objects in the Solar System.

Welcome to the Fall 2015 Eclipse Season

Today is the beginning of SDO's Fall 2015 eclipse season. From today until September 17, 2015, the Earth will pass between SDO and the Sun once each day. SDO orbits at about the longitude of Boulder, Colorado, so the eclipse is at midnight solar time there. This corresponds to roughly 0700 UTC. Here is the first eclipse, right on schedule at 0710 UTC (1:10 a.m. MDT).

This picture shows the edge of the Earth against the Sun in AIA 193. You can see the edge of the Earth is rough, where the absorption of the Earth's atmosphere dims but does not block the light. This is different from the lunar transits, such as the one coming up on September 13, where the Moon's edge is very crisp. That transit occurs near the end of that day's eclipse and coincides with a solar eclipse in the far southern parts of the Earth.

Eclipse season is a result of our geosynchronous orbit. We don't like missing the Sun for up to 72 minutes each day. But the constant contact with SDO allows the high speed data downlink we use to bring the Sun to everyone.

Stationkeeping Maneuver #11 is Today

SDO will execute Stationkeeping Maneuver #11 today from about 2245-2315 UTC (6:45-7:15 p.m. ET). This Delta-V burn is used to keep the observatory within the assigned orbital box. During the maneuver the science data is usually not valid as the spacecraft slews away from the Sun to orient the thrusters in the correct direction.
The next eclipse season starting August 25, 2015, giving us more chances to see the Earth's limb against the Sun. Eclipse season ends September 17.

The next lunar transit on September 13 will have two firsts. The eclipse by the Earth will happen just before the transit and finish while the Moon is still crossing the Sun. At the same time a partial solar eclipse will be visible in the South between Antarctica and Africa. This will be the first time an SDO lunar transit could be seen as a solar eclipse on Earth. The movie of the combined eclipse and transit looks like a race between two spacecraft.

A month later we see another lunar transit on October 12 from 1718 to 1734 UTC (1:18-1:34 pm ET). This is more of a glancing blow but will be cool to watch.

Spring 2015 Eclipse Season has Begun

The spring 2015 eclipse season has begun! Yesterday at 0711 UTC (2:11 am ET) the Earth passed between SDO and the Sun. We can't see the Sun during the eclipse, but we do see interesting shapes as the Earth's edge moves past the Sun. The atmosphere of the Earth absorbs the extreme ultraviolet radiation from the Sun and emphasizes the bumpiness of the emissions.

This eclipse season runs until March 17, 2015.

Fall 2014 Eclipse Season Ends; Lunar Transit is Next

Yesterday saw the end of the Fall 2014 eclipse season. If you look carefully in the upper right corner of this AIA 211 sequence you can see the limb of the Earth. The image at 0629 UTC looks dimmer and the corona is missing because of the atmosphere of the Earth absorbing the sunlight. The image is darker over most of the polar cap, although that is easier to see if you use the SDO data browser. Select the times for 22-Sept-2014 and AIA 211 to watch the dimming of the Sun caused by the atmosphere of the Earth.

The Sun appears dimmer in the upper right corner where the Earth's atmosphere is absorbing the EUV light.

Our next lunar transit is Wednesday, 24-Sept-2014, from 0650-0720 UTC (2:50-3:20 am ET). This movie from the SDO FDS team shows that the Moon will cover less than half of the solar disk during this transit. There are a lot of bright active regions in that part of the Sun, so the sharp edge of the Moon will probably cover something interesting.

Our last lunar transit is 22-Nov-2014, from 2225-2305 UTC (5:25-6:05 pm ET). This movie from the SDO FDS team shows that the Moon will cover only a small part of the Sun during this transit. There aren't a lot of bright active regions in that part of the Sun, but the sharp edge of the Moon often covers something interesting. This is the fourth and final lunar transit that SDO will see in 2014.
Edited 14:45 ET to correct the movie of tomorrow's transit.

An Astronomical Picture of SDO

One of the cool things about knowing astronomers is the clever things they do with cameras. Here is one example. William Livingston, a solar astronomer living in Tucson, AZ, has taken pictures of the geostationary satellite ring since about 2001. These satellites tend to be big, and stay in one place over the Earth. By taking a long exposure (here about 9 hours), the satellites are almost points of light while the stars are long trails. (A nine hour star trail would cover 135 degrees of the sky.) Here is an example from March 2014. You can see 40 satellites in the center of the picture, all but one labeled with their name. SDO orbits the Sun every 24 hours, but at an angle to where these satellites orbit. Because it does not hover over the same place on Earth, SDO moves up and down through the geostationary satellites every day. So SDO isn't a point of light, it is another trail moving across the star trails. To help you find it, SDO is labeled on the plot. It is the very faint trail moving downward from between DirecTV 11 and DirecTV 8 to the l in Solar.

Dr. Livingston has been taking these pictures since 2001. I found a link about some of his first pictures. Another link describes the settings for digital cameras if you want to try to take pictures yourself. You'll need a dark sky and a steady mount!

Thanks to Bill for sending me these pictures.

2014 Spring Eclipse Season has Begun

The SDO 2014 Spring Eclipse Season has begun! For the next 3 weeks the Earth will pass between SDO and the Sun around 0730 UTC each morning. They start short and last up to 72 minutes before tapering back to short.

Here is an image from our first eclipse. It is always nice to see the ragged edge of the Earth's atmosphere as the bright spots on the Sun shine through while the dimmer regions disappear. Here we can see AR 11988 near the edge of the Earth, with a coronal hole just to the right. Active regions 11981-11984 are further to the right and are hardly affected by the Earth, although they soon disappear behind the Earth.

When SDO can't see the Sun we don't get data. Eclipses are one of our largest data holes. But the orbit gives us 24/7 access to the data flow. So far we have received 98% of the data, so the eclipses aren't a problem but they are pretty!

Fall 2013 Eclipse Season has begun

The SDO Fall 2013 Eclipse Season has begin. Every day until September 25, 2013 some part of the Earth's shadow will pass through the SDO telescopes. Here are pictures from the first eclipse of the 2013 season. On the top is a He II 304 image from 0659 on September 2 and on the bottom is a AIA 193 image from about a minute later. The Earth's shadow appears more ragged in the 193 image because of the way the gases in that atmosphere absorb the EUV light AIA is observing and the way that light is generated by the Sun. The He II plasma tends to be cooler and be held closer to the Sun's surface while the 193 emitting plasma is hot enough to extend well off the surface. You can see that difference by looking at the glow just off the edge (or limb) of the Sun near the top of the Sun.
You use the SDO data browser to flip through these images and see the interplay between the atmospheres of the Sun and Earth.

Spring 2013 Eclipse Season has Begun

March 2, 2013 saw the first eclipse of the SDO Spring 2013 Eclipse Season. It was a partial eclipse, blocking only the upper left part of the Sun. Here are images from two AIA channels showing the eclipse at around 0715 UTC yesterday. The 193 image on the left shows the highly structured corona with the Earth passing by. The right shows the 1600 bandpass a few minutes later. The 1600 image has a much more uniform flow on the surface of the Sun and a much sharper (though still a little fuzzy) edge of the Earth. There is also a crescent of darkness over the top of the Sun that is not related to the eclipse.

The 2013 Eclipse Season continues until March 26. This season also has a lunar transit on March 11, from 1135-1243 UTC, a momentum management burn at 1901 UTC on March 13, and a station keeping burn at 2339 UTC on March 20.

Looks like March is going to be a busy month!

Fall 2012 Eclipse Season Ends Tomorrow

The Fall 2012 SDO eclipse season ends tomorrow. Here is a look at the penultimate eclipse in the AIA 1600 bandpass. This wavelength of light is absorbed by the Schumann-Runge continuum of molecular oxygen at an altitude of about 110 km. This creates atomic oxygen, which moves upwards and creates the thermosphere. That atomic oxygen also is ionized by solar EUV to create the ionosphere.
At this wavelength the Sun looks like a ball with a thin, lacy network, bright active regions, and dark sunspots. Many of these features are a little above the visible surface of the Sun. They are held up by the solar magnetic fields. Welcome to the chromosphere, a layer of the solar atmosphere that will be studied by the Iris satellite. The people at LMSAL who built AIA and HMI are building Iris and hope to launch it in January.

Fall Eclipse Season has Begun

Today was the beginning of the Fall 2012 eclipse season. This image in AIA 171 shows that the Earth covered about half of the Sun this morning at 0700 UTC.
With the SDO geosynchronous orbit comes an eclipse season twice each year. They last for several weeks; this will end on September 26 (just in time for our next maneuver).

Last Eclipse of the Spring Season

Today we had the last eclipse of the Spring 2012 Eclipse Season. Here are 4 images of the Sun at about 0630 UT today. Comparing the upper left image (1600) with the upper right and lower left we see the different ways the Earth's atmosphere absorbs light from the Sun. Ultraviolet light at 1600 Å is absorbed about 105 km above the surface of the Earth while 193 is absorbed at 130 km and 304 at 150 km. (171 is absorbed at 120 km). The 1600 edge is pretty straight while the others are rougher. Changes across the disk of the Sun are important in the other three channels, but the effects of changes in the Earth's atmosphere at 150 km can be seen at the top of the 304 image.

To really see the effects of the Earth's atmosphere you should use difference images. If all of the solar patterns can be determined you can map the Earth's thermosphere with these partial occultations.

Next on the schedule is a ΔV burn today at 2315 UTC (7:15 pm ET).

Eclipse Season Starts Today

March 6, 2012 marks the beginning of the SDO Spring Eclipse Season. For the next three weeks the Earth will pass between SDO and Sun at about midnight Boulder time. The length of the occultation will vary from short to almost 72 minutes. Thee eclipses are a normal part of life in a geosynchronous orbit.

The AIA data is currently stale (i.e., delayed) but the problem is being looked at.

The Think Scientifically Books are Out

The first two Think Scientifically books are available from SDO Educators Website. Each book focuses on a key science theme and includes a hands-on science lesson, math and language arts activities, and other educational resources that can be easily utilized in the classroom. The books are based on national standards and were written by teachers. Both books can be downloaded as pdf files from this website.

SDO began High Gain Antenna (HGA) handover season on February 23 and all handovers have been successful since then. The FOT is ready for the beginning of eclipse season on March 6. The next momentum unload maneuver in scheduled for March 14.

Fall 2011 Eclipse Season Begins

The Fall 2011 eclipse season started today. Here is an AIA 171 image from 0657 UT with the first eclipse! SDO has eclipse seasons twice a year near each equinox. For three weeks near midnight Las Cruces time (about 0700 UT) our orbit has the Earth pass between SDO and the Sun. These eclipses can last up to 72 minutes in the middle of an eclipse season. The current eclipse season started on September 11 and lasts until October 4. The continuous contact with the ground station our orbit allows was judged to outweigh the loss of some images.

What's Up With the Sun on March 29, 2011?

Two topics need to be covered this week. We'll do one today. What happened while SDO exited the eclipse on March 29? The pictures at the left show images in four AIA wavelengths (304, 171, 193, and 335) at about 07:14:50 UT Tuesday. The edge of the Earth is the ragged line across the southern hemisphere of the Sun. Where is the sharp line seen in the HMI movie from the FirstLight gallery or the edge of the moon in a lunar transit?


The answer is a combination of atmospheric absorption and color tables. The sharp line in HMI is in the visible spectrum and emphasizes the thinness of the troposphere that we live in. Light at the EUV wavelengths of AIA is completely absorbed much higher in the Earth’s atmosphere (at an altitude of about 300 km at the limb). Even small amounts of atmosphere remove the light from the picture. Then the image is processed into an image we can see by changing to a log intensity and scaling to a color table. The log intensity makes the bright bits and dim bits visible in the same image but over-emphasizes the dim background. Even a little absorption is enough to cause a dim region to drop to below the minimum intensity allowed in the color table, hence the irregular border that traces out the dimmer regions seen in the following uneclipsed image.


Eclipse season ends Saturday, so back to images 24/7 on Sunday.


Next topic: protons, hot pixels, and interstellar spaceships.

Spring 2011 Eclipse Season Has Begun

The spring 2011 eclipse season has begun. Every day until April 2, 2011 there will be a short break in the data flow as the Earth moves between SDO and the Sun. The length of an eclipse can be as long as 72 minutes and they happen at about midnight at our ground station in Las Cruces, NM (0700 UT).

The EVE calibration rocket flight from WSMR is scheduled for 3/22 between 1800-1830 UTC.