How to read a STEREO image

October 26, 2016 by Lina Tran, NASA
Composite animation of coronal mass ejection as observed by STEREO. Credit: NASA Goddard/STEREO

In the same way that two eyes give humans a three-dimensional perception of the world around us, the twin spacecraft of NASA's Solar Terrestrial Relations Observatory mission, or STEREO, enable us to understand the sun in 3-D. Thanks to this mission, which launched on Oct. 25, 2006, we can see and study the sun from multiple viewpoints – crucial for understanding solar activity and the evolution of space weather.

One of STEREO's key instruments is called a coronagraph, which is used to study the corona, the sun's outer atmosphere. Each of STEREO's coronagraphs has a metal disk called an occulting disk. The occulting disk blocks the sun's bright light and makes it possible to discern the detailed features of the surrounding corona, which is about one million times dimmer than the sun. Much like the way the bright headlights of a semi-truck at night hide just how big the truck is, the brightly shining sun makes it difficult to study the much fainter corona.

In celebration of the mission's 10th anniversary, here is a guide to reading a STEREO image. Watch the video below, created with imagery of a massive July 2012 , to learn the key features of STEREO coronagraph data.

Space, in color

Each STEREO spacecraft has two coronagraphs with occulting disks of different sizes. The colors you see in the image are not true to life; scientists color the images to quickly tell which instrument in particular the image is from. In this video, the coronagraph image is colored blue.

Occulting disk

The black circle in the center of the coronagraph image is the occulting disk, which blocks the disk of the sun. The occulting disk mimics a total solar eclipse seen from Earth, in which the moon perfectly blocks the sun and allows observations of the massive corona.

The sun, in extreme ultraviolet light

Sometimes STEREO coronagraph images incorporate imagery from another one of STEREO's instruments called the Extreme UltraViolet Imager, which captures the sun in a type of light that is invisible to human eyes. Later, these images are colorized. These light images are sometimes imposed over the occulting disk to help give a sense of the sun's size and position, and to provide more information as to which direction a solar eruption is headed. Extreme ultraviolet light images highlight active regions on the sun – regions where intense magnetic activity can give rise to solar eruptions. Here, STEREO observed the CME bursting forth from this active region.

NASA’s STEREO mission observed a coronal mass ejection on July 23, 2012 – one of the fastest CMEs on record. The video uses STEREO imagery from this rare event to describe features to pay attention to when viewing STEREO data. Credit: NASA’s Goddard Space Flight Center/STEREO/Joy Ng, producer
Stars

Stars are often present in STEREO coronagraph images. These are the steady, brightly shining specks in the background.

Diffraction patterns

Faint ripples around the edge of the occulting disk result from diffracted light. When light enters the telescope, it hits the edge of the metal disk and bends, or diffracts, around the disk.

Streamers

Radial structures flowing out from the corona are called streamers. Solar material in streamers and the corona flow out into space to form the solar wind that fills our solar system.

Coronal mass ejections

Coronal mass ejections are eruptions of solar material that shoot far out into space, often accelerating particles ahead of them to near-light speeds. On July 23, 2012, STEREO-A saw this CME – one of the fastest on record. Scientists call this sort of CME a halo CME because the solar material forms a complete ring around the sun.

High-energy particle snow

As the CME expands beyond STEREO's field of view, a flurry of what looks like snow floods the image. These are high-energy particles flung out ahead of the CME at near-light speeds, striking the charge-coupled device in STEREO's camera. The immediacy and intensity of this "snowstorm" in space following the CME reflects just how fast and strong the eruption is: Less than an hour after the start of this eruption, accelerated particles traversed approximately 93 million miles from the sun to STEREO.

Explore further: Image: SOHO captures bright filament eruption

Related Stories

Image: SOHO captures bright filament eruption

May 5, 2015

An elongated solar filament that extended almost half the sun's visible hemisphere erupted into space on April 28-29, 2015, in a large burst of bright plasma. Filaments are unstable strands of solar material suspended above ...

Proba-3—set the controls for the verge of the sun

September 12, 2016

By converging in orbit, a pair of small satellites will open a new view on the source of the largest structure in the Solar System: the Sun's ghostly atmosphere, extending millions of kilometres out into space.

NASA's STEREO-A resumes normal operations

November 19, 2015

On Nov. 9, 2015, NASA's Solar and Terrestrial Relations Observatory Ahead, or STEREO-A, once again began transmitting data at its full rate. For the previous year, STEREO-A was transmitting only a weak signal—or occasionally ...

Sun has "eureka!" moment

August 27, 2012

(Phys.org)—At the onset of a series of coronal mass ejections (CMEs) on August 20, 2012, this bulbous CME certainly resembled a light bulb. It has the thin outer edge and a bright, glowing core at its center. CMEs are often ...

NASA establishes contact with STEREO mission

August 23, 2016

On Aug. 21, 2016, contact was reestablished with one of NASA's Solar Terrestrial Relations Observatories, known as the STEREO-B spacecraft, after communications were lost on Oct. 1, 2014. Over 22 months, the STEREO team has ...

Recommended for you

Apple pivot led by star-packed video service

March 25, 2019

With Hollywood stars galore, Apple unveiled its streaming video plans Monday along with news and game subscription offerings as part of an effort to shift its focus to digital content and services to break free of its reliance ...

How tree diversity regulates invading forest pests

March 25, 2019

A national-scale study of U.S. forests found strong relationships between the diversity of native tree species and the number of nonnative pests that pose economic and ecological threats to the nation's forests.

Scientists solve mystery shrouding oldest animal fossils

March 25, 2019

Scientists from The Australian National University (ANU) have discovered that 558 million-year-old Dickinsonia fossils do not reveal all of the features of the earliest known animals, which potentially had mouths and guts.

Earth's deep mantle flows dynamically

March 25, 2019

As ancient ocean floors plunge over 1,000 km into the Earth's deep interior, they cause hot rock in the lower mantle to flow much more dynamically than previously thought, finds a new UCL-led study.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.