Using the Solar & Heliospheric Observatory Satellite (SOHO) to Determine the Motion of Coronal Mass Ejections (CMEs)

Kareena Shah
5 min readFeb 10, 2023

What are Coronal Mass Ejections?

Coronal Mass Ejections (CMEs) are large bursts of electrified gas that are periodically emitted from the Sun’s plasma and magnetic core which is known as the corona. In fact, when these CMEs are directed towards the Earth, they are responsible for the auroras and the majestic “northern lights” seen in the night sky.

The breathtaking “northern lights” are caused by CMEs directed at Earth.

CMEs threaten aspects of space exploration

Our Earth is able to effectively redirect these harsh and extremely hot flares due to its magnetosphere or layer of atmosphere that is responsible for protecting us from the particles that are emitted from the Sun. When a CME hits Earth’s magnetosphere, the magnetosphere peels open like an onion and streamlines the solar winds to hit the atmospheric poles. Upon impact, the strength of Earth’s magnetic field greatly decreases for 6–12 hours after which the magnetic field starts to gradually recover within a span of a few days.

A depiction of Earth’s magnetic field protecting our planet from solar particles. Credit: NASA/GSFC/SVS

While humans on Earth are well-protected from these solar flares, they pose a great threat to modern technologies both on Earth and outside of Earth. Most satellites orbiting Earth are communication satellites and CME-magnetosphere interactions which can lead to geomagnetic storms that can make these satellites highly charged disrupting key components. Electrical grids on Earth have an even higher chance of being damaged as the geomagnetically induced currents can greatly affect the conductive materials on Earth such as pipelines, communication cables, and power lines, thus leading to widespread blackouts. Imagine that.

Additionally, astronauts in outer space are under the constant threat of being hit (probably killed 💀) by a stray CME.

Leveraging preexisting data from SOHO:

But before we start, you must be wondering: What is SOHO?

SOHO is a satellite that was launched in December of 1995 with the sole mission of studying our Sun. Over the years it has collected data on the Sun’s internal (deep core) and external structure (outer corona) as well as the solar winds that are emitted into the solar system. To date, it slowly orbits the Sun around Lagrange point L1.

Source: ESA

I decided to investigate some preexisting data on previously studied CMEs from the Solar & Heliospheric Observatory Satellite (SOHO) satellite.

The Process:

Step 1:

This is an example of an image taken from one of the corona graphs on LASCO (Large Angle and Spectrometric Coronagraph), which is a set of three coronagraphs that image the solar corona and was one of the instruments of the SOHO mission. In these images, you will see a black disk, known as the occulting disk, which blocks out the disk of the Sun and the inner corona. The white circle in the images outlines the size and the location of the Sun. On the bottom of the image, there are tick marks that indicate units of the Sun’s diameter. And to the right of the disk, there is a hazy, whitish “blob” which is the CME erupting from the Sun. Five of these images were taken at different time stamps.

Step 2:

The next step in this process is to select a feature that is present in all five images. An example of this can be the outermost extent of the bright structure (CME) or the inner edge of the dark loop shape. Using the tick marks, you then measure the position of this feature in each image.

In this step, I chose the outermost extent of the bright structure (CME).

Step 3:

The measurements on each image can be converted into kilometers using a simple ratio as follows:

For reference, the diameter of the Sun is 1.4 million km

Step 4:

Using the time and position data you now have, the average velocity of the feature you have chosen can be calculated in a time interval. The following equation gives you average velocity, v.

Step 5:

Using the velocity and time data that you now have, the average acceleration of the feature you have chosen can be calculated in a time interval. The following equation gives you average acceleration, a.

Step 6:

Now all the results you have for the feature you have measured can be recorded in the data table similar to the one below. My results are as follows:

Feature: I analyzed the outermost extent of the bright structure (CME)

Step 7:

You can also repeat these measurements on another sequence of images from other CMEs. There is an online catalog of CME movies available. (Yashiro, S., and N. Gopalswamy, 2006). Once you place the movie, identify where the CME occurs and scale the images using tick marks as was done with the first set of images discussed above.

Sample image from CME movie:

Why does this matter?

Determining and measuring various features of CMEs is paramountly important to scientists and researchers in order to get a better understanding of how CMEs typically function and behave. If we are able to obtain this information and understanding, then we can predict potential CME interactions with satellites and other space technologies that can be severely negatively affected and cause huge catastrophic events such as widespread blackouts. We can then accordingly take action from preventing these events from happening and thus protecting human civilization from coming to a halt. Therefore, this research and the use of SOHO is extremely important to understand and continue for our societies to remain stable and safe.

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An inquisitive 17yo, Kareena Shah is embarking on an unconventional journey to work towards making space exploration and inhabitation a reality and along the way solve the world water crisis.

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**Reference: Olson, Andrew. “Using the Solar & Heliospheric Observatory Satellite (SOHO) to Measure the Motion of a Coronal Mass Ejection.” Science Buddies, 11 Sep. 2020.



Kareena Shah

A 17-year-old space tech enthusiast interested in leveraging space technology to make space exploration and inhabitation a reality.