I took a look at the project at the administrator added link and from there think I found the project you are referencing is the "Using the Solar & Heliospheric Observatory Satellite (SOHO) to Measure the Motion of a Coronal Mass Ejection" one at: http://www.sciencebuddies.org/science-f ... p020.shtml
I am familiar with the SOHO mission and it's data...so I hope i'm answering the right question. The technique to determine actual position of the CME from the image of the screen is to relate 2 ratios where you have 3 knowns and 1 unknown which can be directly solved for. This is the (d_screen/d_actual) = (s_screen/s_actual) equation.
1) measure the diameter of the outer edge of the white circle (this represents the size and location of the Sun) on the print out with a ruler in cm (I suggest converting to km).
2) divide the above number (d_screen) by what we know to be the actual diameter (d_actual) of the Sun (1.4 million km) to determine the scaling ratio (a very small number - I came up with 5.67x10^-12).
3) per the direction, pick a feature of the CME that is visible in all images and measure to it from the outer edge of the white circle representing the Sun, through the edge of the occulting disk where the CME emerges. This is s_screen.
4) solve for s_actual = s_screen*(d_actual/d_screen). Make sure you maintain unit agreement.
5) the Time Interval (t2 - t1) is the time difference between any two measurements (say 1st and 2nd, 2nd and 3rd, 3rd and 4th, etc...). SOHO images are time stamped so in the example given the images were taken at 0805, 0836, 0927, 1025, and 1123 cooresponding to delta_t (min) of 31, 51, 58, and 58 there is no time difference for the first measurement because we don't know when the CME errupted, only when we first detected it above the occultation disk at 0805.
6) solve for average velocity using given equation. Again, the first measurement block will be blank. Making sure of unit agreement velocity is in km/s.
7) solve for average acceleration in similar manner. The first 2 blocks will be blank because the first velocity measurement is in the second line of data. Unit agreement, acceleration is in km/s^2.
This is alot to try and explain in what amounts to an email, so I hope I didn't muddy the waters further. Please post back with any further questions.
I hope this helps.
"As the circle of light increases, so does the circumference of darkness around it."
~ Albert Einstein