Excerise

Using the images of ISON from Part 1, answer the questions below.

1. Measure the diameter of the coma of the comet. Do not include the tail. Make this measurement in units of pixels and how your work. Hint: the graph tool in Maxim will be handy for this measurement. An example of the graph tool is shown below.
2. The answer to question 1 is the angular size of ISON’s coma. Now, convert this angular size into a linear size using the Small Angle Formula and an image pixel scale of 0.725 arcseconds per pixel. Show your work and give your answer in km.
3. Now, find both the angular size and linear size of ISON’s tail in km. Show your work. 
4. Measure the distance traveled between two images of ISON in pixels. Then, find what this is in angular distance using the image pixel scale from question 2. Show your work.
5. Using the Small Angle Formula and the distance to ISON, determine how far the comet traveled in km. Show your work.
6. Using the FITS header (crt+f), determine how much time passed between your two measurements.
7. Now, calculate the speed of the comet in km/s. Show your work.
8. Is this the true velocity of the comet? Explain and be sure to include any assumptions you made in this calculation.

Tips:

• The pixel scale is 0.725 arcsec per pixel. 
•  Note that the orientation of the image is: N is up (i.e. increasing declination up), E is to the left (i.e. increasing right ascension to the left).  
• Stellarium will report coordinates of celestial bodies, including your ‘hypothesis’ body (question 2)
• The graph tool in Maxim (shown below) is useful for determining pixel separation between any two points, avoiding the need to use Pythagorean theorem.