Friday, August 19, 2011

Inconstant Star

Pulsations of S Cassiopeiae

Here's the third example of my not widely shared observations made at Winfree Observatory at Randolph Macon Woman's College (now called Randolph College).

Some things we want to remain constant:
  • Good health!
  • Good friends!
  • The Sun!!!
Without a constant Sun we are all in big trouble! Is the Sun truly constant? Fortunately, solar energy output doesn't vary much. For example, look at this graph:
From 1975 to 2007 the Sun's power output (measured in watts per square meter arriving at Earth) only changed by about 0.1 percent. Consequently, Earth didn't freeze or fry by deadly amounts. But many stars on the path to extinction are not constant. Some of these stars drastically change brightness while pulsating in and out! One such star is called S Cassiopeiae (the variable star S in the constellation Cassiopeia). This star is located by the red X to left of the constellation Cassiopeia in the picture below:
(click to enlarge)
S Cassiopeiae slowly pulsates and changes brightness with a period of 612 days. Perhaps a drastically sped up version of its appearance would look something like this:

I measured the brightness of S Cassiopeiae at Winfree Observatory from 2001 to 2009. Here's a graphical record of my observations:
(click to enlarge)
The vertical scale is an astronomer's (logarithmic) scale of brightness measured through a photometric green filter (also known as a visual, or V, filter). The smaller the magnitude, the brighter the star. The horizontal scale shows elapsed time, measured in days, running from September, 2001 to February, 2009. There are gaps in the graph because many times observations were impossible. Sometimes the view to S Cassiopeiae was blocked by trees. Sometimes the weather was bad for weeks on end. Sometimes the telescope was down for repairs.The brightest measurement I have is magnitude 8.45 and the dimmest measurement is magnitude 16.61. This corresponds to a change in brightness by a factor of about 1840! In other words, the star S Cassiopeiae can become 1840 times brighter than its minimum brightness! If our Sun varied this much we would all be dead!


  1. I feel reassured that the sun is not going to die anytime soon. =)

  2. I like how you have chosen to dramatize your variable star measurements by comparisons with the sun. Yikes!


People say I'm crazy doing what I'm doing
Well they give me all kinds of warnings to save me from ruin
When I say that I'm o.k. well they look at me kind of strange
Surely you're not happy now you no longer play the game

People say I'm lazy dreaming my life away
Well they give me all kinds of advice designed to enlighten me
When I tell them that I'm doing fine watching shadows on the wall
Don't you miss the big time boy you're no longer on the ball

I'm just sitting here watching the wheels go round and round
I really love to watch them roll
No longer riding on the merry-go-round
I just had to let it go

John Lennon