Lightcurves and What They Tell Us
|Date||Brightness (Magnitude)||Date||Brightness (Magnitude)|
|April 21||9.2||June 20||8.7|
|April 27||9.3||June 26||8.3|
|May 3||9.7||July 2||8.6|
|May 9||9.9||July 8||9.1|
|May 15||9.6||July 14||9.1|
|May 21||9.8||July 20||9.2|
|May 27||9.9||July 26||9.5|
|June 2||9.7||Aug 1||9.9|
|June 8||9.1||Aug 7||9.7|
|June 14||8.8||Aug 13||9.7|
Here we have shown how bright the object would look to us through a telescope if we measured it every 6 days for a few months. This gives us a light curve of the object we have measured. But light curves can be generated for any physical measurement which is repeated over and over in time. So, if I measured the number of X-rays being emitted by a star during every second for an hour, I could generate a light curve from my observations. Or I could count how many people passed in front of me during a ten minute time interval while I sat on a park bench during my lunch hour. I could generate a light curve for this as well, but it would have no astronomical value (of course!). Astronomers call them light curves because it is usually some part of the electromagnetic spectrum (i.e. light) that we measure as a function of time and use to help us understand our universe.
How do we use light curves to tell us something useful?
If the light curve you measured looked like Figure 2, then you could identify your object as an eclipsing binary star. We can also tell from this light curve that it takes 10 days for one of the stars in the binary to orbit around the other one complete time. Astronomers would say this as "the orbital period of the binary system is 10 days."
|Click here to test your knowledge of light curves.|
|Click here to go to M31's light curve and solve for its velocity.|
|Click here to return to the beginning and try a different approach.|