Chris asked -
What do the various dots represent, and what should
the graph, overall, be telling me? [ http://www.astrosurf.com/snweb2/2005/05cs/05csCurv.htm ]
The dots tell you the brightness in magnitudes of one star - supernova sn2005cs in M51 - seen through a clear eyepiece and through various colored filters. The significance of the curve is you can use it, and similar curves for other supernova or for variable stars, to make a rough guess of whether it is worth it to try to look for the variable star using the aperature and light gathering power of your scope. The "x" axis is in Julian Days. Use the AAVSO Julian Day Calendar for 2005 and calculator as a decoder ring to convert to standard calendar dates. Day 3560 is July 8. To find a particular day, go to the left from 3560, counting backwards. http://www.aavso.org/observing/aids/jdcalendar.shtml http://www.aavso.org/observing/aids/jd2005.pdf The "y" axis is brightness of star in magnitudes as seen unfiltered and through various standard filters. The color codes for the filters are at the bottom of the graph are at the bottom. Here is a decoder ring for the various codes: Filter Photometry type VSNET Code None "R" USNO CR None "V" Uncalibrated C R "R" USNO R R "R" Calibrated Rc B "B" Calibrated B V "V" Calibrated V I "I" Calibrated Ic Looking at just the clear circles - the unfiltered "V" magnitude points, at the left hand side of the graph the supernova is observed at mag 16 on Julian Day 3548 (June 26). Two days later on June 28 (Julian Day 3550), it has brightened to mag 13.4. By Julian Day 3558 (July 6), the supernova has passed its peak and has dimmed to mag 14.4. Although 14.4 is pretty dim, in a related thread on this listserve, titled "M-51 SN picture" and posted today by Patrick, he was able to capture the supernova on a photograph on July 7 (Julian Day 3559) using a camera and 14 inches of aperature. The supernova is much dimmer than a 13.9 reference star to the left of galaxy (in Patrick's picture). Patrick's picture << http://www.trilobyte.net/paw/temp/M51SN001.JPG >> The other color filters are used to measure the brightness of the star through standard passbands of light. By tracing the curves for each set of colored dots, you can see that the supernova was brighter in the red and infrared bands than in the more energetic blue light band. The differences between the bands and the time-shape of the curve is used by professional astronomers to determine the type of supernova. For amateurs, primary use of the light curve is to decide if the variable star (a supernova in this instance) is too dim to bother with using your available aperature. Enjoy - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com