CN+Milestone+Map+-+Light+Curves

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=Explain a light curve and be able to discern the different parts of a light curve.=

A light curve is a plot of a variable star’s changing brightness or magnitudes. A light curve also can tell you the type of variable star that produced the light curve, but not for every variable star. A light curve allows you to plot the changing brightness of a variable star over time, known as it's magnitude. As the star gets brighter the magnitude should decrease and as the variable star dims the magnitude should increase. The date and time is in the Julian date and all you have to record is the date and time of your observations and the brightness estimate. (__Observing Variable Stars__)

You can choose between a line, point or bar chart for your light curves. The point chart is the most commonly used of the three charts. A point chart displays each brightness estimate as a point correctly correlated with the proper date and time. (__Observing Variable Stars__)

The time interval is usually displayed along the horizontal axis or x-axis while the brightness estimate is displayed along the vertical axis or y-axis. (__Observing Variable Stars__)

Light curves allow you to see the variation in brightness that a variable star is experiencing. Depending on the star, you can see it vary over a period of seconds, minutes, hours, days, months, and years. (__Observing Variable Stars__)

"If you take measurements of the brightness of a variable star and graph them over time, you create your **//light curve//**. Notice how light curves are "folded" by the period of variability of the star. For example, if the star is known to repeat its variability every 7.0 days, then the horizontal time axis wraps around to the origin again every 7.0 days. This measurement of time "folded" using the period is called **//phase//**, and can be expressed either in days, or as the fraction of the star's cycle from start (0.0) to finish (1.0). Here are two such light curves of Cepheid variable stars:" ([|Light Curves])

"You may notice that both Cepheid variables above brighten to their maximum faster than they dim to their minimum. They are "classical Cepheids," as is our star, Delta Cephei." ( [|Light Curves])

"Not all light curves are the same for each type of star though. Here is a light curve for an eclipsing binary."([|Light Curves])



References: Observing Variable Stars by Gerry A. Good http://imagine.gsfc.nasa.gov/docs/science/how_l1/light_curves.html http://www.ifa.hawaii.edu/users/mendez/ASTRO110LAB07/variables.html