light curve

(astrophysics) A graph showing the variations in brightness of a celestial object; the stellar magnitude is usually shown on the vertical axis, and time is the horizontal coordinate.

Graphs of the intensity of radiation from astronomical objects as they change with time. Variations may be caused by the changing perspective from the Earth of two stars in orbit around each other, by pulsations that change an individual star's size and surface temperature, by mass ejection or accretion, by explosions, by beams of radiation sweeping across the line of sight from the Earth, or by clouds of very high-energy electrons in powerful magnetic fields. The information contained in the light curve includes the timing of events, such as eclipses or pulses, and the amplitude of changes in the radiation received at Earth.

Each data point in a light curve is a photometric measurement, recorded at a particular time. These points represent measurements of the amount of radiation from the source received at Earth per second per area in a particular bandpass, for example, through a blue filter. In optical light, photometry is affected by the varying transparency of the atmosphere, so that light curves are often obtained as ratios to the intensities of nearby comparison stars. Simultaneous measurements can be made visually, with photometers that have two channels or with imagers, such as charge-coupled devices (CCDs) or photographic emulsions. These relative light curves are put on an absolute scale by means of calibrating measures of the comparison stars taken on clear nights. See also Astronomical photography; Charge-coupled devices; Magnitude (astronomy); Photometry.

Light curve of the asteroid 201 Penelope based on images taken on 6 October 2006 at Mount John University Observatory. Shows just over one full rotation, which lasts 3.7474 hours.

In astronomy, a light curve is a graph of light intensity of a celestial object or region, as a function of time. The light is usually in a particular frequency interval or band.

Light curves can be periodic, as in the case of eclipsing binaries, cepheid variables and other variables, or aperiodic, like the light curve of a nova, a cataclysmic variable star or a supernova.

The study of the light curve, together with other observations, can yield considerable information about the physical process that produces it or constrain the physical theories about it.

In planetology, a light curve can be used to estimate the rotation period of a minor planet or moon. From the Earth there is often no way to resolve a small object in our Solar System, even in the most powerful of telescopes, since the apparent angular size of the object is smaller than one pixel in the detector. Thus, astronomers measure the amount of light produced by an object as a function of time (the light curve). Looking for peaks in the light curve can produce estimates of the rotation rate of the object, assuming that there are parts of the object that are brighter or darker than average. In this case, there is sometimes aliasing, where it is unclear whether there is one or two light curve peaks per rotation period. For example, an asteroid light curve is a light curve of an asteroid, caused by the fact that asteroids are generally non-uniform in shape. This light curve can be used to determine an asteroid's spin rate.^[1]

References

1. ^ Harris, A. W.; Warner, B.D.; Pravec, P.; Eds. (2006). Asteroid Lightcurve Derived Data. EAR-A-5-DDR-DERIVED-LIGHTCURVE-V8.0.. NASA Planetary Data System. Retrieved on 2007-03-15.

External links

• The AAVSO online light curve generator can plot light curves for thousands of variable stars
• Lightcurves: An Introduction by NASA's Imagine the Universe

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