light intensities

Light curve

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.


In botany, a light curve shows the photosynthetic response of leaf tissue or algal communities to varying light intensities. The shape of the curve illustrates the principle of limiting factors; in low light levels, the rate of photosynthesis is limited by the concentration of chlorophyll and the efficiency of the light-dependent reactions, but in higher light levels it is limited by the efficiency of RuBisCo and the availability of carbon dioxide. The point on the curve where these two differing slopes meet is called the light saturation point and is where the light-dependent reactions are producing more ATP and NADPH than can be utilized by the light-independent reactions. Since photosynthesis is also limited by ambient carbon dioxide levels, light curves are often repeated at several different constant carbon dioxide concentrations.


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