Absolute Magnitude

Abstract

When you look at an asteroid through the eyepiece of a telescope, or on a CCD image, it is a rather unexciting point of light. However by analyzing a number of images, information as to the nature of the asteroid can be gleaned. As we have seen in the previous chapter, frequent measurements of magnitude over periods of several minutes for fast rotators, or hours or even days for very slow rotators, can be used to generate a lightcurve. Analysis of such lightcurves yields the rotational period, shape, and pole orientation of the asteroid (Chap. 13). As described in Chap. 10 and 11, measurements of position (astrometry) can be used to calculate the orbit of the asteroid and thus its distance from Earth and the Sun at the time of the observations. By combining the results from photometry and astrometry the absolute magnitude, H, and the slope parameter, G, can be derived. (It is quite common for G to be given a nominal value of 0.015.)