The comet Swift-Tuttle orbits the Sun with a period of about years. Whenever the comet comes close to the Sun in its orbit, it ejects a stream of dust particles, which are then distributed along its orbit. When the Earth passes through their path - a regular occurrence every August - we see a meteor shower, a fabulous spectacle for viewers on Earth.
The last such ejection from Swift-Tuttle took place in Due to the relative orientation of the orbits of Earth and the comet, the meteor shower appears to originate from the constellation Perseus. As dust particles enter the atmosphere, they interact with it and generate light before they disappear. The campaign had three main goals: to determine the orbits that the particles followed before they encountered the Earth, to study the physical properties of the dust by recording the light they emit or their light-curve , and to test the performance of a new camera, known as the Smart Panoramic Optical Sensor Head SPOSH.
The SPOSH camera, a highly sensitive instrument, is built for future use as a night-side imager of planets. It could also be used to observe meteors from space. The test during the Perseid shower showed that the camera, which can image almost the complete sky, performed flawlessly. The top image, obtained with SPOSH during a minute time frame with 2-second exposures, shows that stars appear to describe arcs around the pole star.
The pole star itself shows up as a point, as it hardly moves during the exposure time. Meteors are visible as streaks crossing the path of the stars. One of the cameras used by the ESA team was equipped with an objective grating, which splits up the meteor light into spectral colours. This allows the determination of the chemical composition of the particle.
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The extreme values for a symmetric NC-type light curves are NC 0. Table 1 indicates the measured parameters for the three non-convex light curves shown in Fig.
In this respect the light curves shown in Fig. By definition, we note, no convex light curve will require a complexity qualifier. The D NC values for the light curves shown in Fig. In principle the complexity qualifiers might also be subdivided, with, for example, the flare qualifier FR one might also include information about the relative locations of the flare s along the trail.
The light curve shown in Fig. Such an extended classification scheme, however, is probably only useful if a specific study of flare characteristics is being made. A number of characterization schemes for meteor light curves have been described over the years. In perhaps the first systematic study of light curves, Hoffleit used the position of maximum brightness to quantify a number of light-curve types and to distinguish between the various annual meteor showers.
As a geometrical scheme for the classification of convex light curves this procedure works well, with the location of peak brightness being related to the parabola rotation angle. This method has the distinct weakness, however, of being based upon just three data points. In addition, while the rise and fall slopes were shown to be significantly different from those that might be expected from the ablation of a single, solid-grain meteoroid, there is no clear sense by which individual light curves might be compared, or how the slope might relate to the ablation rate or meteoroid structure.
Furthermore, the F parameter provides no direct quantification of flatness. We suggest at this stage that the F parameter be no longer used in meteor light-curve analysis, unless, that is, it can be shown to have some physically meaningful property. With respect to the F parameter being used to discriminate between distinct meteor showers it appears from the survey studies that have been published to date by, for example, Faloon et al.
One cannot clearly distinguish between different meteor showers or sporadic meteors according to the average F values that have been obtained. The F parameter, as described in Section 6, is generally interpreted as a measure of the skewness of a meteor's light curve, yet whenever it is used in an attempt to describe general shower characteristics it is typically only the average value that is discussed.
This latter step seems to be a redundant procedure since it offers no additional information about the light curve and we would accordingly recommend that the much simpler x max , the relative trail length location of maximum brightness, be measurer, tabulated and analysed in future. In addition, any physical model of meteoroid ablation should make a clear prediction of the time of maximum brightness, and hence it is an observable property of the light curve that can in principle be linked directly to the assumed characteristics of the meteoroid and the mode of atmospheric ablation.
With respect to the basic shape of a meteor light curve, the flatness parameter appears to be a much better measure of a light curve's profile than the F parameter, but again, rather than constructing the S or P parameters, at arbitrary magnitude offsets from maximum we would suggest that the entire light curve be used in its evaluation. In this manner, the A parameter introduced in Sections 3 and 4 seems to be a more useful property of the light curve to determine and quantify.
Once again, therefore, the flatness is potentially a measurable quantity that can be linked to a physical model although the exact characteristics of the linkage are presently unknown. With respect to the theoretical modelling of meteor light curves it seems at this stage that at least three key points need addressing. The second key issue that meteoroid ablation models will have to eventually address, and make clear predictions about, is the relative trail length location of the point of maximum brightness and specifically how this links to the total meteoroid mass and its structure.
This indicates that classic meteor light curve must always be late peaked.
Monitoring Meteor Showers From Space | NASA
These classic meteoroid results, however, represent a special case, and they do not apply directly to meteoroids with a composite structure or which undergo fragmentation. The third key issue that requires attention is the development of a theory to explain the observed profiles, with a clear distinction being made between which features are due to the meteoroid structure, meteoroid composition, meteoroid velocity, the zenith angle of atmospheric interaction and the ablation mode.
Some indication of the effects relating to the velocity and the ablation mode can be gained by looking at the limiting profiles in L space. What basic processes dictate the onset and control of the various ablation modes and the resultant total mass-loss rates, however, are currently topics for continued investigation and debate. It has become, we would argue, increasingly clear in recent years that the range of variation shown by meteor light curves cannot be described by a single parameter or number i. The scheme outlined in the sections above attempts to address this problem by introducing a three-component classification protocol.
The first distinction is made according to whether the light curve is convex C type or non-convex NC type. This distinction is made purely on a geometrical basis and while at some deep level the distinction must say something about the structure of the meteoroid and its ablation mode, it is currently unclear exactly what this connection is.
Plotting an Asteroid Light Curve
The second parameter being introduced is the relative trail length location of maximum brightness x max — this again being a parameter that at some fundamental level must relate to the structure and composition of a given meteoroid. The final parameter introduced is a pseudo-kurtosis measure A. With respect to the non-convex light curves a complexity qualifier has also been introduced, and some example descriptors have been made with respect to Fig. At its core any classification scheme that is not founded upon a detailed physical theory must be an arbitrary construct.
Edwin Hubble's tuning fork diagram of galaxy classification is one such arbitrary, geometric scheme [and indeed, in the modern era it is a geometrical scheme that is being stretched to the very limits of usefulness Van den Bergh ]; likewise, the calculation of stellar and meteor apparent magnitudes, as advocated by Norman Pogson is an arbitrary mathematical rather than geometrically construct.
The point, however, is that arbitrary schemes are highly useful provided that they account for the observed phenomena in a reasonably fashion, and provided that all those concerned with such studies agree to use the methodology. To date no universally accepted scheme for meteor light-curve classification has been adopted by the astronomical community; it is our hope, however, that the procedures outlined in this paper will begin to address this increasingly problematic oversight.
I extend my many thank to Ian Murray for his help in recording and analysing the light-curve data used to generate Figs 1 and 5. Oxford University Press is a department of the University of Oxford. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide.
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Close mobile search navigation Article Navigation. Volume Article Contents. The classification of meteor light curves: an application of hat theory Martin Beech. Oxford Academic.
Google Scholar. Cite Citation. Permissions Icon Permissions. Abstract A three-component, geometrical classification scheme for meteor light curves is developed and presented. Open in new tab Download slide. In this section we consider the class of convex light curves that can be formed in L space. Convexity is here defined in the usual mathematical sense: a light curve is said to be convex if the lines drawn between any two points on the light curve always reside in L M see Fig. The two limiting convex light curves that can be drawn in L space are illustrated in Fig. By inspection, it is clear that all convex light curves within L space will have path-lengths PL bounded above and below by.
For any x max in L space the path-length PL will fall between the limits:. Table 1. Open in new tab. Following the reduction of the observations, a meteor light curve is expressed as a series of data points that annotate the change in the meteor's magnitude over a range of specified time intervals not necessarily equally spaced.