Summary Report for Perseids, 2021

Report Created: 2021-08-26 09:34:55

In 2021, 47 cameras recorded 15845 individual meteor observations identified as Perseids. This included 2451 unified events, meteors observed by more than one camera. The number of unified observations as a percentage of individual observations was 15.4%.

The graphs below show some statistics relating to the individual observations and unified data. The first two show the number of observations by station and by time. The third shows the number of unified events, sorted by the number of cameras that detected each event. (Click on the graphs to see a larger version).

Fireball Activity and Magnitude Analysis

The first graph below shows the distribution of absolute magnitude. Each meteor shower tends to have a unique distribution of magnitudes. A shower with a high ZHR but mostly faint meteors will seem poor visually though radio detectors may show many more events as they are more sensitive. On the other hand a shower with mostly bright events may look spectacular but have an overall low ZHR. We therefore assign each shower a Population Index which is a measure of the average magnitude. For these data, the Population index was __POPINDEX__.
A total of 1 fireballs were observed in the reporting period, defining a fireball as a meteor event with an absolute magnitude of -4 or less. Details of the fireballs are shown in the table below.
Also of interest is the variation of magnitude with start and end altitide. There is usually a correlation between these factors, as small faint meteors will tend to become visible lower and burn up at a higher altitude, whereas conversely large meteors will become visible sooner and may last longer. A straight line fit through the two sets of data will thus often show a convergence towards the right of the graph.

Velocity Distribution

The following graphs show the distribution of observed and heliocentric velocity in the in the unified data. Observed velocity is the velocity as measured from the observer's location. Heliocentric velocity is the true velocity of the meteoroid around the Sun. There can be an appreciable difference between these values due to the velocity of the Earth along its orbit and of the observer they rotate with the Earth.

Altitude and Distance

The following plots shows the distribution of ground distance travelled and the altitude of the start and end of ablation for each individual meteor. Ground distance is the linear distance from the first to the last observed point. The ablation plot gives a visualisation of the vertical distance over which the meteor ablated or burned up. The height at which this occurs will depend on factors such as meteor size, velocity and composition. The maximum observed altitude was 139.2 km and the minimum observed altitude was 31.4 km.

Orbital Analysis

Trajectory and orbit analysis was performed for unified events. The charts below show the distribution of semimajor axis amongst the unified events. Some showers show pronounced clustering of semimajor axis due to gravitational resonances particularly with Jupiter. Extremely large values are also possible and often indicate that the meteoroid has been severely perturbed by close passage near a planet.
Also shown is the position of the apparent radiant of each unified event. These should (obviously) cluster round the radiant of the shower but its normal for shower meteors to be a few degrees away from this, though its important to remember that for most showers, the radiant moves location each night due to the Earths movement through the debris stream. Note that the matching process uses distance from the expected radiant to filter candidate events.