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Wed, 06 Aug 2014 - Why does CMOR show the Delta Aquarids more active than the Perseids?

Nowadays there are many resources on-line that allow you to monitor what is happening in the sky.

However, care should be taken when looking at these as it can be easy to draw an incorrect conclusion.

One such issue occurs in early August. Delta Aquarid-S rates are declining from their July 28-29 peak and the Perseids are rising towards their Aug 12-13 peak. Observers of the night sky are aware that visual Perseid rates are somewhat higher than those for the Delta Aquarids-S. However, inspection of the activity levels display on the Canadian Meteor O Radar Orbit Radar (CMOR) website http://fireballs.ndc.nasa.gov/cmor-radiants/ shows the reverse, with the intensity level being much higher for the Delta Aquarids-S (SDA).

Why is this?

The answer is that the CMOR system is detecting meteors by radar and can detect smaller particles than those belonging to meteors visible to the naked eye ... and smaller particles produce fainter meteors. The Perseid shower is rich in bright meteors but relatively deficient in faint meteors. The Delta Aquarids, however, show the reverse pattern, being relatively deficient in bright meteors, but rich in faint meteors (smaller particles).

Hence, the CMOR graph is merely telling us that the Delta Aquarids are richer in small particles than are the Perseids.

An additional factor to be aware of is that, although the accompanying timestamp changes and the constellations are shown moving across the sky, the intensity levels on the CMOR graphs are only updated once a day. Hence you cannot use the CMOR web page to monitor hour to hour changes in activity.

And if you look at the graphs and are about to say that the displayed constellation locations are not correct for the displayed timestamp, do remember that the star patterns are shown for the timezone of CMOR !

 

Added by: Tracie Heywood