Perseiderne 2018

Nu er der kun 1 god måneds tid til Perseidernes maksimum. Den forventede aktivitet kommer til at ligge omkring gennemsnittet, men der er mulighed for “klumper” den 12 august med ekstra aktivitet til følge. Læs forudsigelsen fra International Meteor Organisation nedenfor.

Perseids
Active: July 17–August 24; Maximum: August 12, 20h to 13, 08h UT (node at λ⊙ = 140◦.0– 140 ◦. 1), but see text; ZHR = 110;
Radiant: α = 48◦, δ = +58◦; Radiant drift: see Table 6;
V∞ =59km/s;r=2.2.

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IMO observations (see WB pp. 32–36) found the timing of the mean or ‘traditional’ broad maximum varied between λ⊙ ≈ 139◦.8 to 140◦.3, equivalent to 2018 August 12, 20h to August 13, 08h UT. The orbital period of the parent comet 109P/Swift-Tuttle is about 130 years. The Perseids produced strong activity from a primary maximum throughout the 1990s. Enhanced activity was last observed in 2016 with additional peaks due to passages through separated dust trails. Such peaks are not to be expected for the 2018 return. Instead, a possible encounter with a Perseid filament is announced for August 12 around 20h UT (λ⊙ ≈ 139◦.79) by Peter Jenniskens. The filament is thought to be an accumulation of meteoroids in a mean-motion resonance. Observations are needed to see what is detectable around this position which is right at the start of the given peak period. An additional potential enhancement due to a very old dust trail on August 13 at 01h37m UT, found in computations by J ́er ́emie Vaubaillon, may give only negligible rates anyway, thus could easily pass unnoticed within the normal main maximum period. Visual observers should break their reports into short intervals (no longer than 15 minutes for both rate and magnitude data) for the entire period, this way allowing to search for signatures of the trail and filament, respectively.

New Moon on August 11 provides perfect conditions for all optical observations. Sites at mid- northern latitudes are more favourable for Perseid observing, as from here, the shower’s radiant can be usefully observed from 22h–23h local time onwards, gaining altitude throughout the night. Regrettably, the shower cannot be properly viewed from most of the southern hemisphere.

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