国际流星组织信息（原文）
Perseids (PER)
Active: July 17–August 24;
Maximum: August 12, 18h15mto 20h45mUT (node at λ⊙ =140.◦0–140.◦1), but see text;
ZHR = 100;
Radiant: α = 48◦, δ = +58◦;
Radiant drift: see Table 6;
V∞= 59 km/s; r = 2.2;
TFC: α = 19◦, δ = +38◦and α = 348◦, δ = +74◦before 2hlocal time;α = 43◦, δ = +38◦and α = 73◦, δ = +66◦after 2hlocal time (β > 20◦N);
IFC: α = 300◦, δ = +40◦, α = 0◦, δ = +20◦or α = 240◦, δ = +70◦(β > 20◦N).
The Perseids produced strong activity from an unexpected primary maximum throughout the1990s, associated with the perihelion passage of their parent comet, 109P/Swift-Tuttle, in 1992.The comet’s orbital period is about 130 years. Further enhanced activity ahead of the usualmaximum was last seen in 2004. Recent IMO observations (see HMO p. 145) found the timingof the mean or ‘traditional’ broad maximum varied between λ⊙∼ 139.◦8 to 140.◦3, equivalentto 2013 August 12, 13h15mto August 13, 01h45mUT. No additional peaks are anticipated thisyear, but this does not guarantee what will occur!The Moon is a waxing crescent approaching first quarter on August 14 for the maximum, sowill set early enough to create no problems for mid-northern observers. Sites at such latitudesare more favourable for Perseid observing, as from here, the shower’s radiant can be usefullyobserved from 22h–23hlocal time onwards, gaining altitude throughout the night. The near-nodal part of the ‘traditional’ maximum interval would be best-viewed from extreme easternEurope eastwards across much of Asia, assuming it happens as expected. All forms of observingcan be carried out on the shower, though unfortunately, it cannot be usefully observed frommost of the southern hemisphere.
