Turning up on the peak night is no help if a bright moon washes the faint meteors out. Enter the peak date and a nearby new moon date and you get the moon age and lit share for that night. Add your session window and the moonrise or moonset time and you also get how many hours fall in real darkness. The three nights either side of the peak are listed too, so you can see which is darker.
Moon age is the days elapsed since the reference new moon taken modulo the mean synodic month. That mean synodic month is 29.530588 days, the figure carried by Britannica, and the lit share turns the age into an angle through one cycle and feeds it to a cosine. The real synodic month wanders between 29.18 and 29.93 days, so a mean-value calculation keeps an error inside one day. Current as of October 2026.
Peak dates and hourly rates change every year, so they are inputs rather than constants. Moonrise and moonset depend on the latitude and longitude of the site, so they are read from a local almanac rather than calculated, and nights where the moon never crosses the horizon are handled by the two whole-session options. Radiant direction and altitude, light pollution and weather are not covered. Treat the figures as a reference and check the local forecast before you set out.
Frequently Asked Questions
A shower's peak date and its hourly rate shift from year to year, so neither can sit in the code as a constant. Look up this year's date in a viewing guide and enter it.
No. Those times depend on the latitude and longitude of the site and cannot be found from a date alone. Enter the time from a local almanac and the moonless stretch is computed from it, or pick one of the whole-session options when the moon never crosses the horizon while you are out.
The math uses the mean synodic month of 29.530588 days. The real synodic month wanders between 29.18 and 29.93 days as the orbit is perturbed, so a difference inside a day can appear.