August 13
The Morning After the Shower
Sun Position
The Sun is in late Leo at around +13° declination. Dawn arrives a few minutes earlier each day in the Northern Hemisphere; Southern Hemisphere mornings are brightening toward spring.
Sky Highlight
The Perseid shower continues into the early hours of August 13, and for many observers the pre-dawn of August 13 delivers the peak. Earth is still moving through the densest part of Comet Swift-Tuttle's debris stream. Rates taper gradually through the following week rather than dropping sharply after the peak date.
Deep Sky Object
M71, a loosely concentrated globular cluster in Sagitta, lies about 12,000 light-years away and is well placed in August evenings for Northern Hemisphere observers. Sagitta, the Arrow, is a tiny but distinct constellation midway between the Summer Triangle stars. M71 sits roughly at its center and is easy in binoculars.
Featured Star
Altair, the A7V main-sequence star 16.7 light-years from Earth, spins so fast (completing a rotation in under nine hours) that its equatorial diameter is about 20 percent larger than its polar diameter, a measurable oblateness confirmed by interferometry. It anchors the southern corner of the Summer Triangle and is unmistakably bright on August nights.
Around This Date
- August 18, 1877Asaph Hall discovered Phobos, the inner moon of Mars, less than a week after finding Deimos, one of the most productive stretches of observational discovery in planetary science.
- August 20, 1977Voyager 2 launched successfully, setting course for Jupiter in what would become the most far-reaching planetary survey mission ever completed.
The shower tapers but doesn't stop, there are still a few swift lines crossing the sky for those willing to watch past the headline.