If your skies are clear after the sun sets on Sunday, Sept. 27 be sure to head outside to see the total blood moon lunar eclipse that happens that night. This will mark the end of a “tetrad” of four total lunar eclipses spaced a half year apart that began back in early 2014. But, perhaps more importantly, it’s the last one visible anywhere until 2018.

Observers in St. Louis lucked out – we can watch every stage of the eclipse, from beginning to end of the partial phases (3¹⁄₃ hours in all) during convenient hours of late twilight or darkness with the moon mostly high in the sky (8:07 p.m. is the start of the partial eclipse, 9:47 p.m. is the max eclipse, 11:27 p.m. is the end of the partial eclipse).

Unlike the lunar eclipse last April 4, which might not even have been precisely total, this one will carry the Moon through the umbra — the dark core of Earth’s shadow — for 1 hour and 12 minutes. Moreover, it’s a big eclipsed moon! The closest lunar perigee of 2015 occurs just 59 minutes before mid-eclipse. The Moon (in Pisces) will appear 13% larger in diameter than it did when eclipsed last April. That’s not enough for anyone but a devoted moon watcher to really notice, but for a spectacle like a lunar eclipse, every little bit helps.

The events that happen to a shadowed Moon are more complex and interesting than many people realize. For example, you can look for the first vestiges of shading on the Moon’s southeastern side (at lower left if seen from the U.S.) about 30 to 45 minutes before the lunar disk begins its dip into the umbra. This duskiness intensifies as the Moon slides deeper into Earth’s penumbra. An astronaut standing on the Moon would see Earth covering only part of the Sun’s face.