August 31
The Last Night of the Month
Sun Position
The Sun is in Virgo at roughly +5° declination. The autumnal equinox is three weeks away; nights are now meaningfully longer than days across the Northern Hemisphere above about 30° N. The Southern Hemisphere approaches its equinox with the same arithmetic from the other side.
Sky Highlight
August 31 closes with a sky that holds both seasons at once: the Summer Triangle still high in the west, the autumn Great Square of Pegasus commanding the southeast, and Fomalhaut rising in the south. For observers in either hemisphere, this transitional night is worth a long session, the summer's signatures are still present, but the autumn curtain is going up.
Deep Sky Object
M2 in Aquarius is well positioned at a reasonable evening hour on August 31, rising in the southeast for northern observers and sitting high for southern observers. At 37,500 light-years and containing hundreds of thousands of stars, it anchors the deep-sky finale of the summer season before Aquarius takes over the autumn sky.
Featured Star
Etamin, the K5III orange giant in Draco 148 light-years away, is nearly circumpolar for observers above 50° N and well placed throughout the night from mid-northern latitudes. Its role in James Bradley's 1725 discovery of stellar aberration makes it one of the few stars with a specific, documented place in the history of physics, a star that proved something about the planet we stand on.
Around This Date
- August 25, 2012Voyager 1 crossed into interstellar space on or about this date, as determined from plasma wave data, the first time a human-made object had exited the heliosphere.
- August 27, 1962Mariner 2 launched from Cape Canaveral, becoming the world's first successful interplanetary spacecraft and the first to directly measure the solar wind in space.
The last night of August: the Summer Triangle still up, the autumn Square rising, and 148 light-years overhead a star that once told us the Earth was moving.