October 5
The River's End
Sun Position
The Sun is in Libra near -5.5° declination. Northern Hemisphere observers are firmly in the shortening-days phase; Southern Hemisphere evenings are extending noticeably toward summer.
Sky Highlight
The Southern Taurid meteor shower begins its long, slow ramp-up in early October, peaking in early November. Individual shower members can be seen throughout the month. They are slow, bright meteors, sometimes producing fireballs. Best viewed from the Northern Hemisphere but the radiant is accessible from the Southern Hemisphere as well.
Deep Sky Object
NGC 1232, a spiral galaxy about 65 million light-years away. NGC 1232 in Eridanus is a large, face-on spiral galaxy with well-defined arms and a small companion galaxy visibly distorting its outer structure, a tidy example of gravitational interaction caught mid-process. Eridanus spans a wide range of declinations; NGC 1232 is best viewed from Southern Hemisphere and southern mid-latitudes of the Northern Hemisphere.
Featured Star
Achernar (α Eri) is a main-sequence B-type star (B6Vep) about 139 light-years away, and it spins so rapidly (close to its breakup speed) that its equatorial diameter is roughly 56% larger than its polar diameter, making it one of the most oblate stars known. It anchors the southern tip of the river Eridanus. Achernar, the river's end, a star too fast to be round.
Around This Date
- October 5, 1923Edwin Hubble photographed what he would soon identify as a Cepheid variable in the Andromeda Nebula, beginning the work that established the existence of external galaxies.
- October 7, 1959The Soviet Luna 3 spacecraft returned the first photographs of the Moon's far side, revealing a surface strikingly different from the familiar nearside.
A star that spins too fast to hold its shape is a useful reminder that the night sky is less static than it looks.