October 28
The Demon's Wink
Sun Position
The Sun is in Scorpius near -17° declination. Both hemispheres are now well past their equinox symmetry, each accelerating toward the extremes of December.
Sky Highlight
Perseus is high in the northeast on October evenings for Northern Hemisphere observers, and Algol is well-placed for observation. Algol dims by about 1.3 magnitudes for roughly five hours every 2.87 days when its dimmer companion eclipses it, an event predictable to the minute. Current eclipse times can be found in almanacs; checking whether Algol is at minimum tonight is a simple but satisfying observation.
Deep Sky Object
NGC 869 / NGC 884 (Double Cluster), an open cluster pair about 7,500 light-years away. The Double Cluster in Perseus is near its highest point in October evenings for Northern Hemisphere observers, and a small telescope shows both clusters simultaneously in many fields of view, each one rich enough to be a showpiece on its own, the pair together among the finest sights in the northern sky. Best for Northern Hemisphere observers; inaccessible from far southern latitudes.
Featured Star
Algol (β Per) is a blue-white main-sequence and subgiant eclipsing pair (B8V + K2IV) about 92.8 light-years away. Its periodic dimming (long noticed as the 'winking eye' of the demon Medusa in Perseus's hand) was first explained scientifically by John Goodricke in 1783, who correctly proposed that a darker body was periodically blocking the brighter star. It was the first eclipsing binary to be understood. Algol, the demon's winking eye, first eclipsing binary explained.
Around This Date
- October 28, 1971Britain launched its Prospero satellite on a Black Arrow rocket from Woomera, Australia, the first and only British-built satellite launched on a British rocket.
- October 29, 1998John Glenn returned to orbit aboard Space Shuttle Discovery, becoming the oldest human to fly in space at 77 years old, more than three decades after his first Mercury orbital flight.
Algol blinks on a schedule precise enough to use as a clock, and it was doing that long before anyone knew why.