January 9
The Demon Star Winks
Sun Position
The Sun lies in Capricornus, about 22.2° south of the celestial equator. In the Northern Hemisphere the days are still short but lengthening; in the Southern Hemisphere this is high summer with long, warm evenings.
Sky Highlight
Algol, the prototype eclipsing binary, dims noticeably every 2.87 days as its companion passes in front, a change visible to the naked eye over a single evening. Best seen from the Northern Hemisphere.
Deep Sky Object
The Double Cluster (NGC 869 and 884), a pair of bright open clusters about 7,500 light-years away in Perseus. A naked-eye smudge from dark northern skies.
Featured Star
Algol (β Per), a blue-white main-sequence / subgiant eclipsing pair in Perseus, 92.8 light-years away. Algol, the demon's winking eye, first eclipsing binary explained.
Around This Date
- January 9, 1839The French Academy of Sciences announced the daguerreotype process, the first widely practical form of photography, which would within decades become the primary tool of observational astronomy.
- January 10, 1946The U.S. Army's Project Diana bounced radar signals off the Moon and detected the return echo, opening the era of radar astronomy and providing a direct measurement of the Earth-Moon distance.
A star that blinks on a schedule older than the schedule.