April 23
The Faintest of Seven
Sun Position
The Sun is in Taurus near +21° declination. Northern hemisphere spring nights are short but clear; southern hemisphere April nights are the longest since the summer solstice passed, good for extended observing sessions.
Sky Highlight
The Lyrids are just past peak but still active, producing 10 to 15 meteors per hour. The days immediately after the Lyrid maximum often yield sporadic Lyrid meteors moving noticeably faster than typical shower members (entering the atmosphere at about 49 km/s) and occasionally producing bright fireballs.
Deep Sky Object
M106 (NGC 4258), spiral galaxy in Canes Venatici, about 24 million light-years. M106 is one of the nearest Seyfert galaxies, with an active nucleus and anomalous spiral arms that are not stellar but gaseous jets from the central black hole; it is a showpiece galaxy for medium-aperture telescopes. Best from northern mid-latitudes.
Featured Star
Megrez (δ UMa) is the faintest of the Big Dipper's seven stars, an A3V main-sequence star 58.4 light-years away. It marks the junction between the Dipper's bowl and handle (the hinge of the asterism) and has been measured to have a slight infrared excess, suggesting a debris disk of dust orbiting at planetary distances.
Around This Date
- April 23, 1858Max Planck was born in Kiel, Germany; his 1900 quantum hypothesis, developed to explain the spectrum of blackbody radiation, became the theoretical foundation for understanding how stars radiate energy.
- April 25, 1990The Hubble Space Telescope was deployed from Space Shuttle Discovery's cargo bay, beginning its operational life in low Earth orbit.
Megrez is the hinge between bowl and handle, the quiet joint at the center of one of the most recognized shapes in the northern sky.