Last Call for Titan Transits
4/29/2025

Saturn’s largest moon, Titan, is set to perform a rare celestial spectacle in 2025—a series of shadow transits across the planet. Unlike Jupiter’s moons, Titan’s shadow is a unique sight, appearing as a tiny, inky dot on Saturn’s surface. These transits occur when Saturn’s rings appear edge-on, a phenomenon that happens only twice in its 29.5-year orbit. With its 16-day orbital period, Titan will provide a dozen such transits visible from North America, mostly in the early morning hours. The article explores Titan’s history, its substantial atmosphere, and past observations, from William Herschel’s 1789 sighting to NASA’s Cassini and upcoming Dragonfly mission. Don’t miss your chance to witness this rare astronomical event!

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Vesta's Core
4/28/2025

Previously believed to have a planetary structure with a core, mantle, and crust, Vesta is now thought to lack a core altogether. This unexpected discovery challenges its classification as a protoplanet and raises questions about its formation. Scientists propose that Vesta may have undergone incomplete differentiation, or it could represent a fragment from the assembly of a larger planet. Data from NASA's Dawn spacecraft provided insights into Vesta's composition, reshaping theories of planetary formation and offering new perspectives on how celestial bodies evolve within the solar system.

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2025-05-12 16:56
Full Moon

2025-05-14
Antares 0.3º north of Moon, occultation Polynesia to Antarctic Peninsula

2025-05-15 09:55
Titan Shadow Transit (~5.75 Hrs)

2025-05-20 11:59
Last Quarter Moon

2025-05-24
Venus 4º south of Moon

2025-05-27 03:02
New Moon lunation 1267

2025-05-30
Mercury at superior solar conjunction

2025-05-31
Venus at greatest elongation west

2025-05-31 09:10
Titan Shadow Transit (~5.75 Hrs)

2025-06-01
Venus at dichotomy

The Association of Lunar and Planetary Observers (ALPO) is an international organization devoted to study the Sun, Moon, planets, asteroids, meteors, and comets. Our goals are to stimulate, coordinate, and generally promote the study of these bodies using methods and instruments that are available within the communities of both amateur and professional astronomers.

The ALPO collects and analyzes observations of various Solar System bodies and associated phenomena and publishes detailed reports concerning these bodies in its quarterly publication the Journal ALPO, otherwise known as The Strolling Astronomer. Membership in the ALPO includes receiving our journal, and back issues can be found in our Publications section.

We welcome and provide services for all individuals interested in lunar and planetary astronomy. For the novice observer, the ALPO is a place to learn and to enhance observational techniques. For the advanced amateur astronomer, it is a place where one's work will count. For the professional astronomer, it is a resource where group studies or systematic observing patrols add to the advancement of astronomy. Further details about the ALPO can be found here.

There are a range of membership levels available starting with annual dues of only $22. See the footer below for links on how you can become a member today.