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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Catch Comet Swan
4/9/2025

Comet SWAN (C/2025 F2) was discovered using the SWAN camera on SOHO by amateur astronomers in March 2025. Officially named on April 8, it is currently visible in the northeastern sky at dawn and will transition to the evening sky by late April. The comet has been brightening and is expected to peak at magnitude 3.6 by its perihelion on May 1, as it passes near the Pleiades cluster. Mid-northern latitude observers are best positioned to view the comet, which offers a rare opportunity for astronomers and skywatchers.

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2025-04-29 07:00
Moon 0.5º north of Pleiades

2025-04-30 18:00
Jupiter 5º south of Moon

2025-05-01
Comet Swan reaches perihelion

2025-05-03 23:00
Mars 2? south of Moon

2025-05-04
Peak of the Eta Aquariid meteor shower

2025-05-04 13:53
First Quarter Moon

2025-05-06
Equinox on Saturn

2025-05-10 08:00
"Spica 0.4? north of Moon, occultation Micronesia to Antarctic Peninsula"

2025-05-12 16:56
Full Moon

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

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.