The Association of Lunar & Planetary Observers is the most active amateur group in the US studying the Moon and planets. The ALPO was founded and led for decades by Walter Haas.
- ALPO issues a monthly PDF newsletter known as The Lunar Observer available to non-members.
- Many recent issues of the main ALPO Journal (subtitled The Strolling Astronomer) are also available free on the ALPO website. The contents of most issues have also been indexed.
- Scanned issues of JALPO back to Volume 31 can be browsed on the NASA ADS with links of the form: