APT Darkness Clock

APT Darkness Clock (APT DC) is a free, ad-free Chrome extension designed to calculate the best times for deep sky astrophotography and night sky observation. It determines the Deep Sky Darkness (DSD) time—the optimal period between the end of evening astronomical twilight and the beginning of morning astronomical twilight when the Moon is below the horizon. This ensures photographers and astronomers can capture faint celestial objects in the darkest skies.

APT DC is derived from a comprehensive desktop application called Astro Photography Tool (APT), which offers a suite of functionalities like camera control, focusing, plate-solving, and scheduling for astrophotography sessions. With APT DC, users can select their location or choose from saved observing sites to get precise timings for DSD and Narrow Band (NB) times, assisting with imaging through narrow band filters where lunar influence is minimal.

This extension is ideal for astrophotographers seeking to optimize their night sky imaging sessions by planning around the most suitable dark periods for enhanced clarity and detail. For support and suggestions, users can visit the dedicated APT forum.