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arXiv · 2604.14151

Visplot: A visibility plot and observation scheduling tool for astronomical observatories

Emanuel Gafton·Illa R. Losada
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Abstract

We present Visplot, a free and open-source tool designed for interactive construction and refinement of nightly telescope observing schedules through a graphical user interface. The software performs hardware-aware observability analysis by explicitly incorporating telescope-specific limits alongside astronomical constraints, in order to determine feasible observation windows for both sidereal and non-sidereal targets. It also generates observing schedules that can be rapidly adapted to changing conditions. Visplot is a browser-based JavaScript application that can be used without installation, while remaining fully customizable through self-hosted deployments. The software computes target altitudes for the specified observatory coordinates on a discretized time grid spanning the entire observing night. Observability windows for individual targets are then derived by evaluating their altitude profiles against the intersection of astronomical constraints (airmass, moon distance, twilight), mechanical telescope boundaries (altitude and hour-angle limits), and custom temporal restrictions defined in coordinated universal time (UTC) or local sidereal time (LST). The scheduling engine operates within these observability windows, selecting and ordering observations using a multi-constraint heuristic optimization scheme. Mandatory targets are scheduled deterministically, while the remaining target pool is ranked using a weighted scoring function that balances user-defined priority, target urgency, altitude, and telescope slew overhead. Originally developed to address operational scheduling requirements at the Nordic Optical Telescope (NOT), Visplot has been in continuous use for a decade and has grown beyond its original development to support astronomers at multiple observatories worldwide, demonstrating its practical value in real-world observational workflows.

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Emanuel Gafton, Illa R. Losada. 2026-04-15. Visplot: A visibility plot and observation scheduling tool for astronomical observatories. https://arxiv.org/abs/2604.14151

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