Star trail stacking calculator

Why stack for star trails and what the response contains

Continuous star trails record Earth's rotation as arcs across the night sky. Photographers usually prefer many medium-length frames stacked in software rather than one ultra-long exposure because each frame can be discarded if it is spoiled, dark and bias frames calibrate the set, and hot pixels are easier to manage. The core planning question is simple: if each frame is open for a fixed number of seconds, how many frames do I need so the total open-shutter time reaches the trail length I want? This calculator answers that with frame_count equal to the ceiling of desired_trail_seconds over single_exposure_seconds. It also returns total_integration_seconds, which is frame count times exposure and is always at least the desired duration because of ceiling, excess_integration_seconds for that surplus, total_session_seconds when you include optional interval_seconds between frames, and trail_arc_degrees estimated from total integration using a fixed mean sidereal day of eighty-six thousand one hundred sixty-four point zero nine zero five seconds. The method tag star_trail_stack_count and a formula string make API clients and worksheets self-describing. There is no camera database and no network path: the engine either evaluates the closed form inside the supported range or rejects the input with invalid_input. Rejected cases include missing fields, non-finite values, non-positive exposure or desired trail duration, negative intervals, and runaway combinations that would demand more than the documented maximum stacked frames. This page does not replace the five-hundred rule or the NPF rule, which estimate how long a single frame can stay open before stars streak when you want points, not trails; use those tools when you are still planning sharp stars, and use this calculator when you deliberately want continuous arcs from a stack.

How exposure, desired trail, and interval are read and stay reproducible

Interval must be non-negative; a negative gap is rejected because it would imply overlapping time travel rather than a physical delay. The preferred fields are single_exposure_seconds for each stacked shutter length and desired_trail_seconds for the continuous open-shutter total you want, but aliases such as exposure, shutter, and sub_exposure for the frame length, and trail_seconds, duration, and trail_duration for the target trail are accepted so spreadsheets, query strings, and typed forms reuse the same contract. Optional interval_seconds, with aliases interval, gap, and delay, models the gap from the end of one exposure to the start of the next, including intervalometer delay and camera readout; it defaults to zero for idealized back-to-back frames. Optional leading plus signs and scientific notation on numeric strings are allowed when they parse as finite decimals; embedded spaces and non-numeric tokens fail with a clear invalid_input message so a bad cell does not become a wrong night plan. An optional precision field, with aliases decimals and dp, chooses how many decimal places to expose for the numeric fields, defaulting to ten and capped at fifteen so JSON goldens stay stable. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline.

Where stack frame counts fit in field work, teaching, and software

On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a classroom demo to an automated pipeline without changing the mathematical result.