Observability time plotter

How to read A/B codes

Quick start (3 steps)

Set location, date, and timezone.
Enter target Right Ascension and Declination (RA/Dec) and observing constraints.
Review observable windows, best interval, and CSV export.

Inputs

Latitude (deg) Longitude (deg, east +) Elevation (m) Date

Time zone mode IANA time zone Coordinated Universal Time (UTC) offset override (min) Step (min)

RA Dec RA unit Dec unit

Minimum altitude (deg) Max sun altitude (deg) Max air mass Horizon correction (deg)

Advanced moon conditions

Max moon altitude (deg) Max moon illumination Min moon separation (deg)

Results

Total observable time (min)	—
Best window	—
Peak altitude (deg)	—
Minimum air mass	—
Resolved TZ	—

Observability chart

Sun altitude Moon altitude Air mass

Definitions & notes

Azimuth: N=0°, E=90°, S=180°, W=270°.
Altitude: horizon=0°, zenith=+90°.
Longitude sign: east positive, west negative.
Observability time plotter (A7) CSV columns are fixed for downstream compatibility.
Best window = longest observable interval; ties resolved by earlier start.
Horizon correction shifts altitude thresholds by the same amount as a simple visibility correction.

How to use Observability time plotter effectively

Use this page when the main question is timing: when a target clears your altitude, moon, twilight, and air-mass rules. It is the flagship timing page for one target and one observing setup.

Best workflow

Enter the site, local date/time range, and target coordinates or resolved object first.
Run once with moderate defaults so you can see the natural window before tightening moon or sky limits.
Use the best window and total observable time to decide whether to open Session Planner Pro, Finder Chart Pro, or a more specialized follow-up page.

FAQ

How is the best window calculated?

All sample points are evaluated against every active condition. The contiguous true segment with the maximum duration becomes the best window, and if equal durations exist, the earliest segment wins.

Why is total observable time sometimes zero?

If at least one condition is too strict (for example high altitude requirement or low sky brightness limit), no time point passes. The UI shows a warning and encourages relaxing constraints.

Can I safely share URLs for reproducibility?

Yes. All form fields are encoded in the URL, so you can reopen exactly the same observing setup and compare results.

What should I enter first?

Start with site, time range, and one target. Moon and air-mass limits are easier to tune after you confirm the baseline window exists.

When should I switch to another astronomy tool?

Open Session Planner Pro when you need to rank several targets, Finder Chart Pro when you need a field chart, and Field Rotation Planner when exposure length on an Alt-Az setup is the real question.

Next steps

Astronomy Session Planner
Rank several targets after you understand the one-target timing window.
Imaging Planner
Check field size and sampling after the timing window is confirmed.
Twilight, sunrise & sunset
Inspect the light boundaries separately if twilight assumptions drive the result.
Moon visibility
Verify the moon path when lunar separation or altitude is the limiting factor.