Calculator Inputs
Example Data Table
| Date | Latitude | Longitude | Timezone | Mode | Elevation (m) | Expected output (example) |
|---|---|---|---|---|---|---|
| 2026-02-04 | 24.860700 | 67.001100 | Asia/Karachi | Civil | 0 | Sunset shown as local date-time |
| 2026-06-15 | 51.507400 | -0.127800 | Europe/London | Civil | 35 | Later sunset; longer day length |
| 2026-12-01 | -33.868800 | 151.209300 | Australia/Sydney | Nautical | 10 | Twilight end time for outdoor tasks |
Example outputs vary by date, latitude, and twilight selection.
Formula Used
This calculator uses a common NOAA-style approximation. It converts your date into a day-of-year value, then estimates the Sun’s position using solar mean anomaly and ecliptic longitude.
It computes solar declination and solves the hour angle: cos(H) = (cos(Z) − sin(Dec)·sin(Lat)) / (cos(Dec)·cos(Lat)).
Here, Z is the zenith angle. Civil, nautical, and astronomical twilight use 96°, 102°, and 108°.
If elevation is enabled, horizon dip increases zenith: Z' = Z + acos(R/(R+h)), making sunset slightly later.
How to Use This Calculator
- Enter your garden’s latitude and longitude.
- Select the date you want to plan for.
- Choose your timezone for scheduling accuracy.
- Pick civil twilight for most gardening routines.
- Enable elevation if you garden on higher terrain.
- Press calculate, then use sunset for task timing.
Why sunset timing matters for gardens
Sunset marks the daily drop in light intensity and leaf temperature. Many crops shift stomata behavior near dusk, changing water demand and nutrient uptake. A location-based sunset estimate helps schedule irrigation, foliar feeding, pruning, and harvest windows with fewer stress events. It also improves worker safety by avoiding low-light tool use. For fruiting plants, consistent dusk timing can improve pollination management and pest control. If you use timers for drip lines or misting, setting them relative to sunset reduces evaporation losses and prevents nighttime humidity spikes that encourage fungal disease in dense canopies.
Latitude, season, and day length patterns
Day length depends mainly on latitude and day-of-year. Near the equator, sunset time changes slowly across seasons. At higher latitudes, summer sunsets can be hours later, while winter sunsets arrive early. Tracking these shifts supports sowing calendars, greenhouse venting plans, transplant hardening, and lighting cutoffs for seedlings.
Twilight modes and practical visibility
Civil twilight ends when the Sun is about 6 degrees below the horizon, often matching the last “usable light” for outdoor chores. Nautical and astronomical twilight represent darker stages and can help plan pest scouting with headlamps, night harvesting, or automated grow lights. Choosing a consistent mode improves week-to-week comparisons.
Elevation, horizon dip, and microclimates
Gardens on hills, balconies, or rooftops may see the horizon differently than nearby ground plots. Elevation can slightly delay sunset because the visible horizon dips lower. The calculator applies a simple dip adjustment, useful for terrace beds and shade houses. Combine this with wind exposure notes, because ridges cool faster after sunset.
Using results to improve operations
Pair sunset time with a task buffer. Finish overhead watering 60 to 90 minutes before sunset to reduce leaf wetness overnight. In greenhouses, align fan cycles and shade cloth closure to twilight changes, then confirm with temperature logs. Record outputs weekly to build a seasonal reference table for planning fertilizer mixes and harvest packing times.
FAQs
Which twilight mode should gardeners use most often?
Civil twilight is usually best because it matches practical outdoor visibility. Use nautical or astronomical only when you need darker thresholds, such as night scouting, lighting automation, or documenting consistent end-of-day conditions.
Why does my sunset differ from a weather app?
Different sources use different definitions of sunset, rounding rules, and refraction models. Small coordinate differences also matter. This tool provides an approximation and lets you choose zenith angles and basic elevation adjustment.
How accurate is the elevation adjustment?
It is a simplified horizon-dip estimate based on Earth radius and observer height. It can improve rooftop or hillside planning, but local terrain, buildings, and haze can dominate real visibility near the horizon.
What latitude and longitude format should I enter?
Use decimal degrees. North and east are positive values; south and west are negative. For best results, copy coordinates from a map pin near the garden bed or greenhouse entrance.
Can I use this for irrigation scheduling?
Yes. Many growers stop overhead watering 60–90 minutes before sunset to reduce overnight leaf wetness. Use the calculated time as a reference point, then confirm with soil moisture readings and weather conditions.
Why does the calculator show no sunset or no sunrise?
In polar regions, the Sun can stay above or below the horizon all day during certain seasons. When the math indicates continuous daylight or darkness, the calculator reports that condition instead of a time.