Sunrise & Sunset Calculator
Introduction
Knowing the exact times of sunrise and sunset is valuable for planning daily activities such as outdoor exercise, photography, farming, and travel. These times vary by location and date due to Earth's rotation and orbit around the sun. This calculator estimates sunrise and sunset times based on latitude, longitude, and date inputs, helping you make informed decisions about daylight hours wherever you are.
Formulas Used to Calculate Sunrise and Sunset
The calculator uses standard astronomical formulas to determine the sun’s position relative to a given location and date. The key steps involve calculating the sun’s declination and the hour angle, which together define when the sun crosses the horizon.
Key Variables
- Latitude (φ): The north-south position on Earth in degrees.
- Declination (δ): The angular position of the sun north or south of the celestial equator, changing throughout the year.
- Hour Angle (H): The angular distance the Earth must rotate before the sun reaches the horizon.
The hour angle at sunrise or sunset is calculated using the formula:
Here, a is the solar elevation angle at sunrise or sunset, typically set to -0.833° to account for atmospheric refraction and the sun’s apparent radius.
Once the hour angle is found, sunrise and sunset times are calculated relative to local solar noon.
Interpreting the Results
The calculator outputs local sunrise and sunset times in hours and minutes, adjusted to your device’s time zone. These times indicate when the sun’s upper edge crosses the horizon, marking the start and end of daylight.
Keep in mind:
- Sunrise and sunset times change daily and vary significantly with latitude and season.
- Near the poles, there can be days with no sunrise or no sunset.
- Times assume a flat horizon and standard atmospheric conditions.
Worked Example
Suppose you want to find sunrise and sunset times for New York City (latitude 40.71° N, longitude 74.01° W) on June 21, 2024.
- Enter latitude: 40.71
- Enter longitude: -74.01
- Select date: 2024-06-21
- Calculate results.
The calculator estimates sunrise at approximately 5:25 AM and sunset at 8:30 PM local time. These times align with typical summer solstice daylight hours in New York City.
Comparison Table: This Calculator vs Other Methods
| Feature | This Calculator | Professional Astronomy Software | Simple Online Lookup |
|---|---|---|---|
| Input Flexibility | Latitude, Longitude, Date | Coordinates, Date, Elevation, Atmospheric Data | Location Name, Date |
| Calculation Accuracy | High (standard formulas with refraction correction) | Very High (includes elevation, refraction, and more) | Moderate (pre-calculated averages) |
| Output Detail | Sunrise and Sunset Times | Sunrise, Sunset, Twilight, Solar Noon, Azimuth | Sunrise and Sunset Times |
| Accessibility | Browser-based, no install | Software installation required | Browser-based |
Limitations and Assumptions
- Elevation: Calculations assume sea level; higher altitudes affect times.
- Atmospheric Conditions: Standard refraction is assumed; weather can alter apparent times.
- Horizon: Assumes a flat horizon; mountains or buildings can delay sunrise or advance sunset.
- Time Zones: Results are shown in your device’s local time zone; traveling across zones requires adjusting inputs accordingly.
- Algorithm Simplification: Uses a balance of accuracy and performance; specialized astronomy tools may provide more precise data.
Frequently Asked Questions
Q: How do I enter coordinates correctly?
Enter latitude and longitude in decimal degrees. Use positive values for north and east, negative for south and west. For example, New York City is approximately 40.71 (lat), -74.01 (lon).
Q: Why do sunrise and sunset times change throughout the year?
Earth’s tilt and orbit cause the sun’s apparent position to shift daily, changing the length of daylight. This variation is most noticeable at higher latitudes.
Q: Does this calculator account for daylight saving time?
The calculator outputs times based on your device’s local time zone, including daylight saving time if applicable.
Q: Can weather affect sunrise and sunset times?
Weather does not change the sun’s position but can affect when the sun is visible. Clouds or fog may delay the apparent sunrise or sunset.
Q: What if I don’t know my exact coordinates?
You can use online maps or GPS apps to find your latitude and longitude with reasonable accuracy for this calculator.
Q: Is this calculator suitable for scientific use?
It provides reliable estimates for everyday planning but may lack the precision needed for scientific or engineering applications requiring detailed atmospheric or elevation data.