All of the information presented on our Sun and Moon pages is based on algorithms and data from the United States Naval Observatory (USNO) and NASA, which we have optimized to efficiently calculate accurate Sun and Moon times. The algorithms have been tested countless times and are monitored periodically to ensure continued accuracy.
However, some factors may influence the apparent movements of the Sun and the Moon that cannot be controlled. For example, while we consider refraction, the extent of its effect depends on atmospheric pressure and temperature. This means our times for sunrise, sunset, moonrise, and moonset may be off by a few seconds if the pressure or temperature greatly deviates from the average values on which we base our calculations (pressure: 101.325 pascals or 0.0147 pounds per square inch (psi), and temperature: 15°C or 59°F).
Please note that our calculations assume a flat horizon, which is at the same altitude as the observer. This means the time and direction of sunrise/sunset and moonrise/moonset may differ if there are mountains or other obstacles in the way.