6 The United States Naval Observatory’s Astronomical Applications

The United States Naval Observatory’s Astronomical Applications

USNO Website Screenshot

One of the contemporary services provided by the United States Naval Observatory to the public is its “Complete Sun and Moon Data for One Day” website. The user can obtain reliable and accurate sunrise, sunset, moonrise, and moonset dates and times for specific locations. Other useful information is also provided about the Sun and Moon’s daily motions specific to the user’s location and desired date.

Phases of the Moon Screenshot

The site provides accurate sunrise and sunset times for the location and date requested, as well as moonrise, moonset, and moon phase information. The transit information is the time when the Sun or Moon will cross the observer’s meridian — that north-zenith-south line which divides the sky into two halves. One half of the sky is rising, the other half of the sky is setting.

Civil twilight is the time when sunlight is visible, even though the Sun has not yet risen. Begin Civil twilight is in the morning before the Sun rises; End Civil twilight is in the evening after the Sun sets.

The data provided for the Moon covers not only moonrise and moonset, but the current lunar phase, percent illuminated, and a photo of what the Moon will look like in the sky.

The USNO also maintains a website cataloging the phases of the Moon. This site allows you to find the phases of the Moon for a specific period of time and number of phases. ¹