Astronomical Almanac

Note: Displayed times and values are generated based on the astronomical formula and your location which can be approximation. This web application will generate an almanac table, calculates and displays a detailed table. The table provides daily information for the specified period, including: Sunrise and sunset times; Civil, Nautical, and Astronomical twilight start and end times; Moonrise and moonset times; Moon illumination percentage; Moon phase name (e.g., New Crescent, Full Moon); and Moon age in days.

This application determines the start and end times for various twilight stages and for sunrise and sunset. The declination angles were determined first for different astronomical events and converted to value: Sun: -0.833°; Civil Twilight: -6.0°; Nautical Twilight: -12.0°; and Astronomical Twilight: -18.0°. The application then iterates through each declination angle (Sun, Civil, Nautical, Astronomical). For each day, it uses a process of quadratic interpolation (quad function) over a 24-hour period to find the exact moments when the sun's altitude matches the twilight declination angle, or the points in time when the sun's center reaches specific angles below the horizon. A standard correction value of -0.833 degrees is used in astronomical calculations to account for both the sun's semi-diameter (~-0.266) [accounts for the fact that the sun is not a point of light, but a disk with an apparent radius] and atmospheric refraction (~-0.567) [the sun's actual position is lower than its apparent position], ensuring that the calculated sunrise and sunset times correspond to the moment the upper limb of the sun's disk appears on the geometric horizon.

The moon phase, illumination, and age are calculated using a date set to UTC (Coordinated Universal Time) noon (12:00:00) for each day, providing a consistent point for phase determination globally. For accurate moon phases dates and precise time in Brunei Darussalam click here. Moon Rise/Set times are calculated based on the user's local time zone. There is a ~0.133 degree correction to the horizon relative to the observer's position for the astronomical objects rise/set effectively incorporates for atmospheric refraction, the effect of the horizontal parallax and semi-diameter. It also checks for cases where the moon is "always up" or "always down" for the entire day and displays the appropriate symbols (----) in the table.

This Astronomical Almanac web application is proudly developed by Hazarry Hj Ali Ahmad (webmaster@bruneiastronomy.org)