Astronomical Society


Julian Date Calculator - $0.99
The Julian Date Calculator gives the user a simple and quick way to convert between Coordinated Universal Time (UTC) in the Gregorian Calendar to the Julian Date, as well as a selection of additional epochs and time systems.

The Julian date (JD) is the number of days and fractions of a day since noon January 1, 4713 BC at Greenwich. The Modified Julian Date (MJD) has an offset of 2,400,000.5 days from the Julian Date and hence starts at midnight November 17, 1858. The Julian Date is often used for scientific time measurement by the astronomy community and was introduced to provide a single system of dates that could be used when working with different calendars.

Sidereal Time - $0.99
The Sidereal Time App gives the user a simple and quick way to determine:
  • Local Apparent Sidereal Time (LAST) based on longitude
  • Rough estimate of LAST based on Time Zone
  • Greenwich Mean Sidereal Time
  • Select one of 30 Stratum-1 NTP servers or add your own to synchronize the clock against the primary network time standard

iTimeZone - World Clock - $0.99
Most world clocks can only show the current date & time in other cities. With iTimeZone, you choose the date, time & current city. Doesn't matter if you pick the past, present, or future time in Boston or Buenos Aires, iTimeZone does the tricky time zone math using all daylight savings time transitions

Sky Time - Free
Sky Time is a simple app that displays Astronomy-related times, including Julian Date and Universal Time. It also makes use of your device's ability to sense location to determine the Sidereal Time.

Sky Time is a useful tool to have to hand when setting up your telescope!
  • Displays local, Julian, Local Sidereal and Universal Time.
  • Night-vision friendly red display.
  • Pop-up descriptions of the times at your fingertips.