Sidereal Calendar
CalculationTime
Sidereal Calendar
A printable star-time planner for local sidereal time, meridian right ascension, longitude assumptions and observing prep notes beside the CalculationTime clockface.
Inputs, result, proof and time.
Use the instrument above, then check the calculation record, assumptions and related tools below.
Printable sidereal calendar
Evening meridian planner
Sydney Observatory notes - July 2027- Longitude
- 151.21 deg
- Clock time
- 21:00
- First LST
- 15:42
- Last LST
- 17:40
MonTueWedThuFriSatSun
Thu, 01 July 2027
15:42 local sidereal time
15:42 RA on the meridian near 21:00Prep date30 June1 day lead
Target band15:42 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Tue, 06 July 2027
16:02 local sidereal time
16:02 RA on the meridian near 21:00Prep date05 July1 day lead
Target band16:02 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Sun, 11 July 2027
16:21 local sidereal time
16:21 RA on the meridian near 21:00Prep date10 July1 day lead
Target band16:21 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Fri, 16 July 2027
16:41 local sidereal time
16:41 RA on the meridian near 21:00Prep date15 July1 day lead
Target band16:41 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Wed, 21 July 2027
17:01 local sidereal time
17:01 RA on the meridian near 21:00Prep date20 July1 day lead
Target band17:01 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Mon, 26 July 2027
17:21 local sidereal time
17:21 RA on the meridian near 21:00Prep date25 July1 day lead
Target band17:21 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Sat, 31 July 2027
17:40 local sidereal time
17:40 RA on the meridian near 21:00Prep date30 July1 day lead
Target band17:40 RAwinter-to-spring right ascensions cross the local meridian around the selected clock time.
Site basis151.21 degEast positive, west negative
Time basisUTC +10Fixed offset, not a live DST database
Observer Notes
Use the sidereal times to choose right-ascension targets near the meridian. Confirm exact target altitude, horizon, weather and daylight-saving rules before observing.
Assumptions
Local sidereal time is estimated from Julian date, Greenwich mean sidereal time and longitude. The selected civil clock time is converted with a fixed UTC offset.
Limits
This is an observing planner, not a precision astrometry service, telescope pointing model, navigation tool, weather forecast or official almanac. Verify exact coordinates and current ephemerides before publication.
Method
The worksheet converts civil clock time into local sidereal time for each date
The calculator converts the selected local clock time to UTC with the entered fixed offset, estimates the Julian date, derives Greenwich mean sidereal time, adjusts it by observing longitude, and prints the right ascension crossing the meridian near that clock time.
Sidereal basis
Sidereal time advances by about 3 minutes 56 seconds per solar day, so the same stars return to the meridian earlier each night.
Print path
The print button opens browser print. The print stylesheet keeps the month grid, sample rows, assumptions, observer notes and source limits.
Limits
This is a practical observing calendar, not a precision telescope pointing model, astrometry service, weather forecast, daylight-saving database or official almanac.
Source Notes
Sidereal time is useful planning context, but exact observing depends on location and target data
CalculationTime uses a compact Greenwich mean sidereal time formula suitable for printable planning sheets. Before publishing observing advice, telescope pointing, classroom data or travel plans, verify the site coordinates, daylight-saving offset, target ephemeris, horizon, weather and local sky conditions.