Solar and sidereal day

Choose the number of daily cycles and compare their durations. The presets select 1, 7, 30 or 365 cycles. The difference is how much longer the same number of mean solar days lasts.

• A mean solar day is nominally 24 hours. A mean sidereal day is approximately 23 h 56 min 4.091 s. For one cycle the difference is approximately 3 min 55.910 s. Earth must rotate a little further for the Sun to return because it also moves around the Sun.
• This is a fixed-period educational comparison, rounded to milliseconds. It is not a calendar interval or a forecast of a specific star’s transit. The sidereal reference is the mean equinox, which moves slowly relative to distant stars.
• A sidereal clock runs faster: about 24 h 3 min 57 s of sidereal time pass in one solar day. That clock gain uses sidereal time units and is not the difference of the two real day lengths shown here.
• UTC days can contain leap seconds. UT1 follows irregular Earth rotation; current UT1−UTC and TAI−UTC need dated IERS data. This tool does not fetch or pretend to show current offsets.
• Allowed: 1–10,000 whole cycles. Edit clears the previous result; Compare or Enter recalculates. The raw input is retained on reload.

Reference: USNO — Sidereal Time.