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Convert Day (d) to Day (Sidereal) (d (sidereal)) instantly.

About these units

Day (d)

A day represents a full rotation of the Earth relative to the Sun, traditionally measured as 24 hours. Although the day is deeply tied to astronomy, its exact length varies due to Earth's gravitational interactions with the Moon, tidal braking, and geophysical processes. The modern civil day uses Coordinated Universal Time (UTC), with occasional leap seconds added to compensate for subtle variations in Earth's rotation. This ensures that civil time remains aligned with the real solar day. Days are fundamental in cultural, religious, biological, and economic cycles. Sleep patterns, work-rest rhythms, calendars, and circadian biology all operate on daily cycles, making the day not just a unit of measurement but a cornerstone of human existence.

Day (Sidereal) (d (sidereal))

A sidereal day is the time Earth takes to rotate exactly 360 degrees relative to the distant stars—about 23 hours, 56 minutes, 4 seconds. In contrast, the solar day is slightly longer because Earth advances in its orbit each day and must rotate extra degrees for the Sun to appear in the same position in the sky. Sidereal days are fundamental to astronomy: telescopes use sidereal time to track stars, which appear in the same position in the sky at the same sidereal moment each night. This unit anchors astronomical observation to the cosmos rather than to the Sun.

More Day converters

Day [d] ↔ Second [s]
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Day [d] ↔ Minute [min]
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Day [d] ↔ Hour [h]
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Day [d] ↔ Week [week]
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Day [d] ↔ Month [month]
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Day [d] ↔ Year [y]
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Day [d] ↔ Millisecond [ms]
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Day [d] ↔ Microsecond [µs]
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Day [d] ↔ Nanosecond [ns]
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Day [d] ↔ Picosecond [ps]
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Day [d] ↔ Femtosecond [fs]
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Day [d] ↔ Attosecond [as]
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Day [d] ↔ Decade [decade]
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Day [d] ↔ Century [century]
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Day [d] ↔ Millennium [millennium]
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Day [d] ↔ Shake [shake]
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Day [d] ↔ Planck Time [tₚ]
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Day [d] ↔ Month (Synodic) [month (synodic)]
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Day [d] ↔ Year (Julian) [y (Julian)]
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Day [d] ↔ Year (Leap) [y (leap)]
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Day [d] ↔ Year (Tropical) [y (tropical)]
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Day [d] ↔ Year (Sidereal) [y (sidereal)]
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Day [d] ↔ Day (Sidereal) [d (sidereal)]
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Day [d] ↔ Hour (Sidereal) [h (sidereal)]
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Day [d] ↔ Minute (Sidereal) [min (sidereal)]
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Day [d] ↔ Second (Sidereal) [s (sidereal)]
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Day [d] ↔ Fortnight [fortnight]
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Day [d] ↔ Septennial [7 years]
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Day [d] ↔ Octennial [8 years]
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Day [d] ↔ Novennial [9 years]
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Day [d] ↔ Quinquennial [5 years]
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Day [d] ↔ Quindecennial [15 years]
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Convert Day to Day (Sidereal)