Sidereal Year to Sidereal Day Conversion Calculator: Free Online Tool

Convert sidereal years to sidereal days with our free online time converter.

From:

Sidereal Year

To:

Sidereal Day

How to Use the Calculator:

Enter the value you want to convert in the 'From' field (Sidereal Year).
The converted value in Sidereal Day will appear automatically in the 'To' field.
Use the dropdown menus to select different units within the Time category.
Click the swap button (⇌) to reverse the conversion direction.

How to Convert Sidereal Year to Sidereal Day

Converting Sidereal Year to Sidereal Day involves multiplying the value by a specific conversion factor, as shown in the formula below.

Formula:

1 Sidereal Year = 366.2564 sidereal days

Example Calculation:

Convert 60 sidereal years: 60 × 366.2564 = 2.1975e+4 sidereal days

Disclaimer: For Reference Only

These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.

Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.

What is a Sidereal Year and a Sidereal Day?

A sidereal year is the time it takes for the Earth to complete one full orbit around the Sun relative to the distant, fixed stars. It represents the true orbital period of the Earth. Its duration is approximately 365.256363 mean solar days (or 365 days, 6 hours, 9 minutes, 9.76 seconds).

A sidereal day is the time it takes for the Earth to complete one full rotation on its axis relative to the distant, fixed stars. It is approximately 23 hours, 56 minutes, and 4.091 seconds long. This is slightly shorter than the 24-hour solar day, which is based on the Earth's rotation relative to the Sun.

Note: The Sidereal Year is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Sidereal Day belongs to the imperial/US customary system.

History of the Sidereal Year and Sidereal Day

The concept of the sidereal year emerged from ancient astronomers observing the Sun's apparent path against the background constellations (the ecliptic). They noticed that the Sun returned to the same position relative to specific stars after a consistent period. This stellar-based measurement was distinct from the tropical year (based on the seasons or equinoxes), which was more relevant for agriculture and calendars. Accurately determining the sidereal year was crucial for understanding the Earth's true orbital motion and for long-term astronomical predictions.

The concept of the sidereal day originates from ancient astronomy. Early astronomers observed that the stars appeared to return to the same position in the sky slightly earlier each day when measured against the Sun's cycle. This discrepancy led to the understanding that the Earth's rotation period relative to the background stars (sidereal) was different from its rotation period relative to the Sun (solar). Accurate measurement of the sidereal day became crucial for precise astronomical observations and timekeeping, allowing astronomers to predict the positions of celestial objects.

Common Uses for sidereal years and sidereal days

Explore the typical applications for both Sidereal Year (imperial/US) and Sidereal Day (imperial/US) to understand their common contexts.

Common Uses for sidereal years

The sidereal year is primarily used in:

Astronomy & Astrophysics: For calculations involving the long-term orbital mechanics of the Earth and other celestial bodies within the solar system. It's fundamental for understanding the actual time it takes for planets to orbit the Sun.
Celestial Mechanics: Used in models predicting the positions of stars and planets over extended periods.
Defining Orbital Periods: Serves as the standard measure for the orbital period of Earth and is used comparatively for other planets.

It is generally not used for civil calendars, which are based on the tropical year to keep alignment with the seasons.

Common Uses for sidereal days

The sidereal day and sidereal time are primarily used in:

Astronomy: To point telescopes accurately at celestial objects. Astronomical observatories use sidereal clocks to know when specific stars or galaxies will be overhead or in a particular position for observation.
Astrophysics: For calculations involving celestial mechanics and the timing of astronomical events.
Satellite Tracking: Used in calculations for positioning and tracking artificial satellites in Earth orbit.
Geodesy: For precise measurements related to the Earth's rotation and orientation in space.

It is generally not used for civil timekeeping, which relies on the solar day.

Frequently Asked Questions

Questions About Sidereal Year (sidereal year)

How long is a sidereal year in days?

A sidereal year is approximately 365.256363 mean solar days, which translates to about 365 days, 6 hours, 9 minutes, and 9.76 seconds.

What is the difference between a sidereal year and a tropical year?

A sidereal year measures the Earth's orbit relative to distant stars (one complete 360° revolution). A tropical year measures the time between successive vernal equinoxes (the start of spring in the Northern Hemisphere). Due to the precession of the equinoxes (a slow wobble in Earth's axis), the tropical year is slightly shorter (about 20 minutes) than the sidereal year (approx. 365.24219 days).

Why do calendars use the tropical year instead of the sidereal year?

Civil calendars, like the Gregorian calendar, are designed to keep the seasons occurring at roughly the same time each year. Since seasons are determined by the Earth's tilt and its position relative to the Sun (marked by equinoxes and solstices), the tropical year is the relevant measure for aligning the calendar with seasonal changes. Using the sidereal year would cause the seasons to gradually drift through the calendar months over centuries.

About Sidereal Day (sidereal day)

How long is a sidereal day in standard time?

A mean sidereal day is approximately 23 hours, 56 minutes, and 4.091 seconds (or about 86,164.091 seconds). This is roughly 3 minutes and 56 seconds shorter than a standard 24-hour solar day.

Why is a sidereal day shorter than a solar day?

A sidereal day measures Earth's rotation relative to distant stars. A solar day measures rotation relative to the Sun. As the Earth rotates, it also orbits the Sun. After one full rotation relative to the stars (one sidereal day), the Earth has moved slightly along its orbit. It needs to rotate a little bit further (about 1 degree, taking nearly 4 minutes) to bring the Sun back to the same apparent position in the sky (completing a solar day).

Is sidereal time the same everywhere on Earth?

No, just like solar time, local sidereal time depends on your longitude. At any given moment, different locations on Earth will have different local sidereal times, corresponding to which part of the celestial sphere is currently crossing their local meridian. However, the duration of a sidereal day is the same everywhere.

Conversion Table: Sidereal Year to Sidereal Day

Sidereal Year (sidereal year)	Sidereal Day (sidereal day)
1	366.256
5	1,831.282
10	3,662.564
25	9,156.41
50	18,312.82
100	36,625.64
500	183,128.198
1,000	366,256.397

All Time Conversions

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