Month to Sidereal Year Conversion Calculator: Free Online Tool

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

From:

Month

To:

Sidereal Year

How to Use the Calculator:

Enter the value you want to convert in the 'From' field (Month).
The converted value in Sidereal Year 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 Month to Sidereal Year

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

Formula:

1 Month = 0.0833302 sidereal years

Example Calculation:

Convert 60 months: 60 × 0.0833302 = 4.99981 sidereal years

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 Month and a Sidereal Year?

A month is a unit of time, used with calendars, that is approximately based on the orbital period of the Moon around the Earth. In the Gregorian calendar, a month can have 28, 29, 30, or 31 days. For conversions, an average month is often defined as 1/12th of a year, which is approximately 30.44 days (365.25 days / 12 months).

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).

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

History of the Month and Sidereal Year

The concept of the month originated from observing the lunar cycle (the period from one new moon to the next, about 29.5 days). Early calendars, like the Roman calendar, were often lunar or lunisolar. The Gregorian calendar, now used internationally, standardized the month lengths (mostly 30 or 31 days) to align the calendar year more closely with the solar year, largely detaching the calendar month from the strict lunar cycle.

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.

Common Uses for months and sidereal years

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

Common Uses for months

Calendars: The primary division of the year for dating and scheduling longer-term events.
Billing & Finance: Common cycle for salaries, rent/mortgage payments, subscriptions, bank statements, and financial reporting.
Planning: Used for medium-term planning (monthly goals, project milestones).
Time Measurement: Expressing durations longer than weeks (e.g., project duration, age of infants, gestation periods).
Seasonality: Often associated with seasonal changes, although this varies by month and hemisphere.

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.

Frequently Asked Questions

Questions About Month (mo)

How many days are in a month?

It varies: 30 days (April, June, September, November), 31 days (January, March, May, July, August, October, December), or 28/29 days (February).

Why do months have different lengths?

The varying lengths are a historical artifact from the Roman calendar adjustments, refined in the Julian and Gregorian calendars, aimed at aligning the calendar year with the solar year while maintaining 12 months.

What is an average month length used for conversions?

For calculations, an average month is often taken as 30.4375 days (365.25 days / 12 months).

Is a month based on the Moon?

Historically, yes. The word "month" is related to "Moon". However, in the Gregorian calendar, the link is approximate; calendar months don't precisely track the lunar phases.

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.

Conversion Table: Month to Sidereal Year

Month (mo)	Sidereal Year (sidereal year)
1	0.083
5	0.417
10	0.833
25	2.083
50	4.167
100	8.333
500	41.665
1,000	83.33

All Time Conversions

Second to Minute Second to Hour Second to Day Second to Week Second to Month Second to Year Second to Millisecond Second to Microsecond Second to Nanosecond Second to Decade Second to Century Second to Millennium Second to Fortnight Second to Planck Time Second to Shake Second to Sidereal Day Second to Sidereal Year Minute to Second Minute to Hour Minute to Day Minute to Week Minute to Month Minute to Year Minute to Millisecond Minute to Microsecond Minute to Nanosecond Minute to Decade Minute to Century Minute to Millennium Minute to Fortnight Minute to Planck Time Minute to Shake Minute to Sidereal Day Minute to Sidereal Year Hour to Second Hour to Minute Hour to Day Hour to Week Hour to Month Hour to Year Hour to Millisecond Hour to Microsecond Hour to Nanosecond Hour to Decade Hour to Century Hour to Millennium Hour to Fortnight Hour to Planck Time Hour to Shake Hour to Sidereal Day Hour to Sidereal Year Day to Second Day to Minute Day to Hour Day to Week Day to Month Day to Year Day to Millisecond Day to Microsecond Day to Nanosecond Day to Decade Day to Century Day to Millennium Day to Fortnight Day to Planck Time Day to Shake Day to Sidereal Day Day to Sidereal Year Week to Second Week to Minute Week to Hour Week to Day Week to Month Week to Year Week to Millisecond Week to Microsecond Week to Nanosecond Week to Decade Week to Century Week to Millennium Week to Fortnight Week to Planck Time Week to Shake Week to Sidereal Day Week to Sidereal Year Month to Second Month to Minute Month to Hour Month to Day Month to Week Month to Year Month to Millisecond Month to Microsecond Month to Nanosecond Month to Decade Month to Century Month to Millennium Month to Fortnight Month to Planck Time Month to Shake Month to Sidereal Day Year to Second Year to Minute Year to Hour Year to Day Year to Week Year to Month Year to Millisecond Year to Microsecond Year to Nanosecond Year to Decade Year to Century Year to Millennium Year to Fortnight Year to Planck Time Year to Shake Year to Sidereal Day Year to Sidereal Year Millisecond to Second Millisecond to Minute