# siderealTime

Greenwich mean and apparent sidereal times

## Syntax

``thGMST = siderealTime(utcJD)``
``thGMST = siderealTime(utcJD, dUT1, dAT)``
``[thGMST,thGAST] = siderealTime(utcJD,dUT1,dAT)``

## Description

example

````thGMST = siderealTime(utcJD)` calculates mean sidereal time at a specific Universal Coordinated Time (UTC), specified as a Julian date.`thGMST = siderealTime(utcJD, dUT1, dAT)` calculates mean sidereal time at a specific Universal Coordinated Time (UTC) at a higher precision using Earth orientation parameters.`[thGMST,thGAST] = siderealTime(utcJD,dUT1,dAT)` calculates mean and apparent sidereal times. NoteApparent sidereal time calculation requires that you download ephemeris data using the Add-On Explorer. To start the Add-On Explorer, in the MATLAB® Command Window, type `aeroDataPackage`. on the MATLAB desktop toolstrip, click the Add-Ons button. ```

## Examples

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Calculate Greenwich sidereal times at 12:00 on January 4, 2019.

```jd = juliandate([2019 1 4 12 0 0]); [thGMST, thGAST] = siderealTime(jd);```

Calculate Greenwich sidereal times at 12:00 for the month of January, 2019:

```dates = datetime([2019 1 4 12 0 0]); dates = dates + days(1:30)'; jdJan = juliandate(dates); [thGMST, thGAST] = siderealTime(jdJan);```

## Input Arguments

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Universal Coordinated Time (UTC) as a Julian date, specified as a scalar.

Tip

To calculate the Julian date for a particular date, use the `juliandate` function.

Data Types: `double`

Difference between the Coordinated Universal Time (UTC) and Universal Time (UT1), specified as a scalar, in seconds.

Difference between International Atomic Time (TAI) and Coordinated Universal Time (UTC), specified as a scalar, in seconds.

## Output Arguments

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Greenwich mean sidereal time, specified as a scalar, in seconds.

Greenwich apparent sidereal time, specified as a scalar, in seconds.

## Limitations

This function requires the Mapping Toolbox™ license.

 Vallado, D. A. Fundamentals of Astrodynamics and Applications. alg. 1 and eqs. 1-63. New York: McGraw-Hill, 1997.