# SolarTime

gives the angle on the celestial equator between the Sun and the local antimeridian for the current location and date.

SolarTime[loc]

gives the solar time angle for the specified location and current date.

SolarTime[date]

gives the solar time angle for the specified date and current location.

SolarTime[loc,date]

gives the solar time for the specified location and date.

SolarTime["MeanTime",loc,date]

gives the mean solar time for the specified location and date.

# Details

• Solar time is typically used when precise orientation with respect to the Sun is required, for example, in applications of solar energy, solar trackers and heliostats.
• SolarTime gives an angle determined by a sundial from the given location at the given date.
• SolarTime returns a Quantity angle expressed in mixed units of hours, minutes and seconds of right ascension, as traditionally done with angles measured along the celestial equator.
• SolarTime[loc,date], equivalent to SolarTime["ApparentTime",loc,date], computes the local apparent or true solar time, based on the celestial position of the true Sun, which moves at irregular speed along the celestial equator.
• SolarTime["MeanTime",loc,date] computes local mean solar time, based on the position of the fictitious mean Sun, which moves at constant speed along the celestial equator.
• SolarTime[loc,date] is equivalent to the difference between the sidereal time of the antipode of loc at date and the right ascension of the Sun for the same date.
• makes use of Here and Now to determine your current location and date.
• Locations in SolarTime[loc,date] can be given as {lat,lon} pairs in degrees, GeoPosition objects or Entity geo locations.
• Date specifications in SolarTime[loc,date] can be given as DateObject expressions or date strings. Input dates are assumed to be given in Universal Time, modified by your local time zone as given by \$TimeZone.

# Examples

open allclose all

## Basic Examples(2)

Find the local apparent solar time for the current location and date:

It is close, but not equal, to the current civil time:

Solar time is returned as an angle in mixed units of right ascension:

Convert to angular degrees:

## Scope(3)

Find the solar time for your current location and date:

Use locations in different formats:

Specify dates as DateObject expressions or date lists:

## Applications(3)

The difference between apparent and mean solar times varies during a year:

This is the so-called equation of time, given in minutes:

Find the minimum and maximum of the values of the equation of time:

Construct a function that finds the civil time of solar noon:

Take all civil noons during a year, ignoring daylight saving changes:

Compute the corresponding solar noons for your location:

Find the durations of all solar days during a year:

The duration varies during the year, with longer days in June and December, and shorter days in March and September:

The shape of the equation of time varies across millennia:

## Properties & Relations(6)

For a given location and date, solar time can also be computed from AstroPosition:

Locations with the same longitude have similar solar time:

Each 15 degrees of longitude correspond to about one hour of solar time:

Solar time is not defined at the poles, because longitude is not uniquely defined at the poles:

Mean solar time for Greenwich was the basis for GMT time:

However, it does not coincide in general with true solar time at Greenwich:

Take a city in West China:

This is the current time at that location, with the unique time zone GMT+8 used in China:

It is shifted by more than two hours with respect to the corresponding solar time:

Take a location and a date:

Compute the sidereal time of the antipode of that location, for that date:

Compute the right ascension of the Sun for that location and date:

Then the solar time is equivalent to this difference, modulo full angles:

Wolfram Research (2021), SolarTime, Wolfram Language function, https://reference.wolfram.com/language/ref/SolarTime.html.

#### Text

Wolfram Research (2021), SolarTime, Wolfram Language function, https://reference.wolfram.com/language/ref/SolarTime.html.

#### CMS

Wolfram Language. 2021. "SolarTime." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/SolarTime.html.

#### APA

Wolfram Language. (2021). SolarTime. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/SolarTime.html

#### BibTeX

@misc{reference.wolfram_2024_solartime, author="Wolfram Research", title="{SolarTime}", year="2021", howpublished="\url{https://reference.wolfram.com/language/ref/SolarTime.html}", note=[Accessed: 18-September-2024 ]}

#### BibLaTeX

@online{reference.wolfram_2024_solartime, organization={Wolfram Research}, title={SolarTime}, year={2021}, url={https://reference.wolfram.com/language/ref/SolarTime.html}, note=[Accessed: 18-September-2024 ]}