# ReferenceAltitude

is an option of Sunrise, AstroRiseSet and related functions that specifies how to define the instant of rise or set of an astronomical body or point on the celestial sphere.

# Details

• ReferenceAltitude can be used to define the instants of beginning and end of civil, nautical or astronomical twilight, as well as different definitions of rise and set of an astronomical object.
• Possible values of the ReferenceAltitude option include:
•  Automatic upper limb of the body crosses zero altitude alt center of the body crosses numeric altitude alt {alt,limb} the given limb of the body crosses numeric altitude alt
• The reference altitude angle alt can be given as a Quantity angle or as a numeric expression interpreted in angular degrees. For the particular case of the Sun, these are the traditional values of reference altitude:
•  "Civil" the center of the Sun has altitude –6 degrees "Nautical" the center of the Sun has altitude –12 degrees "Astronomical" the center of the Sun has altitude –18 degrees
• Possible values for the limb of the body include:
•  "UpperLimb" upper limb of the body "Center" central point of the body "LowerLimb" lower limb of the body limb numeric value between –1 (lower limb) and 1 (upper limb)

# Examples

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## Basic Examples(3)

Find the next instant of the beginning of civil twilight in the morning, for your current geo location:

Find the next instant of the ending of nautical twilight in the evening, for your current geo location:

Find the next two events of Mars crossing altitude 10° on its way up and down in the sky:

## Scope(5)

### Solar Twilight(2)

Compare the instant of sunrise to the standard definitions of civil, nautical and astronomical twilight:

Compare the instant of sunset to the standard definitions of civil, nautical and astronomical twilight:

### Choice of Reference Altitude Angle(1)

Compare the instants for which the Moon crosses different levels of altitude when rising:

### Choice of Astronomical Body Limb(2)

Compare the instants for which different parts of the Moon cross the local horizon when rising:

Compare the instants for which different parts of the Moon cross the local horizon when setting:

## Properties & Relations(1)

Sunrise is defined as the instant when the upper limb of the Sun crosses altitude 0 in the morning:

At that moment, the altitude of the center is negative, corresponding to half the angular size of the Sun:

A few minutes later, the center of the Sun crosses the local horizon:

At that moment, the altitude of the center is zero:

Wolfram Research (2024), ReferenceAltitude, Wolfram Language function, https://reference.wolfram.com/language/ref/ReferenceAltitude.html.

#### Text

Wolfram Research (2024), ReferenceAltitude, Wolfram Language function, https://reference.wolfram.com/language/ref/ReferenceAltitude.html.

#### CMS

Wolfram Language. 2024. "ReferenceAltitude." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/ReferenceAltitude.html.

#### APA

Wolfram Language. (2024). ReferenceAltitude. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/ReferenceAltitude.html

#### BibTeX

@misc{reference.wolfram_2024_referencealtitude, author="Wolfram Research", title="{ReferenceAltitude}", year="2024", howpublished="\url{https://reference.wolfram.com/language/ref/ReferenceAltitude.html}", note=[Accessed: 15-August-2024 ]}

#### BibLaTeX

@online{reference.wolfram_2024_referencealtitude, organization={Wolfram Research}, title={ReferenceAltitude}, year={2024}, url={https://reference.wolfram.com/language/ref/ReferenceAltitude.html}, note=[Accessed: 15-August-2024 ]}