# AstroSubpoint

AstroSubpoint[astro]

returns the geo location on Earth that currently has the given astro at its zenith.

AstroSubpoint[astro,date]

returns the geo location on Earth that has astro on its zenith on the given date.

# Details

• The astro subpoint of the Sun is called the subsolar point. The astro subpoint of the Moon is called the sublunar point.
• In AstroSubpoint[astro,], the astro object is any astronomical body, such as Entity["Star","Sun"] or Entity["Planet","Mars"], a named astro location, like the solar system barycenter "SSB", or a GeoPosition location near the surface of an astronomical body.

# Examples

open allclose all

## Basic Examples(3)

Find the current subsolar point:

Compute the sublunar point on this date:

Find which point on Earth has Mars on its zenith on this date:

Check that the altitude of Mars, as observed from this location on that date, is 90 degrees:

## Scope(3)

Use AstroSubpoint with any astronomical entity:

Compute the current subpoint of the solar system barycenter:

Compute the subpoint of a location on the surface of the Moon:

Compare to the sublunar point, the subpoint of the center of the Moon:

## Applications(1)

Compute the subsolar points during a year at the same time of the day:

They form an analemma:

## Properties & Relations(5)

Compute the subpoint of an astronomical object for a given date:

That object will have an altitude of 90 degrees when observed from that location on that date:

The subpoint of the star Polaris is close to the North Pole:

For a given date, compute the equatorial coordinates and the subpoint of an astronomical object:

The declination of the object coincides with the latitude of its subpoint:

The right ascension of the object does not coincide directly with the longitude of its subpoint:

The difference is given by Greenwich Sidereal Time:

The latitude limits of the subsolar point define the Tropics of Cancer and Capricorn:

Compute the subsolar point on a given date:

The solar time at that moment from that location is always noon:

Wolfram Research (2023), AstroSubpoint, Wolfram Language function, https://reference.wolfram.com/language/ref/AstroSubpoint.html.

#### Text

Wolfram Research (2023), AstroSubpoint, Wolfram Language function, https://reference.wolfram.com/language/ref/AstroSubpoint.html.

#### CMS

Wolfram Language. 2023. "AstroSubpoint." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/AstroSubpoint.html.

#### APA

Wolfram Language. (2023). AstroSubpoint. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/AstroSubpoint.html

#### BibTeX

@misc{reference.wolfram_2024_astrosubpoint, author="Wolfram Research", title="{AstroSubpoint}", year="2023", howpublished="\url{https://reference.wolfram.com/language/ref/AstroSubpoint.html}", note=[Accessed: 30-May-2024 ]}

#### BibLaTeX

@online{reference.wolfram_2024_astrosubpoint, organization={Wolfram Research}, title={AstroSubpoint}, year={2023}, url={https://reference.wolfram.com/language/ref/AstroSubpoint.html}, note=[Accessed: 30-May-2024 ]}