Astres: Obtention of the Sun azimuth and elevation in a place, a date and hour on the Earth

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Presentation	Dialog box of the application
Examples	Syntax

Presentation

This application computes, for a place in the Earth given in geographic coordinates, a day and a local solar hour or UTC, the azimuth and elevation of the Sun.

The azimuth is given in degrees with respect to the North and clockwise; for example, 90° indicates that the Sun is in the Est.
The elevation is given in degrees with respect to the horizontal; for example, 90° indicates that the Sun is at the zenith.

In command line (Astres), angular units introduced in the application must be expressed in degrees, NOT in degrees, minutes and seconds; for example 70° 30' should be expressed as 70.5. Although, in Windows interface (wAstres) you have two possibilities; if you choose degrees, the value with decimals should be indicated at longitude and latitude boxes.

Months are expressed as 1-12 (January-December) and days as 1-31.

Time is expressed in hours; 10:45 is indicated 10.75. Local solar time is considered by default, but it can be in UTC if the /UTC parameter is indicated.

The application calculates the position of the center of the Sun without taking into account atmospheric refraction, which only slightly significantly affects the position at sunrise and sunset. For example, in Barcelona, and in a standard atmosphere (the composition of the atmosphere can slightly change the refractive indices), the maximum correction to be applied to the solar elevation is +0.50 degrees on 06-21-2023 (corrections are greater than 0.1 degrees when the height calculated by Astres is between [-2.70,8.05] at sunrise and between [-2.92,7.81] at sunset, values in degrees), is + 0.57 degrees on 2023-09-22 (corrections are greater than 0.1 degrees when the height calculated by Astres is between [-2.44,7.66] at sunrise and between [-2.81,8.43] at sunset, values in degrees), and is +0.53 degrees on 2023-12-22 (corrections are greater than 0.1 degrees when the height calculated by Astres is between [-3.20,8.69] at sunrise and between [ -2.56,8.41] at sunset, values in degrees). At the intersection of the Equator and Greenwich the values are similarly modest, with a maximum correction less than +0.552 degrees throughout the year, and at the North Pole the maximum correction is less than +0.417 degrees (data calculated with NOAA_Solar_Calculations_day. xls, https://gml.noaa.gov/grad/solcalc/calcdetails.html).

The author is specially grateful to Dr. Josep Girbau, from the Universitat Autònoma de Barcelona, for his help in the writing of this application.

Dialog box of the application

Astres dialog box

Examples

Example for the (Barcelona) in March 27th of 1999 at 10:45 am:
Astres 2.116944 41.42416667 27 3 1999 10.75

Syntax

Syntax:

Astres longitude latitude day month year hour [/UTC]

Parameters:

longitude (Longitude - Input parameter): Longitude in geographic coordinates.
latitude (Latitude - Input parameter): Latitude in geographic coordinates.
day (Day - Input parameter): Day of the month, expressed with a number from 1 to 31.
month (Month - Input parameter): Month of the year, expressed with a number from 1 to 12.
year (Year - Input parameter): Year, expressed with a number as 2013
hour (Hora - Input parameter): Time is expressed in hours; 10:45 is indicated 10.75. Local solar time is considered by default, but it can be in UTC if the /UTC parameter is indicated.

Modifiers:

UTC