# sunpos: Compute the Right Ascension and Declination of the Sun at... In astrolibR: Astronomy Users Library

## Description

Compute the Right Ascension and Declination of the Sun at specified Julian date(s)

## Usage

 `1` ```sunpos(jd, radian=F) ```

## Arguments

 `jd` Julian ephemeris date, scalar or vector `radian` if =TRUE, then all output variables are given in radians rather than degrees (default=FALSE)

## Details

This function uses a truncated version of Newcomb's Sun http://en.wikipedia.org/wiki/Newcomb's_Tables_of_the_Sun. The returned RA and Dec are in the given date's equinox.

Patrick Wallace (Rutherford Appleton Laboratory, UK) has tested the accuracy of a C adaptation of the IDL sunpos.pro code and found the following results. From 1900-2100 sunpos gave 7.3 arcsec maximum error, 2.6 arcsec RMS. Over the shorter interval 1950-2050 the figures were 6.4 arcsec max, 2.2 arcsec RMS.

## Value

 `ra` apparent right ascension of the Sun, referred to the true equator of the specified date(s), in degrees `dec` declination of the Sun, in degrees `elong` ecliptic longitude of the Sun, in degrees `obliquity` obliquity of the ecliptic, in degrees

## Author(s)

FORTRAN routine by B. Emerson (RGO); IDL version by Michael R. Greason, STX, 1988

R adaptation by Arnab Chakraborty June 2013

`cirrange` `nutate` `polyidl` `ten`

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14``` ```# Find the apparent RA and Dec of the Sun on May 1, 1982 # Result: 02 31 32.61 +14 54 34.9 # The Astronomical Almanac gives 02 31 32.58 +14 54 34.9, # so the error in sunpos for this case is < 0.5". jd = jdcnv(1982, 5, 1,0) # Find Julian date jd = 2445090.5 out = sunpos(jd) # Plot the apparent declination of the Sun for every day in 1997 jd = jdcnv(1997,1,1,0) # Julian date on Jan 1, 1997 days = seq(0,365) plot(days, sunpos(jd+days)\$dec, type='b', pch=20, lwd=2) ```

### Example output

```
```

astrolibR documentation built on May 2, 2019, 3:26 a.m.