# Solar functions

### Sunset,Sunrise and twilight.

Probably the most important calculation you can make about the Sun is rise and set times, after all you can’t do most astronomy until it has set (okay, there is solar astronomy and radio astronomy) so there’s a function for that.

 SunRise(days after j2000, Latitude, longitude, index, altitude) Returns the time of sunrise or sunset or twilights in degrees – divide by 360 and multiply by 24 to get decimal hours, alternatively just divide by 360 to get the fraction of a day and use excel cell formatting set to ‘time’. days after J2000.0 is the date in J2000 format longitude and latitude of observer an optional altitude for the Sun can be added to take into account refraction top or bottom of Sun depending on what iot is you want to do the default altitude corresponds to upper limb on mathematical horizon = -0.833 degrees

### Position and size

If you need the suns position ans size – for example to calculate the conditions for a solar eclipse then these functions will help

 Sun(days after J2000, index) Give the date in J2000 format will returnone of the following based on the index. 1. geo-centric  distance in AU 2. Declination in degrees 3. Right Ascension in degrees. Tip use AltAz() to conver the position of the Sun into its altitude SunSize(days after J2000) Returns the apparent angular size of the Sun in arc seconds, handy for solar eclipse calculations

### Recording observations

If you create a log book in Excel you might want to convert your time of observation into the current Carrington number or automatically calculate the relative sunspot number these functions help you do just that.

 CarringtonRotation(Days after J2000) Enter the J2000 format date and the Carrington Rotation Number for the Sun will be returned Sun_RelativeSunspotNo(No of sunspot groups, no of total spots) Returns the relative sunspot number given the number of Sun spot groups and the total number of spots NOTE: the BAA calculate each hemisphere (N/S) separately. SunLongitude(Days after J2000, index) Returns the true or apparent geometric longitude of the Sun, accurate to 0.01 degrees Index 1. True geometric longitude, referred to the mean equinox of the date 2. Apparent longitude, referred to the true equinox of the date

## One thought on “Solar functions”

1. peeramohamed says:

sunrise() frequently used Fn. Thanks

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