For many astrological calculations you need formula. This is the place where you will find them. You can use these formula if you write your own software but you can also use them with a calculator.

For each formula I will give an elaborated example that will enable you to use the formula right away.

You will also find a short explanation about what the formula is all about.

Many of these formulas use goniometric and other mathematical functions. For these functions I will use the following abbreviations:

**sin**: sine**cos**: cosine**tan**: tangent**asin**: arc sine, or inverse sine**acos**: arc cosine or inverse cosine**atan**: arc tangent or inverse tangent**int**: the integer value, the part of a number before the decimal point**abs**: the absolute value, you need to remove any minus sign**^**: raise to a power

I will add formulas on a regular base.

### Overview of available formulas

- Counting the years: historically and astronomically
- Julian day and Julian day number
- Factor t and delta t
- Angle of the ecliptic
- Declinations
- Sidereal time
- MC
- Ascendant

For formula’s of house systems, check the separate Project Houses.