# Calculation Options

This chapter describes standard calculation options available in
*Maitreya*.

The calculation options influence the calculation results and should
therefore be handled **carefully**. Parts of the options (e.g. ephemeris
time option) are pure research features and should not be used for
standard calculation.

## Universal and Ephemeris Time

Universal time is the Greenwich mean time. Ephemeris time is a technical time which is internally used for ephemeris calculations.

The difference between UT and ET can be about one minute of time.

The ephemeris time option can be used to compare the data of Maitreya with standard ephemeris data, e.g. Rosicrucian Ephemeris.

It is recommended to use UT for astrological calculations. ET option is a research feature.

## Geocentric and Topocentric Coordinates

Geocentric calculation assumes the center of the earth as reference point. Topocentric coordinates assume the birth location as reference point.

Difference between normal and topocentric coordinates can be up to 1 degree for the Moon. So this option has big influence e.g. on Dasa calculations.

**Note:** The software only takes into account the longitude and
latitude of the birth place. The altitude of the location is neglected.
This may give an error of about 2 seconds of arc.

## Apparent and True Positions

Apparent positions are the positions where we see the planets in the sky. True positions are "real" positions in the sense that aberrations due to relativistic effects, etc. are taken into account.

The difference between apparent and true positions is quite small.

Most astrologers (and ephemerids) use apparent positions.