The Astrocalculator
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The Astrocalculator

The KStars Astrocalculator provides several modules that give you direct access to algorithms used by the program. The modules are organized by subject:

Coordinate Converters

Earth Coordinates

Solar System

Time Calculators

Angular Distance module


Angular Distance

The Angular Distance tool is used to measure the angle between any two points on the sky. You simply specify the Equatorial coordinates of the desired pair of points, and then press the Compute button to obtain the angle between the two points.

There is also a Batch mode for this module. In batch mode, you specify an input filename which contains four numbers per line: the RA and Dec values for pairs of points. Alternatively, you can specify a single value for any of these four coordinates in the calculator panel (the corresponding values in the input file should be skipped if they are specified in the calculator).

Once you have specified the input filename and an output filename, simply press the Run button to generate the output file.

Apparent Coordinates module


Apparent Coordinates

The Apparent Coordinates module converts the catalog coordinates of a point in the sky to its apparent coordinates for any date. The coordinates of objects in the sky are not fixed, because of precession, nutation and aberration. This module takes these effects into account.

To use the module, first enter the desired target date and time in the Target Time/Date section. Then, enter the catalog coordinates in the Catalog Coordinates section. You can also specify the catalog's epoch here (usually 2000.0 for modern object catalogs). Finally, press the Compute button, and the object's coordinates for the target date will be displayed in the Apparent Coordinates section.

Ecliptic Coordinates module


Ecliptic Coordinates

This module converts between Equatorial coordinates and Ecliptic coordinates. First, select which coordinates should be taken as input values in the Choose Input Coordinates section. Then, fill in the corresponding coordinate values in either the Ecliptic coordinates or Equatorial coordinates section. Finally, press the Compute button, and the complementary coordinates will be filled in.

The module contains a batch mode for converting several coordinate pairs at once. You must construct an input file in which each line contains two values: the input coordinate pairs (either Equatorial or Ecliptic). Then specify which coordinates you are using as input, and identify the input and output filenames. Finally, press the Run button to generate the output file, which will contain the converted coordinates (Equatorial or Ecliptic; the complement of what you chose as the input values).

Equatorial/Galactic Coordinates module


Equatorial/Galactic Coordinates

This module converts from Equatorial coordinates to Galactic coordinates, and vice versa. First, select which coordinates should be taken as input values in the Input Selection section. Then, fill in the corresponding coordinate values in either the Galactic coordinates or Equatorial coordinates section. Finally, press the Compute button, and the complementary coordinates will be filled in.

Horizontal Coordinates module


Horizontal Coordinates

This module converts from Equatorial coordinates to Horizontal coordinates. First, select the date, time, and geographic coordinates for the calculation in the Input Data section. Then, fill in the equatorial coordinates to be converted and their catalog epoch in the Equatorial Coordinates section. When you press the Compute button, the corresponding Horizontal coordinates will be presented in the Horizontal Coordinates section.

Precession module


Precession

This module is similar to the Apparent Coordinates module, but it only applies the effect of precession, not of nutation or aberration.

To use the module, first enter the input coordinates and their epoch in the Original Coordinates section. You must also fill in the target epoch in the Precessed Coordinates section. Then, press the Compute button, and the object's coordinates, precessed to the target Epoch, are presented in the Precessed Coordinates section.

Geodetic Coordinates module


Geodetic Coordinates

The normal geographic coordinate system assumes that the Earth is a perfect sphere. This is nearly true, so for most purposes geographic coordinates are fine. If very high precision is required, then we must take the true shape of the Earth into account. The Earth is an ellipsoid; the distance around the equator is about 0.3% longer than a Great Circle that passes through the poles. The Geodetic Coordinate system takes this ellipsoidal shape into account, and expresses the position on the Earth's surface in Cartesian coordinates (X, Y, and Z).

To use the module, first select which coordinates you will use as input in the Input Selection section. Then, fill in the input coordinates in either the Cartesian Coordinates section or the Geographic Coordinates section. When you press the Compute button, the corresponding coordinates will be filled in.

Planet Coordinates module


Planet Coordinates

The Planet Coordinates module computes positional data for any major solar system body, for any time and date and any geographic location. Simply select the solar system body from the drop-down list, and specify the desired date, time, and geographic coordinates (these values are preset to the current KStars settings). Then press the Compute button to determine the Equatorial, Horizontal, and Ecliptic coordinates of the body.

There is a batch mode for this module. You must construct an input file in which each line specifies values for the input parameters (solar system body, date, time, longitude, and latitude). You may choose to specify a constant value for some of the parameters in the calculator window (these parameters should be skipped in the input file). You may also specify which of the output parameters (Equatorial, Horizontal, and Ecliptic coordinates) should be calculated. Finally, specify the input and output filenames, and press the Run button to generate the output file with the computed values.

Day Duration module


Day Duration

This module computes the length of day as well as sunrise, sun-transit (noon), and sunset times for any calendar date, for any location on Earth. First fill in the desired geographic coordinates and date, then press the Compute button.

Equinoxes and Solstices module


Equinoxes and Solstices

The Equinoxes and Solstices module calculates the date and time of an equinox or solstice for a given year. You specify which event (Spring Equinox, Summer Solstice, Autumn Equinox, or Winter Solstice) should be investigated, and the year. Then press the Compute button to obtain the date and time of the event, and the length of the corresponding season, in days.

There is a batch mode for this module. To use it, simply generate an input file whose lines each contain a year for which the Equinox and Solstice data will be computed. Then specify the input and output filenames, and press the Run button to generate the output file. Each line in the output file contains the input year, the date and time of each event, and the length of each season.

Julian Day module


Julian Day

This module converts between the calendar date, the Julian Day, and the Modified Julian Day. The Modified Julian Day is simply equal to the Julian Day - 2,400,000.5.

To use the module, select which of the three dates will be the input, and then fill in its value. Then press the Compute button, and the corresponding values for the other two date systems will be displayed.

Tip

Exercise:

What calendar date does MJD = 0.0 correspond to?

Sidereal Time module


Sidereal Time

This module converts between Universal Time and Local Sidereal Time. First, select whether you will use Universal Time or Sidereal Time as an input value in the Input Selection section. You must also specify a geographic longitude, and a date for the calculation, in addition to either the Universal Time or the Sidereal Time value. When you press the Compute button, the corresponding value for the other Time will be displayed.

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