# Interactive Tools

This section contains nine interactive tools which allow you to feed in some numerical sets of data and obtain the output. They are fundamental yet essential mathematical models, such as coordinate transformations and conversions between orbital elements and rectangular Cartesian coordinates. Each program was originally written in FORTRAN and converted to Perl in order to get it working on the Web.

Fill in the following boxes and hit the button "Compute" to obtain the results.

## 1. Julian Date

The Julian Date (JD) is the number of mean solar days (and fraction of a day) elapsed since the epoch noon on January 1st, 4713 B.C. Since the astronomical day was defined to count from noon rather than midnight, the Julian Date is always different from UT by 0.5. For example, 1970, 7, 12, 0 (midnight) (UT) = 2440779.5 (JD) .

The folowing program converts the civilian date expressed by the year, month, day, and the time (hour, minute, and second) in Universal Time (UT) into the Julian Date (JD). Also, it provides the day of week for that date.
(Note: This program is only valid for an epoch between March 1900 and Febrary 2100.)

```  Year:
Month:
Day:
Hour:
Minute:
Second:
```

## 2. ETOGEO

This program transforms a given vector from earth centered, earth fixed coordinates to a topocentric geographic coordinate system. The earth fixed system's X-axis is in the direction of the Greenwich Meridian, the Z-axis north, and the Y-axis completing a right-handed system. The geographic system's X-axis points south, the Y-axis east, and the Z-axis zenith.

```
Latitude of Local Coordinate Site (in degrees):
Longitude of Local Coordinate Site (in degrees):
X-component of Vector in Earth Centered, Earth Fixed Coordinates:
Y-component of Vector in Earth Centered, Earth Fixed Coordinates:
Z-component of Vector in Earth Centered, Earth Fixed Coordinates:
```

## 3. ITOE

This program transforms a given vector from M50 equatorial coordinates to earth centered, earth fixed coordinates. The earth fixed system's X-axis is in the direction of the Greenwich Meridian, the Z-axis north, and the Y-axis completing a right-handed system.

```      Hour Angle of the Vernal Equinox (in degrees):
X-component of Vector in M50 Equatorial Coordinates:
Y-component of Vector in M50 Equatorial Coordinates:
Z-component of Vector in M50 Equatorial Coordinates:
```

## 4. ETOI

This program transforms a given vector from earth centered, earth fixed coordinates to M50 equatorial coordinates. The earth fixed system's X-axis is in the direction of the Greenwich Meridian, the Z-axis north, and the Y-axis completing a right-handed system.

```
Hour Angle of the Vernal Equinox (in degrees):
X-component of Vector in Earth Centered, Earth Fixed Coordinates:
Y-component of Vector in Earth Centered, Earth Fixed Coordinates:
Z-component of Vector in Earth Centered, Earth Fixed Coordinates:
```

This program converts from earth centered non-rotating coordinates to right ascension, declination, and radial distance from the origin of the inertial coordinate system. The earth centered non-rotating coordinate system has X-axis pointing toward the vernal equinox, Z-axis pointing toward either the Celestial or Geographic north pole, and Y-axis completing the right handed coordinate system.

```
X-component of Vector in Earth Centered non-rotating Coordinates:
Y-component of Vector in Earth Centered non-rotating Coordinates:
Z-component of Vector in Earth Centered non-rotating Coordinates:
```

This program converts from right ascension, declination, and radial distance into earth centered non-rotating coordinates. The right ascension is measured positive from the X-axis toward the Y-axis in the X-Y plane. The declination is measured positive from the X-Y plane up to the inertial vector.

```
Right Ascension (in degrees):
Declination (in degrees):
Magnitude of Inertial Vector:
```

## 7. OETOPQ

This program calculates the position and velocity vectors in the orbit fixed PQW coordinate system given the orbital elements.

```
Semi-Major Axis:
Eccentricity:
Gravitational Parameter:
Current Time since Chosen Epoch, T0:
Time of Previous Periapsis Passage since Chosen Epoch, T0:
```

## 8. OETORC

This program calculates the position and velocity vectors in the earth centered non-rotating coordinate system given the orbital elements.

```
Semi-Major Axis:
Eccentricity:
Inclination (in degrees):
Longitude of the Ascending node (in degrees):
Argument of Periapsis (in degrees):
Gravitational Parameter:
Current Time since Chosen Epoch, T0:
Time of Previous Periapsis Passage since Chosen Epoch, T0:
```

## 9. PQTOXY

This program converts the position and velocity vectors from the orbit centered coordinate system, PQW, to the inertially fixed coordinate system, XYZ.

```

Longitude of the Ascending node (in degrees):
Argument of Periapsis (in degrees):
Inclination (in degrees):
X-component of Position Vector in PQW Coordinates:
Y-component of Position Vector in PQW Coordinates:
Z-component of Position Vector in PQW Coordinates:
X-component of Velocity Vector in PQW Coordinates:
Y-component of Velocity Vector in PQW Coordinates:
Z-component of Velocity Vector in PQW Coordinates:
```

| Introduction | Outline | Description | Application | Tools | Slide | Links | Bibliography |

```This page is created by
Masaharu Suzuki
The University of Texas at Austin``` Last Modified: Wed Feb 11, 1999 CSR/TSGC Team Web