It covers a novel and a cost effective technique, which provides a magnificent esolution and accuracy. Prevailing online telescopes tend to be very expensive and are restricted to only a small segment of population for access. So the prime Intension of this system Is to develop a cost effective technique to construct an online telescope. Users will be able to enter the celestial coordinates of any celestial object to the web Interface and download realtime CCD images over the internet from the system.
The earth synchronous motor system fixed to the base of the telescope allows it to focus on the celestial object for a long period of time despite earth’s rotation. The web interface developed for the SBIG CCD ST-7 camera allows the user to access the camera over the internet, select an exposure time and download good resolution images of the objects. Features such as web based CCD image acquisition, earth synchronous drive, RA/Dec to HA/Dec celestial coordinate’s conversion modules add value for the product.
This system provides great business opportunltles to produce online telescopes In a comprehensively Inexpensive cost with further enhancements Keywords: Online Telescope, Celestial coordinate conversion, web CCD control INTRODUCTION Astronomy has been an unpopular, yet an emerging field of tudy in Sri Lanka. Since Sri Lanka is the south most land mass in the Indian Ocean in between Australia and South Africa, Sri Lanka plays a pivotal role in observing the Southern Hemisphere.
Even though this telescope cannot Identify faint objects In deep sky due to Its Inexpensive motors, medium range focal length Telescope and low deep sky internet controllable telescope with further investment. controlled through the internet to focus at the celestial bodies and download pictures using the SBIG ST – 7E CCD camera attached to it. Users have the facility to either enter the celestial oordinates, or select one of the heavenly bodies such as Sun, Moon, and Planets for which the ephemerides will be calculated automatically.
The interface displays the currently focused direction of the telescope in terms HA (Hour Angle) and Dec. The user is privileged to select an exposure time for the CCD. The telescope has currently been fixed on the rooftop in equatorial mount where the base of the telescope is 7 degrees inclined from the zenith. This value corresponds to the longitude value of Sri Lanka above the equator.
This inclination makes sure rotating one axis alone (The HA xis) is sufficient to compensate the earth rotation and let the telescope be focused on the desired celestial object despite earth rotation. The system includes the following features 2. 3. 4. 5. 6. 7. 8. 9. Telescope over the internet is a product development project developed for the final year project for the BSc Engineering course of University of Moratuwa, Sri Lanka.
It involves automation of a manual 8″ Schmidt Cassegran 2110 mm telescope into a fully automated telescope which can be Celestial coordinate inputs – RA, Dec coordinates input Database of important celestial objects Automatic ephemerides calculator – Automatically ongitude, latitude as inputs Equatorial synchronous motor drive High resolution motor drivers Manual position setter – Users can manually enter HA, Dec coordinates directly, if they know the focused current direction of the telescope Fine tuning at a resolution of 1 arcmins at both directions Visibility checker – This informs the user if the celestial object can be seen at that particular moment of time. Multiple exposure times – Gives the user a range of exposure times from 0. 20s – 10 mins. Exposure time of 0. 20s is preferred for closer bright objects like moon. These data were gathered after extensive testing 10. Download user editable image format (.
ST7) – This format is used as this format images can be edited using the free CCDOPs software, which the user can install in his client PC. So after downloading the image to his PC, user can do editing such as contrasting, brightness adjustment, noise reduction, 1 1 . Programmed to be fixed anywhere – The admin will only have to adjust the longitude and Latitude METHODOLOGY The components of the system 8″ Schmidt Cassegran 2110 mm optical telescope SBIG ST – 7E CCD (765 * 510) Unipolar and Bipolar stepper motors with Earth synchronous motor system to compensate earth rotation L298 – heat sink fixed Motor control boards Main controller board Telescope Controller Server CCD Controller Server Power system unit The system is divided into 4 subsystems A.
Subsystem 1 (Mechanical Subsystem) The telescope is rotated about two axes, HA (Hour Angle) and DEC (Declination). A Bipolar stepper motor is used for the HA axis and a unipolar stepper used for the DEC axis. Both the motors have been supported with a good, high torque supportable gear system which gives the telescope an overall resolution of 1. 8 arcsec in DEC and 10. 3 arcsec in HA axis. After the construction of the gear system, the gear atios of the DEC and HA axes are 2520 and 3600 respectively. The telescope is mounted in an equatorial mount. Thus the telescope has been mounted with an inclination of 70 with the vertical axis and the initial position of the telescope has been calibrated to point to the North Pole.
Subsystem 3 (Programming logic) The Telescope Controller Server and the CCD controller server are hosted in an 11S 5. 1 server. The website constructed, provides the user with the privilege of manually entering the celestial coordinates or selecting an object. If the user selects one of the predefined objects then the ephemerides of that object for that particular time is calculated prior to the conversion algorithm. This calculation takes the local time, date, longitude and latitude of the observer site as input. After validating the user inputs of Celestial oordinates the algorithm to convert of RAI’ DEC celestial coordinates or ephemerides to HAIDEC Equatorial coordinates is implemented in the client side.
This conversion takes the longitude, latitude of the telescope site, celestial coordinates of the object to be viewed and local time as inputs and calculates the local sidereal time, from which the HA is calculated as shown in (1). Local sidereal HA = Local sidereal Time – RA HA is the degree between the observer’s meridian and the object’s RA. HA is measured westwards from the observer’s meridian. Resulting HA is used to check if the particular bject can be viewed from the location of the telescope as shown in (2). If the validation fails, an error message is displayed to the user saying that this object cannot be viewed as it is out of the visible sky. Then the calculated HA, Dec coordinates are passed to the server side.
The current coordinates of the telescope is read from the data file. It is used to calculate the resultant angle to be turned in both axes to reach the designated position in the celestial globe. The elapsed time calculator module calculates the compensation degrees for the HA axis (Earth movement). This is the angle rotated by the earth synchronous motor etween the previous command and the current command. HA motor loop calculator module and the Dec motor loop calculator module in the Telescope controller server calculates the number of loops to be rotated by each motor. Earth movement is used by the HA motor loop calculation module as shown in (3).
A 12 bit data packet is constructed using the information obtained and transmitted to the main controller board over the serial port. Then the current location of the telescope is saved in the file. HA < 90 or HA > 270 deg Angle to rotate in the HA axis = New HA – (Current HA – earth movement) (3) Fine tuning can be done if the celestial object doesn’t come within the center of field of view. Manual fine tuning up to 1 arcsec is provided. The telescope is calibrated initially to point to the North and Zenith and these coordinates are defined as (0,0). The coordinate system takes these as the reference point. After the initial turn, the telescope rotation compensates for the earth rotation as well.
That is, the time elapsed from the previous command to the present is calculated and HA rotation, time taken for the rotation is calculated based on the steps to be turned and it is compensated with additional steps. After the object is in the center of the field of view, the earth synchronous system compensates the earth movement and keeps the object steadily in the center. Extensive testing has been done to find out the backslash in the gear system in varies positions of the telescope. This backslash has been compensated with necessary no of steps in the programming logic A trade off had to be made between the telescope maximum resolution and time taken for the telescope to reach the designation spot in the celestial globe. When trying to increase the resolution of the telescope system, it affects the rotational time s it takes more time for rotation.