This is a discussion of Radio Eyes telescope tasks. In this context, a task is something you want the telescope to do. Tasks are handled either as individual one-time manual tasks or as one member of a task list. A task list may be stored for reuse in a task file. Tasks are usually created or edited with the Task Editor.
Below is a list of Task Types currently supported or soon to be supported by Radio Eyes:
AZEL - Set the telescope to a
given azimuth and elevation.
RADEC - Set the telescope to a given right ascension and declination.
DRIFT - Perform a meridian drift scan.
DRIFT LOWER CUL - Perform a drift scan at lower culmination.
TRACK - Track an object or given right ascension and declination.
MAP - Not currently implemented.
PARK - Move the antenna to a predefined park position.
CALIBRATE - Activate a calibrator (if supported by the driver).
LOOP - Go back to the beginning of the task list and start over.
END - End tasks here.
(Loop and End are more strictly task list control commands but occur in the task type selection lists within the program and thus are presented here.)
Most tasks have the following properties:
The program needs to know when a task should begin so that it may run the task unattended by a human button pusher. The criteria used to determine this starting time can take on any of the following forms:
The list of Stop Types below specifies the criteria that may be used to stop a task.
Each of these start and stop types except IMMEDIATE will take on a Start or Stop Value specified in HH:MM:SS format.
If our goal is to simply point the telescope to a particular azimuth and elevation without regard to what might be at that position over time, then the AZEL task type is appropriate. When establishing an AZEL task you must supply the Azimuth and Elevation coordinates of interest. Aside from the Start and Stop parameters explained above, these are the only required properties of the AZEL task type. Note that ultimately, all telescope move requests are translated into azimuth and elevation moves at some level. However, the actual AZEL commands may be hidden from the user by the software.
Whereas the AZEL task points the telescope to a particular observer referenced direction, the RADEC task will attempt to point the telescope to a particular position on the celestial sphere. As this sphere is always in motion with respect to the observer, a given right ascension and declination (RADEC) position will be found at a continually changing azimuth and elevation (unless the declination is at one of the celestial poles at +90 or -90 degrees declination). If you tell your telescope to move to a given RADEC, it can do so by sending it to the azimuth and elevation that currently corresponds to the specified right ascension and declination , but unless the telescope position is updated the RADEC requested will immediately begin drifting away from the telescope beam position. If you want to follow a given point in the sky you can do so with the TRACK task type.
The RADEC task type requires right ascension and declination coordinates as parameters
At this point you may be thinking, "This sounds hard. I don't want to have to type in all of these coordinates!" Fear not. Seldom will you manually type in coordinates. The beauty of Radio Eyes is that the graphical interface removes most tasks like that.
Perhaps the most common amateur radio telescope observation is called a meridian drift scan. To perform a meridian drift scan you aim your telescope at some point on the meridian (an imaginary line running North-South through the sky). Over the course of a day all objects at a given declination transit, that is, will cross the meridian and pass through your antenna beam. The declination observed will depend upon your latitude and the elevation to which the antenna is pointed. When a strongly emitting object passes through the beam of your antenna, it should deflect the output of the telescope given there is adequate sensitivity. You can estimate the right ascension of the object by noting the local mean sidereal time that the the maximum deflection occurs.
Except at the equator, all observers on Earth will see one of the celestial poles (+/- 90 deg. declination points) above either their north or south horizons. Objects that are less than the absolute value of the observers latitude in angular distance from the pole will never set. That is, they will circle the pole completely without ever disappearing below the horizon. These objects will cross the observers meridian twice each day. The crossing of the meridian that is made between the pole and the horizon is called the lower culmination. Radio Eyes can help you make lower culmination drift scan observations using the task type DRIFT LOWER CUL.
You could of course accomplish a drift scan by using an AZEL task type with an AZ of 180 or 0 degrees and an elevation calculated from the declination you want to observe. That however requires some calculation. It is easier to select an object that you want to observe in the graphical world of Radio Eyes and to request a drift scan task be created for that object. Radio Eyes will determine the correct elevation and azimuth for drift scan and if the object can be observed at lower culmination will give you the option to do so. You won't have to observe the strip of sky for an entire 24 hours because RE will calculate when the transit will occur and even select appropriate start and stop times for you based upon your beam width.
Selecting an object is covered in the Task Editor help page. For now, remember that an object such as the Sun, moon, one of the planets, or a cosmic radio source from a catalogue can be selected as the target of the drift scan.
The TRANSIT- and TRANSIT+ start and stop types are especially applicable to drift scan tasks. When the program is asked to run a task with one of these start and stop types, it will calculate the next time the specified object will transit. For TRANSIT- it will start the observation at the transit time minus the specified Start Value. If the start value is 01:30:00, it will start the task an hour and thirty minutes before the transit time. Similarly, a Stop Type of TRANSIT+ will stop the observation at Stop Value after the object transits.
Note that Radio Eyes currently does not support off-meridian drift scans directly, though this is planned for future versions.
The telescope is tracking when it is following an object as it moves across the sky. You might want to perform a tracking observation when looking for solar or Jupiter activity, or maybe for pulsar work. Tracking tasks require that either an object or fixed position of RADEC be specified. The actual means by which the tracking is maintained is largely a function of the hardware and software driver components of the telescope. In most cases, tracking will occur in small steps rather than as a continuous motion.
Mapping tasks are not yet implemented but I hope to do that soon. You could meanwhile simulate a raster type mapping scheme by having the telescope complete a series of AZEL or RADEC moves.
Parking is simply moving the telescope to specified park position. The park position (azimuth and elevation) is specified in the definition file for the telescope and not within the task itself. The park position is usually a "safe" position where the telescope is stowed to minimize wind load or other factors.
Calibration is a common but telescope specific task that applies a calibration signal to the telescope input. Calibration must be supported by the telescope driver in order to implement this task.
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