| SETI Net Clock is a small file that will show the local time, the time in Greenwich England and your local sidereal time. It will also convert from Dec/RA to Az/El and back. You may download the latest Clock Here. Its best to use the installer defaults unless you really want to change something. At the end of the install the clock will start and will be up and running. First thing is to set your stations local Latitude and Longitude. I use a site run by the ARRL (the 'hams') for these two numbers. 
Click on the 'Map' button and this is what opens. This is a Mercator projection of the sky with your search area shown. The default is for my Argus SETI station in Del Mar California. As the night progresses this Search Area will move left across the sky and then reappear on the right. Move your mouse over the Sky Map and the upper panel will recalculate the Az/El and DEC/Ra as you go. Left click on the map and that position is remembered as the antenna position. If you click outside of you search area it will be pulled into the area automatically. Right click and this is remembered as the current Star position. This can be anywhere on the map. The size of the spot that represents your antenna is calculated from the frequency you are using and the antennas current Az/El DEC/Ra. It changes as you move through the heavens. 
Click on the 'Ant' button and this is what opens. This is where you tell the software about your particular antenna setup. As you work though this you can always unwind back to a default condition with the button on the lower left. 
Clock Operation:The SETI Net Clock will run continuously. Every second the Julian date/time, UTC and GST are calculated and displayed for you. The LST is calculated based on my location (defaults to the location of SETI Net) until you change it. Change it by entering your Lon and Lat as real numbers. As you enter the digits the new LST will be calculated. You can set your computer clock to within a few milliseconds by using the US government services at: http://www.boulder.nist.gov/timefreq
Or: Atom Time at: http://www.atomtime.com/
Once your LAT/Lon are entered the conversion of DEC/RA corresponding to you location will update. Enter the star coordinates into the Dec and RA boxes and the conversion will show in the Az/El window. If you know the Az/El of an object throw the switch the other way and enter the data into the windows. The results will show in the Dec/RA window on the next clock tick and will update continuously. The clock remembers your LAT/Lon once you enter it. Star Locator:You can use the Star Finder to point to a particular star or to find out which star your antenna is now pointed to. You can use the Star Finder while the clock runs in this version. Point To A Star: - Look up the star Right Ascension (RA) and Declination (Dec) from a star map or other source.
- Press the conversion switch so that the red arrow points right
- Enter the RA and Dec into the boxes. You may enter directly or use the up/down arrows
- Press the red arrow. The necessary Azimuth (Az) and Elevation (El) of your antenna appears.
- From now on the Az and El will be updated as the star moves through the heavens.
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What Star Am I Pointed To: - Set the conversion switch so that the red arrow points to the left
- Enter the Az/El of your antenna into the boxes. Use the up/down arrow or enter directly
- Press the red arrow. Your antennas Dec/RA appears in the boxes.
- Your current Dec/RA will be updated as the star moves.
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Details of the Clock Software:This is a Delphi application that makes use of many controls and components for the user interface but at bottom the heavy lifting is done in the SETI Time library. If you are interested in this library I will send you the Delhi code. Real Time Clock - Its a little known fact( at least it was to me) that your computer hardware clock keeps UTC ( Coordinated Universal Time) time not local time. The internal software converts the internal clock to local time and displays it based on the inputs you give it in the clock setup software. This component makes a system call for the time and date and displays it. Daylight Savings - I wrote a small module that makes a call to the system routine "DayLightSavingsInEffect" to get the answer. Julian Date/Time - This calculation is made by a GetCurrentJulian call to the SETI_Time module. This entry into the library makes a call to the system to get the UTC and then passes that to two calls SETI_TIme function for the Julian_Date_Of_Year and Fraction_Of_Day. It then sums these and returns the answer for display: Result := Julian_Date_of_Year(wYear) + DOY(wYear, wMonth, wDay)+ Fraction_of_Day(wHour, wMinute, wSecond, wMilliseconds);
UTC - Again a call to the system for the time it keeps. GST - This is calculated by a call to the library function ThetaG_JD with the current jullian date. DegToHrs(RadToDeg(ThetaG_JD(GetCurrentJulian))); The return from the library, which performs its calculations in radians is converted to Degrees and then to Hours for display.
LST - The local sidereal time time is calculated by GetGSiderealTime + lon / 15
Greenwich sidereal time is captured first and then the observer Longitude is retrieved from the edit box as a real number. LAT/LON - Entry of these real numbers is though a special Delphi component that I wrote to work around the limitations of the standard Windows Edit box. StarFinder - With these calculation in place the conversion of Dec/Ra to Az/El can be made by a call to the function RADecToAzEl : RADecToAzEl(RAdeg, Decdeg, Latdeg, LonDeg, Azdeg, Eldeg);
When the switch is thrown the conversion is from Az/El to Dec/RA by a call to the function AzElToRADec; AzElToRADec(Azdeg, Eldeg, Latdeg, Londeg, RAStarHrs, StarDeclinationdeg);
Notice that the inputs and the results are in degrees.
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