About The SETI@home Screensaver
DATA INFO
This section contains information about the block of data currently being worked on. It's very important for us to know exact details about this data so we can keep track of it in our database. If a signal is found this information will allow us to go back to that place in the sky and re-examine the correct part of the radio spectrum to check our results.
Where am I looking?
The first line in this section of the display specifies the location in the sky the data was collected from. This is where the telescope was pointed, or more accurately, the piece of the sky that was over the telescope at the time. On the earth, you need two coordinates, latitude and longitude, to locate a place on the globe. Likewise, in the sky you also need two coordinates to find an object on the "celestial sphere". In the sky these coordinates are called "right ascension" and "declination". Latitude and declination are measured in exactly the same way, starting at 0 degrees at the equator (the celestial equator in the case of declination) and moving north 90 degrees to the north pole and -90 degrees to the south pole. Right ascension is a little different from longitude. Longitude is measured east and west from the Greenwich meridian that runs through Greenwich, England. Since it is measured east and west, you can go 180 degrees either way until you reach the international date line on the opposite side of the globe. Right ascension is measured in one direction only, towards the east, and is measured in hours, minutes, and seconds rather than in degrees. There are 24 hours all the way around, each hour being broken into 60 minutes, and each minute being broken into 60 seconds. This links the rotation of the sky to the rotation of the earth very nicely. You can find out where in the sky your data was recorded by looking at the RA and Dec on the first line and finding those coordinates on a star chart.
Note that the Arecibo telescope can only see about 1/3 of the sky. The telescope is fixed in position and can only be pointed through a limited range by moving its receiving antennas. The SETI@home search is limited to declination 0 degrees to 35 degrees north.
The telescope beam is about 1/10 of a degree wide and in the 107 seconds of data collection represented by your slice of data, the telescope beam slews across about 0.6 degrees of the sky. Your data therefore occupies a rectangular area in the sky 1/10 degree high by 6/10 degree wide.
When did I look?
The second line of the Data Info section tells you when the data was recorded. Note that the time given is GMT (Greenwich Mean Time). This is the time on the clock at the Royal Greenwich Observatory in England at a longitude of 0 degrees. All astronomers use this standard to avoid confusion with all the time zones in the world. You are sent 107 seconds of data that was recorded centered at the time on line two.
What telescope was I using?
The next line tells you the source of the data, namely the Arecibo Radio Observatory. Ruling out some natural disaster destroying the telescope, this is not likely to change.
What frequency am I analyzing?
The last line tells you the base frequency of the data you are analyzing. SETI@home looks at a band of the radio spectrum 2.5 MHz wide. The SETI@home project breaks this wide band up into more managable chunks of about 10 kHz each (actually 9765 Hz). This means that every 107 seconds of data recorded for SETI@home actually produces 256 blocks of data! The base frequency number tells you where within the wide 2.5 MHz band your 10 kHz band is located.Combine all the lines and you know where in the sky, when, the frequency listened to and the source of the data. Everything you need to know to uniquely identify the block of data.