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aericbo field of vison
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braunfeld Send message Joined: 25 Feb 09 Posts: 12 Credit: 2,412,971 RAC: 0 |
how much of the celestial sphere does arecibo see at any one point in time? we would like to know this as a percent of the celestial sphere. |
Gary Charpentier Send message Joined: 25 Dec 00 Posts: 30639 Credit: 53,134,872 RAC: 32 |
how much of the celestial sphere does arecibo see at any one point in time? we would like to know this as a percent of the celestial sphere. About 25% of the sky. http://arxiv.org/pdf/1108.3134v2 page 2, 3rd paragraph from bottom If you mean the beam width or the instantaneous amount of sky, for the Arecibo antenna at 2.4 GHz the beamwidth is about 0.028°. A very small percent. http://en.wikipedia.org/wiki/Parabolic_antenna It varies depending on where you have the feed horn and if you want to do the math ... http://www.naic.edu/~astro/aotms/performance/99-02.pdf |
Josef W. Segur Send message Joined: 30 Oct 99 Posts: 4504 Credit: 1,414,761 RAC: 0 |
how much of the celestial sphere does arecibo see at any one point in time? we would like to know this as a percent of the celestial sphere. It says "The survey thoroughly covers 25% of the sky (declinations from -2◦ to +38◦ )." However, calculating coverage from that declination range gives a figure of about 31% of the sky. It's not really a contradiction, the extremes of declination are not used except in very special circumstances. If you mean the beam width or the instantaneous amount of sky, for the Arecibo antenna at 2.4 GHz the beamwidth is about 0.028°. A very small percent. The 3.4 arcmin HPBW of the LBW feed at 1420 MHz is actually fairly close to that for the ALFA feeds which are used for multibeam recordings, and the 2.5 MHz recorded bandwidth is centered at 1420 MHz. The applications base their calculations on 0.05 degree beam_width. Because there are 7 beams the instantaneous coverage works out quite close to 1 square degree, 1/41253 part of the full sphere, or 0.0024 percent. Joe |
braunfeld Send message Joined: 25 Feb 09 Posts: 12 Credit: 2,412,971 RAC: 0 |
so what is the percent of the total celestial sphere is it? i am wondering the following in my original post: if a signal was sent just once what would the probability of arecibo receiving the signal. |
Josef W. Segur Send message Joined: 30 Oct 99 Posts: 4504 Credit: 1,414,761 RAC: 0 |
so what is the percent of the total celestial sphere is it? i am wondering the following in my original post: if a signal was sent just once what would the probability of arecibo receiving the signal. Because the ALFA receiver system is only in use part time, divide the 0.0024% by about 6 to get 0.0004% probability the signal would appear in our recorded data. That assumes the signal is within the frequency range being recorded, of course. According to the Science status page, the science database holds Spikes 2,399,400,523 Gaussians 470,411,523 Pulses 1,152,742,122 Triplets 1,039,693,708 Any one of those could be a signal sent just once. However, multiple observations at different times (persistence) is needed to further reduce that amount of data so it's practical to consider more closely. Joe |
Bob DeWoody Send message Joined: 9 May 10 Posts: 3387 Credit: 4,182,900 RAC: 10 |
No matter how you slice it the answer is not very much. at one time. But being near the equator and during a 24 hour spin of the earth a pretty good swath of the sky can be covered. But it beats not looking at all. A dedicated observatory on the far side of the moon would have a much better chance of finding ET, if ET is sending signals. I still think we should be using the two voyagers to look back toward the sun and determine if their instruments are detecting anything unique in the noise that can be atributed to our being here and if so look for those signs elsewhere. Bob DeWoody My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events. |
Gary Charpentier Send message Joined: 25 Dec 00 Posts: 30639 Credit: 53,134,872 RAC: 32 |
I still think we should be using the two voyagers to look back toward the sun and determine if their instruments are detecting anything unique in the noise that can be atributed to our being here and if so look for those signs elsewhere. From their distance earth is now far far smaller than a single pixel. |
Bob DeWoody Send message Joined: 9 May 10 Posts: 3387 Credit: 4,182,900 RAC: 10 |
I understand that but I was wondering if they would be able to detect anything in the radio frequencies or in spectral analysis if aimed in the general direction of the earth and sun that would show as out of the ordinary. Bob DeWoody My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events. |
Gary Charpentier Send message Joined: 25 Dec 00 Posts: 30639 Credit: 53,134,872 RAC: 32 |
I understand that but I was wondering if they would be able to detect anything in the radio frequencies or in spectral analysis if aimed in the general direction of the earth and sun that would show as out of the ordinary. You want to fly out to them and attach experiments they don't have? Okay. |
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