Using the GAVRT Radio Telescope: The SETI Project Lesson 5: Which Wavelength of Light? Questions? Please contact Carolyn Donelan @ carolyn.donelan@richlandone.org.

Electromagnetic Radiation Image credit: http://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

What electromagnetic radiation reaches the Earth’s surface? Gamma rays, x-rays, most UV rays, and most IR rays are absorbed or reflected by the atmosphere before they reach the ground. Some IR, some UV, and visible light rays make it to the ground. Most radio waves make it to the ground. Image credit: http://www.windows2universe.org/earth/Atmosphere/earth_atmosph_radiation_budget.html

Which radiation would extraterrestrials probably use? Image credit: http://imagine.gsfc.nasa.gov/science/toolbox/emspectrum1.html

What else should we consider? Frequencies < 300Hz are unlikely to be naturally made, so we could concentrate our searches there. However, when considering all possible sources of interference (such as pulsars, quasars, satellites circling the Earth, aircraft radar, and WiFi), we want to focus on an area of the spectrum that won’t be “noisy”.

What else should we consider? Radio frequencies between an atom of neutral hydrogen and a molecule of hydroxyl (one hydrogen and one oxygen), there is a quiet zone called “the water hole”. It is called “the water hole” because H + OH makes H2O (or water!). Image credit: http://www.seti.org/seti-institute/project/details/seti-observations

The Water Hole SETI has been searching for a true signal for 50 years (and hasn’t found one yet). What other frequencies do you think should be investigated? Image credit: http://astronomynow.com/news/n1004/26seti5/

The GAVRT SETI Project The GAVRT SETI Project will search most of the stars in our galaxy, in all the frequencies the telescope (named DSS-28) can reach (in 200 MHz increments). It will take YEARS to complete these scans. Students can help in this effort by examining the data and attempting to reject all RFIs.