Diffraction and Resolution The York College Radio Telescope Ian O’Leary, Tim Paglione, & Waynewright Joseph (York College, CUNY) Abstract We constructed, installed and commissioned a radio telescope at York College. The Small Radio Telescope (SRT) was developed by the MIT Haystack Observatory and is distributed by Custom Astronomical Support Services, Inc. A radio telescope’s main purpose is to receive radio emissions from the universe, especially from atomic hydrogen. We aligned the telescope, calibrated the temperature scale and installed computer software to complete the construction of the SRT. We measured the pointing accuracy and the beam size, and observed the hydrogen spectrum of the Galactic cloud S8. Diffraction and Resolution Most single-dish radio telescope readings are “blurry.” The blurring stems from diffraction which affects all telescopes. For sharper images – better resolution – the diameter of a telescope's collecting area must be substantially larger than the wavelength of the radiation it detects: Resolution  Wavelength/Diameter of dish To have good resolution in the radio, one must have a large telescope. The ideal aperture for a radio telescope operating at 21 cm would be several kilometers, which is very difficult and expensive to design and construct. Organization The telescope was shipped to York College in several parts. The motors came to us pre-assembled and we completed the rest by hand. We positioned the base on the roof of the Academic Core building, directly above the York College TV studio, where the control laptop was located. The connection between the laptop and the telescope was through a vent collar in the roof. The cables were fed through the collar and connected to the motors, calibrator, and digital radio receiver. Commissioning We installed the SRT software on a designated laptop. This program helps control the telescope, access sources, correct/calibrate pointing, calibrate the temperature scale, track sources, examine spectrum and power from the receiver, and record data. We aligned the telescope by tracking the Sun. We tracked the Sun at different offsets and found where the greatest power was received. We rotated the electronic noise calibrator to maximize its power coupling to the receiver. -We also made software adjustments for proper calibration of the power-to-temperature conversion. We observed the hydrogen spectrum from the well-known source S8 (see figure). We installed Virtual Network Computing (VNC) software onto the main laptop to control it from anywhere in the York College network. We measured beam dimensions (resolution) by observing the Sun. -The beam full-width at half maximum, is 7 degrees. Introduction Radio telescopes allow us to observe the expanding universe through radio waves. These radio waves are so low in frequency that they are able to pass through dusty regions that visible light cannot. With this, radio astronomers have access to the entire universe. The first radio telescope was constructed in 1931 by American scientist Karl Jansky. He realized that radio signals moves with the sky every day. Radio astronomy grew from there and has produced many new maps of galaxies, supernovae and the rest of the universe. Construction We installed the base, motors, parabolic dish, and the digital radio receiver on the roof of the Academic Core Building at York College. The base of the telescope is a hexagon with three-foot wide sides. A mast perpendicular to the ground is supported by six support legs. The mast supports the azimuth motor, which is connected to an adaptor pipe supporting the elevation motor. The elevation motor is connected to the parabolic dish, which consists of five parts: four quarter pieces of the dish and an adapter ring, which connects the dish to the elevation drive. The digital radio receiver is supported above the dish by four feed legs. Each motor required a connection to a control box in the York College TV studio directly below the telescope: Two power connections One pulse wire to monitor motor movement One ground wire Also connected to the telescope is an electronic calibrator, which allows calibration of signal temperatures. A control box connects to the SRT and laptop. The digital radio receiver connects to the control box by a coaxial cable. Radio Astronomy Radio astronomy is the study of the Universe in the radio part of the electromagnetic spectrum. Radio waves are a form of electromagnetic radiation with wavelengths that range from approximately 1mm and beyond. Almost all of the radio spectrum is accessible from ground-based observatories, day and night. Radio telescopes collect and concentrate the radio waves from an astronomical source. The signal received is then electronically processed. Radio waves can penetrate dust and allow us to measure the full extent of the universe. The cosmic microwave background radiation (the evidence of the Big Bang) is strongest in the radio. Hydrogen, the most abundant element in the Universe, emits in the radio at a wavelength of 21 centimeters. Other unique sources of radio emission include normal galaxies, such as the Milky Way, radio galaxies and quasars, as well as supernova explosions. Elevation Motor (cover off) Azimuth Motor Adapter Pipe Mast Adapter Ring Electronic Calibrator Status We are currently waiting for a replacement motor sensor which failed after it was exposed to rain. We plan to map the hydrogen emission from the Milky Way when the SRT resumes operation.