For Scientists NEWS GALLERY TELESCOPES + TECH ▼ VISIT US ▼ LEARN ▼ EXPLORE ▼ GIVE Home Interferometry Explained Interferometry Explained Measuring Space with Time The distance to stars is often measured in light years. If a particular star is 10 light years away, it means the light from the star takes 10 years to reach us. The speed of light is constant, so we can use the travel time of light to measure distances. Radio astronomers use this trick to triangulate the precise location of celestial objects. When two antenna dishes look at an object in the sky, they view it from slightly different positions. This means light from the object reaches one antenna a bit before it reaches the other. The time difference is only a tiny fraction of a second, but it means the timing of the two signals are a bit off. When combined, they would overlap or interfere with each other, blurring the signal. But by precisely timing the signal from each antenna, astronomers can correlate them so they don’t interfere. This is known as interferometry. With interferometry, radio astronomers can combine the signals from many antennas, and even many telescopes. It allows them to create an image that is much brighter and sharper than what is possible from a single antenna dish. How to get the best image Many factors can affect the quality of the radio image. Placing antennas far apart makes the image sharper, while placing them close together makes the image brighter. More antennas gather more light, but also make the telescope more expensive to build and operate. Observing for a longer time is usually better, but telescope time must be shared with other astronomers. Even the way antennas are arranged can affect what we see. Interferometry in Action In the below application, you are the astronomer. Pick an image you want to observe below by clicking on it, then click “Next” Build a preset or custom array of antennas to use for your observations. Select the shape and the click the plot button or the use the + and – buttons to add or remove antennae. Click the “Observe” button to simulate the observation results Click the “Back” button to adjust your configuration and try again Check the “Compare to previous” box to see how your observation changed with your new configuration Going Deeper Experiment with different configurations, make several observations and compare them. Hover or click on underlined terms to learn more about them. How does an observation with a “small” configuration compare to one with a “large” configuration? How does the time of the observation effect the final image you observed? Can you get a clear image with only a few antennas? Does your configuration work well for some images but not others? Test your ideas to see what works! CHOOSE SOURCE IMAGE MAKE ANTENNAE CONFIGURATION OBSERVATION RESULTS Choose your source image to observe: NEXT Connect with NRAO Tweets by TheNRAO The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Founded in 1956, the NRAO provides state-of-the-art radio telescope facilities for use by the international scientific community. NRAO telescopes are open to all astronomers regardless of institutional or national affiliation. Observing time on NRAO telescopes is available on a competitive basis to qualified scientists after evaluation of research proposals on the basis of scientific merit, the capability of the instruments to do the work, and the availability of the telescope during the requested time. NRAO also provides both formal and informal programs in education and public outreach for teachers, students, the general public, and the media. The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..." AUI collaborates with the scientific community and research sponsors to plan, build, and operate cutting-edge facilities. We cultivate excellence, deliver value, enhance education, and engage the public. News Gallery Telescopes + Tech Visit Us Learn Explore Give For Scientists About NRAO Ask an Astronomer Historical Archives ACEAP Media Use Social Media Policy NRAO Library Central Development Lab Technology Transfer Careers at NRAO NRAO Diversity Employee Services Visitor Code of Conduct Contact Us NRAO Headquarters 520 Edgemont Road Charlottesville, VA 22903 434-296-0211 More Information Here © 2021 The National Radio Astronomy Observatory