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Track the Movement of the Milky Way With This DIY Radio Telescope

Detect galactic hydrogen using roof flashing, a paint-thinner can, and a software-defined radio

4 min read
The author made a horn antenna out of aluminum flashing and a metal can.

Starry Night: The DIY radio telescope points skyward, under the Milky Way.

Photo: David Schneider

A young friend recently spent a week learning about radio astronomy at the Green Bank Observatory in West Virginia. His experience prompted me to ask: How big a radio antenna would you need to observe anything interesting? It turns out the answer is a half meter across. For less than US$150 I built one that size, and it can easily detect the motions of the spiral arms of the Milky Way galaxy. Wow!

My quest began with a used satellite-TV dish and a “cantenna” waveguide made from a coffee can placed at the dish’s focus. Unfortunately, I had to abandon this simple approach when I figured out that a coffee can was too small to work for the wavelength I was most interested in: 21 centimeters. That is the wavelength of neutral hydrogen emissions, a favorite of radio astronomers because it can be used to map the location and motion of clouds of interstellar gas, such as those in the spiral arms of our galaxy.

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From WinZips to Cat GIFs, Jacob Ziv’s Algorithms Have Powered Decades of Compression

The lossless-compression pioneer received the 2021 IEEE Medal of Honor

11 min read
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Photo of Jacob Ziv
Photo: Rami Shlush
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Lossless data compression seems a bit like a magic trick. Its cousin, lossy compression, is easier to comprehend. Lossy algorithms are used to get music into the popular MP3 format and turn a digital image into a standard JPEG file. They do this by selectively removing bits, taking what scientists know about the way we see and hear to determine which bits we'd least miss. But no one can make the case that the resulting file is a perfect replica of the original.

Not so with lossless data compression. Bits do disappear, making the data file dramatically smaller and thus easier to store and transmit. The important difference is that the bits reappear on command. It's as if the bits are rabbits in a magician's act, disappearing and then reappearing from inside a hat at the wave of a wand.

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