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# A telescope as big as the earth

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Suppose you want to see something so far away that it looks really small in the sky. Think of standing in New York and trying to read the date on a quarter in Los Angelesthat small. Any tiny distortion can ruin the image, but after you correct for these, ultimately, what gets you is refraction = the bending of light at the edge of your telescope. So the bigger your telescope, the higher quality image.

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How big a telescope is practical? The remarkable answer is that there is now a radio telescope "as big as the earth". The trick is done by combining data from 3 telescopes at widely dispersed places on the earth, and waiting for the earth to rotate so that these are in different positions relative to the astronomical target.

Think of a CAT scan. X-rays are sent through the body in all different directions, and received at the opposite side of the body. Each X-ray detector contains information about the entire line of flight of the X-rays, and no single detector can tell you about any single point. By combining the data from all the detectors in the right way, an image can be formed. There's a mathematical way to disentangle the data"deconvolution" is the word they useand with the wide availability of number crunching computers, this has become routine.

The same kind of math is used to deconvolve data from the 3 radio telescopes. The result is the world's first image of a black hole, and it looks just like what the theorists predict it should look like! There's a dark circle at the center, where light goes in but not out, and then there's a bright ring around that circle, where matter falling into the BH has become superhot.

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Josh Mitteldorf, a senior editor at OpEdNews, blogs on aging at http://JoshMitteldorf.ScienceBlog.com. Read how to stay young at http://AgingAdvice.org.
Educated to be an astrophysicist, he has branched out from there to mathematical (more...)

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I am at least 16 years of age

Josh Mitteldorf

(Member since Sep 14, 2006), 42 fans, 595 articles, 379 quicklinks, 983 comments, 11 diaries

For geeks, I didn't mention that the difference between a CAT scan and a "synthetic aperture" of a radio telescope is that the radio telescope incorporates the phase of the arriving wave, and using the phase difference among the 3 sites is critical to reconstructing the image.

Submitted on Friday, Sep 13, 2019 at 8:57:51 PM

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Meryl Ann Butler

(Member since Jun 5, 2006), 83 fans, 617 articles, 1906 quicklinks, 5852 comments, 7 diaries

WOW that's amazing!

Submitted on Friday, Sep 13, 2019 at 9:21:48 PM

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Brian Giffin

(Member since Aug 1, 2010), 60 comments

That's a great video of a difficult to explain subject. Well worth the watching. I'd seen the black hole photo but without an explanation like this, I didn't really believe it. The computer array combined young gamers machines around the world with university machines to get more power. The data set was the largest ever handled.

This first ever photo brought together a worldwide team that cooperated to produce something immediately valued over the whole world. That's a bottom up success.

The next proposal he made, of a low earth satellite to gather the data much quicker for better imaging, would put all the data collection in one place, whoever owns that satellite owns the output.

I like the first data collection technique better, but I'm a luddite.

Josh, I didn't get very far understanding the phase thing ?

Submitted on Sunday, Sep 15, 2019 at 2:44:28 PM

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