“These planets are extremely faint relative to their host star. Trying to image directly an exoplanet, a planet orbiting another star next to its star, is equivalent to trying to image a firefly next to a lighthouse located in New York when observing from Los Angeles.”
Blue Dot · October 2026
Context
Asked to explain in everyday terms what a coronagraph is and why it matters for the new Roman Space Telescope, the scientist sets up why the instrument has to block starlight to see planets.
Transcript
…the first year, year and a half, it was just a bit of a thought experiment. And after a year and a half, NASA asked us if we would be able to make a chronograph work also for this telescope. And the community said yes. And that's when I started to be engaged with the Nancy Grace Space Telescope.
Well, let's talk about the coronagraph, because a lot of people won't know what that is. Can you explain to us, you know, in pretty much everyday terms, what is a coronagraph and why is it important for detecting signatures of other planets around other stars?
Yes, coronagraphs are really key because these planets are extremely faint relative to their host star. So basically, like trying to image directly an exoplanet, so a planet orbiting another star next to its star is equivalent to trying to image a firefly next to a lighthouse located in New York when observing from Los Angeles. Wow.
Yeah, that doesn't sound easy.
That doesn't sound easy. And in more quantitative terms, we're basically looking for planets which are 10 billion times fainter, 10 billion times fainter than the star they orbit at visible wavelengths. And they are very close to them. In fact, they are so close to the star that we need to cancel…
And with the Nancy Grace Space Telescope, it has such a wide field of view. Can you explain to us how the chronograph will work with that huge field of view? Will it allow you to detect lots of exoplanets at once? Or how is it going to work?
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