4 ms·
No, they're quite open about the capabilities of the optics (see https://webb.nasa.gov/content/forScientists/faqScientists.html#nircam https://webb.nasa.gov/con
by LeifCarrotson 3y ago
No, they're quite open about the capabilities of the optics (see https://webb.nasa.gov/content/forScientists/faqScientists.html#nircam https://webb.nasa.gov/content/forScientists/faqScientists.ht...). It's just that Europa is very far away.
Webb's mirror system has an angular resolution of about 0.1 arcseconds. Earth is currently about 630 million km from Europa (Webb is only 1.5 million km away from earth). Because the sine of theta is approximately equal to theta for values of theta near zero, you can get the diameter of a 0.1 arcsecond cone at x km from Earth by multiplying by 0.00000485 = sin(2pi/3603600).
0.1 0.00000485 * 630000000 = 305 km
The article says the pixels are about 320 km, so the math works out pretty close (for astronomy).
Those magnificent images of black holes and galaxies that are way more distant, but also way way bigger. This isn't downscaled when you compare it to gorgeous, sharper images like those at [1], a 340 light-year wide multi-image mosaic of the Tarantula Nebula, which is "only" 161000 light years away, that width is 1/500th the distance and Europa's width is 1/20,000th the distance.
In space, intuition about distances that you've built up from using your eyeballs on human-scale terrestrial objects just doesn't work, you've got to do the math.
[1]: https://www.nasa.gov/feature/goddard/2022/a-cosmic-tarantula-caught-by-nasa-s-webb https://www.nasa.gov/feature/goddard/2022/a-cosmic-tarantula...
- superhumanuser 3y agoThis reply is why I love the audience on HN. Thank you for your detailed comment.
- philomath_mn 3y agoFor the conspiracy theorists: this is the same reason why we can't just point Webb at the moon and get pictures of the lunar landing sites. In terms of arcseconds of the Webb's FOV, the moon landing site is much smaller than these distant galaxies (which blows my mind just how big those distant "objects" are).
- ceejayoz 3y agoWe can image the lunar landing sites with lunar orbiters, though. Footsteps and all! https://www.nasa.gov/mission_pages/LRO/news/apollo-sites.html https://www.nasa.gov/mission_pages/LRO/news/apollo-sites.htm...
- philomath_mn 3y agoRight -- they are a bit closer than Webb :D
- alluro2 3y agoYou obviously mean the fake lunar orbiters. And those footsteps are not human anyway, it's the Moonfoot. /s :)
- jojobas 3y agoNot just that, its infrared sensors require shielding from Earth/Moon (let alone Sun) heat to function as designed, and it would mostly see the dark side of the moon anyway.
- grecy 3y agoThanks for the detailed comment, that is incredibly helpful info.
- jonplackett 3y agoI wish every website I visited had comments of this quality…
- funnybeam 3y agoThis is why I only read Hacker News these days.
- jcims 3y agoNice! Yeah, some things in the sky are actually way bigger than one might think. The first time I saw this composite of the moon and andromeda it kind of blew my mind. https://i.stack.imgur.com/gMZb3.jpg https://i.stack.imgur.com/gMZb3.jpg It’s probably a mental trick but once you know where the Orion Nebula is you can also just barely make it out with the naked eye. https://www.reddit.com/r/Astronomy/comments/aecbbl/the_orion_constellation/ https://www.reddit.com/r/Astronomy/comments/aecbbl/the_orion... This is what it looks like ‘live’ through an 11” telescope if you try to hold your phone with your hands lol, and you can see the ‘fuzziness’ of it, not the color: https://imgur.com/a/nt6FdLV https://imgur.com/a/nt6FdLV