What We're Seeing Through NASA's James Webb Space Telescope
Webb’s First Deep Field
My favorite image in the Universe has long been the Hubble Ultra Deep Field, which in 1995 revealed an absurdly large amount of stuff in an absurdly small slice of space, and gave us a glimpse into the true scale of the cosmos. But last week, one of the incredible images coming from NASA’s new James Webb Space Telescope surpassed it: Webb’s First Deep Field, which is shown above. The image is better in every way than the Hubble Deep Field – brighter, sharper, deeper, and with some neat gravitational lensing to boot.
Inspired by the image, and to help get a sense for just what it is we’re seeing through Webb, over the weekend I whipped up this video (best watched full screen, and with sound):
For the professional astronomers out there, here’s the envelope math behind the figures in the video. Hopefully it checks out.
Webb’s NIRCam has two modules, each of which images 2.2 x 2.2 arc minutes of the sky (source). Since the Webb Deep Field image is square, I assumed one of the two modules was used. The moon on average subtends 31 arc minutes, so the patch of sky imaged by Webb is 2.2 / 31 = 1 / 14th the diameter of the moon, which in the video I rounded to 1/15th.
A 2.2 arc minute square on the surface of a unit sphere has an area of 4.095 x 10^-7. The surface area of a unit sphere is 12.566. 12.566 / 4.095 x 10^-7 = 30,684,000, so Webb images approximately 1 / 30,000,000th of the sky.
A note on the images: they are meant to illustrate the relative scales involved, and are technically inaccurate in several ways. The galaxy overlaid on the Webb Deep Field is obviously not just a higher resolution version of the galaxy shown in it. (We’ll need to wait for whatever telescope comes after Webb for that.) Instead, it is a similar looking galaxy, the Spiral Galaxy NGC 691, imaged by Hubble many years ago. The star field inside of NGC 691 is the Milky Way as viewed, of course, from inside not outside the galaxy, and taken by my friend Jesse Levinson.
Thanks to Steve Seitz for his early feedback on the video, Steve Goldberg for checking my math (any errors remain my own), and again to Jesse for his photo of the Milky Way. (You should see the full resolution version of it!)
Image credits:
Webb’s First Deep Field – NASA, ESA, CSA, and STScI
Moon and M52 Cluster – Adobe Stock, Infinitalavita
Spiral Galaxy NGC 691 – SA/Hubble & NASA, A. Riess et al.
Milky Way Galaxy – Jesse Levinson