This spot was chosen because it had very few foreground stars in the field, and so would be filled with only light from distant galaxies. In Christmas of 1995, over the span of 10 days HST was pointed at a dark spot in the northern constellation, Ursa Major (which has a famous asterism, “The Big Dipper.”). The name, “Deep Field,” is not just illustrative – it refers to the several “Deep Fields” taken with HST! In today’s bite, we investigate a few notable Hubble Deep Fields. Every speck of light, save for the diffraction spiked stars in our own Milky Way, is from a galaxy far, far away. You can learn more about diffraction spikes here. The 8 spikes come from JWST’s non-circular primary mirror (each segment is a hexagon) and support arms for its secondary mirror, while the 4 spikes in the HST images come from the four support arms holding the secondary mirror in place, see here. You’ll notice that there are 8 spikes in the JWST image, but only 4 spikes on every star in the HST image. A draggable comparison of these two images is at the link here. It is so massive its gravitational pull distorts the light from galaxies behind it in a mechanism called “ gravitational lensing.” This field has been imaged before with WFC3 and ACS on the Hubble Space Telescope (HST), shown in the figure below and to the right, and was imaged this past June with JWST. The image, shown in the figure to the bottom left, is titled “Webb’s First Deep Field,” and it is of the field of SMACS J0723.3-7327, a galaxy cluster in the constellation of Volans.

On Monday, the first full-color image from the James Webb Space Telescope (further JWST, read our post here on its naming controversy) was released.

How to turn jws files into spectra