The Hubble Deep Field image, taken in 1995, changed astronomy, and Vox contributor Joss Fong explained the history and impact of the image.
If you hold a pin at arm’s length up in the air, the head of the pin covers approximately the amount of sky that appears in the Hubble Deep Field. The iconic 1995 image is crowded, not because it’s a broad swath of sky but because it’s a broad swath of time. The Hubble Deep Field is more than 12 billion light-years deep.
For reference, here is the image being discussed.
image via R. Williams (STScI), the Hubble Deep Field Team and NASA/ESA