Dark energy spectroscopic instrument creates largest 3D map of the cosmos

What causes the dark radial stripes? Blocked by something in the sky? Downtime?

I know Elite Dangerous has similar artifacts showing small radial areas of the galaxy that our telescopes have surveyed (but it's lines of stars rather than lines of darkness)

For deep background, Michael S. Turner just published a nice review of the past 50 years of cosmology, from when the "errors were in the exponents" ;)

The Road to Precision Cosmology

https://arxiv.org/abs/2201.04741

DESI is just one of the super-mapping scopes to come online in late 2010s-early 2020s. There GAIA about 3/4 through its program to map the positions and movement of 2 billion stars (2%) in the Milky Way. And the Roman telescope will rephotograph much of sky at least once a week, looking objects that change brightness or position- about 10,000,000 expected a night. These could be new asteroids, Planet X, super novea, etc.