The problem is with the exposure. 1min exposures are common in astrophotography, but astronomers are complaining about the types that need night-long exposure -

The problem is with the exposure. 1min exposures are common in astrophotography, but astronomers are complaining about the types that need night-long exposure - ones that try to study cosmology, stellar composition etc. Many observations (like SDSS) are also large field observations that observe many objects simultaneously. Even a single streak can ruin an entire exposure. The odds just grow considerably.