There are many astronomical data sources available on the Internet. This list is not comprehensive but we'd like it to be! Email us if you have additions.
Visual, CCD and PEP data of over 44,000 variable stars.
The All Sky Automated Survey (ASAS)
Photometric database of approx. 10^7 stars brighter than 14 magnitude all over the sky.
The Anglo-Australian Telescope
Searchable image archive.
The Hubble Legacy Archive (HLA)
Online, enhanced Hubble products and advanced browsing capabilities
Northern Sky Variability Survey (NSVS)
An extensive variability survey of the sky north of DEC=-38 with daily time sampling and one year of baseline.