In astronomy, time and distance are closely related. When you look at an object that is (say) 50 light-years away, you of course recognize that you are seeing the light that actually left that object 50 years ago. But there's also historical time - what did that object look like 100 years ago in Earth time? Wouldn't it be great if astronomers could could look back in time that way too?
They can do this if someone 100 years ago took a photograph of that area of the sky, if the photographic plate still exists, and if they can get access to it. The Harvard College Observatory (shown above circa 1900) has collected more than 500,000 astronomical images from around the world, taken from the early 1880's to the late 1980's. This is an amazing "database" but because it is in analog form (large glass plates), it has not been very accessible.
The obvious solution is to scan all those plates into digital form, but to do so requires a scanning method that is fast and accurate. Now there is an instrument and a project to do just that, a project called DASCH (Digital Access to a Sky Century from Harvard), and it's pretty impressive from both an optical engineering and astronomy point of view. There are also some major mechanical, data transfer, and data storage challenges.
This SPIE news article is a good overview of the project, including some photos of the scanner. This 2005 presentation (850 KB PDF) and this 2006 technical paper (659 KB PDF) describe the background and the engineering details. The development, construction, and trial use have been funded by NSF grants, but they are still seeking support to fund the scanning of the complete collection, which is estimated will take five years. I hope they can get the required funding!