Algrund's Orrery

A clockwork model of the nearby planets, as well as both moons and their orbits, Algrund's Orrery improves one's ability to study the stars. It can also be used to create darkness in an area of ten square miles. The darkness has the appearance of true night; it is as if a black sheet is suddenly drawn across the sky making the sun vanish and the stars come out. This effect lasts for one hour and can be used once per day.

History
Uniquely, Algrund’s Orrery accurately depicts the erratic orbit of Morrslieb, which makes it invaluable to astromancers. The Orrery was created by the Dwarf Algrund Nolagrundson and obtained by the Celestial College in the same way they acquire all of their artefacts—with gold.

The Orrery’s ability to create darkness is of obvious use to Vampires, and the Lahmians currently have an agent tasked with infiltrating the College to obtain it. The astromancers tend to sleep all day, so they can observe the stars all night, making a Vampire in their midst less suspicious than she would seem elsewhere but also hampering her ability to move freely at night.

Source

 * Warhammer Fantasy RPG 2nd ED -- Night's Dark Masters (pg. 122).