When you order we request the time, date, and location that you would like to use for your sky map. Then, using the European Space Agency's Hipparcos star catalog, we accurately calculate the positions of the stars for any date and location in the past or future. We also request the title and color of sky chart you would like. Once we create your design we send you preview, allowing you make any changes and further customizations your would like. After you proof your design we do something no one else does: we laser etch it into GLASS and ship it for free to your home.