An Indispensable Sky Map
A star finder (also known as a planisphere) is a circular map with an overlay that turns to show – through an opening in the overlay – the region of the sky that is visible for a specified time, date and location. It is an incredibly useful tool for orienting yourself in the night sky, for identifying constellations, and for planning your stargazing night.
Not everybody sees the same stars around the world. What one sees depends on the latitude, so it is essential that you know yours before buying a star finder. For southern Canada, a star finder designed for 45E north is sufficient.
The way a star finder works is simple. The days and months of the year are shown around the edge of a circular base, and the hours of the day are displayed around the overlay. By turning the overlay to line up the time of your observations with the date, the portion o the sky that is visible will appear through the opening in the overlay. All that remains is to hold the star finder over your head and orient it with respect to North.
The activity simulates a real star search. Simply drag the mouse over the first circle on the top and indicate the date and precise hour that you intend to search the sky overhead. A precise representation of the sky at that precise moment may be viewed onscreen.
Use the star searcher to pinpoint stars, constellations and planets precisely.
Then wait for a starry night to use your star searcher to locate the constellations and stars that fill our sky.
The ASTROLab thanks the National Research Council of Canada for permission to use their electronic planisphere and to allow us to develop an interactive version of it.