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When you need to find your bearings in the night sky a planisphere is indispensable, even in our digital age.
They don't look like much — usually a planisphere is simply two discs of cardboard or plastic fastened together with a central pin — but as a new stargazer, you'll soon discover that this tool is one of the greatest aids to helping you navigate the night sky. In fact, this deceptively simple design will allow you to work out which bright stars are in the night sky on any date and at any time throughout the year.
Although the two discs are pinned together, they can still be rotated independently of each other. Printed over most of the lower disc are the stars, constellations and brighter deep-sky objects that you can see from a given latitude. Marked around the outside of this lower disc are the days and months.
The upper disc will be slightly smaller than the lower one or will have a clear rim, so you can still see the day and month markings underneath. It also has an oval window in it, revealing part of the star chart on the lower disc. The edge of this window represents the horizon with appropriate north, south, east and west markings and everything within it is the visible sky. Just like the lower disc, the upper disc has markings around its edge. In this case, they indicate the time of day. By lining up the date and time, the stars visible in the window will match the ones in the night sky at that time.
The crucial point to keep in mind when using a planisphere is that they are designed to work at specific latitudes. If you try using one too far north or south of the location it has been intended for, you'll find that the stars don't appear in the right positions.
Follow these simple steps and you'll soon be navigating the night sky like a pro
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