Planisphere: Latitude 50°N – for use in the UK and Ireland, Northern Europe, Northern USA and Canada

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For budding stargazers, a planisphere is one of the greatest aids to helping you find your way around the night sky. Like most people, you probably enjoy getting out under a clear night sky to gaze up at the beautiful tapestry of stars and planets overhead. But what if you can't tell Polaris from Pollux, or Saturn from Sagittarius? No problem! Using this simple, easy-to-make Star Wheel, you'll be navigating the night sky with confidence in no time.

Also shown on the typical planisphere will be symbols for double stars and the brighter deep sky objects, DSOs, such as star clusters, nebulae, galaxies, globular clusters and other of deep sky objects. There should be a key printed on the planisphere to show you what each symbol represents. If you are in a fairly light polluted location, you may not be able to see all of the stars, naked eye, that is shown on the planisphere. If your sky is darker you may be able to see more stars that are shown on the planisphere. Naturally, as you move from location to location this will vary. We also measure the Power with our systems which is essentially the error from the reference sphere to the test optic. The reference sphere we use on our system is a very high quality sphere so the closer to zero the Power, the less error between the 2 elements thus ensuring a higher quality optical surface.As with any observation close to the Sun, make certain you don’t look directly at the Sun and, if observing with a telescope or pair of binoculars, wait until after sunset or before sunrise to avoid accidentally pointing them at it. You will also see some more values such as Astigmatism and Coma. Again, these are measured by the interferometer when we take measurements of the optical surface after adjustment. These are values which ideally would be at 0 but as our test optics are all curved lenses, there will always be astigmatism and coma present. The lower the number, the less of these aberations you will effectively see but with most refractors, you can buy field flatteners which will compensate for the coma anyway. The astigmatisms value is explaining the error between the symmetrical curvature of the lens. Basically, no lens will be perfectly symmetrical, the lower the astigmatism, the more symmetrical the lens surface is. Face South and, without moving the map dial, flip the chart over and hold the chart upright, so the word “South” on the blue mask is horizontal. Objects near the horizon line on the planisphere will be low in the sky, near the southern horizon.

Venus will reach its greatest eastern elongation around 4 June and its greatest western elongation around 23 October. In and around these times, Venus will be easily visible as an evening and morning “star” respectively. If you change the direction you’re facing, move the planisphere round so that the corresponding compass point is now at the bottom. A planisphere can help you to learn the constellations or even just identify a bright star you can see at a particular time. If you face north and hold the rivet so that it aligns with Polaris you will have a representation of the entire sky before you. In fact, if the rivet is hollow, as many are, you hold the Planisphere out at arm’s length and sight Polaris through the rivet. Behind you and slightly to your left, as you face north, you will see the constellation of Orion, one of the most easily recognized constellations. See where it is on the planisphere.Usually, there is a center rivet that joins the two disks. At that rivet, there is a marking for the North Star, Polaris. This is the only star that is fixed in the sky as it is aligned with Earth’s axis of rotation. Everything else in the sky appears to move, but Polaris remains fixed. The bottom disk will have the months and dates printed around the edge. These will be used to set the planisphere to show us the sky as it will appear tonight. For more tips, read our guides on how to stargaze and astronomy for beginners or sign up to receive the BBC Sky at Night Magazine e-newsletter.

Many will also have the brighter Messier objects identified on the star chart. For example, the Andromeda Galaxy is also known as Messier 31 or M31. The Messier list of 110 deep sky objects is one of the most popular among armature astronomers and often the first observing list those who are new to the hobby will try to observe. Chandler's planisphere (rotating star-finder wheel) is the finest available" Sky News. Key features: Just remember that the planets are not always in the evening sky. Sometimes the planets are in the morning sky. As the Earth and planets travel around the Sun, a planet may be on the other side of the Sun and so, not visible to us. How It Works – The Top DiskBy lining up the date and time, the stars visible in the window will match the ones in the night sky at that time. Line up the correct date and time and your planisphere will reveal an accurate depiction of the stars in the night sky at that moment. The Planisphere should have an indication of how to hold it up to the sky. Likely there will be markings to indicate which part of the disk should be up when facing north. When the Earth orbits the Sun, at certain times of year the Northern Hemisphere is tilted towards the Sun and the Southern Hemisphere is tilted away from it. For the other half of the year, the reverse happens. Give everyone a set of templates. They should cut out the horizon templates for both hemispheres. They’ll need to cut out the shaded areas in the middle of each template to make the spy window.