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

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For example, 62P/Tsuchinshan will be approaching the Sun in late 2023, with its closest approach to the Sun on 24 December, and its closest point to the Earth on 30 January 2024. At this time of the year it will be within the constellation of Leo, but with a predicted maximum magnitude of 9 you’ll be unable to see this with the naked eye. The bottom disk also has a star chart printed on it. The better ones have the stars printed in such a way that you can tell which will be the brighter stars, shown as bigger disks, and which are the dimmer stars, smaller disks. Often the bright stars will have their name next to them. The dimmer stars may not be named, but their presence will help you recognize asterisms or patterns in the sky. The Big Dipper, for example, is an asterism, a collection of stars that is easily recognized. The belt of Orion would be another asterism. A planisphere is a circular star map that shows the brightest stars and constellations we can see from Earth. It helps you to name the constellations you can see, depending on where you are and what time of year it is.

Coordinate grid lines are shown without being intrusive. Coordinates are shown because they can be useful for cross-referencing with star atlases. There might be other opportunities to spot comets with a pair of binoculars or a telescope later in the year. 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. Kev Lochun is the Deputy Digital Editor of HistoryExtra. As well as commissioning content from expert historians, he can also be found interviewing them on the award-winning HistoryExtra podcast. He was previously Deputy Editor of BBC History Revealed. 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.

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Still facing north, to your left, high in the sky, you will see the group of bright stars that form the W, or M, which is the constellation of Cassiopeia. To your right, toward the eastern horizon, you will see the bright stars Arcturus and Spica. Other measurements such as the PV and RMS are important too. With these measurements, the lower the number the better as it shows less curvature on the lens. The flatter an optical lens, the better it will perform. The PV rating (Peak To Valley) is a measurement from the highest point (Peak) to the lowest point (Valley). From this we get the RMS (Root, Mean, Square). This is a similar figure to the PV and measured exactly the same way. The RMS is basically an average height difference from the PV so again, the lower the better. As you can see form the example below, we measured an RMS of just 0.027 wave which is a very good value.

Tilt the chart to the right or left when you face East or West, so the word “East” or “West” ishorizontal. Face North and hold the chart upright in front of you, so the word “North” on the blue mask is horizontal. Objects near the horizon line on the planisphere will be low in the sky, near the northern horizon.If you change the direction you’re facing, move the planisphere round so that the corresponding compass point is now at the bottom. The stars and these deep sky objects remain fixed in their location relative to each other for all practical purposes. This enables the planisphere to be used as a roadmap of the sky. 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.