{"id":31720,"date":"2022-05-05T13:36:58","date_gmt":"2022-05-05T13:36:58","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=24226"},"modified":"2022-05-05T13:58:13","modified_gmt":"2022-05-05T13:58:13","slug":"how-to-use-a-planisphere","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-to-use-a-planisphere\/","title":{"rendered":"How to use a planisphere"},"content":{"rendered":"

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By Kev Lochun\n \t\t<\/p>

Published: Thursday, 05 May 2022 at 12:00 am<\/p>

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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.<\/p>\n

They don\u2019t look like much, just two discs of cardboard and plastic fastened together with a central pin.<\/p>\n

But this deceptively simple design belies the fact that a planisphere allows you to work out which bright stars are in the night sky and where on any date and at any time throughout the year.<\/p>\n

This basic knowledge is useful for casual stargazers and more serious amateur astronomers alike.<\/p>\n

For more tips, read our guide on how to stargaze<\/a> or sign up to receive the <\/strong><\/em>BBC Sky at Night Magazine<\/strong><\/a> e-newsletter<\/a>.<\/strong><\/em><\/p>\n

View our online gallery showing the history of the planisphere<\/a>.<\/strong><\/em><\/p>\n

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Use a red light torch to help you see your planisphere as this will help preserve your dark-adapted vision. Photo by VW Pics\/Universal Images Group via Getty Images<\/span><\/figcaption><\/div>\n

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A planisphere can help you to learn the constellations or even just identify a bright star you can see at a particular time.<\/p>\n

It can also be a useful aide-m\u00e9moire when planning an observing session.<\/p>\n

Although the two discs are pinned to each other, they can still be rotated independently of each other.<\/p>\n

Printed over most of the lower disc are the stars, constellations and brighter deep-sky objects that you can see from the UK\u2019s latitude.<\/p>\n

Marked around the outside of this lower disc are the days and months.<\/p>\n

What does a planisphere show you?<\/strong><\/h2>\n
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A planisphere is an astronomical tool that can help you navigate the night sky<\/span><\/figcaption><\/div>\n

The upper disc in a planisphere is slightly smaller than the lower one, so you can still see the day and month markings on the larger disc beneath.<\/p>\n

It also has an oval window in it, revealing part of the star chart on the lower disc.<\/p>\n

The edge of this window represents the horizon with appropriate north, south, east and west markings, and everything within it is the visible sky.<\/p>\n

Just like the lower disc, the upper disc has markings around its edge.<\/p>\n

In this case, they denote the time of day.<\/p>\n

By lining up the date and time, the stars visible in the window will match the ones in the night sky at that time.<\/p>\n

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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.<\/span><\/figcaption><\/div>\n

Planispheres are cheap, easy to use, robust (plastic ones more so), lightweight, portable and \u2013 best of all \u2013 they don\u2019t need electricity.<\/p>\n

The one important point to keep in mind when using one is that planispheres are designed to work at specific latitudes.<\/p>\n

If you try using one too far north or south of the location it has been designed for, you\u2019ll find that the stars don\u2019t appear in the right positions.<\/p>\n

UK latitudes vary from 50\u00baN (southern England) to 60\u00baN (northern Scotland).<\/p>\n

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Be sure to check the planisphere\u2019s latitude matches your own.<\/span><\/figcaption><\/div>\n

Why can\u2019t I use a planisphere to find the planets or the Moon?<\/strong><\/h2>\n

Planispheres show objects that are \u2018fixed\u2019 in the night sky relative to Earth \u2013 that\u2019s why they can be used year after year.<\/p>\n

However, this means that they can\u2019t predict the location of planets or the Moon.<\/p>\n

Some manufacturers try to overcome this by printing details of planetary locations for several years on the back, but there is also a line printed on the chart itself that can help.<\/p>\n

The ecliptic<\/a>, often shown as a dotted line, marks the plane of the Solar System, in which most of the planets orbit the Sun.<\/p>\n

If you discover a \u2018star\u2019 in the sky that\u2019s not shown on the planisphere, then it is probably a planet.<\/p>\n

How to use a planisphere<\/strong><\/h2>\n
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