{"id":35911,"date":"2022-08-24T07:07:19","date_gmt":"2022-08-24T07:07:19","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=28805"},"modified":"2022-08-24T07:34:11","modified_gmt":"2022-08-24T07:34:11","slug":"how-to-make-a-sundial","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-to-make-a-sundial\/","title":{"rendered":"How to make a sundial"},"content":{"rendered":"

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By Ade Ashford\n \t\t<\/p>

Published: Wednesday, 24 August 2022 at 12:00 am<\/p>

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In this science and astronomy project we\u2019ve provided plans that you can download and print off at home to help you make your own sundial. It\u2019s a great project for kids, for teaching them about the movement of the Sun across the sky, but also a little bit of science history too.<\/p>\n

You\u2019ll need a good-quality inkjet or laser printer to reproduce the sundial plan from, and we\u2019ve provided a downloadable\u00a0sundial plan (PDF)<\/a> that you can print onto A4 paper.<\/p>\n

You\u2019ll also need a rigid piece of A4-sized card to mount the printed plan. A cereal packet will do, but make it double thickness.<\/p>\n

Use an aerosol-based contact adhesive \u2013 the stuff used by professionals to mount photos \u2013 or a glue stick when you\u2019re sticking the paper plan onto the backing card. Liquid PVA glue (or similar) is hard to apply evenly and may stretch or wrinkle the paper.<\/p>\n

And a craft knife and rule is best. There are some intricate cuts and folds needed to complete the sundial model, so use a sharp blade rather than a pair of scissors, and a ruler as a guide.<\/p>\n

The gnomon, the bit of the sundial that casts a shadow, is formed by a piece of black thread pulled taught between two points on the model. String will suffice, but make sure it doesn\u2019t stretch under tension.<\/p>\n

Finally, you will need clear tape to secure the thread to the sundial.<\/p>\n

For an even simpler sundial project, read our guide on how to make a paper sundial<\/a>.<\/p>\n

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Most kids will have seen a sundial before, but have you ever tried to make your own? Credit: Donald Iain Smith \/ Getty Images<\/span><\/figcaption><\/div>\n

History of the sundial<\/strong><\/h2>\n

Before reliable mechanical clocks were invented at the end of the 17th century, the most accurate means of recording the passing of time was to trace an object\u2019s shadow, cast by the rays of the Sun, on a graduated dial.\u00a0The first evidence of a sundial is Egyptian, and dates from the 15th century BC.<\/p>\n

In the second century AD, Ptolemy\u2019s Analemma described\u00a0in detail how the circles of the celestial sphere could be projected onto a flat plane using trigonometrical principles.<\/p>\n

For the sundial maker this treatise was invaluable, since the motion of an object\u2019s shadow \u2013 the technical term for the part of the sundial that casts a shadow is a \u2018gnomon\u2019 \u2013 could now be described with mathematical precision for any orientation of dial wherever it was on Earth.<\/p>\n

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Greek astronomer Ptolemy at work with a sphere. Photo by Hulton Archive\/Getty Images<\/span><\/figcaption><\/div>\n

With the invention of magnetic compasses at the end of the 14th century, portable directional sundials finally became a reality.<\/p>\n

When most people think of a sundial, they picture a garden, or horizontal, dial mounted on a pedestal.\u00a0On a correctly positioned example, the gnomon will point due north, and its angle to the horizontal will equal the latitude of its location.<\/p>\n

If you own an equatorially mounted telescope, you may recognise this setup as the definition of the polar axis \u2013 parallel to the rotational axis of the Earth.\u00a0A variation of this form, the vertical dial, is often found on the south-facing side of churches and buildings.<\/p>\n

Different types of sundial<\/strong><\/h2>\n

There are several other forms a sundial can take.\u00a0On equatorial dials, the hour scale is a disc that lies at right angles to the gnomon, on the plane of Earth\u2019s equator.\u00a0This makes it difficult to read around the time of the equinoxes, so an improved version is the armillary sphere.<\/p>\n

With this form, the hours are inscribed on a ring with the same centre point as the gnomon. Then there are polar dials, on which the hour scale lies parallel to the gnomon.<\/p>\n

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An armillary sundial in London, UK. Credit: Hoberman Collection \/ Getty Images<\/span><\/figcaption><\/div>\n

The form of sundial that we\u2019re going to make is called the diptych.\u00a0This is a development of the horizontal and vertical sundial that became popular as a portable instrument in the\u00a016th century.<\/p>\n

Our version has been specially designed for the centre of the UK (latitude 54\u00b0 N, longitude 2.5\u00b0 W).<\/p>\n

It has two dials angled at 90\u00b0; a taught thread between their centres forms the gnomon. You\u2019ll be able to tell Greenwich Mean Time with the vertical dial and British Summer Time on the horizontal dial.<\/p>\n

And what\u2019s more, the shadow from a knot or bead at point C on the gnomon thread will mark the solstices and equinoxes.<\/p>\n

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A diptych sundial made by Hans Ducher in Germany, 1574. Credit: Science & Society Picture Library \/ Getty Images<\/span><\/figcaption><\/div>\n

This sundial will always display local, or apparent, solar time: whenever the Sun is exactly due south, the apparent time is precisely midday.\u00a0But unless you live precisely on the Greenwich Meridian, a correction has to be applied due to longitude.<\/p>\n

This is because sundials show local midday four minutes early for every degree of longitude east of Greenwich, and four minutes late for each degree west of it.<\/p>\n

At Lowestoft, the most easterly point of the UK, a sundial shows midday seven minutes before London, whereas at Penzance (longitude 5.5\u00b0 W) a sundial displays noon 22 minutes after Greenwich (see diagram below).<\/p>\n

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The equation of time<\/strong><\/h2>\n

Longitude aside, if you carefully log the apparent time of a sundial against the mean solar time shown on an accurate clock (ignoring British Summer Time) you will notice that the two still don\u2019t match over the course of a year.<\/p>\n

There will be periods when the sundial is fast according to your watch, reaching a maximum of 16.4 minutes at the beginning of November.\u00a0There will also be times when the sundial is slow,\u00a0by as much as 14.2 minutes in February.<\/p>\n

This is known as the \u2018equation of time\u2019, and it is something Ptolemy devoted a whole chapter to in the Almagest.\u00a0It can be expressed as follows:<\/p>\n

Equation of time =\napparent solar time \u2013 mean solar time<\/em><\/strong><\/p>\n

The reason for the discrepancy is down to the eccentricity of the Earth\u2019s orbit, which causes the apparent movement of the Sun along the yearly course of the ecliptic to speed up and slow down, as well as the inclination of the Earth\u2019s orbit to its equator.<\/p>\n

But there are four times a year when\u00a0a sundial on the GreenwichMeridian and clocks would agree: 15 April, 13 June, 1 September and 25 December.<\/p>\n

Contemporary designs which correct for the equation of time, as well as longitude, display clock time very accurately, reconnecting human activity with the ancient cycles of the Sun and stars.<\/p>\n

Follow our step-by-step guide below and create your own sundial.<\/p>\n

Make a sundial: step-by-step<\/strong><\/h2><\/body><\/html>\n
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By Ade Ashford Published: Wednesday, 24 August 2022 at 12:00 am In this science and astronomy project we\u2019ve provided plans that you can download and print off at home to help you make your own sundial. It\u2019s a great project for kids, for teaching them about the movement of the Sun across the sky, but […]<\/p>\n","protected":false},"author":24,"featured_media":35912,"template":"","categories":[1],"acf":{"readingTimeMinutes":"6"},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/77\/2022\/08\/how-to-make-a-sundial.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"By Ade Ashford Published: Wednesday, 24 August 2022 at 12:00 am In this science and astronomy project we\u2019ve provided plans that you can download and print off at home to help you make your own sundial. It\u2019s a great project for kids, for teaching them about the movement of the Sun across the sky, but…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed\/35911"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/rss_feed"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/types\/rss_feed"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/users\/24"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media\/35912"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/media?parent=35911"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/wp-json\/wp\/v2\/categories?post=35911"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}