{"id":33740,"date":"2022-07-20T00:00:00","date_gmt":"2022-07-20T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=33740"},"modified":"2022-07-21T14:12:48","modified_gmt":"2022-07-21T14:12:48","slug":"diy-astronomy-6","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/07\/20\/diy-astronomy-6\/","title":{"rendered":"DIY Astronomy"},"content":{"rendered":"\n

Practical astronomy projects for every level of expertise <\/p>\n\n

DIY ASTRONOMY<\/span><\/h2>\n\n
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Make a paper equatorial sundial <\/h4>\n\n

Tell the time the astronomer\u2019s way with a piece of card and a drinking straw <\/p>\n\n

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The paper equatorial sundial in action <\/figcaption><\/figure>\n\n

Our ancient ancestors had to use the Sun as a clock, something it\u2019s easy to forget while surrounded by modern devices. A fixed object on a sunny day will cast a shadow and as the Sun moves across the sky that shadow will change position. This basic principle underpins most sundial designs and here we show you how to make a paper equatorial sundial. <\/p>\n\n

The time told by the Sun is specific to your location and may differ from the clocks you have in your home. Local noon sees the Sun at its highest point in the sky. If you are on the Greenwich Meridian line, your local noon will agree with your clocks, but for every degree you are east of that line, local time will be four minutes ahead, while it\u2019ll be four minutes behind for every degree west. <\/p>\n\n

Time, gentlemen, please <\/strong><\/h4>\n\n

In our modern interconnected world, time zones have had to be standardised, otherwise bus and train timetables alone would be chaos! The design of sundial we are making here is known as an equatorial sundial, as it utilises the knowledge that the Sun moves at a rate of 15\u00b0 per hour, therefore any shadows being cast will also move by 15\u00b0 each hour. <\/p>\n\n

We can use this information to create a clock face and with it tell the local time using the shadow cast by the sundial\u2019s gnomon (central column or pin).<\/span><\/p>\n\n

It is very simple to make from just two pieces of card and a drinking straw, and is an excellent project for families as children can learn about shadows and local time. You can use this sundial to find out the time of local noon at your location. <\/p>\n\n

Technically, our sundial will work for any latitude. But because the latitude scale on the base is not linear, it would need a much longer piece of card and a much longer gnomon to cover the region between 24\u00b0 north and south of the equator; so our design covers latitudes outside of those regions.<\/span><\/p>\n\n

Our clock face is labelled from 06:00 to 18:00, but you can extend that if you wish. The length of the gnomon and the angle of the clock face can be adjusted for your location using the table online. <\/p>\n\n

Our clock face is for the northern hemisphere, but to adapt it for the southern hemisphere simply label your clock face in the opposite direction. When selecting your card, chose something that is sturdy enough to hold its shape but still easy to fold.<\/span> Because this sundial will work for different locations, you can take it away on holiday with you and see how the result differs from at home.<\/p>\n\n

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What you\u2019ll need <\/strong><\/h4>\n\n\n\n

Two sheets of white A4 card, sheet A trimmed to 23cm x 18cm and sheet B trimmed to 27cm x 18cm. <\/p>\n\n\n\n

A pair of compasses that will allow you to draw a circle with a radius of 8cm (diameter of 16cm). <\/p>\n\n\n\n

A protractor so you can accurately measure your sundial clock face\u2019s divisions. <\/p>\n\n\n\n

A drinking straw to use as a gnomon. We used a straight straw measuring 19cm in length. <\/p>\n\n\n\n

A compass \u2013 you can use a traditional compass or a mobile phone to align your gnomon to north (or south if you\u2019re in the southern hemisphere). <\/p>\n<\/div><\/section>\n\n

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Print a table of the gnomon length and clock face angle for different latitudes \u2013 visit <\/strong>www.skyatnightmagazine.com\/bonus-content\/RNFNUS4\/ <\/a><\/p>\n<\/div><\/section>\n\n

<\/p>\n\n

<\/p>\n\n

<\/p>\n\n

Step by step <\/strong><\/h4>\n\n

Step 1 <\/strong><\/p>\n\n

Start with card sheet A, long edge up. Draw a line across it 5cm from the bottom; this will be our fold line later. Draw a 16cm diameter circle in the centre of the page above the fold line, then draw a horizontal line across the middle of the circle. <\/p>\n\n

\"\"<\/figure><\/div>\n\n

Step 2 <\/strong><\/p>\n\n

Using a protractor, add a mark every 7.5\u00b0 around the bottom half of the circle\u2019s circumference, then draw lines from them to the centre. Starting at the middle line on the right side, label every other line from 06:00 to 18:00, to give the clock face its hour marks. <\/p>\n\n

\"\"<\/figure><\/div>\n\n

Step 3 <\/strong><\/p>\n\n

On sheet B, draw a fold line 3cm from the bottom, and then a 23cm long vertical line up the middle. Mark this \u2018latitude line\u2019 using the measurements in column two of our table online. Fold the bottom 3cm up, then stick sheet A onto this flap to add the clock face. <\/p>\n\n

\"\"<\/figure><\/div>\n\n

Step 4 <\/strong><\/p>\n\n

Measure from the bottom of the gnomon and mark the length that corresponds to your latitude from column three of our table. Make a small hole at the centre of the circle so the gnomon fits snugly, then push the gnomon through as far as your latitude mark.<\/span><\/p>\n\n

\"\"<\/figure><\/div>\n\n

Step 5 <\/strong><\/p>\n\n

Place the end of the gnomon at the correct position on the latitude line for your location; together with the length shown in column three of the table, this will ensure the gnomon and clock face are at the correct angle. Secure it with a small piece of tape or hot glue. <\/p>\n\n

\"\"<\/figure><\/div>\n\n

Step 6 <\/strong><\/p>\n\n

Using a compass, align the sundial accurately with the gnomon pointing north \u2013 or south if you\u2019re in the southern hemisphere \u2013 on a sunny day. Then look where the shadow falls across the clock face and read off the local time for your location. <\/p>\n\n

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<\/p>\n\n

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<\/figcaption><\/figure><\/div>\n\n

Mary McIntyre is an outreach astronomer and teacher of astrophotography<\/p>\n\n

<\/p>\n\n

<\/p>\n\n

<\/p>\n\n

Photos: MARY MCINTYRE<\/p>\n","protected":false},"excerpt":{"rendered":"

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