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Scientific Teachers 2018-06-28T11:18:11+00:00

Understanding the Earth’s Seasons

HELP FOR HIGH SCHOOL STUDENTS AND ADULTS

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Seasonal Sunrise / Sunset Markers

Seasonal Markers are an excellent addition to Analemmatic sundials (Human Sundials)

  • To tell the time of sunrise – Stand on the Date Scale on any date you choose with your back to the sun, view over the morning sunrise marker and follow your shadow over to the hour markers to read the time of sunrise.

  • To see the direction of where the sun rises – Stand on the morning sunrise marker and look over the date scale on any date you choose to see the direction of sunrise. (You may wish to put something on the date scale to mark your chosen date).

  • To see the direction of where the sun sets – Stand on the sunset marker and look over the date scale on any date you choose to see the direction of sunset. (You may wish to put something on the date scale to mark your chosen date).

  • To tell the time of sunset stand on the date scale on any date you choose with your back to the sun, view over the sunset marker and follow your shadow over to the hour markers to read the time of sunset.

SUN DATA FORMULAS

  • Lat = Latitude Dec = Declination t =Time Cos = Cosine Tan = Tangent. To calculate Altitude=90 – Lat +/- Dec

  • Azimuth – To Calculate where the Sunrises Cos(Az)=Sin Dec/Cos Lat. Add 180° for where the sunsets.

  • Path – To calculate at what angle does the sun rise Cos Path =Sin Lat/Cos Dec. Use 2nd function or shift key Cos at the end of the calculations to obtain the answer.

AT WHAT SPEED DOES THE EARTH ROTATE ITS AXIS AT DIFFERENT LATITUDES

  • If we divide the distance of 40,075 kms by the time of the days length 23.95 hrs. We get a rotational speed of 1673 kms /hr at the equator.

  • Or if we divide the distance of 24.901 mls/hr by the time of the days length 23.95hrs. We get a rotational speed of 1039.707 mls/hr at the equator.

  • This speed can be calculated for any Latitude. Cos Lat x Speed at equator.eg Lat 45° = Cos Lat x speed at the equator …. 1673 x Cos 45°=1182kms/hr

  • 2nd method. Lat 60° = Cos 60° x 24.901 = 12450.5 divided by 24 = gives an approximate speed of 518.77 mls/hr

  • To find your surface speed in mls/hr at a particular Latitude. eg Lat 25° = COS(25° x 24,901 miles = 22567.970 miles per day/ (divided by) 24 hours, for an approximate surface speed of 940.33 miles per hour.

Associated Software: The following software is available as freeware to assist in the design of analemmatic dials with seasonal markers.

Analemma.xls, an Excel spreadsheet by Roger Bailey and Helmut Sonderegger.

Hor_analem3SM.bas, a Delta Cad BASIC macro by Fer De Vries for analemmatic dials with Lambert Circles, modified by Roger Bailey to draw seasonal marker lines

FOR MORE INFORMATION

CONTACT: George Marshall
P: 07 4124 2894
M: 04 9025 3266
E: info@interactivesundials.com.au

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