Zero Shadow Day in TanzaniaIn the pictures, see the symmetrical shadow of the light bulb at solar noon at 12:10 pm in Dar on October 9 2014, which is a couple of days before the actual zero shadow day. Besides the symmetrical shadow of the light bulb, observe the almost circular lighted circle around the circular shadow of a long vertical pipe. Tomorrow and the day after, expect to see a perfect circle of light around a circle made by the pipe's at solar noon at 12:10pm in Dar es Salaam. The challenge is to make sure your objects are vertical. To find solar noon search Google for sunrise and sunset times for your town/city and find the extact middle of the period between sunrise and sunset. Be surprised tomorrow to lose your shadow at your local noon (found as above) unless you bend your head forward. For those of us with a bit of a stomach, you may find it even harder unless you squeeze it in, which you will be easier to do before lunch!!! Set up something very narrow and exactly vertical and you will see the shadow literally disappear at your local noontime. For any position on Earth is within the tropical latitudes of 23 and a half degrees north and south of the equator, the Sun is exactly overhead twice a year at your latitude. For us in Tanzania who are between 2 and 11 degrees South of the Equator, the Sun is overhead between February 23 and March 18 before the March equinox and between September 26 and October 22 after the September equinox. It is interesting to look out for the exactly overhead sun during this period because shadows of all vertical objects disappear below the object and you cannot see them. If you stand in the midday Sun on these two days you will not be able to see your own shadow. Go out and find out which day during the September 26 and October 22 period and find out on which day your shadow disappears at midday. Learn more about the zero shadow day from:
Carl Sagan - 13 part TV Series: Cosmos - Eratosthenes https://www.youtube.com/watch?v=G8cbIWMv0rI "The Measure of Eratosthenes" http://www.arvindguptatoys.com/arvindgupta/measure-carlsagan.pdf Calculation of length of shadow on any day at your location Calculation of zero shadow day for your latitude position http://www.iiap.res.in/iya09/VPwkshop/talks/RugvedPund.pdf Sun's Declination (i.e. Latitude) - Check when it matches your latitude to know the day the Zero Shadow day at your location. http://astropixels.com/ephemeris/sun/sun2013.html Construction set up to observe your Zero Shadow Moment http://www.iucaa.ernet.in/~arp/obsetion/zsm/ZeroShadowMoment.htm |