On observations on normal days, when the early morning, the shadow will fall on the west, while the afternoon will fall to the east. At noon, the sun was directly overhead so that the shadow is very short.
"If we look at the day without a shadow of the Sun, about midday when the shadow will fall on the stick so that we do not see his shadow," said Mutoha Arkanuddin of Jogja Astro Club when contacted on Wednesday (29/02/2012).
Although called a day without a shadow of the sun, but the shadow of the sun simply "disappeared" during the middle of the day only. Early morning and late afternoon, the shadow can still be seen by doing a simple experiment the same.
Then, what is the cause of the day without a shadow of the Sun?
The sun had apparent daily and annual motion. In the daily apparent motion, humans on Earth will see the sun as if rising from the east, is directly overhead at noon, and finally sinking in the west.
On the motion of an annual artificial, man who was in latitude zero would see the sun shifts to the north between March 21 to September 23 and shifted to the south between 23 September to 21 March. Exact date of March 21 and 23 September, the Sun is on the equator.
Apparent motion of the Sun as the Sun is making a stopover in the places between 23.5 degrees North latitude to 23.5 degrees south latitude. The sun haven in a place that causes the phenomenon of the day without a shadow of the Sun.
Scientifically, the day without a shadow of the Sun referred to as the Main Transit, ie, when the Sun is at the zenith of a place. So, if the day in Solo occurred the day without a shadow of the Sun, the sun was just stopping point on the citizens of Solo.
Transit Home is not a rare event because it occurs periodically, Mutoha said, in Yogyakarta, for example, day without a shadow of the sun occurred in February.
Unfortunately, the Sun can not be shifted to the west or east. Thus, cities in Indonesia such as Aceh, Jakarta and Jayapura could not enjoy the main transit. City on the equator can see it is Pontianak, each dated March 21.
Eratosthenes Experiment
What are the Main Transit privileges?
"The main Transit 2,200 years ago used by Eratosthenes to measure the circumference of the Earth," says Mutoha.
Eratosthenes compared the phenomena occurring in the city of Shina (Aswan) and Alexandria. He observed that every June 22, a well in the city Shina get a thorough radiation, which means perpendicular to the Sun. Meanwhile, the monument in the city of Alexandria showed a shadow on the same date.
From his observations, Eratosthenes believed that the Earth is round and that Shina and Alexandria is located in the same Meridien. Eratosthenes then find an equation, that the Earth's circumference divided by the distance of two cities located on the same meridian, is equal to 360 degrees divided by the angle between the two cities.
To measure the circumference of the Earth, Eratosthenes calculated the distance Shina - Alexandria is 5000 Stadia (800 km). Measurements are obtained by multiplying the travel time for 50 days with 100-speed train stadia. Stadia is a sports arena used by the Greeks, measuring around 185 meters.
Eratosthenes theorize that sunlight that reaches Earth is running parallel. From this, it is revealed that the angle between Alexandria and Shina is the fifth point of the circumference of Earth, or 7.12 degrees. By his calculations, Eratosthenes get the result that the circumference of the Earth is 250,000 stadia, or 46 300 kilometers.
Eratosthenes calculation is quite accurate, only 15 percent slip from the current calculation. Shina-Alexandria distance of 729 km instead of 800 km. Alexandria and Shina also not located on the same meridian, but different 3 degrees. However, the study results are very reasonable Eratosthenes appreciated.
"Usually, the day without a shadow of the sun becomes an opportunity for us to repeat the same experiment with Eratosthenes. Kala 2,200 years ago he could, we can not cook," said Mutoha. The phenomenon of the Sun Day Without Shadow.
