สำนักงานราชบัณฑิตยสภา

การประดิษฐ์นาฬิกาแดดแบบศูนย์สูตรที่ บอกเวลาได้ถูกต้องตรงกั บเวลามาตรฐานของประเทศไทยโดยมี ความคลาดเคลื่ อนไม่เกิ น ๓ นาที ที่ ระดั บความเชื่ อมั่ นร้อยละ ๙o 224 The Journal of the Royal Institute of Thailand Vol. 38 No. 3 July-Sep 2013 Abstract The invention of the equatorial sundial which can show the time precisely in accordance with the Thailand standard time with less than 3 minutes error and 90% confidence Weerawat Nonghang Department of Physics, Faculty of Science, Srinakharinwirot University; Chitralada School; Science Education Center, Srinakharinwirot University Jaturong Sukonthachat Chitralada School; Srinakharinwirot Physics Education Research Laboratory,Thailand Center Excellent in Physics Nason Phonpoke. Department of Physics, Faculty of Science, Srinakharinwirot University; Science Education Center, Srinakharinwirot University; Srinakharinwirot Physics Education Research Laboratoy, Thailand center of Excellence in Physics. Generally, in order to get the precise time in accordance with the Thailand standard time, we have to add or deduct the time shown from the equatorial sundial with the compensated time resulted from the equation of time in each day. In this research, the equatorial sundial has been developed and invented for the use of Chitralada School in Bangkok in order to facilitate the use of the sundial. As a result, we are able to read the time immediately from the sundial without adding or deducting the time with the said equation of time. The newly invented sundial is composed of 2 parts: the sundial itself and the device for measuring its shadow due to the sun in each day. To use this sundial, both parts should be used harmoniously. That is to say, the shadow measur - ing device will indicate the symbol to adjust the face of the sundial for suitable time in relation with the standard time. Therefore, when we adjust the face of the sundial to meet with the symbol, the shadow shown on the face will show the precise time in accordance with the Thailand standard time without having to do any compensation. The result from the experiments shows that the sundial invented can show the time precisely in accordance with the Thailand standard time with less than 3 minutes error at the 90% level of confidence. Keywords: sundial, equation of time, declination