National Astronomical Research Institute of Thailand (NARIT) Releases timeline of dates and times when the sun is at zenith in 77 provinces of Thailand, occurring twice in 2026.
FacebookNARIT, the National Astronomical Research Institute of Thailand,posted a message about "Timeline of dates and times when the sun is at zenith in 77 provinces of Thailand, twice in 2026." It stated, "The first zenith occurrence starts in the far south on 4 April 2026 at Betong District, Yala Province. During this time, if you are outdoors or observe an object under direct sunlight, it will appear shadowless because the shadow falls directly beneath. However, this may not be the hottest day of the year as it depends on various factors.
Every year, the sun reaches a position directly overhead at various locations across Thailand twice annually. During the date and time when the sun is at zenith in each area, outdoor objects appear shadowless because their shadows fall directly underneath. The first occurrence of the year begins in the far south at Betong District, Yala, on 4 April 2026 at approximately 12:19 PM. Then the sun’s zenith position moves sequentially northward, ending at Mae Sai District, Chiang Rai, on 22 May 2026 at about 12:17 PM. The second occurrence starts from the northern region and moves southward, ending in the far south of the country.
However, although the sun being at zenith means full solar energy is received, the highest temperature depends on many factors such as rainfall, cloud cover, monsoon influences, and accumulated heat, which can affect temperature. Therefore, it may not be the hottest day of the year.
The Earth is spherical and has an axial tilt of about 23.5 degrees relative to the plane of its orbit around the sun. This causes the angle of sunlight incidence to vary by location, so the sun’s zenith position does not occur worldwide but only in tropical countries located between latitudes 23.5 degrees north (the Tropic of Cancer, the northernmost latitude where the sun can be directly overhead) and 23.5 degrees south (the Tropic of Capricorn, the southernmost latitude where the sun can be directly overhead). The zenith position changes throughout the year according to Earth's orbit around the sun within this zone.
Thailand lies within the tropics, between latitudes 5 and 20 degrees north, resulting in the sun passing directly overhead twice per year. The first occurrence is between April and May, and the second between July and September. The exact date and time vary by location due to the observer's position, so each province in Thailand experiences the sun at zenith at different times.
Thanks to the Facebook page of NARIT, the National Astronomical Research Institute of Thailand.