NARIT has released the timeline of dates and times for the "Sun at Zenith" phenomenon across 77 provinces of Thailand in 2026, starting with the first occurrence in Betong District, Yala Province, on 4 Apriland then progressing sequentiallynorthward, concluding at Mae Sai District, Chiang Rai Province.
On 27 March 2026, the Facebook pageNARIT, the National Astronomical Research Institute of Thailand,posted a message unveiling the timeline of dates and times for the Sun at Zenith phenomenon in all 77 provinces of Thailand occurring twice in 2026.
It stated that the first zenith event will occur at the southernmost point on 4 April 2026 in Betong District, Yala Province. During this time, if outdoors or observing an object in direct sunlight, it will appear "shadowless" because the shadows of ourselves or objects fall directly beneath. However, this may not be the hottest day of the year, as that depends on various factors.
Every year, the sun moves to positions directly overhead various locations in Thailand twice annually. During these days and times, outdoor objects appear shadowless because their shadows fall directly underneath.
The first occurrence begins at the southernmost point, Betong District, Yala, on 4 April 2026 at approximately 12:19 p.m. Then, the sun moves to be directly overhead different areas of Thailand, progressing northward until ending at Mae Sai District, Chiang Rai, on 22 May 2026 at about 12:17 p.m. The second occurrence starts from the north and moves sequentially southward, ending at the country's southernmost point.
Although the sun being directly overhead means maximum solar energy, the highest temperature of the year depends on many factors such as rainfall, cloud cover, monsoon influence, and heat accumulation. Therefore, the zenith day may not always be the hottest day.
The Earth is spherical and tilted about 23.5 degrees from the perpendicular to its orbital plane around the sun. This tilt causes different sunlight angles at various locations, meaning the sun at zenith does not occur everywhere globally. It happens only within tropical countries, between 23.5 degrees north latitude (Tropic of Cancer) — the northernmost point where the sun can be directly overhead — and 23.5 degrees south latitude (Tropic of Capricorn) — the southernmost such point. The sun’s zenith position changes throughout the year as Earth orbits the sun within this region.
Thailand lies within the tropics, between 5 and 20 degrees north latitude. As a result, the sun passes near or directly overhead twice a year: once between April and May, and again between July and September. The exact dates and times vary by location, depending on the observer’s position on Earth, so the zenith time differs across provinces in Thailand.
For detailed information on the Sun at Zenith phenomenon across all 77 provinces of Thailand, please visithttps://www.narit.or.th/th/Sun-Overhead-TH-2026
Information courtesy of the Facebook page of NARIT, the National Astronomical Research Institute of Thailand.