We’re bringing you surprising trivia and fun facts about sunlight in a quiz format.
From how long it takes sunlight to reach Earth, to the best season for solar power generation, to unexpected origins in history—discoveries that will make you say “Wow!” the more you learn! Sunlight, essential to our lives and now more familiar than ever thanks to solar power, actually hides some amazing secrets.
With three multiple-choice options, it’s perfect for a fun family quiz time for kids and adults alike.
Ready to dive into the mysteries of the sun together?
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Solar trivia quiz! Take on some surprisingly little-known facts (1–10)
What do you call the aging phenomenon caused by the accumulation of damage to the body from continuous exposure to the sun’s ultraviolet rays?
- natural aging
- photoaging
- oxidative stress
See the answer
photoaging
The aging phenomena that appear due to the accumulation of skin damage from ultraviolet rays in sunlight are called photoaging. Unlike natural aging, photoaging progresses mainly due to external factors such as UV rays. Because it causes spots, wrinkles, and sagging of the skin, UV protection is important.
When is the season in which solar power generation is most efficient?
- Spring (March–May)
- Summer (June–August)
- Autumn (September–November)
See the answer
Spring (March–May)
Solar power has the characteristic that panel conversion efficiency decreases when temperatures are too high, so spring (March to May), when temperatures are moderate and solar irradiation increases, enables the most efficient power generation. In summer, although solar irradiation is high, efficiency declines due to the high temperatures.
Which of the following prefectures is the most suitable for solar power generation?
- Okinawa Prefecture
- Yamanashi Prefecture
- Wakayama Prefecture
See the answer
Yamanashi Prefecture
Yamanashi Prefecture is known as one of the sunniest prefectures in Japan. According to data from the Japan Meteorological Agency, Kofu City in Yamanashi often records the longest annual sunshine duration in the country, making it well-suited for installing solar power facilities. Okinawa Prefecture, while a southern region with strong sunlight, can have fewer sunshine hours than Yamanashi due to frequent typhoons and rain.
What is Japan’s global ranking in terms of installed solar power capacity?
- 1st place
- 2nd place
- 3rd place
See the answer
3rd place
Japan boasts the world’s third-largest installed capacity of solar power. China ranks first, and the United States second. In Japan, the shift toward renewable energy has advanced since the Great East Japan Earthquake, with a particularly rapid increase in the adoption of solar power.
What was the first practical application of solar cells?
- Home appliances
- space satellite
- automobile
See the answer
space satellite
The first practical use of solar cells was on the American artificial satellite Vanguard 1, launched in 1958. It reportedly used solar cells as its main power source and operated in space for 20 days. Because solar cells were first used not on Earth but in outer space, research and practical applications subsequently advanced widely.
What do we call the amount of time that sunlight illuminates the ground, as measured by sunshine recorders at meteorological stations?
- Hours of sunshine
- Hours of clear skies
- sunshine duration
See the answer
sunshine duration
Sunshine duration refers to the length of time during which the sun’s rays directly illuminate the Earth’s surface, measured at meteorological stations and observatories using a sunshine recorder. It is considered important data in fields such as agriculture, daily life, and energy. You can check sunshine duration data for locations across Japan on the Japan Meteorological Agency’s website.
Serotonin is a neurotransmitter in the brain that is secreted when exposed to sunlight. What is its other name?
- Relaxation hormone
- happiness hormone
- stress hormone
See the answer
happiness hormone
Serotonin stabilizes mood and mental state in the brain and brings about feelings of happiness, which is why it is also called the “happy hormone.” Exposure to sunlight increases the secretion of serotonin, making it easier to feel cheerful.



