Sunlight shapes our body clocks, skin and sleep far more than most of us realise

8:19

supplementary video · Quanta Magazine on YouTube ↗

Sunlight shapes our body clocks, skin and sleep far more than most of us realise

the gist

Sunlight sets the timing of our internal body clocks and drives the skin's chemistry, including the synthesis of vitamin D, which helps build bone and teeth and supports immune cells that kill bacteria. Light-sensitive cells at the back of the eye feed signals to a brain region called the suprachiasmatic nucleus, which keeps organs in step with the day and lets them anticipate meals, activity and sleep. Bright daytime light also boosts alertness directly and tends to improve sleep the following night, while artificial light at night pushes people's schedules later and leaves them more tired.

how it works

Specialised cells in the retina detect light and send signals along a direct pathway to the suprachiasmatic nucleus, a cluster of neurons in the hypothalamus that acts as the body's master clock. The clock then coordinates timing signals across organs. Skin uses ultraviolet light to make vitamin D, which the body needs for healthy bone and immune function.

so what

Modern indoor life and electric lighting have weakened the light-dark rhythm humans evolved with, and chronic sleep loss is linked to accidents, heart disease, diabetes and Alzheimer's. Researchers are now studying how the time of day affects how the body responds to food and drugs, so the old idea of matching treatment to the body's daily rhythm is becoming practical.

fun fact

Florence Nightingale, the nursing pioneer, argued in the 19th century that patients needed sunlight as well as fresh air.

Wellcome Collection · CC BY 4.0

source: Wellcome Collection ↗

historyWikipediaclassic1336–1565 · Karnataka, India

Hampi was once one of the world's largest cities, until its Vijayanagara capital was destroyed in 1565

the gist

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.

how it works

The city was built around a fortified core with temples, markets and water structures along the river, supplied by an extensive network of roads and waterworks. When the empire fell, the city was not rebuilt, so its stone monuments were left standing.

so what

Hampi shows how quickly a great city can vanish after a military defeat, and how a ruined capital can remain sacred. Its ruins give historians a view of medieval South Asia that few other sites can match.

fun fact

The name Hampi comes from Pampa, an old name for the Tungabhadra River.

From Wikipedia, the free encyclopedia · text CC BY-SA 4.0

Image: Wikimedia Commons

source: Wikipedia ↗

2 min

politicsshortCNA2:01

False allegations about Singapore’s hand in Indonesia’s markets and a made-up meeting

from CNA

CNA Verify has found close to 400 posts pushing falsehoods tying Singapore to Indonesia’s stock market rout and to a secret meeting that never took place. Together, they drew nearly 12 million views, and some were circulated by accounts that appeared to be working in concert, across multiple social media platforms.

Here’s how the disinformation campaign targeting Singapore was uncovered.

on YouTube: CNA ↗