Wikipedia:Main Page history/2021 September 13b

From today's featured list

World map representing Human Development Index values
World map representing Human Development Index values

The Human Development Index of 189 countries is compiled by the United Nations Development Programme (UNDP) in the annual Human Development Report. The index considers the health, education and income in a given country to provide a measure of human development which is comparable between countries and over time. The Human Development Index (HDI) was first published in 1990 with the goal of being a more comprehensive measure of human development than purely economic measures such as gross domestic product. The index incorporates three dimensions of human development: a long and healthy life, knowledge, and decent living standards. Various indicators are used to quantify how countries perform on each dimension. The indicators are used to create a health index, an education index and an income index each with a value between 0 and 1 which are combined to create the HDI. The data used to calculate HDI comes mostly from United Nations agencies and international institutions. The HDI is the most widely used indicator of human development and changed how people view the concept. (Full list...)

Today's featured picture

Total internal reflection

Total internal reflection is the optical phenomenon in which light waves are completely reflected under certain conditions when they arrive at the boundary between one medium and another. This photograph was taken from near the bottom of the shallow end of a swimming pool. The swimmer has disturbed the water surface above her, scrambling the lower half of her reflection, and distorting the reflection of the ladder. Most of the surface is still calm, giving a clear reflection of the tiled bottom of the pool. The air above the water is not visible except at the top of the frame where the angle of incidence of light waves is less than the critical angle and therefore total internal reflection has not occurred.

Photograph credit: Jean-Marc Kuffer

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