The Airy hypothesis, named after Sir George Biddell Airy, is a theory in astronomy that suggests that the density of the Earth's atmosphere is responsible for the refraction of starlight. The word "Airy" is pronounced /ˈɛəri/ in IPA phonetic transcription, with the first syllable sounding like the word "air" and the second syllable pronounced like the letter "e". The spelling of the word reflects the English language's tendency to preserve the spelling of proper names, even if it doesn't match the pronunciation.
The "Airy hypothesis" refers to a theoretical assumption made in the field of geodesy and physical geodesy, named after the British astronomer and mathematician, Sir George Biddell Airy (1801-1892). It postulates that the density of the earth's material, primarily in terms of rock or terrain, gradually decreases from the crust towards the core, thus creating a gradual decrease in gravitational force with increasing depth.
The Airy hypothesis assumes that the earth can be modeled as a series of concentric shells with continuously decreasing density. These shells are believed to be spherically symmetric and have constant density in each shell. According to the hypothesis, the outermost shell corresponds to the earth's crust, which has the lowest density, while the innermost shell depicts the core with the highest density.
The Airy hypothesis, although acknowledged as a simplification, provides a useful framework for understanding the general behavior of the earth's interior. It has played a significant role in various geodetic and geophysical studies, helping to explain phenomena like gravitational anomalies and the deflection of plumb lines. However, advancements in seismic techniques and other scientific observations have challenged the accuracy of the Airy hypothesis, indicating that the earth's internal structure is more complex and non-uniform than originally proposed. Despite these limitations, the Airy hypothesis remains a valuable theoretical construct that has facilitated numerous investigations in the field of geodesy.
The term "Airy hypothesis" is named after Sir George Biddell Airy, an English mathematician and astronomer who lived from 1801 to 1892. He proposed the hypothesis in 1852 regarding the deflection of a plumb line due to the gravitational attraction of mountains or other landmasses. The term "Airy hypothesis" was coined to refer to his proposition and became widely used in the field of geodesy, the study of Earth's shape and gravitational field.