Newtons theroy

The newtons theroy of it should be trueDuring the first half of the 19th century, scientists such as John Herschel, Fox Talbot, and William Swan studied the spectra of different chemical elements in flames. Gradually, the idea that each element produces a set of characteristic emission lines was established. Each element has several prominent, and many lesser, emission lines in a characteristic pattern. Sodium, for example, has two prominent yellow lines (the so-called D lines) at 589.0 and 589.6 nm -- any sample that contains sodium (such as table salt) can be easily recognized using this pair of lines. One of the most dramatic triumphs of astrophysical spectroscopy during the 19th century was the discovery of helium. An emission line at 587.6 nm was first observed in the solar corona during the eclipse of August 18, 1868, although the precise wavelength was difficult to establish at the time (due to the short observation using temporary set-ups of instruments transported to Asia). Two months later, Norman Lockyer used a clever technique and managed to observe solar prominences without waiting for an eclipse. He noted the precise wavelength (587.6 nm) of this line, and saw that no known terrestrial elements had a line at this wavelength. He concluded that this must be a newly discovered element and called it 'helium'. Helium was discovered on Earth eventually (1895) and showed the same 587.6 nm line. Today, we know that helium is the second most abundant element in the Universe.

We also know today that the most abundant element is hydrogen. However, this fact was not obvious at first. Many years of both observational and theoretical works culminated in 1925, when Cecilia Payne published her PhD thesis entitled 'Stellar Atmospheres'. (Footnote: this was the first ever PhD awarded at Harvard; it was also praised as "undoubtedly the most brilliant PhD thesis ever written in astronomy" nearly 40 years later. She later turned to studies of variable stars, and coined