Flamsteed Astronomy Society

“What the stars have done for us: from Astrology to Astrophysics”  by Francisco Diego — November 5, 2007

Francisco treated us to a new lecture he’s developing as part of an STFC Fellowship project.  Francisco never tackles anything small.  This lecture, “What the stars have done for us...”, sets out to describe the entire development of man’s relationship with the stars and his understanding of them.

His talks starts with an exploration of man’s early connection with the stars — ancient Egyptian illustrations, the Sun & Moon, development of the Constellation patterns, and astrology, including medical astrology (L).

Francisco moves on to cover the development of astronomy over the centuries — navigation, the compass, the appearance of the telescope, the debate over the distance to the stars, and the size of the Universe.  Only in 1838 was the first reliable determination of distance to a star made by Friedrich Bessel.   Using a state-of-the art refractor by Fraunhofer, Bessel was able to measure the annual parallax of 61 Cygni — annual parallax is the apparent change in position of a star against the background stars over a 12 month cycle, seen as the Earth moves in its orbit around the Sun (see our feature on Bradley).

In the 1830s the positivist philosopher Auguste Comte famously said we could never know the composition of the stars:

“We can imagine the possibility of determining the shapes of stars, their distances, their sizes, and their movements; whereas there is no means by which we will ever be able to examine their chemical composition, their mineralogical structure, or especially, the nature of organisms that live on their surfaces....Our positive knowledge with respect to the stars is necessarily limited to their observed geometrical and mechanical behaviour.”

At much the same time Joseph Fraunhofer was observing dark lines in the solar spectrum and by 1860 Kirchhoff had correctly identified the lines as diagnostic of the chemical elements in the Sun.   It was the birth of physical astronomy — the study of the composition of astronomical objects.

Francisco’s talk moves on to compare the total known population of stars — like observing a city from a distance.  He considers the major characteristics of different stars: brightness, colour, and then surface temperature and size, and builds up a very elegant synthesis of the Hertzsprung-Russell (HR) Diagram (R).

Finally he explores the particle physics of stellar fusion reactions before looking briefly at the life cycle of stars and the ultimate origin of mankind — we are stardust.

Just the kind of tour de force we have come to expect from Francisco.



Dr Francisco Diego by Mike DrylandDr Francisco Diego by Mike DrylandDr Francisco Diego by Mike Dryland

Mosaic pavement of a 6th century synagogue at Beit Alpha, Israel. Signs of the zodiac surround the central chariot of the Sun

Astrology & medicine

Dr Francisco Diego [pics: Mike Dryland]

The Hertzsprung-Russell HR-diagram