martedì, novembre 12, 2013

Notre Dame Analemma

Notre Dame Analemma:
ND Analemma (Craig Lent)
Notre Dame Analemma
Craig Lent
This picture shows an analemma, which illustrates the path traced by the Sun in the sky over the course of a year, behind the Golden Dome of Notre Dame’s (my alma mater) Main Building. The image was taken by ND engineering professor Craig Lent. An analemma can be created by photographing, from a fixed location, the Sun in the sky, or by marking its projected image, at the same time over regular daily intervals over the course of a year. As the Earth orbits, the Sun’s daily path rises and falls in the sky due to the fact that Earth revolves at an angle relative to its orbit. Moreover, because the Earth’s orbit is elliptical, the Sun’s position at a given time (say, noon) advances and retreats relative to the time because the Earth’s orbital speed changes over the course of the year, being faster when the Earth is closer to the Sun and slower when it is farther. As a result, the relationship between the speed of the Earth’s orbit to its constant rotation changes, causing the Sun’s apparent motion through the sky to vary.  Read a detailed description of the causes here.