AAQ Solar System Section

Sun

The Sun is the central body of and main source of energy for the Solar System. With an equatorial diameter of 1,392,530 km (109 times the diameter of Earth) it is the largest body in the Solar System and holds approximately 99.85% of the Solar System mass. Composed predominately of hydrogen (~92% by number of atoms and ~ 75% by mass) with the remainder mainly helium, the Sun has a low density (1409 kg/m3) compared to the terrestrial planets (typically >5000 kg/m3). The thermonuclear fusion reaction that converts hydrogen to helium within the core of the Sun is the source of the energy that radiates out into the Solar System. The visible surface from which the Sun’s energy radiates is called the photosphere, it has a temperature of approximately 5500°C. Whilst of upmost importance to us on Earth, the Sun is considered to be an ordinary star with a spectral classification of G2 V, a yellow dwarf main sequence star.

Image courtsey of NASA / ESA

For further information on the Sun visit the following web sites:

SOHO - The Solar And Heliospheric Observatory by NASA and ESA

Spaceweather - Information on solar activity by Spaceweather.com

National Solar Observatory - The solar observatory at Kitt Peak

The Sun provides amateur astronomers with a wide range of observational activities and a wealth of detail that cannot be obtained by viewing other stars. However, the nearness and apparent brightness of the Sun presents the observer with observational hazards not associated with observing stars in the night sky, the greatest hazard being permanent eye damage if safe solar observing practices are not followed. The photosphere of the Sun should not be viewed directly by naked eye at any time. The photosphere can be safely viewed by either projection or by the use of specialist filters specifically designed for solar observing. The filters are used to intercept and greatly reduce the intensity of the sunlight before it enters the observing instrument. Never use an eyepiece filter as they are prone to rapid breakdown endangering your eyesight. The safe viewing methods described above also apply to viewing the transits of Mercury and Venus, partial and annular eclipses of the Sun and the partial phases of a total solar eclipse. Only during the brief time when the Moon’s disk completely covers the Sun’s photosphere (totality) during a total solar eclipse can the upper chromosphere and corona of the Sun be safely viewed by naked eye.

For further information on solar observation methods and safe viewing techniques visit the Stanford University web site shown below. There are many other web sites on the internet that provide solar viewing safety information.

Observing The Sun For Yourself - Information on solar observing techniques by Stanford University

Solar observation activities that can be undertaken include:

Solar Eclipses The next total solar eclipse occurs on 29 March 2006 and is visible from the Atlantic Ocean, central and northern Africa, Mediterranean Sea, Turkey, Russia and Kazakstan. The AAQ is participating in an eclipse expedition to Libya and Egypt organised by Journeys Worldwide. The main item of interest during totality is the beauty and structure of the corona. Other noteworthy features to observe is the presence of large prominences and the upper chromosphere, shadow bands, the approaching shadow and the influence of the eclipse of the behaviour of people and animals. For more information on solar eclipses visit the Eclipse Home Page by Fred Espenak.
	Image courtesy of Stephen Voss
Transit Of Mercury The next transit of Mercury occurs on 8 November 2006 with the entire event visible (weather permitting) from eastern Australia with first contact starting not long after sunrise. May 2003 Transit - an article by Peter Anderson (PDF 285 KB) For more information on planetary transits visit the Eclipse Home Page by Fred Espenak.
	Image courtesy of Tony Dutton
Transit Of Venus The next transit occurs on 6 June 2012 with the entire event visible (weather permitting) from eastern Australia. For more information on planetary transits visit the Eclipse Home Page by Fred Espenak.
	Image courtesy of John Salini
Analemma Observe / photograph the location of the Sun at the same time each day and it will trace out the path of a skewed figure eight as a result of the inclination of the Earth’s axis to the ecliptic and the elliptical orbit of the Earth. For further information visit the Analemma.com website.
Angular Size Change Observe / photograph the Sun at aphelion and perihelion and note the difference in angular size (31.5’ – 32.5’) due to the elliptical orbit of the Earth. The dates of the next aphelion and perihelion are 5 July 2005 and 4 January 2006.
White Light Observing Observe / sketch / photograph sunspots (dark spots) and faculae (bright areas) on the Sun’s photosphere by either project or using white light solar filters. The movement and evolution of sunspots across the photosphere shows the dynamic nature of the Sun and the differential rotation of the Sun’s visible surface (period of rotation varies from ~ 25 days at the equator to ~ 34 days at the poles). Amateur astronomers can contribute to solar astrophysics through submitting data on sunspot activity to bodies such as the AAVSO.
Hydrogen Alpha Observing Observe / photograph prominences, filaments, flares, plages and granulation on the Sun’s chromosphere using hydrogen alpha solar filters. The Sun when viewed at the hydrogen alpha wavelength is an incredibly active body with obvious changes over relatively short time spans from minutes (flares) to hours to days (prominences). For further information visit the following web site. Observing The Sun In Hydrogen Alpha Light