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Solar Observations

The Solar Observation members of ASSA Bloemfontein study the properties of Earth's nearest star, the Sun, doing sunspot counts, measuring solar activity etc.

What you can find on this page:
Monthly Solar Bulletins (National ASSA Solar Section)
Solar Picture
Quick facts about the Sun
How to begin with Solar observations and general information about the Sun
Solar Activities of the Centre and ASSA
Historical notes on Solar Observations from Boyden Observatory
Solar telescopes of the world and terms used
Important solar dates to remember
Internet weblinks
Contact details / become part of the observation efforts

Solar Bulletins - ASSA Solar Section
Find reports of solar observation data on solar activities such as sunspots, solar flares, solar wind, geo-magnetic storms etc, by the solar section of ASSA. Access the national web page (bulletins appear at the upper right corner).

Solar CD - order your copy

"Fun with the Sun!" - all the information you need to start off with your OWN solar observations. Contains solar images, interesting facts and solar data as well as how-to's on solar observations. Cost: R30 (including postage in South Africa). Overseas orders, please request a quote. Send your order and postal details to Jacques van Delft, national Solar Section director.

Solar Picture

Solar image on 1 April 2006
(credit: Jacques van Delft)

Quick facts about the Sun
Mass (kg) 1.9891·1030
Diameter (km) 1.392·106
Escape velocity (km·s-1) 617.7
Luminosity (watt) 3.846·1026
Mass conversion rate (kg·s-1) 4.3·109
Spectral type G2 V
Absolute magnitude +4.83
Apparent visual magnitude -26.7
Distance from Earth (km) 1.47-1.52·108
Core pressure (bar) 2.477·1011
Core temperature (°C) 1.571·107
Rotation period (hours) 609.12
Speed relative to nearby stars (km·s-1) 19.4

How to begin with solar observations

Information pamphlet for interested observers

The Director of the Solar section has compiled an invitation for any interested beginner or advanced observer. Download the word document.

The Sun

At over 1.4 million kilometers wide, the Sun contains 99.86 percent of the mass of the entire solar system: well over a million Earths could fit inside its bulk. The total energy radiated by the Sun averages 383 billion trillion kilowatts, the equivalent of the energy generated by 100 billion tons of TNT exploding each second.
But the energy released by the Sun is not always constant. Close inspection of the Sun's surface reveals a turbulent tangle of magnetic fields and boiling arc-shaped clouds of hot plasma dappled by dark, roving sunspots. [Read on...

Solar Activities of the Centre and ASSA

The Solar observation activities concentrate around studies of the Sun's activity and the impact it has on various aspects of Earth's environment.
Observations of the Sun takes place from Boyden Observatory, where the 20 cm coelostat is used as well as from members' homes in the City and surroundings areas. Most active is Jacques van Delft, who does most studies from Wepener in the Free State.

Current activities include:

- observing solar flares and sunspots on a regular basis or when increased storm activity are detected by Satellites
- the impact of the Sun on climate changes and agriculture (by Jacques van Delft)
- observing and reporting planetary-sun transits

Go to the web page for national ASSA's Solar Section.

Historical notes on solar studies from Boyden
20 cm Coelostat: Boyden Observatory

ASSA Bloemfontein Centre's Solar members and ASSA's Solar Section are priviledged to make use of the 20 cm coelostat solar telescope at Boyden Observatory.

The 20 cm coelostat at Boyden Observatory was obtained around the year of 1972. A variety of different research projects (some sponsored by the CSIR) were performed with the telescope and numerous articles were produced.

See examples of some of the historical solar research (professional) performed from Boyden Observatory:
(Boyden Archives)

Solar Flare Photographed at Boyden Observatory on the 11th of August 1972 at 14h44 SAST.

Two interference filters in series used
(effective halfwidth of 15A)

Read article (229 kb jpeg)
Study of Hydrogen alpha Emmissions from Solar Limb Prominences using Fabry-Perrot interferometry

Read the full article which appeared in the South African Journal of Science, February 1981.

[Page 81] [Page 82] [Page 83]

Solar telescopes of the world

There are three main types of solar telescopes:

Coelostat: "Optical device used to follow the path of a celestial body and reflect its light into a telescope; has a movable and a fixed mirror"
Heliostat: "An instrument consisting of a mirror moved by clockwork, by which a sunbeam is made apparently stationary, by being steadily directed to one spot during the whole of its diurnal period" (these two definitions from the handy WordWeb dictionary) - one flat mirror tracks the beams of the sun and redirect it to a stationary mirror which collects the light and send it to the processing component (e.g. camera).
Siderostat: The sideriostat is a variation of the heliostat. The difference is that the siderostat must be moved in two coordinates while it is tracking the sun.

List of biggest solar telescopes in the world with large focal length:

List of biggest solar telescopes in the world with short focal length:

Dates to remember

Annular solar eclipse of the Sun - 22 September 2006
(refer to 2006 Sky Guide for contact times or go to the JHB Planetarium's site)

Winter Solstice - 21 June 2006, 14h26
Summer Solstice - 22 December 2006, 02h22

National ASSA Solar Section links:

Go to the web page
for national ASSA's Solar Section.

National ASSA Transit of Venus report page: ASSA ToV

Internet weblinks for Solar Activities

Solar Activities and Climatic Change by Jaqcues van Delft:
American Association of Variable Star Observers:
NASA Eclipse Homepage:
SOHO Homepage:
NASA Sun-Earth Viewer (live solar images):
NSO: Solar Research Resources (a wealth of solar links):

Contact Us

For more information or if you would like to participate in solar observations, contact Jacques van Delft at
+27 (0)82 812 5907.

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