The Sun and Solar Wind

Internet Resources

A good Primer on solar features and disturbances from the Science Weather Prediction Center
A solar page with interesting links
Section #18 on the solar wind and IMF in The Exploration of Earth's Magnetosphere
(Also has sections #16 & #17 on the Sun and corona)
A glossary and several interesting pages on solar activity, solar cycles and flares
More detailed info on the Sun and solar disturbances from Windows to the Universe
Solar Flare 10/28/2003

Typical solar wind properties
Current solar wind and IMF conditions. Some explanatory text for these "dials" and other solar wind parameters
Solar wind data plotted for the last 7 days. Data from the Advanced Composition Explorer (ACE) spacecraft
Homes pages for other Sun-observing spacecraft of interest: Ulysses and SOHO (Solar & Heliospheric Observatory)
The Sun-Earth Connections website has images as well as links to other space missions studying the sun and magnetosphere

Basics outline

Solar atmospheric structure
- photosphere: the layer from which visible light reaches the Earth, defining the visible disk of the Sun having a temperature of about 10,000 F (6000 K)
- chromosphere: the thin reddish layer (thin by solar standards; about 1500 miles thick) between the photosphere and corona
- corona: the hot (up to 2,000,000 F) outermost layer of the Sun's atmosphere and source of the solar wind; visible to the eye during a total solar eclipse
Solar features and disturbances
- Sunspots
- Coronal Holes
- Prominences (a.k.a. Filaments if viewed on the solar disk)
- Flares
- Coronal Mass Ejections (CME's)
The Interplanetary Medium
- Solar Wind
- Interplanetary Magnetic Field (IMF)
Solar cycles. The solar influence on Earth goes through several cycles due to the solar rotation, the orientation of Earth with respect to the Sun, and variations in solar processes themselves. Examples include:
- 27-day solar rotation
- 154-day solar periodicity
- annual cycle (due to the tilt of solar rotational axis by 7 degrees and Earth's rotational axis by 23.5 degrees from the ecliptic plane of Earth's orbit)
- 1.3 year solar periodicity
- 11-year sunspot cycle (a.k.a. The Schwabe cycle)
- 22-year magnetic cycle (a.k.a. the double sunspot cycle or The Hale cycle)
- The Gleissberg cycle (an approx. 80 to 90 year cycle)
- The de Vries cycle or Suess cycle (an approx. 205 year cycle)
- The Hallstatt cycle (an approx. 2300 yr cycle)
- The Milankovich cycles due to variations in orbital parameters:
  - precession (wobbling) of Earth's rotational axis - a 26,000 year cycle
  - obliquity (tilting) of Earth's rotational axis - a 41,000 year cycle
  - eccentricity (distortion) of Earth's elliptical orbit - a 100,000 year cycle

Historical outline - sunspots and other solar features

4th c. BC	Possible description of sunspots in Chinese records
325 BC	Theophrastus notes spots on the Sun
165 BC	Chinese begin sporadic record of sunspot observations
Dec 22, 968	Leo Diaconus observes solar corona during eclipse
May 1, 1185	Possible description of solar prominence during eclipse in Russian Chronicle of Novgorod
1607	Johannes Kepler misinterprets a sunspot as the passage of Mercury across the face of the Sun
1610	Galileo and others observe sunspots
1645-1715	Maunder minimum
1843	Samuel Heinrich Schwabe identifies sunspot cycle
1848	Rudolf Wolf devises method to quantify sunspot activity
Sept 1, 1859	Richard Carrington observes solar flare
July 18, 1860	Drawing of solar corona during eclipse shows a coronal mass ejection
1861	F.G.W. Spörer discovers sunspot latitude pattern during sunspot cycle
1863	Carrington discovers differential solar rotation
1892	George Hale observes flares by viewing only red light
1893	Edward Maunder identifies period of infrequent sunspots "The Maunder Minimum"
1908	Hale shows sunspots are associated with intense magnetic fields
1925	Hale and Nicholson identify magnetic cycle
1942	Bengt Edlen finds the corona has high temperatures
1961	H. Babcock proposes theory of magnetic coiling for sunspot formation
1966	22-year solar magnetic cycle (double solar cycle) identified by Chernosky
1973	Coronal holes and coronal mass ejections discovered with X-ray instruments aboard Skylab
May 1996	Last solar minimum
Apr 2000	Last solar maximum (Progression of the current cycle)

Historical outline - solar wind and interplanetary medium

c. 600	Chinese astromoners attribute pointing away of comet tails to the Sun's "life force" chi
1903	Kristian Birkeland proposes stream of electrons from Sun causes auroras
1919	Frederick Lindemann suggests particles of both polarities, protons as well as electrons, come from the Sun
Feb 28, 1942	S. E. Forbush detects Ground Level Enhancement due to energetic protons associated with a solar flare
1943	Cuno Hoffmeister revives idea of "solar corpuscular radiation"
1951	Ludwig Biermann analyzes comet ion tail deflection to support existence of corpuscular radiation
1958	Eugene Parker provides theory for corpuscular radiation; calls it the solar wind
1959	Konstantin Gringauz with data from Lunik 2 probe finds evidence for solar wind
1962	Mariner 2 probe shows solar wind is a permanent feature; finds 27-day intervals in variations
1963	Interplanetary Magnetic Field identified