1. SOHO Project Scientist Team Sun’s size vs. other stars  The Sun can be described as an average star, a yellow dwarf– bigger than some, smaller than others

2. SOHO Project Scientist Team Early Western science  Galileo (1600s) -- agreed with Copernicus and was one of the first scientists to systematically observe and keep records of the Sun and sunspots. He correctly identified sunspots as part of the Sun and determined the Sun’s rotation : 25.4 days.

3. SOHO Project Scientist Team More modern solar science  Sir Isaac Newton (late 1600s) - concluded that stars were tremendously far away and that they gave light like the Sun  William Herschel ( 1780s) – infrared light  Heinrich Schwabe (1843) - determined the appearance of sunspot cycles  Robert Bunsen (1860s) - invented the spectroscope to determine the elements found in the Sun  George Hale (1908) - discovered the magnetic fields of sunspots  Albert Einstein (1920s) - proposed that sunlight was made of particles. No one believed himself until it was proven 10 years later. Sir Isaac NewtonWilliam Herschel Albert Einstein

4. SOHO Project Scientist Team Solar Spectrum  Huygens (1690): light travels as waves, just likes ocean waves  Sir Isaac Newton (1704): light from the Sun can be split into a rainbow by shining it through a prism.  Bunsen and Krichhoff: devised the first spectroscope to measure the color of light given off by elements heated by a flame  They found that each kind of atom has a special “fingerprint” I.e. a unique set of spectral lines when the electrons are excited at high temperatures  In 1868 during a solar eclipse Janssen observed the solar spectrum and found “fingerprints” (spectral lines) he did not recognize.  This new element was named HELIUM after Helios, the Greek word for Sun

5. SOHO Project Scientist Team Solar Spectrum  Ultraviolet radiation. Chemical rays or latent light referred to what we now call ultraviolet radiation. During the early years of the development of spectroscopy it was discovered that "invisible" rays were emanating from the Sun. In 1800 William Herschel investigated the heating power of rays in the solar spectrum. He found that the maximum heating effect was located just beyond the visible red end of the solar spectrum. Initially called "heat rays“ they later became known as infrared radiation. Soon afterwards came the discovery of ultraviolet radiation or "chemical rays" by German scientist R.W Ritter. He found a blackening effect on silver chloride due to unseen rays beyond the blue end of the spectrum.

6. SOHO Project Scientist Team The Sun  The Sun is 333,400 times more massive than the Earth and contains 99.86% of the mass if the entire solar system  It consist of 78% Hydrogen, 20% Helium and 2% of other elements  Total energy radiated: 100 billion tons of TNT per second  Core pressure: 340 billion times Earth’s air pressure at sea level  Every second 700 billion tons of hydrogen are converted into helium  4 billion tons is converted into energy each second  The Sun will run out of fuel in 5 billion years

7. SOHO Project Scientist Team The Sun’s Structure  Core  Where the energy is created.  Nuclear reactions burn every second about 700 million tons of hydrogen into helium.  Inside the core the particles are packed so tightly, and the temperature is so hot, that individual atoms ram into each other, forming heavier helium atoms and releasing energy

8. SOHO Project Scientist Team The Sun’s Structure  Radiation Zone  Where energy is transported by radiation.  Although the photons travel at the speed of light, they bounce so many times through the dense material that they use about a million years to escape the Sun.  Convection Zone  Energy transported by convection (just like boiling soup) where heat is transported to the photosphere.

9. SOHO Project Scientist Team The SOHO Spacecraft Mass: 1800 Kg Size: 4 x 9 m The total mass of the spacecraft at launch was 1 850 kg (payload 655kg). Its overall length along the sun-pointing axis is 4.3 metres, and the span of the extended solar panels is 9.5 metres.

10. SOHO Project Scientist Team Solar Radiation 1991 1994

11. SOHO Project Scientist Team The Sun – our closest star

12. SOHO Project Scientist Team Sunspots  Dark areas (umbra, penumbra)  Strong magnetic fields  Inhibit energy transport from solar interior  Cooler areas, and therefore darker  Frequency varies with the 11-year solar cycle Close-up of sunspots Light and dark in this magnetic scan of the Sun indicate concentrated areas of intense magnetic field lines.

13. SOHO Project Scientist Team Sunspots Sharpest ever pictures of the Sun – SWT LaPalma Close-up of sunspots

14. SOHO Project Scientist Team The Solar Corona  The corona is the area just above the surface. While the surface is about 5,000 o Celsius, the temperature in the corona reaches about 2 million degrees Celsius. What causes this rapid increase in tempera- ture is still one of the big mysteries in solar physics. 5,000 o C 2,000,000 o C The black circle divides two images. Corona Solar interior Surface

15. SOHO Project Scientist Team Total solar eclipse video This video of the June 21, 2001 eclipse seen in Africa shows the Sun just as it is going into totality

16. SOHO Project Scientist Team Total eclipse photos Credit: Serge Koutchmy, IAP, 1991

17. SOHO Project Scientist Team 3 Weeks of EIT observations Fe XII 195 Å (1.500.000 K) 17 May - 8 June 1998

18. SOHO Project Scientist Team Plages  This solar image is taken through a 10Å wide filter centered on the K line of Calcium ( Å).  Bright, filamentary structures, most easily seen near the limb

19. SOHO Project Scientist Team Filaments/Prominences  This image is taken through a filter centered on a spectral line of Hydrogen (H, wavelength Å) that forms above the surface of the Sun  Interesting new features seen on this image are filaments, dark string-like structures visible on the disk, and prominences, bright structures extending outward over the limb  Physically, filaments and prominences are one and the same, namely condensations of cooler gas high up in the solar atmosphere.

20. SOHO Project Scientist Team Prominences  Some filaments and prominences can reach impressive sizes, and remain visible very far above the solar disk. This prominence was photographed in June 1946 again through a filter centered on H, and extends some 200000 km above the solar surface

21. SOHO Project Scientist Team TRACE: “the new kid on the block”

22. SOHO Project Scientist Team Rotation tangles these field lines Solar rotation causes magnetic field lines to become twisted and stretched to thbreaking point. These eventually break and reconnect, creating heat, intense active regions, and solar blasts of charged particles.

23. SOHO Project Scientist Team What is the Solar Wind?  A constant stream of particles flows from the Sun’s corona, with a temperature of about a million degrees and with a velocity of about 450 km/s. The solar wind reaches out beyond Pluto's orbit (about 5900 million kilometers). The drawing shows how it pushes on and shapes the Earth’s magnetosphere (the dotted line).

24. SOHO Project Scientist Team The extended corona /solar wind LASCO -Large Angle and Spectroscopic Coronagraph Observe the corona from 2 - 32 Rs in white light with overlapping fields of view

25. SOHO Project Scientist Team The Sun as seen with SOHO (EIT/LASCO), TRACE, and RHESSI

26. SOHO Project Scientist Team SOHO Captures Planet Gathering

27. SOHO Project Scientist Team Comets observed with SOHO/LASCO (over 500 comets discovered so far!)

28. SOHO Project Scientist Team Comet 96P/Machholz  Discovered in 1986, observed by SOHO in 96.  12 times brighter in 2002 that expected

29. SOHO Project Scientist Team Comet NEAT (C/2002 V1)

30. SOHO Project Scientist Team Solar Activity Cycles and Climate Variations The Sun varies on all timescales. 11 year cycle (Schwabe cycle) 22 year cycle (magnetic cycle) 80-90 year cycle (Gleissberg) 180-210 year cycle (Seuss)  Sir William Herschel (1796): Suggested a correlation between number of sunspots and the price of wheat

31. SOHO Project Scientist Team From Solar Min towards Solar Max

32. SOHO Project Scientist Team Aurora Borealis

33. SOHO Project Scientist Team What is Space Weather?  SPACE WEATHER refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space born and ground-based technological systems and that can affect human life or health. “Space Weather” effects on installations on Earth not a new phenomena 17 November 1848: Telegraph wire between Pisa and Florence interrupted September 1851: Telegraph wire in New England disrupted. The following is a transcript between Portland and Boston (1859): Portland: “Please cut off your battery, let us see if we can work with the auroral current alone” Boston: “I have already done so! How do you receive my writing?” Portland: “Very well indeed - much better that with batteries”

34. SOHO Project Scientist Team The Biggest Sunspot Group in 10 Years ALASKA (Zimmerman) Nice (Benvenuto)  AR 9393 developed a complex delta-gamma magnetic field configuration while rotating towards the center of the Sun  An X-flare and CME was observed on 29 March 2001 causing a severe geomagnetic storm on Earth  Aurora was observed south in Europe

35. SOHO Project Scientist Team The 14 July 2000 Event

36. SOHO Project Scientist Team Solar Activity Cycles and Climate Variations Eddy, 1976, Science, 192, 1189 TemperatureSolar activity During the Little Ice Age, London’s Thames River froze in winter in the 17th Century, a very rare event. Friis-Christensen & Lassen, 1991, Science, 245, 698 "Winter Scene with Frozen Canal" by Aert van der Neer

37. SOHO Project Scientist Team The Sun-Earth Connection  How do the planet respond to solar variations?  Disruption of technology based systems  Harm humans in space  Climate change

38. SOHO Project Scientist Team Navigation systems - GPS  When the ionosphere between the satellites and the user becomes turbulent and irregular, the signal may “scintillate” and prove difficult to track  loss of signal lock on one or several satellites  Both single and dual frequency systems may be affected  The Total Electron Content (TEC) along the path of a GPS signal can introduce a positioning error ( up to 100 m)  The effects on GPS could be one of the most significant space weather effects due to the planned reliance of this system in the future.