 The Sun can be described as an average star, a yellow dwarf– bigger than some, smaller than others
SOHO Project Scientist Team

 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.
SOHO Project Scientist Team

 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 Newton William Herschel Albert Einstein
SOHO Project Scientist Team

 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
SOHO Project Scientist Team

 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.
SOHO Project Scientist Team

 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
SOHO Project Scientist Team


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
SOHO Project Scientist Team

 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.
SOHO Project Scientist Team

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.
SOHO Project Scientist Team

1991
1994
SOHO Project Scientist Team

SOHO Project Scientist Team


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
Light and dark in this magnetic scan of the Sun indicate concentrated areas of intense magnetic field lines.
Close-up of sunspots
SOHO Project Scientist Team

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

 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 temperature is still one of the big mysteries in solar physics.
5,000 o C
Corona
Solar interior
Surface
2,000,000 o C
The black circle divides two images.
SOHO Project Scientist Team

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

SOHO Project Scientist Team

Fe XII 195 Å (1.500.000 K) 17 May - 8 June 1998
SOHO Project Scientist Team

 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
SOHO Project Scientist Team


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.
SOHO Project Scientist Team


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
SOHO Project Scientist Team

SOHO Project Scientist Team

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.
QuickTime™ and a
Cinepak decompressor are needed to see this picture.
SOHO Project Scientist Team

 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).
SOHO Project Scientist Team

LASCO -Large Angle and Spectroscopic Coronagraph
Observe the corona from 2 - 32 Rs in white light with overlapping fields of view
SOHO Project Scientist Team

SOHO (EIT/LASCO), TRACE, and RHESSI
SOHO Project Scientist Team

SOHO Project Scientist Team

SOHO Project Scientist Team

 Discovered in 1986, observed by SOHO in 96.
 12 times brighter in 2002 that expected
SOHO Project Scientist Team

SOHO Project Scientist Team

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
SOHO Project Scientist Team

SOHO Project Scientist Team

SOHO Project Scientist Team

 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”
SOHO Project Scientist Team

 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
ALASKA (Zimmerman)
Nice (Benvenuto)
SOHO Project Scientist Team

SOHO Project Scientist Team

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

 How do the planet respond to solar variations?
 Disruption of technology based systems
 Harm humans in space
 Climate change
SOHO Project Scientist Team


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.
SOHO Project Scientist Team