Particle Precipitation A Not Very Brief History of the Aurora in Observations and Theory How do… • My House • Ofer Lahav • Arnold Schwarzenegger • And Queen Elizabeth the first …come together to help our understanding of the aurora and form the basis of my model? Introduction • History of the • New Theories Aurora in • Solar Observations observations • What does the Solar • History of the Wind Do? Aurora in theories • Current Auroral • Kristian Birkeland observations of • Birkeland’s interest Experiments • My Model • Birkeland’s theories History of the Aurora Observations Oldest Observations • Cro- Magnon people of southern France drew possible aurora 30,000 years ago • First civilisation to study them was China • They began observational record in 687bc • One per 40 years average • Oldest auroral related story from 2600BC • Mentioned in the Old Testament 5x Oldest Observations • Greeks (Plutarch) began in 467BC • Macedonian military failure circa 360BC • First Roman records (Dionysus) circa 460BC • Titus Caesar records aurora above Palestine when he destroyed Jerusalem in 44BC shortly before JC’s death • Then one thousand years of silence… Oldest Observations • First book on the aurora 1490 • Name ‘Aurora’ coined in 17 th Century • Gassend or Galileo? • Revival in interest cut short after Maundy Minimum hits post the 1621 aurora • Current burst of research began 19th C • The Star Lords of 1880 Oldest Observations • Lots of related observations… • Sunspots recorded from 28BC • Galileo puts telescope on them from 1610 • Coronal measurements from 1715 • Continuous Geomagnetic Data from 1836 • …even so, no definite link to the Sun made until the 20 th C, though a couple of close attempts… History of the Aurora Theory Oldest Theories • Many mentions of the aurora in folklore • Dragons and the aurora • Bifrost in Norse mythology • Scandinavians linked aurora to dead women, especially virgins, and children • Eskimos whistled and clapped • One tribe carried knives to guard against the souls of their dead enemies Oldest Theories • “Whistling aurora” • Many cultures claim to have heard crackling and whistling sounds from the aurora • These cultures are diverse in other ideas about the Northern lights, but maintain the sounds are real • No sounds recorded or predicted Oldest Theories • Some folklores turned into theories… • Reflected sunlight from glaciers, herring… • The Greeks had a go • Xenofanes “Accumulation of moving and burning clouds” • Hippocrates and Aeschylus refl. Sunlight • Aristotle, sun = steam, + fire element = aurora Oldest Theories • After the Dark Ages came more explanations • A Gas, which causes earthquakes, is released from the ground • Russians believed the aurora were due to a giant frozen sea and spent decades looking for it • 1733 Marian proposes Ice crystals… Oldest Theories • Edmund Halley first solved the riddle! • In 1716 he described field aligned currents • He was ignored • Swede Celsius declared aurora were related to geomagnetism in 1741 – stolen • Cavendish correctly estimated the altitude of the aurora in 1790 • He was ignored Oldest Theories • 19th Century saw mapping of the aurora • 1859 saw link between eruptions on the Sun and the aurora • Angstrom proved through spectroscopy that the aurora were due to gases – but the theory hadn’t been developed enough • Carlheim- Gyllensköld described global behavior of the Northern Lights 1882/ 3 Oldest Theories • Experiments to describe Northern Lights included shooting electricity through the atmosphere • This produced a glow, but not auroral • A French attempt to recreate the experiment was hit by lightning, ending both the experiment and part of the team leader’s beard Oldest Theories • It wasn’t until the 20 th Century that a full explanation of the aurora was cobbled together • Carl Stormer mapped the flow of electrons down the field lines in 1907 • He was ignored • But he was following the work of another man… Kristian Birkeland Kristian Birkeland • Born in Christiana, now Oslo, 13 th December 1863 • Had extensive CV from agriculture to medicine to weaponry to Cosmology • Wrote a book on his exploits • Theorist, observationalist, Experimenter, inventor • He was ignored – died June 15 th 1917 Kristian Birkeland • Nominated for Nobel prize 7 times • Proposed Radiation Suite to cure SAD • Inspired by discovery of X- rays • Proposed a neutral Solar Wind • Created first Nitrogen Fixer for fertiliser • Proposed an early Dark Matter theory • And invented the Rail Gun Kristian Birkeland • Electromagnetic Cannon • Demonstration failed • Dinner with Sam Eyde • Birkeland- Edye • Norsk Hydro 1905 • QuiniteQ • Pop culture Kristian Birkeland His Experiments Kristian Birkeland Kristian Birkeland • Norwegian Aurora Polaris Expedition • 1899- 1900 1902- 1903 • First ground based magnetometer measurements of the aurora • The book of the expedition included chapters on the Rings of Saturn and the origin of the Sun • Available from UCL library Kristian Birkeland His Theories Kristian Birkeland • Developed a series of theories on the back of an age of enlightenment in Physics • Discoveries of x- rays led to Terella exp. • Sir Arthur Eddington’s theories on the internal mechanics of stars led to Solar Wind theory • Eddington was from my home town Kristian Birkeland • Eddington Develops TE for internal state • What happens at the edge of TE? • LTE in between • Birkeland realised there would be an overall neutral release of particles from the outer layers of the Sun – the Solar Wind • He also said that space must be filled with these particles Kristian Birkeland • Used his terrella experiment to predict these ‘cathode rays’ would be channelled towards the pole • This channelling would be field aligned – hence Birkeland currents • There they strike various atoms in the sky and the excitation leads to emission • Particle Precipitation is born… Further Work New Theories New Theories • 1916 Birkeland proposes semi- neutral SW • 1951 Ludwig Biermann’s comet tails • Predicts the correct velocity • 1957 Sidney Chapman realises the hot Corona “will not be confined” • 1958 Eugene Parker realises Chapman and Biermann are describing same effect • Writes general theory of SW expansion New Theories • Paper submitted to Astrophysical Journal • He was ignored by the reviewers • Editor Chandrasehkar saves the paper • 1962, Spitzer works out pressure exerted on spherical Corona • The SW begins after LTE breaks down • - nonLTE still a vibrant area of research New Theories • Hannes Alven supports Field- Aligned Currents in a paper • 1969, Milo Schield, Alex Dessler and John Freeman coin the term ‘Birkeland Currents’ to describe field aligned currents • Halley must be delighted! Further Work New Solar Observations New Solar Observations • 1959 Luna 1 directly observes the SW • 1962 Mariner- 2 begins measuring the SW • 1973 Triad measures Birkeland Currents • 1973 Skylab solar observations link SW to the Sun directly • 1990, Ulysses measures high latitude winds • Two Solar Winds! New Solar Observations New Solar Observations • Fast Wind • Slow Wind • Coronal Holes • Equator. Streamers • Uniform • Highly Variable • 3 mil. pcm protons • 11 mil. pcm protons • 700 km/ s • 350 km/ s • 2*10^ 12 / m2/ s • 3.7*10^ 12 / m2/ s • 2.8*10^ 5 K • 5.5*10^ 4 K • 1.3*10^ 5 K e- • 1.9*10^ 5 K e- New Solar Observations New Solar Observations • Late 90’s, SoHO discovers expansion of high latitude solar wind far faster than can be explained through hydrodynamics • Corona also hotter than can be currently explained • Supersonic acceleration 4 times closer to the Solar Core than Parker estimated New Solar Observations New Solar Observations The Solar Wind Its effects Solar Wind • 1961 James Dungey comes up with the idea of reconnection – imagining field lines as isobars, particles are channelled down ‘neutral’ points between the SW and earth’s magnetosphere • The channelled particles hang around and area accelerated within the field • They are later channelled into the ovals • Dungey Cycle Solar Wind Solar Wind • Dungey and Vasyliunas cycles seen on Saturn to help create the aurora • Jupiter relies on Io • Ion spews out volcanic ash, it is beaten to an ionic pulp, that is channelled down into the atmosphere in a similar way to SW particles on other planets Solar Wind • Other effects of the SW include bow shocks, atmospheric scavenging and occasional lost satellites • Remnant field on Mars could produce low level solar driven aurora • Aurora’s seen in varying orders of magnitude on most planets • Uranus? Observations of Interest What do we do? Observations • UCL has spectrograph in Svalbard • http:/ / www.apl.ucl.ac.uk / research/ earth_observation/ ucl_ spectro.html • Looks at H- Beta, some OI, OII, O2+ and N2+ lines • Lines produced at different heights in different situations – collisional and recom • Protons! Observations Observations Observations Observations Observations • Some lucky people go to Hawaii • Especially for UKIRT • Planetary Observations – aurora elsewhere • Looking for recombination lines mostly • H atmospheres make identifying ions problematic – assuming there are any involved at all – electrons Jov ian auroral regions v iew ed in H3+ emis s ion Observations • Lots of work done by satellite • Little atmospheric absorption • Can view incoming particle stream • Can put satellites in most active regions • Produce maps of magnetic field on all planets • Can treat all planets the same! Observations Observations • Work also done by rockets • Sampling the particles • Measuring Volume Emission Rates