Hale COLLAGE (CU ASTR-7500) “Topics in Solar Observation Techniques” Lecture 1: Introduction, motivation, & history Spring 2016, Part 1 of 3: Off-limb coronagraphy & spectroscopy Lecturer: Prof. Steven R. Cranmer APS Dept., CU Boulder

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Brief overview Goal of Part 1: To introduce you to the world of off-limb solar observation techniques & diagnostics 1.Introduce basic concepts in radiative transfer 2.Coronagraphic occultation: why & how? 3.Off-limb visible continuum: formation & diagnostics 4.Off-limb emission lines: formation & diagnostics 5.(mini) Bridging “remote-sensing” and “in-situ” techniques Goal of Lecture 1: 1.Give bird’s eye perspective on observing the Sun above the limb 2.Summarize history of these observations

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 August 1, 2008, Mongolia Image: Miloslav Druckmüller,

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere solar wind ISM corona photosphere chromosphere

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere solar wind ISM corona photosphere chromosphere

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere solar wind ISM corona photosphere chromosphere

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere MercuryEarthJupiter Voyager 1, 2 Pluto

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere MercuryEarthJupiter Voyager 1, 2 Pluto protons electrons oxygen ions

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Big picture: the heliosphere remote sensing in situ probes

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Observation regions techniques Low/Inner Corona where most coronal heating occurs Outer/Extended Corona where most solar wind acceleration occurs transition from collisional (MHD) to collisionless (kinetic) Inner heliosphere r ~ 1 to 1.3 R  r ~ 1.5 to 10 R  r > 60 R  direct imaging eclipses, coronagraphs, heliospheric imagers in situ probes radio sounding?

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Off-limb diagnostics Plasma density Plasma velocity Plasma temperature Magnetic field Plasma fluctuations Direct: (incl. elemental abundances, ionization states) (vector) (incl. non-Maxwellian velocity distributions) (vector) (waves, shocks, eddies, jets, solitons, …) Properties of (primordial?) dust Rates of { mass, momentum, energy } transfer Indirect:

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 History: observing above the limb

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Total eclipses G. Tempel, 1860E. Holden, 1889 Sun and Moon have ~ equal solid angles; coincidence? anthropic? Wondrous/terrifying events for all of human history. First photographs: 1851, but drawings remained “better” for decades.

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Eclipse expeditions 1919: Eddington’s validation of general relativity 1898 Lick Observatory expedition, Jeur, India Reminiscence from Hendrick van der Hulst ( )

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 The chromosphere “sierra” “blood red streak” “pink transparent gas” “flames, beams, and streamers, as transient as those of our own aurora borealis.” “saw-teeth … for a circular saw” “full lake red” However… Lockyer’s “chromo” color probably refers to the full range of bright emission lines! Photos: Fred Espenak Sketch: N. Lockyer

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Norman Lockyer & Pierre Janssen 1868: They independently took note of a strange line in the solar spectrum: almost overlapping with known lines… it was suggested to be a new element: Sodium Helium 1869: Lockyer founded Nature. In 1st issue, editorialized that these lines were “…bizarre and puzzling to the last degree!” On closer inspection, off-limb eclipse spectra contained several other unknown emission lines… “coronium?” ApJ, 1921

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 The coronium heating problem? Coronium: “green line” at nm “red line” at nm “yellow line” at nm Aurorium / Geocoronium: green line at nm red line at 630 nm Nebulium: blue-green lines at 495.9,500.7 nm There was a proliferation of proposed elements, but atomic physics eventually caught up to the observations: [Fe XIV] [Fe X] [Ca XV] [O I] [O III]

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Mounting evidence for a hot corona Alfvén (1941) summarized the evidence and concluded that T ~ 10 6 K “Coronium” lines are associated with high ionization states of heavy elements (Grotrian, Edlén: late 1930s) Spectral line Doppler widths (both emission & absorption) are consistent with high T If observed radial dependence of electron density is in hydrostatic equilibrium, it demands high T (van der Hulst) During flares, Earth’s ionosphere is enhanced: UV & X-rays (still unobserved in 1940s) must be coming from Sun. What kind of source produces such photons? A hot one!

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Parallel history: the solar wind 1850–1950: Evidence builds for outflowing magnetized plasma from the Sun:  solar flares  aurora, telegraph snafus, geomagnetic “storms”  comet ion tails point anti-sunward (no matter comet’s motion) 1859 Kristian Birkeland’s 1895 experiments concluded Sun emits “cathode rays”

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Discovery of the solar wind 1958: Eugene Parker put the pieces together: the million-degree corona has such a high gas pressure that it naturally expands! : Intermittent detection: Russian Lunik, Venera; American Explorer : Marcia Neugebauer & colleagues got continuous data from Mariner 2 on its journey to Venus. Parker’s prediction was vindicated.

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 where the heating takes place (later: where flares, CMEs, particle acceleration occur) where the solar wind is accelerated Eclipses are nice, but we really want a more consistent view of: Goal: Observe off-limb, outside of eclipses

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Invention of the coronagraph Despite some earlier attempts to block out the Sun in telescopes, the first successful instrument was built by Bernard Lyot in the 1930s… and improved throughout the next decades. L to R: 1930 … 1938 … 1941

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Space opens up the X-ray and UV 1940s: re-purposed German V-2 rockets at White Sands, NM (Naval Research Laboratory) 1950s: rapid detector development 1960s: first dedicated satellites 1970s: John Kohl’s first UV+C+S 1980s-1990s: ISTP, SOHO, & beyond...

Lecture 1: Introduction, motivation, & historyHale COLLAGE, Spring 2016 Next time Define some basic properties of radiation Then… Why is blocking the Sun needed? (quantitative) Physical optics… not just geometric ray tracing