2000 February 22, SPS 1020 (Introduction to Space Sciences) Read TNSS Ch. 3 (The Sun) and Ch. 4 (Space Physics) for Thursday; Also read TNSS Chs. 14 and 15 (Jovian planet interiors and atmospheres) and Ch. 16 (Planetary Rings) for Tuesday, February 29. --------------- THE SUN (Revisited, for some of you) and SPACE PHYSICS: ------------------------------------------------------ Solar and space physics, the study of fields, particles, and waves in interplanetary space, are inextricably linked. They're mainly about electric and magnetic properties of *plasmas*, or gases so hot theyÕre ionized. There are many reasons to study solar and space physics: - Solar physics is a major input into climate models, as we've seen. - We do space physics here at Florida Tech: Profs. Moldwin, Rassoul, and Jin and the GPL (Geospace Physics Lab). - The Sun and space are great natural laboratories for studying plasma physics => Might be useful for harnessing nuclear fusion, the process that powers the Sun (and H-bombs)? We have nuclear fission now: it uses rare uranium and plutonium fuel. H fusion would use hydrogen (from seawater): practically unlimited? Cheap? Safe? Might also be a not-bad rocket engine. The details are left as an exercise for the student... - Solar physics drives space physics: the *solar corona*, its outer atmosphere, becomes and drives the *solar wind*, the outflowing plasma that interacts with the planets' magnetic fields - The solar wind and the radiation belts in Earth's *magnetosphere* (region where its magnetic field dominates the flow of plasma around it) affect radio communications, and age the electronics in satellites. There are now > $100G worth of commerical communications satellites in orbit. Profs. Rasoul, Moldwin, and Jin should get bigger research budgets... - Space physics is good for astronauts to know: it requires *on-site humans*, with *hands.* Moldwin has instruments in Greenland; Al Weatherwax (grad-school buddy) builds instruments at S. Pole - The astronaut's life might depend on it: space radiation is a *hazard*! The surface and outer layers of the Sun, and the interplanetary medium, are dominated by electricity, magnetism, and plasma effects, so we should examine them: Brief primer on electricity and magnetism (Physics 2 material, but just the basics here.) ----------------------------------------------- - Electricity and magnetism are inextricably linked: observed, and James Clerk Maxell, 1865, electromagnetic theory. (Einstein's favorite). - Magnets always have two poles, N and S. Unlike poles attract, like poles repel. - Moving magnets make electric current (Faraday's law: how electric generators work) - Moving electric charges, or electric *current*, makes a magnetic field (Ampere's law: how electic motors work). => Combination of the two: *dynamo*: circulating conducting material inside Earth generates its magnetic field - Magnetic fields, like gravity fields, can be depicted with field lines. These are lines of constant force: they're where a compass needle would be deflected by an equal amount. - *Magnetic moment* is an absolute measure of the strength of a magnetic field. - All light is electromagnetic radiation: a light ray can be thought of as a crossed electric field and magnetic field, oscillating as they move along. The only difference between radio waves or optical light or gamma rays is the wavelength of the waves. Plasma physics basics: --------------------- - Plasma = Greek for jelly; seemingly has mind of its own. - Generally occurs only at T > 10^4 K: fluorescent lights, the Sun & stars, aurorae, rocket exhaust - Plasmas conduct electricity, and so have and affect magnetic fields, and are affected by them. - A plasma is made of 2 components: the electrons and the ions. => Just about anything you do to plasma will make waves, of some sort! Heat transfer basics: heat can be transferred in 3 ways: -------------------- Convection (heat transferred by mass motion, as in boiling water) Conduction (heat transferred by motions of indiv molecules/atoms/particles) Radiation (heat transferred by e/m radiation) THE SUN (Beware of cheap, UNSAFE solar filters!) ------- Energy generated by nuclear fusion in its core (T > 15 million K). E = mc^2 p-p chain: Solar neutrino problem: due to new neutrino physics (neutrino oscillations) Can now see inside Sun: _seismology_! Here, *helioseismology* (helios = Greek, "Sun") Sound waves (p-mode, or pressure waves: slinky demo), from convective hammering => "5 minute" oscillations Unlike terrestrial seismology in that we don't have phase information => can't solve inverse problem (take data and make a model): must guess at models, fit data The GONG project: 6 telescopes around Earth, to continuously monitor Sun SOHO satellite: observes at high resolution and in extreme ultraviolet (million-degree corona) Also rivers, jet streams, tornadoes on Sun! Also Yokoh (soft X-rays: inner, million-degree corona) and TRACE (EUV, inner, million-degree corona) Note that outer layers HEAT UP! Must have an extra energy input, other than heating from interior. Sound waves from convective interior => heat chromosphere Magnetism (specifically, magnetic reconnection, or "short circuiting":) => heats corona, accelerates solar wind? Sunspots - tubes of magnetism punching through solar surface (photosphere) Usually occur in pairs Vary on 11-year cycle (22-year magnetic cycle) Migrate over surface: butterfly diagram During the Maunder minimum (1645-1715), almost no sunspots coincided with Europe's "Little Ice Age": connected? We appear now to be going into an especially active trend. Also, the "solar constant" (total flux = 1340 W/m^2) isn't so constant - satellite measurements Other magnetic activity: Prominences - buoyant tubes of magnetized gas, moving out from Sun (over hours/days) Can be 5e5 km high! Flares - much more powerful, and faster: sudden _short circuit_ in magnetic field Corona: changes shape over Sun's 22-year magnetic cycle Coronal mass ejections (CMEs) - discovered by Skylab! Coronal holes - almost always present at poles of Sun Investigated by Ulysses spacecraft (flew over poles of Sun, 1994-1995). Solar wind twice as fast (800 km/s), versus 450 km/s near Earth: unknown why.