Lectures 18-19
The Sun-Earth Connection and the Edges of the Solar System
3/9/09 Habbal Lecture 19 1 Mighty magnets on the Sun
Sunspots are also used to measure the rate of the rotation of the Sun: 25 days at equator, 28 days at poles
3/9/09 Habbal Lecture 19 2 Loops of bright gas often connect sunspot pairs
Approx size of the Earth
• Solar magnetic fields rise far above the surface, with sunspots at the base of the arches. • These loops can trap bright, hot gas. 3/9/09 Habbal Lecture 19 3 Other spectacular magnetic structures: Prominences
Magnetic activity also causes prominences that erupt high above the Sun’s surface.
3/9/09 Habbal Lecture 19 4 Other important aspects of solar magnetism
Charged particles spiral along magnetic field lines
3/9/09 Habbal Lecture 19 5 How does solar activity vary with time?
• The sunspot cycle, or the variation in the number of sunspots on the Sun’s surface, has an average period of 11 years. • In fact, the solar magnetic field reverses orientation every ~11 years, resulting in a 22-year magnetic cycle.
3/9/09 Habbal Lecture 19 6 How does solar activity vary with time?
• At solar minimum, sunspots form at mid-latitudes. As cycle progresses, they form closer to the equator. • Cycle varies in time. Maunder minimum (1645-1715) had virtually no sunspots. Coincides with the “Little Ice Age” in Europe and North America.
3/9/09 Habbal Lecture 19 7 The Sun through time: the Solar Magnetic Cycle in X-rays
(Courtesy Yohkoh SXT)
3/9/09 Habbal Lecture 19 8 Babcock model of the solar cycle:
The winding and twisting of the Sun’s magnetic field causes the 11-year sunspot cycle
3/9/09 Habbal Lecture 19 9 Solar Flares
Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space.
3/9/09 Habbal Lecture 19 10 Solar flares as seen projected against the solar surface
Solar Flares in H α (Big Bear Solar Observatory) 7 August 1972 3/9/09 Habbal Lecture 19 11 Carrington’s flare: 1 September 1859
3/9/09 Habbal Lecture 19 12 The first record of a flare dates back to 1 September 1859. It was noted independently by to R. C. Carrington and R. Hodgson. Carrington was observing sunspots when he reported: “Two patches of intensely bright and white light broke out … I hastily ran to call someone to witness the exhibition with me, and on returning within 60 seconds, was mortified to find that it was already much changed and enfeebled. Very shortly afterwards the last trace was gone.” Carrington noticed that the sunspots were precisely the same after the sudden conflagration as they were before: “The phenomenon took place at an elevation considerably above the general [visible] surface of the Sun, and accordingly, altogether above and over the great [sunspot] group in which it was seen projected. “ Carrington noted that this event took place in the middle of a very intense magnetic storm at the Earth, which lasted from 28 August to 4 September. However, a definite link between individual events and terrestrial disturbances was not established until the following century. Although Carrington himself noted that “a swallow does not make a summer”, this was the first direct link between solar activity and its influence on earth.
3/9/09 Habbal Lecture 19 13 How does solar activity affect humans?
3/9/09 Habbal Lecture 19 14 The Solar Wind
3/9/09 Habbal Lecture 19 15 Extension of the corona into space
3/9/09 Habbal Lecture 19 16 First interplanetary space detection of an outflow from the Sun: Mariner 2, 1962
• Continuous outflow from the Sun • Different flow speeds • Anticorrelation between density and velocity • Recurring high speed streams
Neugebauer and Snyder 1964 3/9/09 Habbal Lecture 19 17 The Solar Wind in 3D: the Ulysses mission The first space mission to orbit the Sun out of the ecliptic plane
3/9/09 Habbal Lecture 19 18 ULYSSES velocity measurements from the first polar pass
Polar plot of solar wind velocity
Background = composite image of the Sun from SOHO at solar minimum
Positive polarity magnetic field
Negative polarity magnetic field
3/9/09 Habbal Lecture 19 19 Ulysses 2nd Polar Pass: Different phase of the solar cycle
White light images of the corona
1997 1998 1999 Solar Minimum
velocity
30 15 0 -15 -30 3/9/09 North HabbalHeliolatitude Lecture 19 (deg) South 20 McComas et al, GRL, 30, 1517, 2003 3/9/09 Habbal Lecture 19 21 The Sun’s bursty outflows
• Also known as Coronal Mass Ejections or CMEs • Caused by: - the eruption/disruption of prominences - and/or a flare
3/9/09 Habbal Lecture 19 22 time Eruption of a prominence
3/9/09 Habbal Lecture 19 23 Close-up of the fine details within a CME
3/9/09 Habbal Lecture 19 24 Charged particles streaming from the Sun with the solar wind can disrupt electrical power grids and disable communications satellites.
3/9/09 Habbal Lecture 19 25 Energetic particles high in Earth’s atmosphere cause auroras (Northern Lights).
3/9/09 Habbal Lecture 19 26 Interaction of the solar wind with the Earth’s magnetic environment
3/9/09 Habbal Lecture 19 27 The termination of the solar wind
Voyager 1 crossed the termination shock on December 16, 2004, 27 years after its launch, at a distance of about 100 AU. 3/9/09 Habbal Lecture 19 28 3/9/09 Habbal Lecture 19 29 What have we learned? • What causes solar activity? — The stretching and twisting of magnetic field lines near the Sun’s surface causes solar activity. • How does solar activity affect humans? — Bursts of charged particles from the Sun can disrupt communications, satellites, and electrical power generation. • How does solar activity vary with time? — Activity rises and falls in 11-year cycles.
3/9/09 Habbal Lecture 19 30