Dr Dash will be on travel for the next two weeks (off to Africa).

We will have a guest lecturer and Justin will be available to answer questions.

Homework 9 and 10 will become due during this time period.

Sunspots …

Regions with strong magnetic fields

Cooler than other parts of the Sun’s surface (4,000 K) and thus not as bright as their surroundings.

Recall: Cooler objects emit less radiation per surface area.

Loops of bright gas often connect sunspot pairs, leading one spot to have one magnetic polarity and the other the opposite polarity.

Magnetically Linked Spots

solar flare: a violent explosion in the sun’s atmosphere

Magnetic activity causes solar flares that send bursts of X-rays and charged particles into space.

An active region on the Sun that produced a powerful flare shown over a period of about four hours. The glowing gas flowing around the relatively stable magnetic field loops above the Sun's photosphere has a temperature of over ten million degrees Celsius. These flows occurred after

violently unstable magnetic reconnection events above the Sun produced the flare.

Magnetic activity also causes solar prominences that erupt high above the Sun’s surface.

The corona appears bright in X-ray photos in places where magnetic fields trap hot gas.

Active Sun: Coronal Loops• Coronal loops are

tracing magnetic field lines in the corona

• Coronal loops are rooted in the photosphere, one end with positive polarity, and the other end negative polarity

Coronal mass ejections send bursts of energetic charged particles out through the solar system.

An active region on the Sun that produced a powerful flare shown over a period of about four hours. The glowing gas flowing around the relatively stable magnetic field loops above the Sun's photosphere has a temperature of over ten million degrees Celsius. These flows occurred after

violently unstable magnetic reconnection events above the Sun produced the flare.

How does solar activity affect humans?

Charged particles streaming from the Sun can disrupt electrical power grids, disable communications satellites, and cause aurora (“northern and southern lights”).

How does solar activity vary with time?

The number of sunspots rises and falls in 11-year cycles.

The sun rotates faster at its equator than away from the equator.

The sunspot cycle arises from the winding and twisting of the Sun’s magnetic field produced by this differential rotation.

Moving outward from the Sun, we come to…

The Terrestrial Planets

Mercury EarthVenus Mars

• Made of metal and rock; large iron core • Desolate, cratered; long, tall, steep cliffs• Very hot and very cold: 425°C (day), –170°C (night)

Mercury

• Nearly identical in size to Earth; surface hidden by clouds • Hellish conditions due to an extreme greenhouse effect:• Even hotter than Mercury: 470°C, day and night

Venus

• An oasis of life• The only surface liquid water in the solar system• A surprisingly large moon

Earth and Moon to scale

Earth

• Looks almost Earth-like, but don’t go without a spacesuit!• Giant volcanoes, a huge canyon, polar caps, more…• Water flowed in the distant past; could there have been life?

Mars