Announcements

• Pick up graded homework

• Seminar on gravitational waves today, 1:00, SL 240

• No class this Friday!

• Test next week on material through today’s class

Our Sun

18 October 2006

Today:

• Basic facts about the sun

• Solar details: Granulation, sunspots, magnetic fields, flares, prominences, corona, solar wind

• What is the sun made of?

Basic facts about the Sun

• Distance from earth: 150 million km (400 x as far as moon)

• Angular diameter: 1/2 degree (same as moon)• True diameter: 110 x earth’s diameter• Mass: 330,000 times earth’s mass• Average density: 1.4 times that of water• Intensity of sunlight at earth’s location: 1400 watts per

square meter• Total power output: 3.9 x 1026 watts• Surface temperature: 5800 K• Made of ionized gases

Basic facts about the Sun

• Distance from earth: 150 million km (400 x as far as moon) measured using radar

• Angular diameter: 1/2 degree (same as moon)• True diameter: 110 x earth’s diameter (400 x moon’s)• Mass: 330,000 times earth’s mass gravity!• Average density: 1.4 times that of water mass/volume• Intensity of sunlight at earth’s location: 1400 watts per

square meter measure directly• Total power output: 3.9 x 1026 watts calculate• Surface temperature: 5800 K from power or spectrum• Made of ionized gases too hot for anything else!

Sunspots, Granulation

For current images and sun news, see www.spaceweather.com

Electromagnetism

• The sun is made of ionized atoms and electrons -- electrically charged particles

• Charged particles in motion create magnetic fields

• Magnetic fields can “trap” electrically charged particles (which can move parallel to the field but can’t go far in perpendicular directions)

Magnetic activity around sunspots

Visible light Magnetic field map Far-ultraviolet light

Magnetic activity around sunspots

(Ultraviolet light images)

Solar Prominences

Solar Prominences

The Solar Corona

The Solar Corona and Solar Wind

Solar Wind and Earth’s Magnetic Field

Charged particles (mostly from the sun) are deflected by earth’s magnetic field; some are trapped and move back and forth along helical paths. They reach earth’s atmosphere mostly in the polar regions.

Aurora (Northern/Southern Lights)

From Earth From the Space Shuttle

What is the sun made out of?• 74% hydrogen (by mass)• 25% helium• 1% all other elements (oxygen, carbon,

nitrogen, neon, aluminum, silicon, iron, . . . )

The Periodic Table

Masses and rarities increase (mostly) toward the bottom of the table.