The Sun Miss Butler Astronomy 12 March 22,

THE SUN SOL The Sun’s scientific name is Sol (hence the name “Solar System”)

WHAT IS THE SUN? Centre of the Solar System A foci for all planets in the Solar System A yellow star Luminous Composed of plasma (an ionized gas) made mostly of hydrogen and helium.

OUR STAR’s SIZE 1,400,000,000 m diameter The Sun could hold 1.3 million Earth’s!

THE SUN’S MASS 750 times the mass of all of the Solar System’s planets put together Between 98% and 99% of the Solar System’s mass 332,830 times the mass of Earth! x kg (1,989,000,000,000,000,000,000,000,000,000kg)

OUR STAR – KEY FACTS DENSITY: 1410 kg/m 3 –At the Sun’s centre, the density is more than 150 times that of water! TEMPERATURE: –Average temperature: Approximately 6270Kelvin –6000°C –This is the same temperature as the Earth’s core! ATMOSPHERE: –Made up of immense clouds of glowing gas –Stretches far into space –Can only be seen during total solar eclipses

OUR STAR Surface temp = 5500°C Core temp = 15 million°C

KEY FACTS The obliquity (or axial tilt) of the Sun is 7.25°

KEY FACTS 1) The Sun has no moons or rings. 2) The Sun has natural satellites – the planets, dwarf planets, and smaller celestial bodies 3) Distance from Earth: 1 AU 4) The closest planet is Mercury 5) The farthest planet is Neptune

Classifying the Sun 1) “Jovian” – made of gases 2) “Classical” – can be seen with the naked eye –Scientists used to think the Sun was a planet!

GRAVITATIONAL PULL Acceleration due to gravity = 274 m/s 2 Compared to Earth’s 9.81 m/s 2

GRAVITATIONAL PULL F g =mg EarthSun F g = 70 x 9.81F g = 70 x 274 = N = 19,180 N

OUR STAR – TIMES! The core rotates at the same rate but the outer parts of the Sun do not! 34 Earth days to rotate at Poles 25 Earth days to rotate at Equator There is no period of revolution…

OUR STAR – TIMES! Our Sun is estimated to be approximately 4.5 billion years old. It should last another 5 billion years. Made initially from a cloud of dust. Matter fell inwards, creating heat, eventually causing nuclear fusion and producing its own light and energy.

BRIGHTNESS −26.74 visual magnitude Brightest object in sky from Earth

STUDYING THE SUN Ancient civilizations studied the sky and stars Many had Sun gods –Amaterasu (Japan) –Helios, Apollo (Greek) –Freyr, Sol (Norse) –Huitzilopochtli (Aztec) –Inti (Inca) –Liza (West African) –Re/Ra (Egyptian)

STUDYING THE SUN In 1609 Galileo built his first telescope He saw Sunspots

STUDYING THE SUN 1960’s PIONEER 5 to 9 Orbited the sun –Solar wind –Solar flares –Magnetic fields

STUDYING THE SUN 1974 & 1976 HELIOS High-velocity passes close to Sun’s surface –Solar wind –Magnetic field

STUDYING THE SUN 1980 SOLAR MAXIMUM MISSION –X-rays –Gamma rays –Ultraviolet radiation –From flares and sunspots

STUDYING THE SUN 1990 ULYSSES 1 st polar orbiting probe Still in operation “Fly by”

STUDYING THE SUN 1991 YOHKOH Earth-orbiting satellite observed high-energy radiation

STUDYING THE SUN 1995 SOHO Studies the Sun’s interior and surface

STUDYING THE SUN 1998 TRACE Studies the Corona

SUN MYTHS “What if the sun collapses into a black hole? Bad Astronomy: If the Sun collapses into a black hole, the Earth and all the other planets will get sucked in. Good astronomy: If the Sun were to collapse into a black hole, we would feel no difference in the gravity as measured at the Earth. “ (Note the quotations as I have copied this!!!)

Sources Information from “Universe: the definitive visual guide” senior editor: Peter Frances