The Sun: Our Planet's Pulsating Star

2. The Sun is the most prominent feature in the solar system It contains about 98% of the total mass of the solar system The interior of the Sun can hold over 1.3 million Earths

3. Birth of the Sun • The Sun was formed around 4.6 billion years ago within a protoplanetary disc of gas and dust • The central regions of the disc began to coalesce and collapse • When the Sun had contracted enough, nuclear reactions began at the core, causing the Sun to shine as a star An artists image of a protoplanetary disc

4. The Sun has been active for 4.6 billion years and has enough fuel at its core to burn for another 5 billion years • The Sun rotates every 25 days at the equator to every 36 days at the poles • Deep down everything appears to rotate every 27 days

5. The Sun is called a main sequence star • Stars in the main sequence spend most of their active lives in a stable state fusing hydrogen to helium • Bigger stars fuse hydrogen to helium at a faster rate and live shorter lives • Smaller stars fuse hydrogen to helium at a slower rate and live longer lives The vast majority of stars lie in the main sequence

6. The Sun orbits the center of the Milky Way Galaxy in the same way as the Earth orbits the Sun • It takes about 250,000 million years to complete one orbit traveling at approximately 250 kilometers/second

7. The Sun’s outer layer is called the photosphere • It has a temperature of 6000oC(11,000oF) • It’s mottled appearance is due to turbulent eruptions at the surface • Sunspots appear in the area of the photosphere

8. Sunspots • Sunspots are dark depressions on the photosphere with a temperature of 4000oC (7000oF) which is cooler than the surrounding area • Sunspots change over a period of days and move across the Sun as it rotates • They have a strong magnetic field associated with them and last from a few days to a few weeks

9. Faculae are bright luminous hydrogen clouds which form in the photosphere near sunspots They put out more radiation than normal and increase the solar irradiance While sunspots make the Sun look darker, faculae make it look brighter Faculae

10. Solar energy is created deep within the core • Here the temperature is 15,000,000oC (27,000,000oF) • The pressure is so intense that nuclear reactions take place • Energy is carried to thesurface by both radiation and convection

11. The pressure at the Sun’s core is so intense that it causes hydrogen nuclei to fuse together to form one helium nucleus The difference in mass is expelled as energy It is carried to the Sun’s surface by radiation and convection and is released primarily in the form of electromagnetic radiation (i.e. light) Energy produced in the core takes a million years to reach the surface Nuclear Reactions In the Core

12. Convection occurs because heated fluids, due to their lower density, rise and the cooled fluids fall The heated fluid will rise to the top of a column, radiate heat away, then fall to be reheated, rise and so on A convection cell forms when a packet of fluid becomes trapped in this cycle Very large convection cells on the Sun show a pattern that looks like rice grains, called granulation Convection granulation cells

13. The chromosphere is above the photosphere where temperature is between 6000°C and 20,000 °C • Solar energy passes through this region on its way from the core • Spicules and solar flares arise in the chromosphere

14. The chromosphere contains spikes of superheated gas called spicules that rise through it Spicules are short-lived phenomena corresponding to rising jets of gas that move upward at high speed usually lasting only 10 minutes More than 100,000 spicules “tickle” the solar atmosphere at any time Spicules

15. Solar Flares • Solar flares are eruptions in the chromosphere • High energy particles and gasses are emitted lasting minutes to hours • Flares produce sunquakes similar to an 11.3 magnitude earthquake on Earth and release 40,000 times more energy than the 1906 San Francisco earthquake Image taken by SOHO in 1999

16. Corona • The corona is the outer part of the Sun’s atmosphere with extremely high temperatures around 1,000,000°C (1,800,000°F) • The outer region of the corona stretches far into space and consists of particles traveling away from the Sun • The corona can only be seen during a total solar eclipse

17. A solar eclipse happens when the moon passes between the Sun and the Earth The corona is a million times fainter than the surface of the Sun so the only time it can be seen is during a total exlipse Ancient people often thought that eclipses were signs from angry gods or omens of doom Solar Eclipse

18. A solar prominence, or filament, is an arc of gas that erupts from the sun They can loop thousands of miles into space They are held above the Sun’s surface by strong magnetic fields and can last many months Prominences are larger than the Earth, which would easily fit under it Prominences Prominences Prominences on the Sun, with the Earth shown to scale

19. Coronal Mass Ejections (CME’s) are huge bubbles of plasma ejected from the Sun Solar plasma is heated to tens of millions of degrees and electrons, protons, and heavy nuclei are accelerated to near the speed of light The CME’s disrupt the solar wind and can strike the Earth disrupting communication and navigation systems, satellites and power grids, sometimes with catastrophic results Coronal Mass Ejections

20. Solar Wind • Solar winds are streams of highly ionized gas that blow continuously outward through the Solar System • The temperature of the corona is so high that the Sun cannot hold on to it and the solar winds stream from the Sun at one million miles per hour • This distorts the Earth’s magnetosphere

21. Flares and CME’s are the most powerful particle accelerators in the solar system • A CME can erupt with the energy of 200 billion Hiroshima bombs • Radiation from a flare could kill a spacewalking astronaut • The Earth’s magnetosphere shields us from these energetic particles Solar Wind

22. The aurora “dances” in the polar regions as the solar wind interacts with the Earth’s magnetic field and energizes electrons and ions in the Earth’s upper atmosphere The energized molecules and atoms in the thin polar atmosphere then glow at different colors The Aurora Borealis

23. The Sun has enough fuel to last for another 5 billion years At the end of it’s life it will have used up all its hydrogen When there is no longer any source of heat to balance gravity its core will then collapse The Future of the Sun

24. This collapsed core will become compressed and heated causing it to produce a new surge of power (from the burning of helium into carbon at the core and hydrogen into helium in shells around the core) and begin to swell This phase is called a redgiant and it will ultimately grow so large it will swallow the Earth The Future of the Sun

25. After about a billion years as a red giant it will shed its outer layers forming a planetary nebula (which, by the way, has nothing to do with planets) The planetary nebula phase is fleeting and lasts only about 10,000 years The Future of the Sun This is the Helix Nebula—an example of a planetary nebula

26. Having run out of fuel the core of the Sun will shrink to a hot (~30,000°C) white dwarf only a few thousand miles in diameter A white dwarf is a stable star held up by electron degeneracy pressure, an exotic state of matter It will radiate left-over heat for billions of years until it cools to a blackdwarf A black dwarf is a cold dark mass that has no internal source of energy The Future of the Sun

27. SOHO • SOHO (The Solar & Heliospheric Observatory) was launched on December 2, 1995 by NASA and the European Space Agency (ESA) • It became operational in March 1996 and was meant to operate until 1998 but has been so successful that its mission has been approved until 2007

28. SOHO • SOHO is designed to study the internal structure of the Sun, its outer atmosphere, and the origin of the solar wind • It helps us understand the interactions between the Sun’s and the Earth’s environment better than ever • It provides uninterrupted views of the Sun and may help solve some puzzlingriddles of ourclosest star

29. Mankind will not remain on Earth forever, but in its quest for light and space will at first timidly penetrate beyond the confines of the atmosphere, and later will conquer for itself all the space near the Sun. - Konstantin E. Tsiolkovsky