Transcript Chapter 26
Chapter 26 The Sun and the Solar System Chapter 26.1 The Sun’s Size, Heat and Structure Size More than 1,000,000 earth’s would fit inside the sun The sun’s diameter is 110 times the earth’s Compared to other stars it is just average in size If the sun was a bottle cap the largest star, Epsilon Aurigae, would be the size of a football field Sun’s Energy Fusion – the combining of the nuclei of lighter elements to form heavier elements is the source of energy of all stars E = mc2 – this equation shows the relationship between mass and energy – Matter can be converted into energy Due to intense heat and pressure, atoms get torn apart into the nuclei and electrons. This results in H & He existing as a plasma These nuclei normally repel each other, however, due to their speed, over crowding and heat, they are forced to fuse. When 4 Hydrogen nuclei come together, they produce a Helium nucleus. A byproduct of this is energy. Sun’s Layers During the fusion reaction, energy is produced inside the sun that pushes outward is balanced by the force of gravity drawing the layers inward Core – mostly plasma H & He – Temperature ≈ 15,600,000°C Radioactive Zone – surrounds the core – Near the core ≈ 8,000,000°C – Near the convection zone (next layer) ≈ 2,000,000°C Convection Zone – rising and falling currents carry energy to sun’s surface Photosphere – visible surface of the sun – Consist of granules – 1,000km wide, 20 minute life – Temperature ≈ 6,000°C Inner atmosphere – chromosphere – Area where solar prominences take place Outer atmosphere – corona – visible during total solar eclipses Chapter 26.2 Features of the Sun Sun is 150,000,000km away from earth, this distance is known as an Astronomical Unit (A.U.) Sunspots – Dark spots on the photosphere – Some are barely visible while others are 4 times larger than Earth – Small one may last a few hour – large ones months – Are very hot and bright – look dark because the photosphere is so much hotter and brighter than the sunspots – Move from left to right across surface This gave evidence that the sun rotates – An increase in sun spots may result in increased solar flares, solar winds and auroras – Sunspot activity peaks every 11 years Sun’s rotation – At the equator – 25 days – At the poles – 34 days Solar winds – corona gives off a constant stream of electrically charged particles – Mostly protons and electrons – The earth’s magnetic field will reflect most of them p.514 – Auroras – bright lights at the earth’s poles caused by solar wind particles interacting with earth’s magnetic field – Holes in the corona (coronal holes) and solar flares are sources of solar winds Chapter 26.3 Observing the Solar System: A History The movement of Planets and Stars As we watch the sun go across the sky it appears to move as we stand still. For 2,000 years it was the belief that the earth was the center of the universe, it is called geocentric (earth centered) Stars were thought to have been holes in a celestial sphere that surrounded earth. Behind the sphere was a source of intense light The changing positions of constellations gave basics for the 1st calendars Some points were not fixed in constellation, they wandered. Astronomists believe those point of lights were closer (Planets) Most of the time the planets move eastward however they stop and then move west for a few weeks, then back eastward, this is known as retrograde motion. Chapter 26.4 History of Astronomers Ptolemy – lived in Egypt in the 2nd century AD Geocentric Model – explained retrograde motion by the use of epicycles – perfect spheres the planet revolved on while on the planetary sphere Copernicus Polish astronomer (1473-1543) proposed a heliocentric (sun centered) solar system Could explain retrograde by the different speeds the planets (including earth) went around the sun (p. 578) Tycho Brahe 16th century observational astronomer made in-depth study of the moon and planets throughout their orbits identified a number of unexpected occurrence if the orbits were round Died before he could apply his data Kepler Used Tycho’s work and found out that the orbits were elliptical rather than round Created 3 laws of planetary motion 1st law planets travel in elliptical orbits with the sun at one focus 2nd law Planets travel faster when closer to the sun – this law is also known as the equal area law – planets sweep out equal area in equal time 3rd Law or Harmonic Law is used to find a planets mean distance from the sun – Period2 = Distance3 period – time taken to revolve around the sun distance – mean distance between the planet and the sun The average speed of earth in its orbit is 30km/sec Newton (1642 – 1727) English scientist mathematician Newton identifies gravity as the force that keeps the earth in orbit around the sun The strength of gravity is proportional to the masses and indirectly to their distance