UNIT 5: Astronomy ➢ Comet - loose collections of ices, dust, and small rocky particles that originate in the outer reaches of the solar system ➢ Asteroids and meteoroids - composed of rocky and/or metallic material with compositions somewhat like the terrestrial planets. ◦ small bodies (planetesimals) remaining from the formation of the solar system, making them about 4.6 billion years old ◦ They are distinguished according to size: ▪ Asteroids are larger than 100 meters in diameter ▪ Meteoroids have diameters less than 100 meters. ➢ Venus - brightest planet in the sky, has a thick, heavy atmosphere composed of 97 percent carbon dioxide, a surface of relatively subdued plains and inactive volcanic features, a surface atmospheric pressure 90 times that of Earth’s, and surface temperatures of 475° C (900° F) ◦ rotates in the opposite direction of the other planets (retrograde motion) at an agonizingly slow pace ◦ composition of the Venusian interior is probably similar to Earth’s. ◦ Venus’ weak magnetic field means its internal dynamics must be very different. Mantle convection is thought to operate on Venus, but the processes of plate tectonics, which recycle rigid lithosphere, do not appear to have contributed to the present Venusian topography ➢ Stellar evolution we can learn a great deal of information about the relationships among the sizes, colors, and temperatures of star ➢ Titan – Saturn’s Moon ◦ are the only satellites in the solar system known to have substantial atmospheres. ➢ Evidence for an expanding universe came from the study of red shifts in the spectra of galaxies. Edwin Hubble concluded that the observed red shifts, later called cosmological red shifts, were the result of the expansion of space. This evidence strongly supports the big bang model of an expanded universe. One question that remains is whether the universe will expand forever or gravitationally contract in the “big crunch ➢ Impact crater - Depressions that are the result of collisions with bodies such as asteroids and comets. ➢ Orion nebula - a well-known emission nebula that is bright enough to be seen by the naked eye ◦ It is located in the constellation Orion in the sword of the hunter. ➢ Chromosphere - The first layer of the solar atmosphere found directly above the photosphere ➢ H-R Diagram - Einar Hertzsprung and Henry Russell independently studied the relationship between the true brightness (absolute magnitude) of stars and their respective temperatures. Their work resulted in the development of a graph, called a Hertzsprung– Russell diagram (H-R diagram), that employs these intrinsic stellar properties. By studying H-R diagrams, ➢ Hipparchus (2nd century B.C.) - Probably the greatest of the early Greek astronomers ◦ best known for his star catalogue. ◦ determined the location of almost 850 stars, which he divided into six groups according to their brightness. (This system is still used today.) ◦ Measured the length of the year to within minutes of the modern value and developed a method for predicting the times of lunar eclipses to within a few hours ➢ Constellations – 5,000 years ago people began naming the configurations of stars, called constellations, in honor of mythological characters or great heroes. ◦ Today, 88 constellations are recognized that divide the sky into units ➢ Cosmologist - a scientist who studies the field of cosmology,which is the branch of astronomy and physicsthat focuses on understanding the largescalestructure, origin, evolution, and ultimate fate ofthe universe. ➢ Spectroscopy - Study of spectra ◦ Types of galaxies ▪ Spiral ▪ Elliptical ▪ Irregular ➢ The extremely narrow band of electromagnetic radiation we can see (which is labeled as visible light) is sometimes referred to as white light ◦ White light consists of an array ofwaves having various wavelengths, a fact easily demonstrated with a prism. ➢ Earth’s rotation can be measured in two ways, making two kinds of days. ◦ Mean solar day - timeinterval from one noon to the next,which averages about24 hours. ◦ Sidereal day - the time it takesfor Earth to make one complete rotation with respect to a star other than the Sun, a period of 23 hours, 56 minutes,and 4 seconds. ➢ Kuiper Belt - Named in honor of astronomer Gerald Kuiper, who predicted its existence, the ◦ hosts comets that orbit in the outer solar system, beyond Neptune. The face of the moon ➢ Jovian planet - The Jupiter-like planets: Jupiter, Saturn, Uranus, and Neptune. These planets have relatively low densities ◦ VS Terrestrial Planets are categorized by: ▪ Location ▪ Size ▪ Density ➢ Jovian vs Terrestrial Planet Atmosphere ▪ differ with temperature and gravity ➢ Ecliptic - The yearly path of the Sun plotted against the background of stars ➢ Galaxies – collections of interstellar matter, stars, and stellar remnants that are gravitationally bound ➢ Oort Cloud - Named for Dutch astronomer Jan Oort ◦ consists of comets that are distributed in all directions from the Sun, forming a spherical shell around the solar system ➢ Three Main types of Bright Nebulae ◦ Emission ◦ Reflection ◦ Planetary ➢ Two Types of Terrain of Lunar Surface ◦ Dark Lowlands or Maria - appeared smooth, resembling seas on Earth ▪ The Apollo 11 mission showed conclusively that the maria are exceedingly smooth plains composed of basaltic lavas. ▪ These vast plains are strongly concentrated on the side of the Moon facing Earth and cover about 16 percent of the lunar surface ◦ Highly Cratered Highlands or Terrae- resemble Earth’s ontinents, so the first observers dubbed them terrae (Latin for “land”). ▪ now generally referred to as the lunar highlands because they are elevated several kilometers above the maria. ▪ Rocks retrieved from the highlands are mainly breccias, pulverized by massive bombardment early in the Moon’s history. ◦ The arrangement of terrae and maria result in the legendary “face” of the “man in the moon ➢ Solar Prominence - a large, bright feature extending outward from the Sun's surface. ◦ anchored to the Sun's surface in the photosphere, and extend outwards into the Sun's hot outer atmosphere, called the corona. ➢ Solar Flare - brief outbursts that normally last an hour or so and appear as a sudden brightening of the region above a sunspot cluster.
