History: All ancient cultures observed the cycles of the sky. Ex. Stonehenge. Astronomical Cycles Many astronomical events repeat in regular cycles (ex. Phases of the moon). The repetition of cycles help us understand them. Some cycles have been useful - timing of seasons, migration of animals - these were astronomy’s practical contributions. Celestial Sphere The stars in space are in different directions and at different distances - space is 3-dimensional. However, stars are so far from Earth t

Every ancient culture observed the night sky and tried to understand it. Ancient Greek astronomers established the foundation of modern astronomy. Studying the sky systematically. Using logic (as in their philosophy). Using geometry (that they invented). Created the foundation of the Scientific Method that we still use. What is Earth’s Shape? Earth looks flat to us. Aristotle argued that Earth is a really huge sphere. The part we see is so small that it looks flat. His evidence included: During

Inertia Galileo developed the idea of inertia. Newton used it as his 1st law of motion. Net force = The sum of all forces pulling in various directions. If the net force = 0, inertia is constant. A body that is not moving will remain motionless = constant velocity. A moving body’s motion will remain constant at the same speed and in the same direction = constant velocity. Speed and Velocity Speed is a change of position in some amount of time, such as m/s or km/h. Velocity is a speed in a partic

Astronomical Information To understand objects beyond Earth, we need information from those objects. Meteorites. Moon rocks. Cosmic rays. Very little information on all these 3. Learning from Light We study the properties of light on Earth to understand the light from beyond Earth. Newton discovered white light is the mixture of all colors. Sorting white light into the different colors produces the spectrum of light. Studying the spectrum of light is how we learn light’s information. Properties

Telescopes Galileo made the first astronomical telescope in 1609 revolutionary impact back then. Telescopes are still being improved today. 10 largest telescopes have all been built since 1993. Much larger telescopes are being built today. We can also send telescopes into space and to objects in the solar system. Seeing Light We see by the light that enters the pupil of our eye. Pupil is a circle with an area = πR2pupil. Our pupil’s maximum diameter is about 8 mm when it expands - “adapts” to

Earth Characteristics Earth as a Planet We know a tremendous amount about Earth - the study of geology. Earth is also the closest planet to us. We use Earth’s general properties, structures, and physical processes as a guide to understanding the other planets of the solar system. Earth’s Shape In Chapter 2 we learned: Aristotle noted evidence that Earth is a sphere. Eratosthenes measured Earth’s radius. However, Newton’s laws of motion and gravity (Chapter 3) show that the spinning Earth is not

The Moon's Characteristics Moon’s Basic Properties We have already learned the methods to find some of the Moon’s basic properties: The Moon’s distance from Earth is found using the method of parallax (Ch 2) = 384,400 km. The Moon’s diameter is found from its distance and angular diameter. Because the Moon’s mass is only 0.012 MEarth, its gravity is weak and its escape velocity is low (Ch 3). Therefore it cannot hold an atmosphere. Therefore it has no erosion from wind or rain. Moon’s Surface B

Strategy to Observe Other Solar Systems Our solar system extends to about 100,000 AU 20 X 1012 from the Sun. Any further, we would be closer to another star. Our solar system contains planets, dwarf planets, many moons, asteroids, and comets. However, there are systematics to our solar system that help us understand how it and other solar systems formed. Components of the Solar System Sun is the heart of the solar system It is much more massive than the sum of all the other members of the sola

Mercury Mercury is hard to study from Earth because: It is the planet nearest to the Sun, so the sunlight makes it hard to observe. It is the smallest major planet. It does not have a moon. Therefore, it was not until we sent a satellites to Mercury that we started to learn about it. Mercury’s Mass and Radius Mercury’s radius can be measured from Earth using its angular size and distance (Ch 2) although its small size limits the accuracy 2440 km. Finally in 1974 our Mariner 10 space probe me

Jupiter Is the largest and most massive planet in our solar system. Radius is derived from angular size and distance. 11 times the radius of the earth, the we know the volume and it can hold 1400 Earths. Mass measured from the orbits of its many moons M 4π2 d3/ p2 Average density 1.33 gm/cm3, just slightly more than water. This tells us that it is mostly hydrogen. Rotation takes only 9.9 hours even though it is so large very high speed causes Jupiter to have a bulging equator. Jupiter’s

Goals: Survey orbitals and pp, of small bodies in the solar system, meteor, meteors and meteorites Asteroids minor planets Comets Pluto Dwarf planets plutoids Meteoroids and Meteors Meteoroids are objects orbiting the Sun that are too small to observe. Sizes are from about 1 m down to less than 1 mm. Speeds are >= 10 km/s and faster, much faster than a bullet. When they hit Earth the friction with our atmosphere heats and vaporizes them, creating a meteor “shooting star” alerting us to thei