Astronomy 1010 Planetary Astronomy Fall_2015 Day-17 Course Announcements Dark Sky nights Mon. 10/5 & Wed. 10/7 starting at 7:30pm at the Observatory. Exam-2 will be Friday, Oct. 9 SW-chapter 4 posted: due Mon. Oct. 5 SW-chapter 5 posted: due Fri. Oct. 9 Definitions & Terms -1 Light: The primary source of information in astronomy for all objects. When we say light we are talking about everything from gamma-rays to radio-waves. This does NOT include gravity waves. Tides can affect the solid part of Earth, too. A gravitational pull can stretch and deform a solid body. Results in friction, which generates heat. Friction also opposes the rotation of Earth, causing Earth to very gradually slow its rotation. Days lengthen by about seconds every century. Earths mass is large compared to the Moons, so tidal forces on the Moon are strong. Moons rotation and orbital period are locked: tidal locking. This means the Moons rotation period equals its orbital period. Because of tides, Earth is not a perfect sphere. Earths leading edge creates an acceleration on the Moon in its orbit, resulting in a bigger orbit. The lunar month increases by seconds per century. Gravitational objects create Roche limits within which the effects from their tidal forces can destabilize other objects. Planets, stars, and galaxies can be affected. Galaxies can be distorted with tidal tails. Moons of planets can have great internal activity because of tides, perhaps allowing for conditions for life. In order to leave a planets surface, an object must achieve a velocity greater than the planets escape velocity. Therefore, Earths escape velocity is MATH TOOLS 4.3 The net tidal force is the difference in force on the two sides of the planet. The Moons tidal forces on Earth are 2.2 times as strong as the Suns tidal forces on Earth, resulting in greater lunar tides than solar tides. MATH TOOLS 4.4 Almost all knowledge of the universe beyond Earth comes from light. Light can tell us about objects in space: temperature, composition, speeds, and more. Light moves at 300,000 km/s in a vacuum. First measured by Rmer when observing Jupiters moons. Speed is slower in other materials, e.g., glass. Light is a wave of combined electricity and magnetism, called an electromagnetic wave. Changing electric and magnetic fields create a self-sustaining electromagnetic wave. Wavelength ( ): length between crests. Amplitude: height. Frequency (f): number of waves that pass by each second. Period (P): time to complete one cycle. A long wavelength means low frequency. A short wavelength means high frequency. The speed of light, c, is constant. Visible spectrum: small range of wavelengths that humans can see. Red light = longest wavelength ( ~ 750 nm). Violet light = shortest wavelength ( ~ 380 nm). Roy G. Biv. Visible light is just one small part of the electromagnetic spectrum: Gamma rays X-rays UV Visible IR Microwave Radio increasing increasing f decreasing Lecture Tutorial EM Spectrum: (pg. 47) Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on. If you get stuck or are not sure of your answer, ask another group. i_Clicker Question Light & Spectra: EM Spectrum Parameters Light & Spectra: Number Line: EM Spectrum: Option-2