1. Chapter 18 – Studying Space Astronomy – The study of space, stars the visible universe. Year – The amount of time required for the Earth to orbit the sun once. Month – The amount of time required for the moon to orbit the Earth once. Derived from the old English word “moonth”. Day – The amount of time required for the Earth to rotate once on its axis.

2. Early Astronomers Ptolemy – Circa 140 C.E., developed the theory that placed the Earth at the center of the universe. Successful in that this belief persisted for over 1500 years and did accurately predict the motions of the planets. Nicholai Copernicus – Developed a new theory that placed the sun at the center of the universe (heliocentric) and had the Earth and other planets orbiting it. Tycho Brahe – Used a mural to get precise measurements of the planets orbits which helped future astronomers. Johannes Kepler – Demonstrated that the planets followed elliptical orbits and developed the three laws of planetary motion which are still in use by various space agencies today. Galileo Galelei – Invented and was the first to use a telescope to observe the moon and planets. Isaac Newton – His insights into gravitational forces explained how planets and moons are able to stay in their orbits. Edwin Hubble – Proved the existence of galaxies beyond ours.

3. Telescopes A device that collects and focuses electromagnetic radiation from objects in space making it observable. Optical Telescopes – The most common type of telescope it is designed to collect and focus visible light for close observation. Refracting Optical Telescope – The simplest type uses two lenses to magnify light. Cannot perfectly focus and their size is limited due to sagging of the glass lens. Reflecting Optical Telescope – Uses a mirror to gather light and reflects it to a lens eyepiece where it is magnified. Can gather more light, focuses a perfect image and can be made larger so this type is preferred by professional astronomers. Hubble Space Telescope – A reflecting telescope placed in orbit in 1980 to avoid atmospheric interference and can see very faint objects in space.

4. Electromagnetic Spectrum All of the wavelengths of electromagnetic radiation such as visible light, microwaves, radio waves etc. For visible light, the longest wavelength is the color red and the shortest is the color blue. The invisible part makes up most of the spectrum and the shorter wavelengths are blocked by the Earth’s atmosphere which acts as a protective shield. X-Ray wavelengths are completely blocked so to observe them, x- ray telescopes are placed in orbit to detect them.

5. Nonoptical Telescopes Detect nonvisible radiation. Radio Telescopes – Detect radio waves and can be used anytime. V.L.A. – The very large array is composed of 27 radio telescopes linked by computer. Chandra X-Ray telescope – Placed in space. Infrared and gamma ray telescopes detect much more sensitive information.

6. Mapping the Stars Constellation – A pattern of stars in the sky, many of which were given Greek names. Astrolabe – An instrument used to describe the location of a star. Zenith – An imaginary point directly above any observer. Horizon – The point where the sky and the Earth appear to meet. Altitude – the angle formed between an object and the horizon. Celestial Sphere – An imaginary sphere surrounding the Earth used as a reference guide for scientists to map the sky. Ascension – How far an object is from the Vernal Equinox, the point where the sun rises on the first day of spring, and measures East and West. Declination – Measures North and South from the celestial equator.

7. Circumpolar stars – Stars near the poles that can be seen all year long and all night long. Light Year – The distance light will travel in a vacuum in one Earth year approx. 6 trillion miles or 9 trillion km. Stars are much farther away than the planets and require another more useful scale than miles or kilometers. Scientists have observed that the universe is expanding and the visible light from other galaxies is shifted into red wavelengths. This was confirmed by the Hubble Space Telescope’s observations of distant stars.

8. Doppler Shift Red Shift – The apparent change in color towards the red end of the spectrum that occurs when an object is moving quickly away from an observer. Blue Shift – The apparent change in color towards the blue end of the spectrum that occurs when an object is moving quickly towards an observer.