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Astronomy Unit 2 Telescopes Celestial Spheres/Constellations Apparent Motion of the Stars Motion of the Planets Telescopes Vocab Words for this section are: – – – – Reflecting Telescope Refracting Telescope Radio Telescope Space Telescope Telescopes Hans Lippershey was the inventor of the telescope in 1608. Galileo was the first to use a telescope to study the sky in 1609. The invention and use of the telescope began a huge number of discoveries in the field of astronomy. Telescopes 3 types of telescopes – Optical Telescopes study visible light. Reflecting telescopes use mirrors to bounce light from an objective lens to an eyepiece lens Refracting telescopes use lens to bend light and magnify images coming through an objective lens. – Radio Telescopes study radio waves from earth. – Space Telescopes travel out of Earth’s atmosphere to study the other types of radiation not visible to the naked eye, and the radiation that cannot make it through earth’s protective atmosphere. Telescopes Optical Telescopes study the visible light section of the electromagnetic spectrum. They uses mirrors and/or lenses to magnify the light. Telescopes One type of Optical Telescope is the Reflecting Telescope – Within this telescope there are mirrors to bounce the light traveling through. Telescopes Another type of Optical telescopes is the Refracting Telescope – Within this telescope there are lenses to bend the light traveling through. Telescopes Radio Telescopes use a parabolic antenna and a receiver to study radio waves. – Radio Waves are a type of radiation that is not normally visible to the naked eye. Telescopes Space telescopes travel out of earth’s atmosphere to study all different types of radiation that can not make it through earth’s atmosphere. – Examples are the Hubble Space Telescope and the Chandra Space Telescopes Celestial Sphere/Constellations Vocab words for this section are: – – – – – – – – – Celestial Sphere Declination Right Ascension Constellation Circumpolar Constellation North Circumpolar Constellation South Circumpolar Constellation Zodiac Ecliptic Celestial Sphere/Constellations A celestial sphere is similar to a globe of the sky. – It is an imaginary sphere where the sun, the moon, and all the other stars appear to be combined. Celestial Sphere/Constellations To locate on the celestial sphere, you use declination and right ascension. – Declination measures angular distance North or South of the celestial equator Between 0 and 90 degrees – Right Ascension measures distances eastward, along the celestial equator from the vernal equinox Goes up to 360 degrees Celestial Sphere/Constellations The 88 recognized constellations by the International Astronomical Union are plotted on the Celestial Sphere. Some constellations are close enough to a celestial pole that they are visible in certain locations on earth all year long. These constellations are called Circumpolar Constellations. Celestial Sphere/Constellations Constellations close to the N. Celestial Pole are North Circumpolar Constellations – They are visible from the North Pole all year long! Constellations close to the S. Celestial Pole are South Circumpolar Constellations. – They are visible from the South Pole all year long! Celestial Sphere/Constellations These are the North Circumpolar Constellations Celestial Sphere/Constellations These are the South Circumpolar Constellations Celestial Sphere/Constellations The ecliptic is the apparent path the sun traces out in the sky throughout the year. – It is visible on the celestial sphere! Along the ecliptic there is a band of 12 constellations. They are called the zodiac constellations – These are where astrological signs come from. The constellation that rises and sets during the month of your birthday is supposedly your “sign.” Celestial Sphere/Constellations The 12 constellations of the zodiac are: Apparent Motion of the Stars Vocab Words for this section are: – – – – Constellation Circumpolar Constellation Diurnal Circles Parallax Apparent Motion of the Stars We have previously discussed circumpolar constellations. – This concept deals with how stars appear to move throughout the year. Apparent Motion of the Stars If you trace the path a star makes each day, it would trace out a Diurnal Circle. – This the circular path a star appears to take each day. We can’t see stars during the daytime because of the sun, so we don’t actually see the circle. Apparent Motion of the Stars Diurnal Circles Apparent Motion of the Stars Stars also display parallax. – Parallax is the apparent movement of an object due a change in the viewer’s position. – You can try it with your finger. Hold your finger in front of your face. Close your left and view your finger from your right eye. Quickly switch eyes. Go back and forth a few times. Your finger should appear to move even though it isn’t actually moving. As the earth moves around the sun, it changes our viewing position of stars. This causes them to display parallax! Apparent Motion of the Stars We use a stars parallax (or apparent shift) relative to “fixed” background stars, to determine the distance to stars. Stars that are further away display less of a parallax, than stars that are close to us. Motion of the Planets Vocab Words for this section are: – – – – – – Sidereal Motion Prograde Retrograde Kepler’s 1st Law of Planetary Motion Kepler’s 2nd Law of Planetary Motion Ellipse Motion of the Planets A sidereal day actually takes 23 hours, 56 minutes and 4.09 seconds – This is the amount of time it takes the earth to get back to the same location it was at previously. – We don’t use this as a day because the earth not only rotates, but it moves a little bit around the sun in its revolution during each rotation. This is where we get the 24 hour day from. Motion of the Planets As we watch planets move across the sky, they move relative to their background “fixed” stars. – Planets normally move westward across the night sky. This is called Prograde motion. – Sometimes planets appear to begin moving “backward” or eastward across the night sky. This is called Retrograde motion. Please not that if you look these words up, the directions will be backwards because Astronomers pretend like you are living on the planet looking out. For our purposes we define the word as how it looks in the night sky! Motion of the Planets The planets don’t actually switch directions. – What is happening is our orbits around the sun (the earth’s and whichever planet we are looking at) are catching up with each other. – This makes the planet appear to move backwards for a small portion of time. See the animation at the following website to help you understand prograde vs. retrograde motion: Prograde vs. Retrograde Motion Motion of the Planets Johannes Kepler developed 3 laws for how the planets move around the sun. He did this after making detailed studies and observations as to how the planets are moving. – We are going to study the first 2! These laws don’t only apply to planets, but they also apply to how moons orbit their parent planets! Motion of the Planets Kepler’s First Law of Planetary Motion Planets follow elliptical orbits, with the Sun at one focus of the ellipse. Motion of the Planets The planets move around the sun in an elliptical shape with the sun at one of the foci. – An ellipse appears as a squashed circle. It is defined as a closed loop where the sum of the distances from 2 points (the foci) to every point on the line is constant. Motion of the Planets This means there are times throughout the year where the earth is closer and further from the sun. – The earth is actually closer to the sun in December, our winter! It is about 147,450,000 km from the sun – The earth is further from the sun in June, our summer! It is about 152,400,000 km from the sun Motion of the Planets Kepler’s 2nd Law of Planetary Motion As a planet moves in its orbit, it sweeps out an equal amount of area in an equal amount of time. Motion of the Planets Kepler’s 2nd Law implies that when a satellite is closer to its parent object, it actually travels faster than when it is further away! – When we are closer to the sun we travel slightly faster than when we are further away. – This is due to the gravitational pull the parent object has on the satellite. The pull the sun has on the earth – On average the earth travels at 29.78 km/s Motion of the Planets Kepler’s Laws apply to ALL the planets that orbit the sun. Kepler’s Laws also apply to how every moon orbits its parent planet!