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The Dimensions Program Optical Interferometer Project Laboratory A Telescope Figure 1 Milky Way Galaxy Artist Concept, Courtesy of planetquest.jpl.nasa.gov Project Grant Team Prof. Kathryn Kozak Project Designer Coconino Community College Flagstaff, Arizona Patricia L. Hirschy Principal Investigator Asnuntuck Community College Enfield, Connecticut John S. Pazdar Program Director Asnuntuck Community College Enfield, Connecticut Prof. Mary Beth Orrange Project Tester Erie Community College Buffalo, New York Dennis C. Ebersole Principal Investigator Northampton Community College Bethlehem, Pennsylvania The Universe On a clear night, the sky becomes a portrait of brightly shining stars and beautiful azure hues. Fig 2 Image of Night Sky in Flagstaff, AZ Courtesy of Dan & Cindy Duriscoe, FDSC, Lowell Obs., USNO There are so many stars in the sky, and there could be planets surrounding these stars. A system that has a star and planets surrounding it is called a solar system. In order to find more solar systems, it is important to know what we can about the different stars that exist in the universe. One star we know a great deal about is our sun. Our sun has a diameter of 1,400,000 kilometers (km), its mass is 330,000 times that of the Earth, and it has a core temperature of 14,000,000 degrees Celsius. We also know a great deal about the planets in the solar system, the Milky Way Galaxy. Fig 3 Image of Sun, from NASA Goddard Space Flight Center Courtesy of NASA Optical Interferometer – Lab A - 2 Milky Way Galaxy In order to find more stars that can have solar systems around them, we need to find out information about stars and then if we can, information about the planets surrounding them. Fig 4 Milky Way Galaxy Planets Courtesy of photojournal.jpl.nasa.gov/index.html The following table lists different information about the Milky Way Galaxy planets. Table 1 Planet Diameter (in kilometers) Distance from Sun (in kilometers) Mass (in kilograms scientific notation) 4,878 57,910,000 3.30 X 1023 Venus 12,104 108,200,000 4.87 X 1024 Earth 12,756 149,600,000 5.98 X 1024 Mars 6,794 227,940,000 6.43 X 1023 Jupiter 142,984 778,330,000 1.90 X 1027 Saturn 120,536 1,426,940,000 5.69 X 1026 Uranus 51,118 2,870,990,000 8.69 X 1025 Neptune 49,528 4,497,070,000 1.02 X 1026 Mercury Optical Interferometer – Lab A - 3 Astronomy In order to know more about a star, we need astronomy. Astronomy is the study of stars, planets, galaxies, comets, gaseous clouds, the space between the galaxies, and any other celestial objects. Astronomers, the scientists that do astronomy, use telescopes to make images of celestial objects that are far away. Telescopes have been around for centuries and improvements have been made to allow the astronomers to see more detail of the stars and planets. Resolution How much detail an astronomer can see is called the resolution of the telescope. The more resolution then the more detail to the image. To gain resolution, astronomers make big telescopes with really big mirrors or lenses. Since this is expensive and hard to do, astronomers have developed a new type of telescope called an Optical Interferometer (Pronounced: In•ter•fer•om•e•ter). An Optical Interferometer is a type of telescope that is a collection of tubes and mirrors that brings light in from different locations and then combines the light into one image. The individual mirrors can be far apart and thus can increase the resolution of the telescope. This produces more detail that is required for a better image. Fig 5 The Center of Milky Way Galaxy Courtesy of NASA / JPL-CAL TEC. Spitzer Space Telescope * IRAC Spitzer Science Center/Caltech ssc2006-02a Optical Interferometer – Lab A - 4 The Dimensions Program Optical Interferometer Project Laboratory B Site Figure 1 State of Arizona, Courtesy myonlinemaps.com Project Grant Team Prof. Kathryn Kozak Project Designer Coconino Community College Flagstaff, Arizona Patricia L. Hirschy Principal Investigator Asnuntuck Community College Enfield, Connecticut John S. Pazdar Program Director Asnuntuck Community College Enfield, Connecticut Prof. Mary Beth Orrange Project Tester Erie Community College Buffalo, New York Dennis C. Ebersole Principal Investigator Northampton Community College Bethlehem, Pennsylvania Arizona The State of Arizona has 113,998 square miles, with a width of approximately 310 miles and length of approximately 400 miles. Its population is approximately 6,500,000 and is ranked as the 15th largest in the United States by population. Fig 2 State of Arizona Courtesy of University of Texas Library at Austin Flagstaff The City of Flagstaff, located in the center of the state, is close to a large flat tract of land called a mesa. It was on this tract of land that a joint venture between the US Naval Observatory, Naval Research Laboratory, and Lowell Observatory decided to build the Navy Prototype Optical Interferometer (NPOI). Optical Interferometer – Lab B - 2 Anderson Mesa To build an interferometer, first a suitable site must be found, such as a mesa. A mesa is an isolated hill having a level top with steeply sloping sides. One such mesa is The Anderson Mesa and is located 15 miles southeast of the City of Flagstaff. The NPOI is located on a piece of land that is approximately 375 meters by 375 meters and shown in the lower right quadrant in Figure 3 below. A flat site is desirable, so the cost of the supports that hold the NPOI can be held to a minimum. The supports go to the bedrock and range from 4 feet to just over 15 feet. Drilling much deeper would be too costly. Fig 3 Anderson Mesa Courtesy of Lowell.com. Optical Interferometer – Lab B - 3 Interferometer Site Once the site is picked then it is necessary to orient the NPOI taking advanced of the Anderson Mesa’s flat land. The NPOI doesn’t have a dome like normal telescopes, but three long spokes that are 120o degrees apart. To complete the interferometer two support facilities must built, a Control and Maintenance Building and a Tracking Optical Delay Paths and Beam Combining Building. The Tracking Optical Delay Paths and Beam Combining Building, located in the center of Figure 4, contains the necessary equipment to combine images from the three spokes. The major portion of the Tracking Optical Delay Paths and Beam Combining Building has a length of 13.5 meters, a width of 6.75 meters, and a height of 4 meters. The Control and Maintenance Building, located between the Tracking Optical Delay Paths and Beam Combining Building and the domed buildings in the lower left quadrant of the Figure 4, has a length of 16.5 meters, a width of 6.5 meters, and a height of 4 meters. Fig 4 Image of Naval Prototype Optical Interferometer, Lowell Observatory, Flagstaff, AZ Courtesy of Lowell Observatory, Flagstaff, AZ Optical Interferometer – Lab B - 4 The Dimensions Program Optical Interferometer Project Laboratory C Optical Interferometer Figure 1 Site map of the NPOI at Lowell Observatory’s Anderson Mesa facility, Flagstaff, AZ - Courtesy of Lowell Observatory Project Grant Team Prof. Kathryn Kozak Project Designer Coconino Community College Flagstaff, Arizona Patricia L. Hirschy Principal Investigator Asnuntuck Community College Enfield, Connecticut John S. Pazdar Program Director Asnuntuck Community College Enfield, Connecticut Prof. Mary Beth Orrange Project Tester Erie Community College Buffalo, New York Dennis C. Ebersole Principal Investigator Northampton Community College Bethlehem, Pennsylvania Building the Optical Interferometer An Optical Interferometer is an array, or arrangement, of mirrors that are placed along arms. The NPOI has three arms and each arm has three tubes that are kept under vacuum. Each arm of the NPOI has three 6-inch diameter tubes, with the longest being 250 meters long (see Figure 1 cover page for location). The NPOI collects light using two different methods, one for “Mapping a Celestial Object” using the Imaging Array and the other for “Mapping the Sky” using the Astrometric Array. Method One (Mapping a Celestial Object) One method is through Imaging Array Siderostat Stations that can be moved to different locations along an arm (see Figure 1 cover page for location). Because of the three tubes, there can actually be three Imaging Array Siderostat Stations on each arm. Mirrors located at each Imaging Array Siderostat Station collect light. The light is then directed down the tubes to the Tracking Optical Delay Paths and Beam Combining Building (see Figure 1 cover page for location). Fig 2 Imaging Array Siderostat Station being Installed on the Array, 1998. Courtesy of Lowell Observatory The reason for collecting at different locations along an arm is that it allows the astronomers to change the amount of resolution by moving the mirrors along the arms. They can also have three different mirrors collecting at one time on each arm, thus utilizing the telescope three times more in one night instead of just once. Each mirror is atop piers, which is 6 feet in diameter and sit on pads that have dimensions of 1 foot thick by 10 feet wide by 20 feet long. Fig 3 Vacuum Tubes along an Arm of the NPOI, Courtesy of Lowell Observatory Optical Interferometer – Lab C - 2 Long Fixed Path Optical Delay Vacuum Tubes (See Figure 1 cover page for location) Once light is collected using the mirrors, the light travels down the vacuum tubes to the combining building. If the mirrors are far apart, then the beams need to be aligned using the Long Fixed Path Optical Delay Vacuum Tubes. These tubes are 20 inches in diameter and 110 meters long. The tubes have mirrors in them that come up to reflect the light back at different intervals. This allows scientists to combine the light at the right time. Fig 4 Long Fixed Path Optical Delay Vacuum Tubes Courtesy of Lowell Observatory Fast Delay Lines Inside the Combining and Maintenance Building (see Figure 1 cover page for location), the light travels through Fast Delay Lines. These lines are 18 meters long and 20 inches in diameter. Fig 5 Fast Delay Lines Courtesy of Lowell Observatory At this point the light from all the mirrors is combined into the mapping of a “celestial object” image that is viewed from the Control and Maintenance Building. Optical Interferometer – Lab C - 3 Method Two (Mapping the Sky) The second method to collect light on the NPOI is through three Astrometric Array Siderostat Stations that are fixed on each arm (see Figure 1 cover page for location). These are used to help create accurate maps of the sky. This is mostly what the U.S. Naval Observatory is interested in, since part of its mission is to keep accurate maps of the sky for navigation purposes. These Astrometric Array Siderostat Stations are located inside Astrometric Huts that are 10 meters in length, 4.5 meters in width, and 2.5 meters in height. The light from these three stations is also directed along the Long Fixed Path Optical Delay Vacuum Tubes to the Tracking Optical Delay Paths and Beam Combining Building (see Figure 1 cover page for location). Fig 6 Three of four Astrometric Array Siderostat Stations located at fixed positions Courtesy of Lowell Observatory At this point the light from all the mirrors is combined into the mapping of a “sky” image that is viewed from the Control and Maintenance Building. Optical Interferometer – Lab C - 4 The Dimensions Program Optical Interferometer Project Laboratory D Light-Years Figure 1 Milky Way Galaxy Artist Concept, Courtesy of NASA/JPL-Caltech/R Hurt (SSC) Project Grant Team Prof. Kathryn Kozak Project Designer Coconino Community College Flagstaff, Arizona Patricia L. Hirschy Principal Investigator Asnuntuck Community College Enfield, Connecticut John S. Pazdar Program Director Asnuntuck Community College Enfield, Connecticut Prof. Mary Beth Orrange Project Tester Erie Community College Buffalo, New York Dennis C. Ebersole Principal Investigator Northampton Community College Bethlehem, Pennsylvania Light-Years Once the Optical Interferometer is built, astronomers can start to collect data. They collect many different types of data about stars, such as their distance from the Earth, the size of the star (usually measured in comparison to our sun), and the temperature of the star. To measure the distance from Earth, astronomers use a unit of measure called a “light-year”. A “light-year” is how far light can travel in one year. Since the speed of light in a vacuum is 3 X 108 meters per second, (300,000,000 meters per second) then it becomes possible to figure out how far light can travel in one year. One light-year is about 9.45 X 1015 meters (9,450,000,000,000,000 meters). Messier 81 The reason light-years are used, is because traveling at the speed of light in light-years would tell how many years it would take to get to that place. As an example, the galaxy Messier 81, Figure 2, which is a spiral galaxy like the Milky Way galaxy, is about 11,000,000 light-years from Earth and is about 50,000 light-years across. So if traveling at the speed of light, it would take 11,000,000 years to get from the Earth to Messier 81, and once there it would take 50,000 years to travel across it. Fig 2 Spiral Galaxy – Messier 81, Courtesy of NASA/JPL-Caltech/S. Willner (Harvard-Smithsonian Center for Astrophysics) Optical Interferometer – Lab D - 2 IM Pegasi There are many different types of star systems in the universe. One such type is called a binary star system. Binary stars make up many of the stars we see in the night sky. Binary stars are ones where there are two stars that rotate around a common center of mass. There is usually a brighter star, called the primary, and a weaker star, called the companion star. Fig 3 Binary Star IM Pegasi with an Artist’s Depiction of the Star System. Courtesy of NRAO/AUI and Ryan Ransom, York University; and NRAO/AUI The Binary Star IM Pegasi image in Figure 3 is an artist’s depiction of what a binary star system looks like. IM Pegasi is approximately 300 light-years from Earth. The primary star is about 13 times the size of the Sun and is know as a “Red Giant”. The companion star is roughly the same size as the sun and is called a “Dwarf Star”. Optical Interferometer – Lab D - 3 Zeta Orionis In 1998, a research team at Lowell Observatory, using the Optical Interferometer, found that the star Zeta Orionis was a double star, Figure 4. Zeta Orionis is the left most star in Orion’s belt in the constellation Orion. It is approximately 800 light-years from the Earth. The primary star has a diameter 20 times the size of Earth’s sun. Because of the increase resolution of the Optical Interferometer, this discovery was made. This is why the Optical Interferometer is so important to the advancement of astronomy. Fig 4 Image of Zeta Orionis, taken by the NPOI Courtesy of Lowell Observatory Mizar A and Mizar B Another binary system is the Mizar system in the Big Dipper, Figure 5. Mizar A and Mizar B are two stars that rotate around each other every thousands of years or so. It has been known that Mizar A is itself a binary system, and was imaged for the first time by the Optical Interferometer in 1996. The period of this system is 20 years. Mizar B has also been determined to be a binary system with a period of about 6 months. Mizar B has not been imaged yet. The whole system is 78 light-years from Earth. Fig 5 Image of Mizar A Courtesy of Lowell Observatory From telescopes, astronomers can find out many things about stars. In addition to the size and distance from the Earth, astronomers can also determine how bright they are, what they are made of, and approximately how much longer they will exist. When they do die out, astronomers can also tell how they die and what they will look like afterwards. Astronomy answers the question of what happens in the universe. An Optical Interferometer helps to figure out what is happing in the universe because of its increase resolution. So understanding what an Optical Interferometer is used for, how to build an Optical Interferometer, and then actually gathering data from it is helping to make new discoveries in astronomy, and thus learn more about the universe. Optical Interferometer – Lab D - 4