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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