Title: Radio Astronomy and the NRAO
1Radio Astronomy and the NRAO
- Phil Jewell
- Assistant Director for Green Bank Operations
- National Radio Astronomy Observatory
VIP Visit to Green Bank 8 May 2004
2Presentation Overview
- What is Radio Astronomy?
- What is the National Radio Astronomy Observatory?
- What are the differences between single dishes
and Interferometers? - What makes Green Bank and the GBT special?
3What is Radio Astronomy?
- Radio waves are part of the electromagnetic
spectrum, along with the infrared, visible light,
ultraviolet, x-rays, and gamma rays. - Radio astronomy studies cosmic electromagnetic
emission from about 10 MHz to 1000 GHz
(wavelengths from about 30 meters to 0.3 mm.)
From Living with a Star NASA/UCB
4What can we do with Radio Astronomy?
- Radio waves have lower energy than light waves,
x-rays, etc. Whereas light waves come from very
hot objects such as stars, radio waves usually
come from cooler objects. Astronomers use the
whole electromagnetic spectrum to probe the
universe. - Because radio waves have long wavelengths, they
pass through dust that obscure light waves. This
allows radio astronomers to probe to the heart of
star forming regions, to disks around the nuclei
of galaxies, and possibly to the event horizons
of black holes.
5What sorts of things do Radio Astronomers Observe?
- Solar System objects
- The Sun, planets, asteroids, and comets
- From their own emission, or in some cases, from
radar echoes - The structure of the Milky Way and other
galaxies. - Can trace the gas and dust through the emission
of atomic and molecular spectral lines - The star formation process
- Can use molecular spectral line and dust emission
to trace the collapse of interstellar clouds - Neutron stars
- Extremely dense, collapsed stars that are
rotating as fast as 1000 times a second. - An incredible laboratory for basic physics that
cannot be replicated on Earth.
6What sorts of things do Radio Astronomers
Observe? contd
- Black hole physics
- Incredible energy engines in the nuclei of
galaxies and quasars - The origin and structure of the universe and
galaxies within it - Astrochemistry
- Almost 130 molecules some quite complex -- are
known in the interstellar medium - Some are of biological significance and may be a
key to the formation of life on the early Earth
7What is the National Radio Astronomy Observatory?
- Since 1956, the NRAO has been the premier radio
astronomy observatory in the U.S. - Its primary mission is to operate and develop
unique radio astronomical telescopes and related
instruments for use by researchers at
universities and institutes in the U.S. and
around the world. - The NRAO is headquartered in Charlottesville,
Virginia and presently operates three main
instruments - The Robert C. Byrd Green Bank Telescope (GBT)
- Green Bank, West Virginia
- The Very Large Array (VLA)
- Near Socorro, New Mexico
- The Very Long Baseline Array (VLBA)
- 10 telescopes in an array from St. Croix, US
Virgin Islands to Mauna Kea, Hawaii - The NRAO is also in charge of the North American
contribution to the construction and operation of
the Atacama Large Millimeter Array (ALMA), an
international project being built in Chile. - The ALMA North American Science Center will be in
Charlottesville.
8The Robert C. Byrd Green Bank Telescope
9The Very Large Array
27, 25-meter diameter telescopes located on the
Plains of San Augustin near Socorro, New
Mexico. EVLA expansion project underway which
will give x10 improvement in sensitivity.
10The Very Long Baseline Array (VLBA)
10, 25-meter diameter telescopes for ultra-high
angular resolution
11Atacama Large Millimeter Array
64, 12-meter diameter dishes for millimeter and
sub-millimeter- wave imaging, presently under
construction in Chile.
12NRAO Headquarters FacilitiesCharlottesville,
Virginia
HQ NA ALMA Science Center (Edgemont Road on UVa
Campus)
NRAO Technology Center (Ivy Road)
13Interferometers and Single Dishes
- Radio Astronomy telescopes come in two basic
flavors, single dishes and and arrays of dishes,
known as interferometers
14Interferometers
- Interferometers arrays of antennas that work
together -- provide - very high angular resolution
- imaging through earth rotation synthesis
- Their angular resolution is set by the farthest
distance between antennas - Modern interferometers have extraordinary high
resolution imaging capability. Examples - NRAO Very Large Array -gt EVLA
- NRAO Very Long Baseline Array
- Atacama Large Millimeter Array (ALMA)
15Single Dishes
- Single dishes are limited in their angular
resolution by the size of the dish, but - They are very sensitive to large scale emission
that may be missed by interferometers, and - They have very high sensitivity to weak, extended
emission - In addition, they allow
- Easy use of innovative instrumentation
- Comparatively easy to build an instrument for one
dish rather than 27 or 64 - So single dishes and interferometers provide
complementary information and capabilities, which
is why the NRAO has both types of telescope.
16Single Dishes and Interferometers -- Sensitivity
to Structures on Different Angular Scales
- Example
- The large scale structure of the GBT image of the
Omega Nebula (M17) would not be detected by most
interferometers. - And conversely, an interferometer might be able
to image a tiny site of star formation in this
cloud that would be seen only as a point by a
single dish.
17Why is there an observatory in Green Bank?
- The National Radio Astronomy Observatory was
founded in 1956 - Green Bank was the first site of the Observatory
and served as its first headquarters until 1967
when it was moved to Charlottesville. - Green Bank was chosen for its sheltered location
and natural protection from radio frequency
interference, yet proximity to the population
centers on the east coast. - In the late 1950s, the region around Green Bank
was given special protection by the Federal
Communications Commission and became the National
Radio Quiet Zone.
18National Radio Quiet Zone
Owing to the sensitivity of radio astronomy
observations, the NRQZ is critical to the
continued success of radio astronomy in Green
Bank, and the GBT in particular.
19The story of the GBT The 300 Foot
20The 300 Foot in collapse Nov. 1988
21What makes the GBT special?
- Size
- Unblocked main aperture
- Precision Control System
- Active Surface
- Sensing systems
- Frequency coverage
- National Radio Quiet Zone location
22GBT Size
- Largest fully-steerable telescope in the world
- At 16.7 Million Pounds (7600 metric tons),
probably the largest moving structure on land. - Despite size and mass, built to extremely high
precision - Why is the GBT so big? Sensitivity
23Conventional optics with symmetric (blocked) feed
supports
Effelsberg 100 m Telescope
NRAO 140 Foot Telescope
24Unblocked aperture
- 100 x 110 m section of a parent parabola 208 m in
diameter - Cantilevered feed arm is at focus of the parent
parabola
25GBT Pointing and Surface Compensation Systems
- To overcome distortions in its reflecting surface
that result from gravity and thermal changes, the
GBT is equipped with a fully active surface
(motor actuated, computer controlled) - Various temperature and position sensing systems
and computer models will be used to point the
telescope and command the surface actuators - Ultimately, this will allow the GBT to work to
115 GHz or 2.6 mm wavelength
26GBT active surface system
- Surface has 2004 panels
- average panel rms 68 ?m
- 2209 precision actuators
27Surface Panel Actuators
- One of 2209 actuators.
- Actuators are located under each set of surface
panel corners
- Actuator Control Room
- 26,508 control and supply wires terminated in
this room
28Discrete HI Clouds in the Galactic Halo
Artists rendition of the Milky Way with
actual GBT data in the inset Lockman (2002).
29Continuum Images of the Rosette Nebula
Ghigo Maddalena (2003)
30GBT / Arecibo radar image of the Moon
B. Campbell et al. (2004)
31(No Transcript)