The birthplace of planetary radio astronomy: The Seneca, Maryland observatory 50 years after Burke and Franklin's Jupiter radio emission discovery. Leonard N. Garcia1, James R. Thieman2, Chuck A. Higgins3 1QSS Group Inc., NASA/GSFC Code 630, Greenbelt,

1
The birthplace of planetary radio astronomyThe
Seneca, Maryland observatory 50 yearsafter Burke
and Franklin's Jupiter radio emission
discovery.Leonard N. Garcia1, James R. Thieman2,
Chuck A. Higgins31QSS Group Inc., NASA/GSFC Code
630, Greenbelt, MD 20771, 2NASA/GSFC, 3Middle
Tennessee State University, Murfreesboro, TN
37132.

The Mills Cross Array
The array was based on the design of Mills and
Little and used phase-switch receivers based on
the design of Ryle. The array consisted of two
linear arrays of 66 dipoles spanning 2047 feet
arranged to form a slightly flattened X. The
array operated at 22 MHz. Half-power beam width
was 1.6 x 2.4 degrees. The addition of extra
cables allowed the beam to be moved in
declination.
Abstract Burke and Franklin's discovery of radio
emissions from Jupiter in 1955 effectively marked
the birth of the field of planetary radio
astronomy. The discovery was made near Seneca,
Maryland using the Department of Terrestrial
Magnetism/Carnegie Institution of Washington's
(DTM/CIW) Mills Cross Array. Fifty years later
little evidence of this 96-acre X-shaped array of
dipoles remains. The site, now known as the
McKee-Beshers Wildlife Management Area, is owned
by the State of Maryland Department of Natural
Resources. Radio Jove (http//radiojove.gsfc.nasa.
gov), a NASA/GSFC education and public outreach
project, will recognize the 50th anniversary of
this discovery through an historic reenactment
using the Radio Jove receiver and dual-dipole
array system. We describe some results of our
search through the DTM/CIW archives, our visit to
the site to look for evidence of this array, and
other efforts at commemorating this anniversary.
The Discovery and Announcement

A view along one end of the array. The receivers
were housed in an army surplus truck visible in
the distance. Undated photo about 1954. Courtesy
of the Archives of the Carnegie Institution of
Washington.
The Department of Terrestrial Magnetism of the
Carnegie Institution of Washington (DTM/CIW)
initiated a 22 MHz sky survey using the Mills
Cross array. Acting as a transit instrument, the
array swept through a relatively narrow range of
declinations over several weeks and was then
shifted by about 1 degree in declination by the
addition of phasing cables. In the first 3 months
of 1955, DTM scientists Bernard Burke and Kenneth
Franklin were testing the array and mapping the
northern sky, progressively moving the beam to
more southerly declinations. During their survey
they detected intermittent bursts of interference
obscuring an unknown extended source in 9 out of
31 records. In Franklins account of the
discovery, they originally attributed this
interference to a farmhand driving home from a
date late at night Franklin, 1959. The extended
radio source at RA7h 30m and Dec.22 degrees
was being studied as part of a presentation for
the 92nd AAS meeting in April 1955. Initially,
data with the obscuring interference was not
included in their study. When these data were
included they recognized that the interference
occurred at almost the same sidereal time.
Further analysis showed that over several months
this interference drifted slightly in sidereal
time. In March 1955, they traced the RA of the
antenna beam when the interference was received
and compared it against the RA of several
celestial objects. Only Jupiter matched both the
RA of the beam position and its drift. Had the
data containing the interference not been
included during the search for the unknown
extended source they might never have made this
discovery. Had they been mapping towards more
northerly declinations, Jupiter would have
quickly drifted out of the beam. As it was they
were inadvertently tracking Jupiter. A search of
earlier data using other antennas at the Seneca
site found that Jupiter had been detected but not
recognized in 1954 during observations of an
occultation of the Crab Nebula by the solar
corona. Confirmation of their discovery came from
Australian C.A. Shain of the CSIRO who went back
through 18 MHz observations made in 1950 and 1951
and found several instances of Jupiter data not
recognized at the time.
An aerial view facing West of the Mills Cross and
surroundings. The location of the array is
indicated. The Y-shaped line of trees below
center and the trail running right-left in the
foreground assisted us later in identifying the
former location of the array. Courtesy of the
Archives of the Carnegie Institution of
Washington.
2047 feet long, 66 dipoles

Where was the Seneca Observatory?
This map with handwritten notes marks the
location of antennas on the farm leased from Mr.
Brockett Muir. The notes were made by Merle
Tuve, director of the Department of Terrestrial
Magnetism. (Dated 1956 and courtesy of the
Archives of the Carnegie Institution of
Washington.)
Comparison with current maps show that this
property is now part of the McKee-Beshers
Wildlife Management Area, about 20 miles
northwest of Washington D.C., south of River Road
along the northern shore of the Potomac River and
north of Tenfoot Island.
Leonard Garcia (Leonard.Garcia_at_gsfc.nasa.gov)
with a copy of the map overlaid on an aerial
photo of the site. Jim Thieman
(left) (James.R.Thieman_at_nasa.gov) and Chuck
Higgins (right) (Higgins_at_physics.mtsu.edu) looking
for artifacts at the McKee- Beshers Wildlife
Management Area Bill Pine, Leonard
Garcia, Max Kepler,and Jay Friedlander exploring
the discovery site.
The discovery by Burke and Franklin (1955) of
radio emissions from Jupiter has opened a new
field of radio astronomy - John D. Kraus, AJ,
61, 182, 1956.
The Site Visit August, 2004
Press Coverage
The Washington Post and Times Herald April 7, 1955
The Washington Star April 7, 1955
The New York Times April 6, 1955
The New York Times April 10, 1955
We gratefully acknowledge the assistance of
Shaun Hardy, archivist at the Carnegie
Institution of Washington. We also acknowledge
Jim Gass, Jay Friedlander and Steve Kortenkamp
for their help in the archival research. Burke,
B. F. and Franklin, K.L., Observations of a
variable radio source associated with the planet
Jupiter, JGR, 60, 213-217, 1955. Franklin, K.L.
An account of the discovery of Jupiter as a radio
source, AJ , 64, 37-39, 1959. Franklin, K.L., The
discovery of Jupiter bursts, in Serendipitous
discoveries in radio astronomy, editors
Kellermann and Sheets, pp. 252-257, 1983.
Acknowledgements and References
The Historic Marker
In recognition of the 50th anniversary of
the discovery of Jupiters radio emissions, the
Maryland Historical Trust will erect a roadside
historic marker along River Road near the former
Seneca Observatory. The marker will read
PLANETARY RADIO EMISSIONS DISCOVERY SITE   IN
1955 SCIENTISTS BERNARD BURKE AND KENNETH
FRANKLIN FROM THE CARNEGIE INSTITUTION OF
WASHINGTON ACCIDENTALLY DISCOVERED
NATURALLY-GENERATED RADIO WAVES FROM JUPITER
USING A 96-ACRE ANTENNA ARRAY. THIS DISCOVERY
LED TO GREATER UNDERSTANDING OF PLANETARY
MAGNETIC FIELDS AND PLASMAS AND OPENED A NEW
WINDOW IN OUR EXPLORATION OF THE SOLAR SYSTEM.
Comparison of the map with current and past
aerial photos (note the trail and Y-shaped line
of trees ) provided clues on where the Mills
Cross array had been 50 years ago Our estimate
for the Mills Cross array location is
indicated. (Lat 39.078064,Long 77.393771)
Courtesy Terraserver web site.