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J-1 (Japanese rocket)
J-2 (American rocket engine)
Jacobi, Karl Gustav Jacob (1804–1851)
Jacquard, Joseph Marie (1752–1834)
Jacob, François (1920–2013)
jade
James, William (1842–1910)
James Clerk Maxwell Telescope
James Webb Space Telescope
jansky (unit)
Jansky, Karl Guthe (1905–1950)
Janssen, (Pierre) Jules César (1824–1907)
Janus
JAPAN IN SPACE
Japanese launch vehicles
Japanese satellite names
JAPANESE SPACECRAFT
JAS (Japanese Amateur Satellite)
Jason (satellite series)
jasper
Jastrow, Robert (1925–2008)
jaundice
jaw
JAWSAT
Jeans, James Hopwood (1877–1946)
Jeans length
Jeans-Jeffreys tidal hypothesis
Jeep
Jefferson, Thomas (1743–1826)
Jeffreys, Harold (1891–1989)
jejunum
jellyfish
Jemison, Mae C. (1956–)
Jenner, Edward (1749–1823)
JERS (Japanese Earth Resources Satellite)
jet (astrophysical)
jet engine
Jet Propulsion Laboratory (JPL)
jet stream
jetavator
Jewel Box (NGC 4755)
Jikiken
Jilin meteorite
JIMO
Jindai (aka MABES)
Jiuquan Satellite Lunch Center
Jodrell Bank Observatory
John C. Stennis Space Center
John F. Kennedy Space Center
John H. Glenn Research Center at Lewis Field
Johnson, Clarence L. (Kelly) (1910–1990)
Johnson solid
Johnson Space Center
Johnsville Centrifuge
joint (anatomy)
joint (geology)
Joint Astronomy Centre
joint stability
jökulhlaup
Joliot-Curie, Irène (1897–1956)
Jordan, (Marie-Ennemond) Camille (1838–1922)
Josephson, Brian David (1940–1995)
joule (unit)
Joule, James Prescott (1818–1889)
Joule's laws
Joule-Thomson effect
Jovian
Joy, Alfred Harrison (1883–1973)
JPL
jugular foramen
jugular vein
Julia set
Julian calendar
Julian date
Julian epoch
Juliet
Jung, Carl Gustav (1875–1961)
Juno (asteroid)
Juno (rocket)
Jupiter
Jupiter (rocket)
Jupiter Icy Moons Orbiter (JIMO)
Jupiter-type comet
Jurassic period
juvenile hormone