January 7 

7 January 1610

Galileo's observations of the moons of Jupiter in Sidereus Nuncius (1610). Credit: History of Science Collections, University of Oklahoma Libraries

On January 7, 1610, Galileo Galilei (1564–1642) discovered the four moons of Jupiter, now called the Galilean satellites – Io, Europa (that day Io and Europa were seen as a single point of light, they were seen as separate bodies the following night), Ganymede and Callisto. By January 15, Galileo concluded that the stars were actually bodies orbiting Jupiter. The discovery was announced in the Sidereus Nuncius ("Starry Messenger"), published in Venice in March 1610. The moons were the first celestial objects that were confirmed to orbit an object other than the Sun or Earth.

 

   Galileo named his discovery the Medicean Stars, in honour of Medici brothers (the ruling dynasty in Florence), but the names that eventually prevailed were chosen by Simon Marius (1573–1625), who had discovered the moons independently at about the same time as Galileo. At the suggestion of Johannes Kepler (1571–1630), he named them after four lovers of the god Zeus (the Greek equivalent of Jupiter) in his Mundus Jovialis (1614). 

 

   The Galilean moons are, in increasing order of distance from Jupiter: Io (3643 km in diameter), Europa (3121 km), Ganymede (5268 km in diameter – the largest moon in the Solar System) and Callisto (4820 km). The three inner moons — Io, Europa, and Ganymede — are in a 4:2:1 orbital resonance with each other.

 

Galileo Galilei, portrait by Domenico Tintoretto, c. 1602-1607

  

Image of Jupiter from the DART spacecraft in 2022. From left to right are Ganymede, Jupiter, Europa, Io and Callisto.

Credit: NASA/Johns Hopkins APL

 

Galilean satellites as seen by the New Horizons spacecraft in February 2007, from left to right: Io, Europa, Ganymede and Callisto.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

 © 2026, Andrew Mirecki

 

7 January 1785

 

The first flight across the English Channel. Contemporary engraving. Credit: Wikimedia Commons

On January 7, 1785, the first flight across the English Channel, in a hydrogen balloon, was made by Jean-Pierre Blanchard (1753–1809) and Dr. John Jeffries (1745–1819). They flew from Dover Castle, Kent, England to Guînes, Pas-de-Calais, France. 

 

   The balloon was approximately 8.2 meters (27 feet) in diameter. A gondola was suspended beneath the gas envelope, equipped with oar-like devices that were intended to steer and propel the balloon. The flight took about two and a half hours, from about 1:00 p.m. to 3:30 p.m. During the flight, all ballast, crew's equipment and most of their clothing were jettisoned. 

Blanchard and Jeffries Crossing the English Channel. Credit: Wikimedia Commons

Balloon with Blanchard and Jeffries leaving Dover. Oil on canvas, by E.W. Cocks, ca. 1840. Credit: Science Museum, London

© 2026, Andrew Mirecki

 

 

7 January 1785

Engineering model, S-10, of the Surveyor lunar lander at the Smithsonian's National Air and Space Museum. It was reconfigured to represent a flight model of Surveyor III or later, since it was the first to have a scoop and claw surface sampler. Credit: Mark Avino. Smithsonian's National Air and Space Museum

Surveyor VII, the last of the series of Surveyor lunar probes, was launched on January 7, 1968. It successfully landed on the Moon near the outer rim of the crater Tycho on January 10, 1968. The spacecraft had returned a total of about 21,000 pictures of itself and its surroundings and studied the chemical composition of the lunar surface. The last communication with the lander was on February 21, 1968.

   Surveyor VII was the fifth and final spacecraft of the Surveyor series to achieve a lunar soft landing. The primary objectives of the Surveyor program, a series of seven robotic lunar softlanding flights, were to support the coming crewed Apollo landings by: 

(1) developing and validating the technology for landing softly on the Moon; 

(2) providing data on the compatibility of the Apollo design with conditions encountered on the lunar surface; and 

(3) adding to the scientific knowledge of the Moon. 

The specific objectives for this mission were to: 

(1) perform a lunar soft landing (in a highland area well removed from the maria to provide a type of terrain photography and lunar sample significantly different from those of other Surveyor missions); 

(2) obtain postlanding TV pictures; 

(3) determine the relative abundances of chemical elements; 

(4) manipulate the lunar material; 

(5) obtain touchdown dynamics data; and, 

(6) obtain thermal and radar reflectivity data. Surveyor 7 was the only Surveyor craft to land in the lunar highland region.

   The basic Surveyor spacecraft structure consisted of a tripod of thin-walled aluminum tubing and interconnecting braces providing mounting surfaces and attachments for the power, communications, propulsion, flight control, and payload systems. A central mast extended about one meter above the apex of the tripod. Three hinged landing legs were attached to the lower corners of the structure. The legs held shock absorbers, crushable, honeycomb aluminum blocks, and the deployment locking mechanism and terminated in footpads with crushable bottoms. The three footpads extended out 4.3 meters from the center of the Surveyor. The spacecraft was about 3 meters tall. The legs folded to fit into a nose shroud for launch.

The launch of Surveyor VII from LC-36A on January 7, 1968. Credit: NASA

   A 0.855 square meter array of 792 solar cells was mounted on a positioner on top of the mast and generated up to 85 Watts of power which was stored in rechargeable silver-zinc batteries. Communications were achieved via a movable large planar array high gain antenna mounted near the top of the central mast to transmit television images, two omnidirectional conical antennas mounted on the ends of folding booms for uplink and downlink, two receivers and two transmitters. Thermal control was achieved by a combination of white paint, high IR-emittance thermal finish, polished aluminum underside. Two thermally controlled compartments, equipped with superinsulating blankets, conductive heat paths, thermal switches and small electric heaters, were mounted on the spacecraft structure. One compartment, held at 5 - 50 degrees C, housed communications and power supply electronics. The other, held between -20 and 50 degrees C, housed the command and signal processing components. The TV survey camera was mounted near the top of the tripod and strain gauges, temperature sensors, and other engineering instruments are incorporated throughout the spacecraft. One photometric targets was mounted near the end of a landing leg and one on a short boom extending from the bottom of the structure. Other payload packages, which differed from mission to mission, were mounted on various parts of the structure depending on their function.

   A Sun sensor, Canopus tracker and rate gyros on three axes provided attitude knowledge. Propulsion and attitude control were provided by cold-gas (nitrogen) attitude control jets during cruise phases, three throttlable vernier rocket engines during powered phases, including the landing, and the solid-propellant retrorocket engine during terminal descent. The retrorocket was a spherical steel case mounted in the bottom center of the spacecraft. The vernier engines used monomethyl hydrazine hydrate fuel and MON-10 (90% N2O2, 10% NO) oxidizer. Each thrust chamber could produce 130 N to 460 N of thrust on command, one engine could swivel for roll control. The fuel was stored in spherical tanks mounted to the tripod structure. For the landing sequence, an altitude marking radar initiated the firing of the main retrorocket for primary braking. After firing was complete, the retrorocket and radar were jettisoned and the doppler and altimeter radars were activated. These provided information to the autopilot which controlled the vernier propulsion system to touchdown.

   Surveyor VII was similar in design to Surveyor VI, but the payload was the most extensive flown during the Surveyor program. It carried a television camera with polarizing filters, an alpha-scattering instrument, a surface sampler similar to that flown on Surveyor III, bar magnets on two footpads, two horseshoe magnets on the surface scoop, and auxiliary mirrors. Of the auxiliary mirrors, three were used to observe areas below the spacecraft, one to provide stereoscopic views of the surface sampler area, and seven to show lunar material deposited on the spacecraft. It also carried over 100 items to monitor engineering aspects of spacecraft performance. Surveyor VII had a mass of 1039 kg at launch and 306 kg at landing.

Diagram of the landing sequence of the Surveyor spacecraft. Credit: NASA

   Surveyor VII was launched at 06:30:00.54 UT on 7 January 1968 on an Atlas-Centaur from launch complex 36A of the Eastern Test Range at Cape Kennedy. The spacecraft was put into an Earth parking orbit and then transferred to a lunar trajectory by a second burn of the Centaur upper stage. Surveyor VII separated from the Centaur at 07:05:16 UT. A midcourse maneuver was performed at 23:30:10 UT on 7 January 1968. Touchdown occurred at 01:05:36.3 UT on 10 January 1968  at 40.9812º S, 11.5127º W (as determined from Lunar Reconnaissance Orbiter images), less than 2.4 kilometers from the center of the target circle, on an ejecta blanket about 29 kilometers north of the rim of Tycho crater in the lunar highlands.

   During the first lunar day, 20,993 television pictures were obtained. An additional 45 pictures were obtained during the second lunar day. The alpha-scattering instrument, after completing its background count in the intermediate position, failed to deploy the remainder of the distance to the lunar surface. The surface sampler was then brought in to action and, by means of a series of intricate maneuvers, was able to force the alpha-scattering instrument to the surface. The surface sampler was later used to pick up the alpha-scattering instrument after the first chemical analysis had been completed and to move it to two other locations for additional analyses. These delicate operations demonstrated the versatility of the surface sampler as a remote manipulation device and the precision with which its operations can be controlled from the Earth.

Surveyor VII landing site near Tycho crater, as viewed by the Lunar Reconnaissance Orbiter.

Credit: NASA/GSFC/Arizona State University

Approximately 66 hours of alpha-scattering data were obtained during the first lunar day on three samples: the undisturbed lunar surface, a lunar rock, and an area dug up by the surface sampler. An additional 34 hours of data were obtained on the third sample during the second lunar day. The surface sampler dug a number of trenches and conducted static and dynamic bearing­ strengths of the lunar material. The performance of the instrument and its controllers was outstanding.

  In addition to acquiring a wide variety of lunar surface data, Surveyor VII also obtained pictures of the Earth and performed star surveys. Laser beams from the Earth were success­fully detected by the spacecraft's television camera in a special test of laser-pointing techniques.  

   Post sunset operations were conducted for 15 hours after local sunset at the end of the first lunar day at 06 :06 GMT on January 25, 1968. During these operations, additional Earth and star pictures were obtained, as were observations of the solar corona out to 50 solar radii. Operation of the spacecraft was terminated at 14:12 GMT on January 26, 1968, 80 hours after sunset. Second lunar-day operations began at 19:01 GMT on February 12, 1968, and continued until 00:24 GMT on February 21, 1968.

A Surveyor VII landing site panorama, using newly digitized data. 

Credit: NASA/JPL-Caltech/University of Arizona Lunar and Planetary Laboratory/Gary Rennilson

The scoop of the surface sampler, shown in the middle of the photograph, being used to help deploy the sensor head of the Alpha Scattering Experiment (on the left) on January 12, 1968.  

Credit: NASA (from Andrew LePage. Surveyor 7: The Mission to Tycho. Drew Ex Machina)

The Surveyor photograph of the partially sunlit Earth, taken by Surveyor VII at 09:06 UT on January 20, 1968, shows two narrow laser beams sent to the Moon from the Kitt Peak National Observatory, near Tucson, Ariz., and the Table Mountain Observatory, near Los Angeles. The blue-green argon-ion laser beams seen within the white circle on the photograph each contained only about 1 watt of power. This was an engineering test to gain experience for the Apollo laser-ranging retroreflector experiment.

Credit: NASA (from Andrew LePage. Surveyor 7: The Mission to Tycho. Drew Ex Machina)

Surveyor VII, sitting on the ejecta blanket of Tycho Crater. Lunar Reconnaissance Orbiter image NAC M175355093L, image width is 500 m. Inset is zoomed 4x. Credit: NASA/GSFC/Arizona State University

© 2026, Andrew Mirecki

 

7 January 1976

 

Eleanor F. Helin in 1973. Credit: NASA/JPL-Caltech

A near-Earth asteroid (2062) Aten was discovered at the Palomar Observatory by American astronomer Eleanor Helin (1932–2009) on January 7, 1976. 

   With a perihelion 0.79 au, an aphelion 1.14 au and an orbital period of 347 days, it was the first asteroid found to have a semi-major orbital axis of less than one astronomical unit and a period of less than one year. A group of near-Earth objects (Aten asteroids) is named after it. 

Orbit of (2062) Aten. Credit: NASA Solar System Dynamics

© 2026, Andrew Mirecki

7 January 1985

Artist's depiction of Sakigake spacecraft. Credit: JAXA

Sakigake, Japan's first interplanetary spacecraft, known before launch as MS-T5, was launched from Kagoshima Space Center by M-3S-II launch vehicle on January 7, 1985. It was the first deep space spacecraft launched by any other country other than the Soviet Union or the United States. 

   Sakigake was a test probe similar to a later and almost identical probe called Suisei. It aimed to demonstrate the performance of the new launch vehicle, test its ability to escape from Earth gravity, and observe the interplanetary medium and magnetic field. It flew by comet 1P/Halley at a distance of 6,99 mln km on March 11, 1986.

   Sakigake made an Earth swingby on January 8, 1992. The closest approach was with a geocentric distance of 88,997 km. This was the first planet-swingby for a Japanese spacecraft. During the approach, Sakigake observed the geotail. The second Earth swingby was on June 14, 1993 at 40 Re, and the third on October 28, 1994 at 86 Re.

   The spacecraft carried three instruments to measure plasma wave spectra, solar wind ions, and interplanetary magnetic fields, all of which worked normally. The spacecraft was spin-stabilized at two different rates (5 and 0.2 rpm). It was equipped with hydrazine thrusters for attitude and velocity control, star and sun sensors for attitude determination, and a mechanically despun off-set parabolic dish for long-range communication. it had s mass of 138.1 kg.

   There were plans for the spacecraft to go on to an encounter with 21P/Giacobini-Zinner in 1998, but the flyby had to be abandoned because of a lack of propellant. Telemetry contact was lost on November 15, 1995, though a beacon signal continued to be received until January 7, 1999.

M-3SII Satellite Launch Vehicle 1 with Sakigake spacecraft. Credit: JAXA

Launch of Sakigake. Credit: JAXA

© 2026, Andrew Mirecki

7 January 1998

The fully assembled Lunar Prospector spacecraft mated atop the Star 37 Trans Lunar Injection module. Credit: NASA

Lunar Prospector spacecraft was launched from Cape Canaveral aboard a four-stage Athena II rocket on January 7, 1998, at 2:28:44 UT. It was designed for a low polar orbit investigation of the Moon, including mapping of surface composition and possible deposits of polar ice, measurements of magnetic and gravity fields, and study of lunar outgassing events. The spacecraft carried 6 experiments: a Gamma Ray Spectrometer (GRS), a Neutron Spectrometer (NS), a Magnetometer (MAG), an Electron Reflectometer (ER), an Alpha Particle Spectrometer (APS), and a Doppler Gravity Experiment (DGE).

  The spacecraft was a graphite-epoxy drum, 1.37 meters in diameter and 1.28 meters high with three radial 2.5 m instrument booms. A 1.1 m extension boom at the end of one of the 2.5 m booms held the magnetometer. Total initial mass (fully fueled) was 296.4 kg. It was spin-stabilized (nominal spin rate 12 rpm) with its spin axis normal to the ecliptic plane. The spacecraft was controlled by 6 hydrazine monopropellant 22-Newton thrusters, two aft, two forward, and two tangential. Three fuel tanks mounted inside the drum held 137.7 kg of hydrazine pressurized by helium. The power system consisted of body mounted solar cells which produce an average of 186 W and a 4.8 amp-hr rechargeable NiCd battery. Communications were through two S-band transponders, a slotted, phased-array medium gain antenna for downlink, and an omnidirectional low-gain antenna for downlink and uplink. There was no on-board computer, all control was from the ground, commanding a single on-board command and data handling unit. Data were downlinked directly and also stored on a solid-state recorder and downlinked after 53 minutes, to ensure all data collected during communications blackout periods were received.

Launch of Athena II rocket with Lunar Prospector. Credit: Department of Defense

   Lunar Prospector spacecraft entered orbit around the Moon on January 11, 1998, and orbited it for almost 19 months, collecting data to compile the first complete maps of the Moon's composition and gravity. The mission ended on July 31, 1999, with the spacecraft deliberately impacting the lunar surface near the south pole, to create a dust cloud that was studied from Earth.

 

Artist's concept of the Lunar Prospector. Credit: NASA/Ames

A gravity map of the Moon made by Lunar Prospector. Mascons are shown in orange-red. Credit: NASA

© 2026, Andrew Mirecki