February 15
15 February 1564
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| Galileo Galilei, portrait by Domenico Tintoretto or Francesco Apollodoro, c. 1602–1607. Credit: National Maritime Museum/Wikimedia Commons |
Galileo Galilei, Italian natural philosopher, astronomer, and mathematician who played a major role in the Scientific Revolution was born in Pisa, Italy, on February 15, 1564. In 1589 he became professor of mathematics at the University of Pisa, and then from 1592 to 1610 at the University of Padua. In 1610 he was appointed philosopher and chief mathematician to the Grand Duke of Tuscany.
Galileo was one of the first scientists to use a telescope for astronomical observations in 1609–1611. His discoveries include mountains on the Moon, stars of the Milky Way, the phases of Venus, the four largest moons of Jupiter (now called the Galilean satellites), and the analysis of the motion of sunspots. Although most of these discoveries were made independently by others, no one understood their significance as Galilei did. His observations provided evidence for the Copernican heliocentric cosmological model and against the old Ptolemaic system.
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| Two of Galileo's first telescopes; in the Museo Galileo, Florence |
Through an innovative combination of experiment and mathematics, Galileo made contributions to the science of motion and established the foundations of modern mechanics. He formulated an approximation to the law of inertia, the composition of motion, the laws that in free fall the distance fallen increases as the square of the time elapsed and that the velocity acquired is directly proportional to the time, the isochronism of the pendulum, and the parabolic path of projectiles.
His major written works are Sidereus Nuncius (Sidereal Messenger) in 1610, Dialogue Concerning the Two Chief World Systems, Ptolemaic and Copernican (1632) and Discourses and Mathematical Demonstrations Relating to Two New Sciences (1638).
The Dialogue depicts a debate between two characters representing the Ptolemaic system, which places Earth at the center of the universe, and the Copernican system, which posits that the Sun is the center and Earth and other planets revolve around it. After the book's publication, Galileo was accused by the Inquisition of supporting Copernicanism and summoned to Rome to stand trial, which began in April 1633. The trial concluded on June 22, 1633. Galileo was found guilty of “vehement suspicion of heresy” due to controversial beliefs, such as the cosmological thesis that the Earth moves and the methodological principle that the Bible is not a scientific authority. The Dialogue was banned, and Galileo was sentenced to house arrest for the rest of his life. During this time, he published his most important contribution to physics, the Two New Sciences. Galileo died in Arcetri, near Florence, on 8 January 8, 1642.
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| Drawings of the Moon by Galileo Galilei, Sidereus nuncius, 1610 |
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| Drawing of sunspots by Galileo Galilei, Istoria e dimostrazioni intorno alle macchie solari e loro accidenti, 1613 |
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| Frontispiece and title page of the Dialogue Concerning the Two Chief World Systems (1632) |
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| Galileo Galilei, portrait by Justus Sustermans, c. 1640. Credit: Royal Museums Greenwich/Wikimedia Commons |
References:
Encyclopedia Britannica: Galileo
Finocchiaro, Maurice A. Galilei, Galileo. The Biographical Encyclopedia of Astronomers. 2007 Springer Science+Business Media, LLC
© 2026, Andrew Mirecki
15 February 1845
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| The Leviathan of Parsonstown, the 6 foot telescope of William Parsons, 3rd Earl of Rosse (1800-1867). The photo also features Lawrence Parsons, 4th Earl of Rosse (1840-1908). Credit: National Library of Ireland on The Commons |
The Leviathan of Parsonstown (the Great Rosse Telescope) saw its first light on February 15, 1845. The 72-inch (1.83 m) aperture reflecting telescope, was built by William Parsons, 3rd Earl of Rosse (1800-1867) on his estate, Birr Castle, at Parsonstown (now Birr) in Ireland. It was the largest telescope in the world from 1845 until the construction of the 100-inch (2.5 m) Hooker Telescope in California in 1917.
Parsons improved the techniques of casting,
grinding and polishing large telescope mirrors from speculum
metal, an alloy of approximately two parts copper to one
part tin by weight, and constructed steam-powered grinding
machines for parabolic mirrors. His 3 foot (91 cm) mirror of
1839 was cast in smaller pieces and then fitted together
before grinding and polishing; its 1840 successor was cast
in a single piece. In 1842, Parsons cast his first 6 foot
(1.83 m) mirror, but it took another five casts before he
had two ground and polished mirrors. Speculum mirrors
tarnished rapidly; with two mirrors, one could be used in
the telescope while the other was being re-polished. The
telescope tube and supporting structure were completed in
1845, and the telescope had its first light on February 15,
1845, but was not put into regular use until 1848.
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| William Parsons, 3rd Earl of Rosse |
The mirror was 5 inches (13 cm) thick and
weighed almost 3 tons. This required a mirror cell to
support and to prevent the mirror deforming under its own
weight. The length of the wooden tube and mirror box was
about 54 feet (16.5 m); including the mirror it weighed
about 12 tons. The tube was supported at the mirror end by a
"universal joint", a hinge with two axes, which allowed the
tube to be inclined through a large range of altitude and
also to be turned through a limited range of azimuth. The
tube could be moved about ten degrees on either side toward
the side walls. Two supporting walls are 7 metres apart, 12
metres high, and 21.6 metres long. The observer had access
to the eyepiece from chairs mounted on the walls and was
able to observe an object for at most an hour and a half.
The telescope was used primarily to observe
nebulae when weather conditions permitted. Lord Rosse, his
assistants and visiting astronomers discovered the spiral
nature in over a dozen nebulae, today known to be spiral
galaxies. Rosse's telescope was the first to reveal the
spiral structure of M51, a galaxy nicknamed later as the
"Whirlpool Galaxy", and his drawings of it closely resemble
modern photographs.
The use of the Great Telescope had gradually
come to an end in the late 1880s, and was was partly
dismantled after 1908. The telescope was reconstructed in
1996–97 as a tourist attraction, and a new mirror was installed in 1999.
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| Earl of Rosse's 72-inch (1.8-meter) telescope at Birr Castle, Ireland. Credit: Robert S. Ball: The Story of the Heavens, 1886 |
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| One of the two the original mirrors of Lord Rosse six foot telescope now in the Science Museum in London. Credit: Wikimedia Commons |
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| Drawing of the Whirlpool Galaxy (M51) by William Parsons, 3rd Earl of Rosse, in 1845 from his 72-inch telescope |
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| Drawing of M33, the Triangulum spiral galaxy, on the ground of observations by William Parsons, 3rd Earl of Rosse |
See also: 60-inch telescope at Mount
Wilson, Hooker Telescope, Hale Telescope
© 2026, Andrew Mirecki
15 February 2011
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| The nucleus of comet Tempel 1 as seen by the Stardust-NExT spacecraft during closest approach at 04:39 UTC on February 15, 2011. Credit: NASA/JPL-Caltech/Cornell |
In 2007 NASA approved an extended mission for the Stardust spacecraft, which had successfully completed its mission to comet 81P/Wild (Wild 2) by collecting and returning dust samples from the comet’s coma to Earth. The extended mission, Stardust-NExT (for New Exploration of Tempel) flew by comet 9P/Tempel (Tempel 1), the target of the Deep Impact mission, which delivered an impactor into the surface of Tempel 1 on July 4, 2005. This was the first time that a comet was visited twice.
The primary goal of Stardust-NExT was to use the spacecraft camera, NAVCAM, to obtain high-resolution images of the nucleus to:
(a) Look for changes on the comet’s surface that might have occurred between the 2005 perihelion passage and that in January 2011.
(b) To extend coverage of the surface to regions not imaged by the Deep Impact.
(c) To image the impact site where Deep Impact’s impactor hit the surface.
All three of these goals were achieved. The 2005 impact threw up so much ejecta that the cameras on the main Deep Impact spacecraft could not see the surface in the impact area, and therefore the size of the crater that had been excavated could not be determined. In addition to the NAVCAM camera, the spacecraft carried two experiments to study the comet’s dust environment: the Dust Flux Monitoring Instrument (DFMI) designed to determine the fluence and size distribution of dust particles and the Comet and Interstellar Dust Analyzer (CIDA) designed to measure the elemental composition of individual dust grains.
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| Another image of comet Tempel 1 taken by NASA's Stardust-NExT mission at 04:38 UTC on February 15, 2011. Credit: NASA/JPL-Caltech/Cornell |
To reach Tempel 1 the spacecraft performed an Earth flyby on January 14, 2009 and some dozen subsequent trajectory correction maneuvers. The targeted flyby distance was 200 km. The actual flyby occurred at 178 km at a speed of 10.9 km/s on February 15, 2011 at 04:39:10 UTC. In addition to distant images on approach and departure, 72 images were obtained within ±4 min of closest approach: the best images obtained were at 11 m/pixel.
The solar phase angle varied from 81° on approach through 15° at closest approach, reaching 98° on departure. DFMI data were collected from 22 min before to 8 min after closest approach (-14,000 km to +5,200 km from the nucleus). CIDA collected spectra for 2 h around closest approach (±78,000 km).
The images acquired showed changes in the terrain and revealed portions of the comet never seen by Deep Impact spacecraft in 2005. The impact site from Deep Impact was also observed, though it was barely visible due to material settling back into the crater.
Stardust/NExT underwent a decommissioning burn and was commanded into safe mode with its transmitter off on March 25, 2011 at 00:30 UTC.
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| Tempel 1 Impact Site. This pair of images shows the before-and-after comparison of the part of comet Tempel 1 that was hit by the impactor from NASA's Deep Impact spacecraft. The left-hand image is a composite made from images obtained by Deep Impact in July 2005. The right-hand image shows arrows identifying the rim of the crater caused by the impactor. The crater is estimated to be 150 meters in diameter. This image also shows a brighter mound in the center of the crater likely created when material from the impact fell back into the crater. Credit: NASA |
See also: Stardust Wild 2 flyby, Stardust Annefrank flyby
References:
J. Veverka et al., Return to Comet Tempel 1: Overview of Stardust-NExT results. Icarus. Volume 222, Issue 2, February 2013. https://doi.org/10.1016/j.icarus.2012.03.034.
15 February 2013
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| The Chelyabinsk meteor was seen as a fireball, caught here on a car's dashboard camera. Image Credit: RIA Novosti |
On February 15, 2013, an asteroid approximately 20 meters in diameter and with an estimated initial mass of 13,000 tonnes entered Earth's atmosphere and exploded in a meteor airburst over Chelyabinsk Oblast, Russia, at an altitude between 27–30 kilometers above the ground. This is the largest meteor airburst on Earth known since the Tunguska impact in 1908, with an estimated total energy release of about 500 kilotons of TNT. More than a ton of fragments (LL5 chondrites) were found.
The Chelyabinsk airburst was observed globally by multiple instruments—including infrasound, seismic, US government sensors and more than 400 video cameras—at ranges up to 700 km away. The resulting airblast (shock wave travelling through the air from an explosion) shattered thousands of windows in urban Chelyabinsk, with flying glass injuring many residents. The shockwave from the explosion traveled twice around Earth and was recorded by 17 infrasound stations throughout the world, including a station in Antarctica.
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| This sequence of video stills, captured by Aleksandr Ivanov in Kamensk-Uralskiy, shows the breakup of the Chelyabinsk meteor over the course of 2.4 seconds. Credits: A. Ivanov/Popova et al. /Science |
The fireball was first recorded at 97-km altitude, moving at 19.16 ± 0.15 km/s with entry angle 18.3 ± 0.2° with respect to the horizon. Combined with the best kinetic energy estimate, an entry mass of 1.3 × 107 kg (with a factor of two uncertainty) and a diameter of 19.8 ± 4.6 m was derived.
Size and speed suggest that a shock wave first developed at 90 km. Observations show that dust formation and fragmentation started around 83 km and accelerated at 54 km. Peak radiation occurred at an altitude of 29.7 ± 0.7 km at 03:20:32.2 ± 0.1s UTC (09:20 local time), at which time spaceborne sensors measured a meteoroid speed of 18.6 km/s. An integrated radiated energy was 3.75 × 1014 J and a peak brightness 2.7 × 1013 W sr-1. These values correspond to an estimated energy equivalent of about 530 kt of TNT. The peak brightness was equivalent to an absolute astronomical magnitude of -28 (referenced to a range of 100 km) in the silicon bandpass, making the airburst appear 30 times brighter than the Sun to an observer directly under this point. Airburst energy estimates from different techniques are in the range of 400–600 kt of TNT.
Fragmentation left a thermally emitting debris cloud in this period, the final burst of which occurred at 27.0-km altitude, with dust and gas settling at 26.2 km and with distinctly higher billowing above that location. The dust cloud split in two due to the buoyancy of the hot gas, leading to two cylindrical vortices. The biggest surviving fragment of the asteroid, with a mass of 600–700 kg and with a diameter of 0.75 m, flew another 70 km after the explosion and fell into the Chebarkul Lake, piercing an eight-meter hole in the ice of the lake.
According to official reports, the shockwave caused damage to an area of around 6,500 km2, more than 7,320 buildings were affected and 1,613 people asked for medical assistance, most hurt by falling glass. 112 people were hospitalized, two in serious condition. No deaths were reported.
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| The Chelyabinsk meteor trace. Credit: A. Alishevskikh |
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| Collapsed wall of the Chelyabinsk Zinc Plant company after the airblast. Credit: A. Pospel/Wikimedia Commons |
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| An 8-m-wide hold in the ice of Chebarkul Lake, made by a fragment of the Chelyabinsk meteor. Credit: Sergei Ilnitsky |
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| The largest fragment of the Chelyabinsk meteorite at the exhibition of The State Museum of the South Ural History. Credit: Vyacheslav Bukharov/Wikimedia Commons |
See also: Tunguska event, Sikhote-Alin meteorite, Great Daylight Fireball, Tagish Lake meteorite, Sulawesi superbolide
References:
Popova, Olga P., et al. "Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization." Science 342.6162 (2013): 1069-1073. https://doi.org/10.1126/science.1242642
Brown, Peter G., et al. "A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors." Nature 503.7475 (2013): 238-241. https://doi.org/10.1038/nature12741
Emel'Yanenko, Vacheslav V., et al. "The orbit and dynamical evolution of the Chelyabinsk object." Meteoritics & Planetary Science 49.12 (2014): 2169-2174. https://doi.org/10.1111/maps.12382
Gorkavyi, Nick, Alexander Dudorov, and Sergey Taskaev, eds. Chelyabinsk Superbolide. Springer Nature, 2019.
© 2026, Andrew Mirecki
15 February 2024
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| IM-1 Odysseus lunar lander in preparation for launch. Credit: NASA Marshall Space Flight Center/Intuitive Machines |
The Intuitive Machines IM-1 Odysseus lunar lander was launched on 15 February 2024 at 06:05 UT on a SpaceX Falcon 9 from Kennedy Space Center. The lander deployed from the second stage at 06:53 UT. The spacecraft continued in a 185 x 60,000 km Earth orbit, followed by a translunar injection and a maneuver to put it in a 100 km lunar orbit.
Odysseus landed on the Moon at Malapert A crater near the south pole on February 22, at 23:23:53 UT. It landed in a 1 km diameter crater on a slope of about 12 degrees, at 80.13 degrees S, 1.44 degrees E, roughly 1.5 km from the planned landing position. Some of the landing gear broke upon impact, and Odysseus tipped over and was resting at a 30 degree angle to the horizontal, but was still operational. Some data were received from the science payloads. It was losing sunlight and powered down on February 28. No communications were received the next lunar day, and the mission was ended.
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| The Falcon 9 carrying Intuitive Machines’ IM-1 Odysseus lunar lander lifts off Kennedy Space Center Launch Complex 39A. Credit: NASA/Kim Shiflett |
The mission objective was to place a NOVA-C lander, called Odysseus, at crater Malapert A near the south pole of the Moon. The commercially built lander carried five NASA payloads and commercial cargo. The scientific objectives of the mission included studies of plume-surface interactions, radio astronomy, and space weather interactions with the lunar surface. It was also to be demonstrating precision landing technologies and communication and navigation node capabilities. IM-1 was selected through NASA's Commercial Lunar Payload Services (CLPS) initiative, in which NASA contracts with a commercial partner, in this case Intuitive Machines, that provides the launch and lander.
The Odysseus Lander is a hexagonal cylinder, 4.0 meters tall and 1.57 meters wide, on 6 landing legs with a launch mass of 1908 kg. It was capable of carrying approximately 100 kg of payload to the surface. It used solar panels to generate 200 W of power on the surface, using a 25 amp-hr battery and a 28 VDC system. Propulsion and landing used liquid methane as fuel and liquid oxygen as an oxidizer powering a 3100 N main engine mounted on the bottom of the lander. Communications were via S-band. The NASA payload included the Laser Retro-Reflector Array (LRA), Navigation Doppler Lidar for Precise Velocity and Range Sensing (NDL), Lunar Node 1 Navigation Demonstrator (LN-1), Stereo Cameras for Lunar Plume-Surface Studies (SCALPSS), and Radio wave Observation at the Lunar Surface of the photoElectron Sheath (ROLSES). In total there were five NASA and four commercial payloads planned.
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| The Intuitive Machines Nova-C lunar lander spacecraft separates from the launch vehicle that delivered it to orbit. Credit: SpaceX |
See also: IM-1 Odysseus landing, IM-2 Athena
References:
NASA Space Science Data Coordinated Archive
© 2026, Andrew Mirecki
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