1966, EPIMETHEUS IS DISCOVERED BY RICHARD WALKER

Today, The Grandma has received the wonderful visit of one of her closest friends, Joseph de Ca'th Lon.

 

Joseph likes Astronomy and they have been talking about Epimetheus, the inner satellite of Saturn.

 

They have been talking about Epimetheus, the satellite of Saturn, that was discovered by astronomer Richard Walker on a day like today in 1966.

Epimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.

Epimetheus occupies essentially the same orbit as the moon Janus. Astronomers assumed that there was only one body in that orbit (disbelieving that two moons could share nearly identical orbits without colliding), and accordingly had difficulty determining their orbital characteristics. 

Observations were photographic and spaced widely apart in time, so that while the presence of two objects was not obvious, the observations were difficult to reconcile with a reasonable orbit.

Audouin Dollfus observed a moon on 15 December 1966, which he proposed to be named Janus.

On 18 December, Richard Walker made a similar observation which is now credited as the discovery of Epimetheus. However, at the time, it was believed that there was only one moon, unofficially known as Janus, in the given orbit.

Twelve years later, in October 1978, Stephen M. Larson and John W. Fountain realised that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits.

This was confirmed in 1980 by Voyager 1, and so Larson and Fountain officially share the discovery of Epimetheus with Walker. A moon that was probably Epimetheus appeared in two Pioneer 11 images and was designated 1979S1, there is uncertainty though because the two images were not enough to allow a reliable orbit to be calculated.

More information: NASA

Epimetheus received its name in 1983. The name Janus was approved by the IAU at the same time, although the name had been used informally since Dollfus proposed it shortly after the 1966 discovery.

Epimetheus's orbit is co-orbital with that of Janus. Janus's mean orbital radius from Saturn is, as of 2006 (as shown by green color in the adjacent picture), only 50 km less than that of Epimetheus, a distance smaller than either moon's mean radius. In accordance with Kepler's laws of planetary motion, the closer orbit is completed more quickly. Because of the small difference it is completed in only about 30 seconds less. Each day, the inner moon is an additional 0.25° farther around Saturn than the outer moon. As the inner moon catches up to the outer moon, their mutual gravitational attraction increases the inner moon's momentum and decreases that of the outer moon.

This added momentum means that the inner moon's distance from Saturn and orbital period are increased, and the outer moon's are decreased. The timing and magnitude of the momentum exchange is such that the moons effectively swap orbits, never approaching closer than about 10,000 km. At each encounter Janus's orbital radius changes by ~20 km and Epimetheus's by ~80 km: Janus's orbit is less affected because it is four times more massive than Epimetheus.

The exchange takes place close to every four years; the last close approaches occurred in January 2006, 2010, 2014 and 2018. This is the only such orbital configuration of moons known in the Solar System (although, 3753 Cruithne is an asteroid which is co-orbital with Earth).

The orbital relationship between Janus and Epimetheus can be understood in terms of the circular restricted three-body problem, as a case in which the two moons (the third body being Saturn) are similar in size to each other.

There are several Epimethean craters larger than 30 km in diameter, as well as both large and small ridges and grooves. The extensive cratering indicates that Epimetheus must be quite old. Janus and Epimetheus may have formed from a disruption of a single parent to form co-orbital satellites, but if this is the case the disruption must have happened early in the history of the satellite system. From its very low density and relatively high albedo, it seems likely that Epimetheus is a very porous icy body. There is considerable uncertainty in these values, however, and so this remains to be confirmed.

The south pole shows what might be the remains of a large impact crater covering most of this face of the moon, and which could be responsible for the somewhat flattened shape of the southern part of Epimetheus.

There appear to be two terrain types: darker, smoother areas, and brighter, slightly more yellowish, fractured terrain. One interpretation is that the darker material evidently moves down slopes, and probably has a lower ice content than the brighter material, which appears more like bedrock. Nonetheless, materials in both terrains are likely to be rich in water ice.

A faint dust ring is present around the region occupied by the orbits of Epimetheus and Janus, as revealed by images taken in forward-scattered light by the Cassini spacecraft in 2006. The ring has a radial extent of about 5000 km. Its source are particles blasted off their surfaces by meteoroid impacts, which then form a diffuse ring around their orbital paths.

Along with Janus, Epimetheus acts as a shepherd moon, maintaining the sharp outer edge of the A Ring in a 7:6 orbital resonance. The effect is more obvious when the more massive Janus is on the resonant (inner) orbit.

More information: NASA

Saturn is accompanied by a very large
and diverse collection of moons.
They range in size from a few kilometers
across to as big across as the U.S.

Carolyn Porco

497 BC, THE 1ST SATURNALIA FESTIVAL IN ANCIENT ROME

Today, The Grandma has been reading about Saturnalia, the ancient Roman festival and holiday in honour of the god Saturn, that is celebrated on a day like today since 497 BC.

Saturnalia is an ancient Roman festival and holiday in honour of the god Saturn, held on 17 December of the Julian calendar and later expanded with festivities through to 23 December.

The holiday was celebrated with a sacrifice at the Temple of Saturn, in the Roman Forum, and a public banquet, followed by private gift-giving, continual partying, and a carnival atmosphere that overturned Roman social norms: gambling was permitted, and masters provided table service for their slaves as it was seen as a time of liberty for both slaves and freedmen alike.

A common custom was the election of a King of the Saturnalia, who gave orders to people, which were followed and presided over the merrymaking. The gifts exchanged were usually gag gifts or small figurines made of wax or pottery known as sigillaria. The poet Catullus called it the best of days.

Saturnalia was the Roman equivalent to the earlier Greek holiday of Kronia, which was celebrated during the Attic month of Hekatombaion in late midsummer. It held theological importance for some Romans, who saw it as a restoration of the ancient Golden Age, when the world was ruled by Saturn.

The Neoplatonist philosopher Porphyry interpreted the freedom associated with Saturnalia as symbolizing the freeing of souls into immortality. Saturnalia may have influenced some of the customs associated with later celebrations in western Europe occurring in midwinter, particularly traditions associated with Christmas, the Feast of the Holy Innocents, and Epiphany.

In particular, the historical western European Christmas custom of electing a Lord of Misrule may have its roots in Saturnalia celebrations.

More information: History

In Roman mythology, Saturn was an agricultural deity who was said to have reigned over the world in the Golden Age, when humans enjoyed the spontaneous bounty of the earth without labour in a state of innocence. The revelries of Saturnalia were supposed to reflect the conditions of the lost mythical age.

The Greek equivalent was the Kronia, which was celebrated on the twelfth day of the month of Hekatombaion, which occurred from around mid-July to mid-August on the Attic calendar.

The Greek writer Athenaeus also cites numerous other examples of similar festivals celebrated throughout the Greco-Roman world, including the Cretan festival of Hermaia in honor of Hermes, an unnamed festival from Troezen in honor of Poseidon, the Thessalian festival of Peloria in honor of Zeus Pelorios, and an unnamed festival from Babylon. He also mentions that the custom of masters dining with their slaves was associated with the Athenian festival of Anthesteria and the Spartan festival of Hyacinthia. The Argive festival of Hybristica, though not directly related to the Saturnalia, involved a similar reversal of roles in which women would dress as men and men would dress as women.

Saturnalia underwent a major reform in 217 BC, after the Battle of Lake Trasimene, when the Romans suffered one of their most crushing defeats by Carthage during the Second Punic War. Until that time, they had celebrated the holiday according to Roman custom (more Romano). It was after a consultation of the Sibylline Books that they adopted Greek rite, introducing sacrifices carried out in the Greek manner, the public banquet, and the continual shouts of io Saturnalia that became characteristic of the celebration. 

Cato the Elder (234-149 BC) remembered a time before the so-called Greek elements had been added to the Roman Saturnalia.

Saturn also had a less benevolent aspect. One of his consorts was Lua, sometimes called Lua Saturni (Saturn's Lua) and identified with Lua Mater, Mother Destruction, a goddess in whose honor the weapons of enemies killed in war were burned, perhaps in expiation.

Saturn's chthonic nature connected him to the underworld and its ruler Dīs Pater, the Roman equivalent of Greek Plouton (Pluto in Latin) who was also a god of hidden wealth.

In sources of the third century AD and later, Saturn is recorded as receiving dead gladiators as offerings (munera) during or near the Saturnalia. These gladiatorial events, ten days in all throughout December, were presented mainly by the quaestors and sponsored with funds from the treasury of Saturn.

More information: Academus

It was luxuries like air conditioning
that brought down the Roman Empire.
With air conditioning their windows were shut,
they couldn't hear the barbarians coming.

Garrison Keillor

PIONEER 11 SPACECRAFT, STUDYING JUPITER & SATURN

Today, The Grandma has received the wonderful visit of one of her closest friends, Joseph de Ca'th Lon.

Joseph loves astronomy and they have been talking about Pioneer 11, the robotic space probe launched by NASA on a day like today in 1973.

Pioneer 11, also known as Pioneer G, is a 260-kilogram robotic space probe launched by NASA on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays.

It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter. Later, Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System.

Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.

Approved in February 1969, Pioneer 11 and its twin probe, Pioneer 10, were the first to be designed for exploring the outer Solar System. 

More information: NASA

Yielding to multiple proposals throughout the 1960s, early mission objectives were defined as:

-Explore the interplanetary medium beyond the orbit of Mars.

-Investigate the nature of the asteroid belt from the scientific standpoint and assess the belt's possible hazard to missions to the outer planets.

-Explore the environment of Jupiter.

Subsequent planning for an encounter with Saturn added many more goals:

-Map the magnetic field of Saturn and determine its intensity, direction, and structure.

-Determine how many electrons and protons of various energies are distributed along the trajectory of the spacecraft through the Saturn system.

-Map the interaction of the Saturn system with the solar wind.

-Measure the temperature of Saturn's atmosphere and that of Titan, the largest satellite of Saturn.

-Determine the structure of the upper atmosphere of Saturn where molecules are expected to be electrically charged and form an ionosphere.

-Map the thermal structure of Saturn's atmosphere by infrared observations coupled with radio occultation data.

-Obtain spin-scan images of the Saturnian system in two colors during the encounter sequence and polarimetry measurements of the planet.

-Probe the ring system and the atmosphere of Saturn with S-band radio occultation.

-Determine more precisely the masses of Saturn and its larger satellites by accurate observations of the effects of their gravitational fields on the motion of the spacecraft.

-As a precursor to the Mariner Jupiter/Saturn mission, verify the environment of the ring plane to find out where it may be safely crossed by the Mariner spacecraft without serious damage.

Pioneer 11 was built by TRW and managed as part of the Pioneer program by NASA Ames Research Center. A backup unit, Pioneer H, is currently on display in the Milestones of Flight exhibit at the National Air and Space Museum in Washington, D.C. Many elements of the mission proved to be critical in the planning of the Voyager program.

Pioneer 10 and 11 both carry a gold-anodized aluminum plaque in the event that either spacecraft is ever found by intelligent lifeforms from other planetary systems.

The plaques feature the nude figures of a human male and female along with several symbols that are designed to provide information about the origin of the spacecraft.

More information: NASA

 The vision of NASA is to reveal the unknown
for the benefit of all humankind.

Victor J. Glover

PHOEBE, THE AMAZING IRREGULAR SATELLITE OF SATURN

Today, The Grandma has received the wonderful visit of one of her closest friends, Joseph de Ca'th Lon.

Joseph loves Astronomy, and they have been talking about Phoebe, the satellite of Saturn that became first to be discovered with photographs, taken in August 1898, by William Henry Pickering on a day like today in 1899.

Phoebe is an irregular satellite of Saturn with a mean diameter of 213 km.

It was discovered by William Henry Pickering on March 18, 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Station of the Carmen Alto Observatory near Arequipa, Peru, by DeLisle Stewart. It was the first satellite to be discovered photographically.

Phoebe was the first target encountered upon the arrival of the Cassini spacecraft in the Saturn system in 2004, and is thus unusually well-studied for an irregular satellite of its size. Cassini's trajectory to Saturn and time of arrival were specifically chosen to permit this flyby. After the encounter and its insertion into orbit, Cassini did not go much beyond the orbit of Iapetus.

Phoebe is roughly spherical and has a differentiated interior. It was spherical and hot early in its history and was battered out of roundness by repeated impacts. It is believed to be a captured centaur that originated in the Kuiper belt.

Phoebe is the second largest retrograde satellite in the solar system after Triton.

Phoebe was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart. It was the first satellite to be discovered photographically.

More information: NASA

Phoebe was named after Phoebe, a Titaness in Greek mythology that was associated with the Moon. It is also designated Saturn IX in some scientific literature.

The IAU nomenclature standards have stated that features on Phoebe are to be named after characters in the Greek myth of Jason and the Argonauts.

In 2005, the IAU officially named 24 craters (Acastus, Admetus, Amphion, Butes, Calais, Canthus, Clytius, Erginus, Euphemus, Eurydamas, Eurytion, Eurytus, Hylas, Idmon, Iphitus, Jason, Mopsus, Nauplius, Oileus, Peleus, Phlias, Talaus, Telamon and Zetes).

Phoebe's orbit is retrograde; that is, it orbits Saturn opposite to Saturn's rotation. For more than 100 years, Phoebe was Saturn's outermost known moon, until the discovery of several smaller moons in 2000.

Phoebe is almost 4 times more distant from Saturn than its nearest major neighbor (Iapetus), and is substantially larger than any of the other moons orbiting planets at comparable distances.

All of Saturn's regular moons except Iapetus orbit very nearly in the plane of Saturn's equator. The outer irregular satellites follow moderately to highly eccentric orbits, and none are expected to rotate synchronously as all the inner moons of Saturn do, except for Hyperion.

The Phoebe ring is one of the rings of Saturn. This ring is tilted 27 degrees from Saturn's equatorial plane, and the other rings. It extends from at least 128 to 207 times the radius of Saturn; Phoebe orbits the planet at an average distance of 215 Saturn radii.

The ring is about 40 times as thick as the diameter of the planet. Because the ring's particles are presumed to have originated from micrometeoroid impacts on Phoebe, they should share its retrograde orbit, which is opposite to the orbital motion of the next inner moon, Iapetus. Inwardly migrating ring material would thus strike Iapetus's leading hemisphere, contributing to its two-tone coloration. Although very large, the ring is virtually invisible -it was discovered using NASA's infrared Spitzer Space Telescope.

Material displaced from Phoebe's surface by microscopic meteor impacts may be responsible for the dark areas on the surface of Hyperion. Debris from the biggest impacts may be the origin of the other moons of Phoebe's group (the Norse group) -all of which are less than 10 km in diameter.

Phoebe is roughly spherical and has a diameter of 213±1.4 km, approximately one-sixteenth that of the Moon.

Phoebe rotates every nine hours 16 minutes and it completes a full orbit around Saturn in about 18 months. Its surface temperature is on average -198.2 °C.

Most of Saturn's inner moons have very bright surfaces, but Phoebe's albedo is very low (0.06), as dark as lampblack. The Phoebean surface is heavily scarred, with craters up to 80 kilometres across, one of which has walls 16 kilometres high.

Phoebe's dark coloring initially led to scientists surmising that it was a captured asteroid, as it resembled the common class of dark carbonaceous asteroids.

These are chemically very primitive and are thought to be composed of original solids that condensed out of the solar nebula with little modification since then.

However, images from Cassini indicate that Phoebe's craters show a considerable variation in brightness, which indicate the presence of large quantities of ice below a relatively thin blanket of dark surface deposits some 300 to 500 metres thick. In addition, quantities of carbon dioxide have been detected on the surface, a finding that has never been replicated for an asteroid.

It is estimated that Phoebe is about 50% rock, as opposed to the 35% or so that typifies Saturn's inner moons. For these reasons, scientists are coming to think that Phoebe is in fact a captured centaur, one of a number of icy planetoids from the Kuiper belt that orbit the Sun between Jupiter and Neptune.

Phoebe is the first such object to be imaged as anything other than a dot.

Despite its small size, Phoebe is thought to have been a spherical body early in its history, with a differentiated interior, before solidifying and being battered into its current, slightly non-equilibrium shape.

More information: Science on a Sphere

Apart from one regio named after Phoebe's daughter, Leto, all named features are craters named after characters from the Greek legend of Jason and the Argonauts.

Phoebe formed in the Kuiper belt within three million years after the origin of the Solar System. This was early enough that sufficient radioactive material was available to melt it into a sphere and stay warm enough to have liquid water for tens of millions of years.

Unlike Saturn's other moons, Phoebe was not favorably placed for the Voyager probes. Voyager 2 observed Phoebe for a few hours in September 1981. In the images, taken from a distance of 2.2 million kilometres at low phase angle, the size of Phoebe was approximately 11 pixels and showed bright spots on the otherwise dark surface.

Cassini passed 2,068 kilometres from Phoebe on 11 June 2004, returning many high-resolution images, which revealed a scarred surface. Because Voyager 2 had not been able to produce any high quality images of Phoebe, obtaining them was a priority for the Cassini mission and its flight path was deliberately designed to take it close by; otherwise, Cassini would likely not have returned images much better than Voyager's.

Because of Phoebe's short rotation period of approximately 9 hours, 17 minutes, Cassini was able to map virtually the entire surface of Phoebe. The close fly-by enabled the mass of Phoebe to be determined with an uncertainty of only 1 in 500.

More information: The European Space Agency

Voyager found Saturn to be a planet with a complex interior,
atmosphere, and magnetosphere.
In its rings -a vast, gleaming disk of icy rubble-
the mission recorded signs of the same physical mechanisms
that were key in configuring the early solar system
and similar disks of material around other stars.

Carolyn Porco

THE GREAT CONJUNCTION OF JUPITER AND SATURN

Joseph de Ca'th Lon and The Grandma continue enjoying together talking about science.

Joseph likes Astronomy and they have been talking about the great conjunction of the planets Jupiter and Saturn that has occurred today. 

They have visited the Garraf Astronomical Observatory to enjoy this conjunction.

A great conjunction is a conjunction of the planets Jupiter and Saturn, when the two planets appear closest together in the sky.

Great conjunctions occur approximately every 20 years when Jupiter overtakes Saturn in its orbit. They are named great for being by far the rarest of the conjunctions between naked-eye planets.

The spacing between the planets varies from conjunction to conjunction with most events being 0.5 to 1.3 degrees. Very close conjunctions happen much less frequently, though the maximum of 1.3° is still close by inner planet standards: separations of less than 10 arcminutes have only happened four times since 1200, most recently in 2020.

On average great conjunction seasons occur once every 19.859 Julian years (365.25 days). This number can be calculated by the synodic period formula 1/(1/4332.59−1/10759.22) giving c. 7253.46 days -the average frequency of Jupiter overtaking Saturn from the Sun's POV due to the net effect of their 4332.59 and 10759.22-day orbits.

In practice Earth's orbit size can cause great conjunctions to reoccur up to some months away from the average time or the time they happen on the Sun. Since the equivalent periods of other naked eye planet pairs are all under 27 months this makes great conjunctions the rarest.

More information: BBC-Sky at Night Magazine

Occasionally there is more than one great conjunction in a season when they occur close enough to opposition: this is called a triple conjunction, which is not exclusive to great conjunctions.

The most recent great conjunction occurred on 21 December 2020, and the next will occur on 4 November 2040. During the 2020 great conjunction, the two planets were separated in the sky by 6 arcminutes at their closest point, which was the closest distance between the two planets since 1623.

The closeness is the result of one of the three approximately equally spaced longitude zones where great conjunctions occur shifting into the vicinity of one of the two longitudes where the two orbits appear to intersect when viewed from the Sun, which has a point of view similar to Earth.

The great conjunction zones revolve in the same direction as the planets at the rate of approximately one-sixth of a revolution per four centuries thus creating especially close conjunctions on an approximately four-century cycle. 

 

More precisely, the location in the sky of each conjunction in a series should increase in longitude by 16.3 degrees on average, making one full cycle relative to the stars on average once every 2,634 years. If instead, we use the convention of measuring longitude eastward from the First Point of Aries we have to keep in mind that the equinox circulates once every c. 25,772 years so longitudes measured that way increase slightly faster and those numbers become 17.95 degrees and 2,390 years.

 

The longitudes of close great conjunctions are currently about 307.4 and 127.4 degrees, in the constellations of Capricornus and Cancer respectively.

Earth's orbit can make the planets appear up to about 10 degrees ahead of or behind when they are at the optimal point, which also is true for any other part of their orbits.

Saturn's orbit plane is inclined 2.485 degrees relative to Earth's, and Jupiter's is 1.303 degrees.

Interestingly, the ascending nodes of both planets are similar, 100.6 degrees for Jupiter and 113.7 degrees for Saturn, so that if Saturn is above or below Earth's orbital plane Jupiter usually is too, this is partly caused by Earth's orbit being tilted relative to all the large planets.

Because the orbit inclination directions of Jupiter and Saturn align reasonably well it would be expected that no closest approach will ever be much worse than Saturn's orbit tilt (2.485°) minus Jupiter's (1.303°). Indeed, between the year 1 and 3000, the maximum conjunction distances were 1.3 degrees in 1306 and 1940.

More information: Time and Date

Conjunctions in both years occurred when the planets were tilted most out of the plane: longitude 206 degrees (therefore above the plane) in 1306, and longitude 39 degrees (therefore below the plane) in 1940.

When studying the great conjunction of 1603, Johannes Kepler thought that the Star of Bethlehem might have been the occurrence of a great conjunction. He calculated that a triple conjunction of Jupiter and Saturn occurred in 7 BC, −6 using astronomical year numbering.

A triple conjunction is a conjunction of Jupiter and Saturn at or near their opposition to the Sun.

In this scenario, Jupiter and Saturn will occupy the same right ascension on three occasions or same ecliptic longitude on three occasions depending on which definition of conjunction one uses, this is due to apparent retrograde motion and happens within months.

The most recent triple conjunction occurred in 1980 and 1981 while the next will be in 2238 and 2239. Lights in the sky that look like especially bright stars are commonplace. Jupiter & Saturn only appear to be in the same spot for a moment, but they spend weeks approaching and departing from each other.

They are visibly separate, distinct objects for the vast majority of the same evening on which the conjunction occurs, something wise men are not likely to miss. Aside from the 7 BC conjunction occurring at the wrong time, the Star of Bethlehem as described moves west, but makes a sharp turn to the south, a movement no star or planet can actually make.

Great Conjunctions never appear to be leading southward to any particular building in Isreal. Additionally, there are other, better candidates for the Star ofBethlehem.

The astronomers from the Cracow Academy, Jan Muscenius, Stanisław Jakobejusz, Nicolaus Schadeck, Petrus Probosczowicze, and others observed the great conjunction of 1563 to compare Alfonsine Tables (based on a geocentric model) with the Prutenic Tables (based on Copernican heliocentrism).

In the Prutenic Tables the astronomers found Jupiter and Saturn so close to each other that Jupiter covered Saturn, actual angular separation was 6.8 minutes on 25 August 1563.

The Alfonsine Tables suggested that the conjunction should be observed on another day but on the day indicated by the Alfonsine tables the angular separation was a full 141 minutes.

The Cracow professors suggested following the more accurate Copernican predictions and between 1578 and 1580 Copernican heliocentrism was lectured on three times by Valentin Fontani.

More information: Space

The great conjunction of 2020 was the closest since 1623 and eighth closest of the first three millennia AD, with a minimum separation between the two planets of 6.1 arcminutes. This great conjunction was also the most easily visible close conjunction since 1226, as the previous close conjunctions in 1563 and 1623 were closer to the Sun and therefore more difficult to see. It occurred seven weeks after the heliocentric conjunction, when Jupiter and Saturn shared the same heliocentric longitude.

The closest separation occurred on 21 December at 18:22 UTC, when Jupiter was 0.1° south of Saturn and 30° east of the Sun. This meant both planets appeared together in the field of view of most small and medium sized telescopes, though they were distinguishable from each other without optical aid.

During the closest approach, both planets appeared to be a binary object to the naked eye. From mid-northern latitudes, the planets were visible one hour after sunset at less than 15° in altitude above the southwestern horizon in the constellation of Capricornus.

The conjunction attracted considerable media attention, with news sources calling it the Christmas Star due to its proximity to Christmas.

More information: Earth Sky

 We must believe then, that as from hence
we see Saturn and Jupiter;
if we were in either of the Two,
we should discover a great many Worlds
which we perceive not;
and that the Universe extends so in infinitum.

Cyrano de Bergerac

THE CASSINI-HUYGENS LAST MISSION IN SPACE

The Cassini–Huygens

The Cassini–Huygens mission was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class unmanned robotic spacecraft comprised both NASA's Cassini probe, and ESA's Huygens lander which would be landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.

Launched aboard a Titan IVB/Centaur on October 15, 1997, Cassini was active in space for more than 18 years, with 13 years spent orbiting Saturn, studying the planet and its system after entering orbit on July 1, 2004. The voyage to Saturn included flybys of Venus, Earth , the asteroid 2685 Masursky, and Jupiter. 

Its mission ended on September 15, 2017, when Cassini was commanded to fly into Saturn's upper atmosphere and burn up, in order to prevent any risk of contaminating Saturn's moons, some of whose environments could potentially bear life, with stowaway terrestrial microbes. 

The Cassini–Huygens

The mission is widely perceived to have been successful beyond expectation. Cassini-Huygens has been described by NASA's Planetary Science Division Director as a mission of firsts, that has revolutionized human understanding of the Saturn system, including its moons and rings, and our understanding of where life might be found in the Solar System.

Cassini's original mission was planned to last for four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, branded the Cassini Equinox Mission. The mission was extended a second and final time with the Cassini Solstice Mission, lasting another seven years until September 15, 2017, on which date Cassini was de-orbited by being allowed to burn up in Saturn's upper atmosphere.

More information: NASA

The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; it was successfully landed by parachute on Titan on January 14, 2005. It successfully returned data to Earth for around 90 minutes, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than our own. Cassini continued to study the Saturn system in the following years.

Landed on Saturn's largest moon Titan

At the end of its mission, the Cassini spacecraft executed the Grand Finale of its mission: a number of risky passes through the gaps between Saturn and Saturn's inner rings. 

The purpose of this phase was to maximize Cassini's scientific outcome before the spacecraft was destroyed. The atmospheric entry of Cassini effectively ended the mission, although data analysis and production will continue afterwards.

Until September 2017 the Cassini probe continued orbiting Saturn at a distance of between 8.2 and 10.2 astronomical units from the Earth. It took 68 to 84 minutes for radio signals to travel from Earth to the spacecraft, and vice versa. Thus ground controllers could not give real-time instructions for daily operations or for unexpected events. Even if response were immediate, more than two hours would have passed between the occurrence of a problem and the reception of the engineers' response by the satellite.

More information: Cassini-The Grand Finale

We must believe then, that as from hence we see Saturn and Jupiter; 

if we were in either of the Two, 

we should discover a great many Worlds which we perceive not; 

and that the Universe extends so in infinitum.
 

Cyrano de Bergerac

JOSEPH DE CA'TH LON DISCOVERS THE COMET HALE-BOPP

Joseph de Ca'th Lon in Arizona Desert

I was astonished first time I saw it. It was like a big fired arrow crossing the starred sky. 

I felt very small in the middle of our unknown Universe.

My interest in Astronomy is old, since I was a teenager. I have always had an incredible feeling to look up into the sky.

The sky is a big map and we can find past answers, present mysteries and it will be a useful guide for the future generations. 

Joseph de Ca'th Lon, New Mexico, 1995

Comet Hale–Bopp, formally designated C/1995 O1, is a comet that was perhaps the most widely observed of the 20th century, and one of the brightest seen for many decades.

Joseph and Hale-Bopp in Cairo

Hale–Bopp was discovered on July 23, 1995 separately by Alan Hale and Thomas Bopp prior to it becoming naked-eye visible on Earth. 

Although predicting the maximum apparent brightness of new comets with any degree of certainty is difficult, Hale–Bopp met or exceeded most predictions when it passed perihelion on April 1, 1997. 

It was visible to the naked eye for a record 18 months, twice as long as the previous record holder, the Great Comet of 1811. 

Accordingly, Hale–Bopp was dubbed the Great Comet of 1997.

More information: NASA

Hale had spent many hundreds of hours searching for comets without success, and was tracking known comets from his driveway in New Mexico when he chanced upon Hale–Bopp just after midnight. The comet had an apparent magnitude of 10.5 and lay near the globular cluster M70 in the constellation of Sagittarius. 

Joseph and Hale-Bopp over Indian Cove, 2013

Hale first established that there was no other deep-sky object near M70, and then consulted a directory of known comets, finding that none were known to be in this area of the sky. 

Once he had established that the object was moving relative to the background stars, he emailed the Central Bureau for Astronomical Telegrams, the clearing house for astronomical discoveries.

Bopp did not own a telescope. He was out with friends near Stanfield, Arizona observing star clusters and galaxies when he chanced across the comet while at the eyepiece of his friend's telescope. He realized he might have spotted something new when, like Hale, he checked his star maps to determine if any other deep-sky objects were known to be near M70, and found that there were none. He alerted the Central Bureau for Astronomical Telegrams through a Western Union telegram. 

Brian G. Marsden, who had run the bureau since 1968, laughed, Nobody sends telegrams anymore. I mean, by the time that telegram got here, Alan Hale had already e-mailed us three times with updated coordinates.

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The following morning, it was confirmed that this was a new comet, and it was given the designation C/1995 O1. The discovery was announced in International Astronomical Union circular 6187.

Hale–Bopp's orbital position was calculated as 7.2 astronomical units (AU) from the Sun, placing it between Jupiter and Saturn and by far the greatest distance from Earth at which a comet had been discovered by amateurs.Most comets at this distance are extremely faint, and show no discernible activity, but Hale–Bopp already had an observable coma. 

Joseph and Comet Hale-Bopp over Lake Mono

An image taken at the Anglo-Australian Telescope in 1993 was found to show the then-unnoticed comet some 13 AU from the Sun, a distance at which most comets are essentially unobservable. Analysis indicated later that its comet nucleus was 60±20 kilometres in diameter, approximately six times the size of Halley.

Its great distance and surprising activity indicated that comet Hale–Bopp might become very bright indeed when it reached perihelion in 1997. However, comet scientists were wary, comets can be extremely unpredictable, and many have large outbursts at great distance only to diminish in brightness later. Comet Kohoutek in 1973 had been touted as a 'comet of the century' and turned out to be unspectacular.

The comet likely made its previous perihelion 4,200 years ago, in July 2215 BCE. The estimated closest approach to Earth was 1.4 AU, and it may have been observed in ancient Egypt during the 6th dynasty reign of the Pharaoh Pepi II (Reign: 2247 - c.2216 BCE). 

Pepi's pyramid at Saqqara contains a text referring to an "nhh-star" as a companion of the pharaoh in the heavens, where "nhh" is the hieroglyph for long hair.

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 Reality is determined not by what scientists or anyone else says or believes but by what the evidence reveals to us.

Alan Hale