Planets/Mercury Lecture

Mercury is a spheroidal rocky object in orbit around the Sun. It is part of the Solar System.

On the right is a computer program result for the orbit of Mercury. View is from above the ecliptic (North Pole). Mercury is in yellow. A circular orbit with the same semi-major axis is in grey for reference. The orbit is plotted in brighter colours above the ecliptic and darker below. Major axis is drawn showing perihelion (q) and aphelion (Q). Positions show every 5 days before and after the perihelion on May 20, 2006. For illustration the size of the sphere is inversely proportional to the distance from the Sun. The Sun is in the center. Yellow segment points toward the vernal point. Data for the plot is from the Jet Propulsion Laboratory.

Solar System
The picture dictionary display on the right shows Mercury's approximate position in the Sol (or Sun) or the Solar System.

Planets
The image on the right is an animation of the revolutions of Mercury, Venus and Earth around the Sun. Mercury takes 88 days to complete an orbit, thus the animation shows it revolving around the Sun approximately 4.14 times (yellow trail) compared to Earth's 365 days (blue trail).

As the animation at right suggests, if Earth and Mercury were coplanar in their orbits around the Sun, Mercury would transit across the Sun at least three times in an Earth year.

This can also be directly derived from the known synodic period for Mercury with the Earth of 115.88 d.

"Mercury zips around the sun faster than any other planet. It travels about 112,000 mph (180,000 km/h) along its elliptical orbit. The planet gets as close as 29 million miles (47 million km) to the sun, and as distant as 43 million miles (70 million km) from the sun."

Theoretical planetary Mercury
Perhaps the simplest theory for the formation of Mercury would be as a part of the solar nebula from which the Sun may have originated. If this theory is correct the orbital pole of Mercury should align with the geographic pole of the Sun to a high degree.

An orbital pole is either end of an imaginary line running through the center of an orbit perpendicular to the orbital plane, projected onto the celestial sphere. It is similar in concept to a celestial pole but based on the planet's orbit instead of the planet's rotation.

The north orbital pole of a celestial body is defined by the right-hand rule: If you curve the fingers of your right hand along the direction of orbital motion, with your thumb extended parallel to the orbital axis, the direction your thumb points is defined to be north.

At right, is a snapshot of the planetary orbital poles. The field of view is about 30°. The yellow dot in the centre is the Sun's North pole. Off to the side, the orange dot is Jupiter's orbital pole. Clustered around it are the other planets: Mercury in pale blue (closer to the Sun than to Jupiter), Venus in green, the Earth in blue, Mars in red, Saturn in violet, Uranus in grey partly underneath Earth and Neptune in lavender. Dwarf planet Pluto is the dotless cross off in Cepheus.

Calculations using the determined orbital parameters of Mercury suggest that its current orbit has been stable for at least 2,000 years.

However, historical observations suggest that Mercury's orbital position may have changed to what it is now.

Planetary astronomy
The diagram on the right shows how Mercury's orbital period and rotational period are locked in a 3:2 resonance.

After one orbit, Mercury has rotated 1.5 times, so after two complete orbits the same hemisphere is again illuminated.

Sun-Mercury system
In the image on the right sunspot #923, which is just below the equator at the left-hand side, is much bigger than Mercury. Two more sunspots are on the right-hand side at the equator. Mercury is a small black dot in the lower middle of the solar disk. The picture was taken with a white filter.

The diagram in the second image from the top on the right shows that because "Mercury and Venus orbit the Sun within Earth's orbit, they stay close to the Sun in the sky as seen from Earth. At their greatest angular distance from the Sun they are said to be at elongation. Here the two planets are shown at eastern elongation; they set after the Sun and appear as evening stars."

The third down image on the right shows "five versions of observations that NASA's Curiosity made about one hour apart while Mercury was passing in front of the sun on June 3, 2014. Two sunspots, each about the diameter of Earth, also appear, moving much less than Mercury during the hour."

"This is the first transit of the sun by a planet observed from any planet other than Earth, and also the first imaging of Mercury from Mars. Mercury fills only about one-sixth of one pixel as seen from such great distance, so the darkening does not have a distinct shape, but its position follows Mercury's expected path based on orbital calculations."

"This is a nod to the relevance of planetary transits to the history of astronomy on Earth."

"Observations of Venus transits were used to measure the size of the solar system, and Mercury transits were used to measure the size of the sun."

"The observations were made on June 3, 2014, from Curiosity's position inside Gale Crater on Mars. In addition to showing the Mercury transit, the same Mastcam frames show two sunspots approximately the size of Earth. The sunspots move only at the pace of the sun's rotation, much slower than the movement of Mercury."

Prehistory
The prehistory period dates from around 7 x 106 b2k to about 7,000 b2k.

“Saturn has been known since prehistoric times.

Paleolithic
The paleolithic period dates from around 2.6 x 106 b2k to the end of the Pleistocene around 12,000 b2k.

Mesolithic
The mesolithic period dates from around 13,000 to 8,500 b2k.

"All that we have considered up to now indicates that Saturn [Arka] once exploded in a nova-like burst of light. The date of this event I would be hard-put to specify, even approximately, but possibly it took place about ten thousand years ago. The solar system and reaches beyond it were illuminated by the exploded star, and in a matter of a week the Earth was enveloped in waters of Saturnian origin."

Ancient history
The ancient history period dates from around 8,000 to 3,000 b2k.

Hominins “lived without town or laws, speaking one tongue under the rule of Jove. But after Mercury explained the languages of men (whence he is called hermeneutes, ‘interpreter,’ for Mercury in Greek is called Hermes; he, too, divided the nations) then discord arose among mortals.”

“The meaning is clearly that Hermes invented one language for one people, another for another. The whole account reminds one of the Biblical Tower of Babel.”

"In my understanding Mercury was once a satellite of Jupiter, or possibly of Saturn. In the course of the events which followed Saturn’s interaction with Jupiter and its subsequent disruption, Mercury was pushed from its orbit and was directed to the sun by Jupiter. It could, however, have been a comet and the entwined snakes of the caduceus may memorialize the appearance it had when seen by the inhabitants of the Earth."

Apparently 5102 b2k (before the year 2000.0), -3102 or 3102 BC, is the historical year assigned to a Hindu table of planets that does include the classical planet Mercury. "Babylonian astronomy, too, had a four-planet system. In ancient prayers the planets Saturn, Jupiter, Mars, and Mercury are invoked; ... and one speaks of "the four-planet system of the ancient astronomers of Babylonia." "

Enki
"Enki ... is a god [dingir] in Sumerian mythology ... Beginning around the second millennium BCE [~4000 b2k], he was sometimes referred to in writing by the numeric ideogram for "40," occasionally referred to as his "sacred number."   The planet Mercury, associated with Babylonian Nabu (the son of Marduk) was in Sumerian times, identified with Enki.

Hermes
Hermes Greek : Ἑρμῆς is son of Zeus and the Pleiade Maia. In the Roman adaptation of the Greek pantheon, Hermes was identified with the Roman god Mercury, who, is inherited from the Etruscans. The Thracian princes identified him with their god Zalmoxis, considering his ancestor.

Nabu
Nabu (in Biblical Hebrew Nebo נבו) is the Assyrian and Babylonian god of wisdom and writing, worshipped by Babylonians as the son of Marduk and his consort, Sarpanitum, and as the grandson of Ea.

In Chaldean mythology, Nebo was a god whose worship was introduced into Assyria by Pul [Tiglath-pileser III] (Isa. 46:1; Jer. 48:1). The great temple at Birs Nimrud was dedicated to Nebo.

Ningishzida
"The caduceus was an emblem of the Babylonian deity Ningishzida, and an astronomical tablet from Boghazkoi [Boghaz Keui, in Anatolia] identifies Ningishzida with Nebo-Mercury (Weidner, Handbuch der babylonischen Astronomie, p. 61 )."

Thoth
Thoth in the Greeks' interpretation was the same as their god Hermes) and Shmounein in the Coptic rendering. The Greeks related Thoth to their god Hermes due to his similar attributes and functions. Egyptian mythology also credits him with the creation of the 365 day calendar. Originally, according to the myth, the year was only 360 days long and Nut was sterile during these days, unable to bear children. Thoth gambled with Khonsu, the Moon, for 1/72nd of its light (360/72 = 5), or 5 days, and won. During these 5 days, Nut gave birth to Kheru-ur (Horus the Elder, Face of Heaven), Osiris, Set, Isis, and Nepthys.

In the Ogdoad cosmogony, Thoth gave birth to Ra, Atum, Nefertum, and Khepri by laying an egg while in the form of an ibis, or later as a goose laying a golden egg.

Early history
The early history period dates from around 3,000 to 2,000 b2k. ~ 3300 b2k: The earliest known recorded observations of Mercury are from the Mul.Apin tablets. These observations were most likely made by an Assyrian astronomer around the 14th century BC. The cuneiform name used to designate Mercury on the Mul.Apin tablets is transcribed as Udu.Idim.Gu\u4.Ud ("the jumping planet").

~ 2900 b2k: Babylonian records of Mercury date back to the 1st millennium BC. The Babylonians called the planet Nabu after the messenger to the gods in their mythology.

~2400 b2k: The ancient Greeks of Hesiod's time knew the planet as (Stilbon), meaning "the gleaming", and (Hermaon).

The Romans named the planet after the swift-footed Roman messenger god, Mercury (Latin Mercurius), which they equated with the Greek Hermes, because it moves across the sky faster than any other planet.

In ancient China, Mercury was known as Chen Xing (辰星), the Hour Star. It was associated with the direction north and the phase of water in the Wu Xing. Hindu mythology used the name Budha for Mercury, and this god was thought to preside over Wednesday. The god Odin (or Woden) of Germanic paganism was associated with the planet Mercury and Wednesday. The Maya may have represented Mercury as an owl (or possibly four owls; two for the morning aspect and two for the evening) that served as a messenger to the underworld.

Classical history
The classical history period dates from around 2,000 to 1,000 b2k.

Later Greeks called the planet Apollo when it was visible in the morning sky, and Hermes when visible in the evening. Around the 4th century BC, Greek astronomers came to understand that the two names referred to the same body.

Recent history
The recent history period dates from around 1,000 b2k to present.

On the right is Ibn al-Shatir's model for the appearances of Mercury. This model occurred in the 14th century, or 700-600 b2k.

On the left is the frontispiece "of Riccioli's 1651 New Almagest. [In it mythological] figures observe the heavens with a telescope and weigh the heliocentric theory of Copernicus in a balance against his modified version of Tycho Brahe's geo-heliocentric system, in which the Sun, Moon, Jupiter and Saturn orbit the Earth while Mercury, Venus, and Mars orbit the Sun. The old Ptolemaic geocentric theory lies discarded on the ground, made obsolete by the telescope's discoveries. These are illustrated at top and include phases of Venus and Mercury and a surface feature on Mars (left), moons of Jupiter, rings of Saturn, and features on the moon (right). The balance tips in favor of Riccioli's "Tychonic" system."

The second page down on the left is dated to 1661, 339 b2k, and describes the theory of Ptolemy.

The page on the right is a chart of the Solar System up to the orbit of the planet Saturn. The tracks of three comets are indicated, which appeared in the years 1662, 1680 and 1682, respectively. The page is dated to 1727, 273 b2k.

Hypotheses

 * 1) Sufficient evidence may exist to demonstrate that the apparently stable orbit of Mercury today was arrived at within hominin collective and recorded history.