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Even though we are currently living in an era of knowledge, scientific discovery and understanding, know that both the science and the terminology developed by those of ancient times to comprehend and describe the heavens as well as to predict futures events, continues to be used in this modern day.
So, again, know and understand, that the most important aspect of understanding the concepts of astronomical science today, is that all of the terminology used is based on the earthbound perspective, or what is now called Observational Astronomy.
When it comes to Astronomy, there are two primary types, that being Observation Astronomy and Physical Astronomy. However, like many other scientific studies, there are always sub-divisions of the primary study types.
Observational verses Physical Astronomy
A good example of how Observational Astronomy is different from Physical Astronomy is found when examining the
Great Conjunction of Jupiter and Saturn in December 2020.
Observational Astronomy revealed that on the evenings of 19-21 December 2020, the conjunction which occurred during the evening twilight and was a celestial event called a
Great Conjunction whereupon the two celestial objects passed within less than one degree of each another in the night sky.
A Great Conjunction is a somewhat rare celestial event occurring only once every twenty years or more. However, this year, these two planets passed by closer than they have for more than four hundred years, The last time the two planets were closer occured during the time when Galileo, who we now call the Father of Observational Astronomy. Further, at that time, he was viewing that Great Conjunction with the newest technology of his day, a telescope.
As seen from the photographs that I took during that celestial event, the two planets came to within a very close proximity. In fact, during the December 2020 great conjunction, the two planets were separated in the sky at their closest approach by 6 arc-minutes (0°6'), the closest observational distance between these two planets since 1623.
When viewing the angular distance of a planet from the Sun, with the Earth as the reference point, the amount of that angular distance, measured in degrees, is called the elongation. An elongation of 0°: is called conjunction; an elongation of of 90° is called quadrature, and an elongation of 180° is called opposition.
Positional Astronomy, also know as Spherical astronomy, is a branch of observational astronomy used to locate astronomical objects on the celestial sphere, as seen at a particular date, time, and location on Earth. It relies on the mathematical methods of spherical trigonometry and the measurements of astrometry.
In simplest terms, opposition is when a celestial object, (specifically, one that is part of the solar system) is, on the side opposite of the earth in relation to the Sun (solar system primary).
However, modern Physical Astronomy reveals that during this same great conjunction on 21 December 2020, the closest these two planets actually get to one other is a distance of more than 456 million miles.
Thus, in the following paragraphs, be fully aware that the terminology being discussed was created when the science was based entirely upon Observational Astronomy. Too, keep in mine as you learn the terminology, remember that all of the Observational Astronomy science is based on what an earthbound viewer sees, or that which is called apparent phenomena.
Physical Astronomy is different in that it is a branch of astronomy that applies the laws of physics to study the nature, composition, structure and dynamics of celestial objects and phenomena. This is an astronomical model that endeavors to provide a mathematical description of the largest scale structures and dynamics of the universe and which implies that celestial bodies all obey identical physical laws to those on the Earth, including the three laws of Newtonian mechanics, stated by Isaac Newton in his Philospophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) originally published in 1687.
Newton used them to investigate and explain the motion of many physical objects and systems. In the time since Newton, new insights, especially around the concept of energy, built the field of classical mechanics on his foundations. In modern times, limitations to Newton′s laws have been discovered; then, new theories were consequently developed, such as quantum mechanics and relativity to address the physics of objects in more extreme cases.
Also know as apparent motion phenomena, this is what appears to be happening in the celestial sphere when celestial objects move about in their orbits. From the Earth′s perspective, the other planets are observed to move closely along an imaginary arc-circle in the sky known as the ecliptic (see below), which is also the apparent path of the Sun′s movement on the celestial sphere (see below).
For instance, the Sun appears to move from east to west across the sky every day. This is an apparent phenomena because with relation to the Earth, the sun never moves and it is the Earth that really moves, it fact it is the rotation of the Earth on its north-south axis that causes this optical illusion. Again, this is apparent motion, which is when celestial objects, the Sun, Moon, Stars, Planents, all appear to move across the sky. The celestial object move across the sky in an arc, all movement occurs at a constant rate of about 15° per hour or 360° in 24 hours. The movements of celestial objects over a 24 hour period are called daily motion. Retrograde motion of a celestial object is also an apparent motion.
The rise and set of a planet as observed from the Earth is related to its apparent motion relative to the Sun. This apparent motion depends on whether the planet is nearer the Sun than the Earth (an inferior planet) or further away from the Sun than the Earth (a superior planet).
A good example of both Observational Astronomy and Apparent Phenomenon is when the planets align in the night sky along the ecliptic. From the Earthbound Perspective the several planets all appear to be in close proximity of each other. This phenomenon is from observation astronomy because as we know, there are millions of miles between each celestial object. This is also Apparent Phenomenon because the movement of each celestial object in their own orbit brings each to this position to create this Planetary Alignment.
Nevertheless, what a grand creation we have to observe from our Earthbound Perspective. This creation is truly one that we could never grow tired of, but only marvel at the vastness and multitude of variability of the phenomenon.
Inferior-Superior Planets
Mercury and Venus are inferior planets in the Solar System. They are closer to the Sun than the Earth. Mars, Jupiter, Saturn, Uranus and Neptune are superior planets in the Solar System. They are further away from the Sun than the Earth.
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For an inferior planet, the conjunction is called inferior conjunction if the planet is between the Sun and the Earth, and is called superior conjunction if it is on the opposite side of the Sun from the Earth.
When an inferior planet follows the Sun and appears east of the Sun in the evening, it is in eastern elongation. When an inferior planet precedes the Sun and appears west of the Sun in the morning, it is in western elongation. As both the orbits of an inferior planet and the Earth are elliptical rather than circular, the greatest elongation varies from 18° to 28° for Mercury and from 47° to 48° for Venus respectively.
At inferior conjunction, an inferior planet may appear as a dark dot moving across the Sun′s disc. This is known as the
Transit of the inferior planet. Such phenomenon does not occur every year because the orbit of the inferior planets do not lie exactly on the plane of the orbit of the Earth, which is the planet that has an orbit closest to the plane of the ecliptic. Mercury has an inclination to the ecliptic of 7.005 ° and Venus has an inclination to the ecliptic of 3.39458°:.
A superior planet at opposition is closest to the Earth and appears the brightest. At conjunction, a superior planet will be invisible due to the glare of the Sun.
Spherical astronomy is a branch of observational astronomy used to locate
celestial objects on the
celestial sphere, as seen at a specific date, time and location upon the Earth, relying on the mathematical methods of spherical geometry and the measurements of astrometry and based on the kinematics (a sub-field of physics that describes the motion of points, objects, and systems of objects, without considering the forces that cause them to move) of the Solar System and our galaxy, the Milky Way.
Simple Definition
As its name suggests, the study of spherical astronomy, using physics and the language of mathematics, purports to describe and understand the positions and motions of objects which occur in the night sky.
Spherical Astronomy Discussion
This is a field that today is often neglected, and yet it is still the foundation of many branches of astronomy for observations and research, even if this is not always clearly evident. Every observer is confronted with problems involving spherical astronomy in practical work.
For example, for someone to observe a certain astronomical object such as the Big Dipper constellation (ursa major), it is necessary to find its location, or coordinates, on the celestial sphere (night sky). The processing of observed data also often involves methods, many of which are based on spherical astronomy.
The system of locating coordinates on a sphere, be it a point on the globe of the earth or the celestial sphere is defined by two coordinates but this assumes that the coordinate system itself is uniquely defined. Probably, the one most often used is the Geographic Coordinate system. The geographic coordinate system that observers use to locate a point upon the surface of the Earth is defined by three coordinates: Latitude, Longitude and Altitude.
Latitude is measured from 0° at the equator and up to 90° at it′s poles, positive to the north and negative to the south. Circles parallel to the equator are called latitude and become smaller in diameter as the number of degrees increase.
Longitude is a plane that cuts through the imaginary line which is the polar axis of the Earth and is also perpendicular to the equator. An international agreement has established the zero longitude (or meridian) at the Royal Observatory, Greenwich, England. Longitude is measured from 0° to 180°, positive to the west of Greenwich and negative to the east.
Altitude is a measurement of a point in relation by determining how high above sea level the point is located.
Using Spherical Astronomy
The celestial equator and celestial sphere are practical tools for spherical astronomy, allowing observers to plot positions of objects in the sky when their distances are unknown and in fact, to spherical astronomy, even unimportant.
As part of spherical astronomy, the observer looks at our solar system as if it is all points of light on the celestial sphere which is more commonly called the night sky. Also, from the perspective of the observer on Earth using spherical astronomy, the Moon, the Sun and all of the Planets are seen to be on the celestial sphere and traveling along the ecliptic. The ancients believed all of the celestial objects were attached to the outer area of the celestial sphere with the earth in it′s middle.
Even thought in somewhat more modern times, physical astronomy moved the Sun to the middle of the sphere with the celestial solar system objects orbiting the Sun, spherical astronomy continues to be a tool for plotting, tracking and predicting both objects and event within the celestial heavens.
Furthermore, the Sun and all the planets encircling the Sun, all being upon the ecliptic plane, can be depicted as objects which all sit atop a table. Thus, some moderns believe that this table top description of the solar system suggests that the formation process of the solar system was first an enormous disk of material, possibly spinning like a top, out of which was formed the sun, the planets, the asteroid belt, the comets and all the other solar system objects.
However, this is entirely speculative because how the creator actually formed the solar system has not been revealed to man. What God has chosen to tell mankind can be found at Genesis 1:1 which simply informs us: In the beginning God created the heaven and the earth.
The ecliptic is an imaginary line forming a great circle in the heavens which represents the apparent annual path of the sun. This path is the one the sun takes as it appears to an earthbound viewer. Too, this imaginary line is drawn by the path of the sun and planets upon the inside of the
celestial sphere as shown in this photo.
From the perspective of an earthbound observer, the sun appears to move around the earth in an arc across the sky. In modern astronomy science, this path of the sun is called the ecliptical path, or more commonly the ecliptic. Too, this apparent path of the sun continues completely around the earth, creating a circle, which when extended outward from the earth throughout the entire solar system can be said to forms a plane. These same earthbound observers can see that the planets are following the ecliptic path, the same path the sun takes.
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In Physical Astronomy, this conjoined path establishes that all the planets orbit the sun in essentially the same plane. With all these objects circling the sun, their orbit creates an imaginary plane which is called the Ecliptic Plane.
Thus, the Sun and all of the planets are said by some to be situated on top of a table as if some one had set dinnerware for a meal.
The ecliptic plane is the mean plane of the apparent path in the sky that the Sun follows over the course of one year as seen from earthbound viewers, and this plane is the basis of the ecliptic coordinate system.
This plane of reference is coplanar with the orbit of the Earth around the Sun and as seen by the ancients was instead, the path of the Sun around the Earth.
Too, the ecliptic plane is tilted 23.5 degrees with respect to the celestial equator which is caused by the spin axis of the Earth being tilted the same 23.5 degrees with respect its orbit around the Sun. (See Celestial Equator and Celestial Sphere below.)
Celestial Equator
In Observational Astronomy, the
celestial equator is the imaginary plane, perpendicular to the
Earth′s Axis that extends from the Earth′s equator outward to the celestial sphere. Again, from the perspective of earthbound viewers, the Sun, the Moon and the Planets all appears to travel, not along the celestial equator but instead, along the ecliptic.
On the exact day when the Sun passes over a location directly above the Earth′s equator, (or in other words, when the path of the sun intersects the celestial equator) the people on earth will be experiencing one of the two equinoxes, either the vernal equinox at the beginning of spring, or the autumnal equinox at the start of autumn.
Also, when the Sun passes through the location that is the furthest from the celestial equator, and ninety degrees from the equinoxes, the people on earth will be experiencing on ot the two solstices, either the estival solstice at the beginning of summer or the hibernal solstice at the beginning of winter
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Thus, the celestial plane, created by the angle that the earth is tilted from the ecliptical plane, is the reason for the sun, the moon and the planets to appear to travel along an arc through the sky.
(m5pr-solarsystem) The Solar System Model and Ecliptic Plane (Not to Scale)
Physical Astrology shows that this angle, as measured between the celestial equator and the ecliptic, has the tilt of the Earth currently (23 December 2020) at 23.43655 degrees. Also, Physical Astrology has found that the
Earth′s tilt varies during a cycle of about 41,000 years.
The Earth, being so tilted at 23.44° with respect to the ecliptic results in what know to astronomers as the obliquity of the ecliptic. Interesting, if man was living on a different planet in this solar system, except Mars which has a tilt of 25°, the resulting celestial equator would be very different. See Solar System Model above
Further, this same arc seen from the Earth has provided Physical Astrology with the understanding that the earth′s axis is tilted with respect to the ecliptic, a tilt that this science understands is what provide the seasonal variations in the amount of sunlight and climate received on the surface.
Both the celestial and ecliptic planes, according to Observational Astronomy extend outwards from the Earth to the celestial sphere upon which all celestial objects are said to exist, or be holes in this sphere where the object′s light is allowed to come through.
The solar system model in spherical astronomy has the moon, the planets and sun orbiting the Earth while traveling around the ecliptic on the celestial sphere.
Remember, this is the perspective of earthbound viewers looking outward.
When looking up at the heavens, all the objects appeared to be located on the sphere at the same distance from the earth.
So, the celestial sphere was an imaginary sphere of arbitrarily large radius with the Earth located inside the sphere at the center.
Thus, the night sky in spherical astronomy is called the celestial sphere. The equator of the earth projected upon that sphere is called the celestial equator. The highest location on the celestial sphere is where the North Star is located which is directly above the Earth′s northern pole.
When the ecliptical plane extends outward from the earth, it intersects the Sun and all the Planets. Pluto, however, has been demoted from being a planet because it is not on the ecliptic plane. In fact, it′s orbit is more elongated, or eccentric, than any of the planetary orbits and is inclined at 17.1 degrees to the ecliptic. Thus, like all other non planet objects, it only intersects the ecliptic twice in it′s orbit.
The ecliptical plane also intersects the Moon but only when the Moon enters the lunar orbital nodes. The Moon has an inclination of 5.14° from the ecliptic and only crosses the ecliptic twice as it orbits the earth. These two crossings of the ecliptic are referred to as the Lunar Nodes and it is only when the moon is in these two lunar nodes can there be full eclipses, either lunar or solar.
(m5pr-lunarnodes) The Lunar Nodes and Ecliptical Plane
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