Precession, Constellations and the Aquarius Equinox Epoch

Total Page：16

File Type：pdf, Size：1020Kb

Bulletin of the AAS • Vol. 52, Issue 3 (AAS236 abstracts) Precession, Constellations and the Aquarius Equinox Epoch S. Durst1 1International Lunar Observatory Association (ILOA), Kamuela, HI Published on: Jun 01, 2020 Updated on: Jul 15, 2020 License: Creative Commons Attribution 4.0 International License (CC-BY 4.0) Bulletin of the AAS • Vol. 52, Issue 3 (AAS236 abstracts) Precession, Constellations and the Aquarius Equinox Epoch Earth axial precession, called “Earth's 3rd Motion”, is the geo-dynamic process which results in the Sun appearing from Earth at any equinox to move counter-clockwise on the ecliptic through constellations of the zodiac: The Precession of the Equinoxes. Through evolving 21st Century techniques (such as VLBI and astronomy from the Moon), accurately observing the Earth’s rotation / precession may help more precisely determine the apparent arrival of the Sun on the ecliptic in the constellation of Aquarius at the time of the vernal equinox, which is now calculated about 2597 AD using the IAU 1928 / current map. With the approach to J2000.0 / New Millennium from the 1960s / 1970s especially, astrophysics and astrometry scientists have been focusing intensely on Earth Precession rates and expressions. Work on Precession and Rotation of the Earth has accelerated since 1930, when the 88 constellations and their boundaries — fixed by Delporte along strict lines of declination and right ascension as they existed at epoch 1875.0 — finally became ratified and published by the International Astronomical Union (IAU). We will also discuss our efforts to form a Working Group with the focus on Earth Precession, Constellations and Epochs — much of which is to be advanced at the planned Galaxy Forum South America 2020 Bariloche on 8 December at which experts will meld research and ideas for astronomy from the Moon, VLBI, precession and the history of constellations in various cultures. 2.

Copy Link

Recommended publications

Equatorial and Cartesian Coordinates • Consider the Unit Sphere (“Unit”: I.E
Coordinate Transforms Equatorial and Cartesian Coordinates • Consider the unit sphere (“unit”: i.e. declination the distance from the center of the (δ) sphere to its surface is r = 1) • Then the equatorial coordinates Equator can be transformed into Cartesian coordinates: right ascension (α) – x = cos(α) cos(δ) – y = sin(α) cos(δ) z x – z = sin(δ) y • It can be much easier to use Cartesian coordinates for some manipulations of geometry in the sky Equatorial and Cartesian Coordinates • Consider the unit sphere (“unit”: i.e. the distance y x = Rcosα from the center of the y = Rsinα α R sphere to its surface is r = 1) x Right • Then the equatorial Ascension (α) coordinates can be transformed into Cartesian coordinates: declination (δ) – x = cos(α)cos(δ) z r = 1 – y = sin(α)cos(δ) δ R = rcosδ R – z = sin(δ) z = rsinδ Precession • Because the Earth is not a perfect sphere, it wobbles as it spins around its axis • This effect is known as precession • The equatorial coordinate system relies on the idea that the Earth rotates such that only Right Ascension, and not declination, is a time-dependent coordinate The effects of Precession • Currently, the star Polaris is the North Star (it lies roughly above the Earth’s North Pole at δ = 90oN) • But, over the course of about 26,000 years a variety of different points in the sky will truly be at δ = 90oN • The declination coordinate is time-dependent albeit on very long timescales • A precise astronomical coordinate system must account for this effect Equatorial coordinates and equinoxes • To account
[Show full text]
Obliquity Variability of a Potentially Habitable Early Venus
ASTROBIOLOGY Volume 16, Number 7, 2016 Research Articles ª Mary Ann Liebert, Inc. DOI: 10.1089/ast.2015.1427 Obliquity Variability of a Potentially Habitable Early Venus Jason W. Barnes,1 Billy Quarles,2,3 Jack J. Lissauer,2 John Chambers,4 and Matthew M. Hedman1 Abstract Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could have been in solid form, implying a low-mass atmosphere. We investigate how the obliquity would have varied for a hypothetical rapidly rotating Early Venus. The obliquity variation structure of an ensemble of hypothetical Early Venuses is simpler than that Earth would have if it lacked its large moon (Lissauer et al., 2012), having just one primary chaotic regime at high prograde obliquities. We note an unexpected long-term variability of up to –7° for retrograde Venuses. Low-obliquity Venuses show very low total obliquity variability over billion-year timescales—comparable to that of the real Moon-inﬂuenced Earth. Key Words: Planets and satellites—Venus. Astrobiology 16, 487–499. 1. Introduction Perhaps paradoxically, large-amplitude obliquity varia- tions can also act to favor a planet’s overall habitability. he obliquity C—deﬁned as the angle between a plan- Low values of obliquity can initiate polar glaciations that Tet’s rotational angular momentum and its orbital angular can, in the right conditions, expand equatorward to en- momentum—is a fundamental dynamical property of a pla- velop an entire planet like the ill-fated ice-planet Hoth in net.
[Show full text]
3.- the Geographic Position of a Celestial Body
Chapter 3 Copyright © 1997-2004 Henning Umland All Rights Reserved Geographic Position and Time Geographic terms In celestial navigation, the earth is regarded as a sphere. Although this is an approximation, the geometry of the sphere is applied successfully, and the errors caused by the flattening of the earth are usually negligible (chapter 9). A circle on the surface of the earth whose plane passes through the center of the earth is called a great circle . Thus, a great circle has the greatest possible diameter of all circles on the surface of the earth. Any circle on the surface of the earth whose plane does not pass through the earth's center is called a small circle . The equator is the only great circle whose plane is perpendicular to the polar axis , the axis of rotation. Further, the equator is the only parallel of latitude being a great circle. Any other parallel of latitude is a small circle whose plane is parallel to the plane of the equator. A meridian is a great circle going through the geographic poles , the points where the polar axis intersects the earth's surface. The upper branch of a meridian is the half from pole to pole passing through a given point, e. g., the observer's position. The lower branch is the opposite half. The Greenwich meridian , the meridian passing through the center of the transit instrument at the Royal Greenwich Observatory , was adopted as the prime meridian at the International Meridian Conference in 1884. Its upper branch is the reference for measuring longitudes (0°...+180° east and 0°...–180° west), its lower branch (180°) is the basis for the International Dateline (Fig.
[Show full text]
1 the Equatorial Coordinate System
General Astronomy (29:61) Fall 2013 Lecture 3 Notes , August 30, 2013 1 The Equatorial Coordinate System We can define a coordinate system fixed with respect to the stars. Just like we can specify the latitude and longitude of a place on Earth, we can specify the coordinates of a star relative to a coordinate system fixed with respect to the stars. Look at Figure 1.5 of the textbook for a definition of this coordinate system. The Equatorial Coordinate System is similar in concept to longitude and latitude. • Right Ascension ! longitude. The symbol for Right Ascension is α. The units of Right Ascension are hours, minutes, and seconds, just like time • Declination ! latitude. The symbol for Declination is δ. Declination = 0◦ cor- responds to the Celestial Equator, δ = 90◦ corresponds to the North Celestial Pole. Let's look at the Equatorial Coordinates of some objects you should have seen last night. • Arcturus: RA= 14h16m, Dec= +19◦110 (see Appendix A) • Vega: RA= 18h37m, Dec= +38◦470 (see Appendix A) • Venus: RA= 13h02m, Dec= −6◦370 • Saturn: RA= 14h21m, Dec= −11◦410 −! Hand out SC1 charts. Find these objects on them. Now find the constellation of Orion, and read off the Right Ascension and Decli- nation of the middle star in the belt. Next week in lab, you will have the chance to use the computer program Stellar- ium to display the sky and find coordinates of objects (stars, planets). 1.1 Further Remarks on the Equatorial Coordinate System The Equatorial Coordinate System is fundamentally established by the rotation axis of the Earth.
[Show full text]
2 Coordinate Systems
2 Coordinate systems In order to find something one needs a system of coordinates. For determining the positions of the stars and planets where the distance to the object often is unknown it usually suffices to use two coordinates. On the other hand, since the Earth rotates around it’s own axis as well as around the Sun the positions of stars and planets is continually changing, and the measurment of when an object is in a certain place is as important as deciding where it is. Our first task is to decide on a coordinate system and the position of 1. The origin. E.g. one’s own location, the center of the Earth, the, the center of the Solar System, the Galaxy, etc. 2. The fundamental plan (x−y plane). This is often a plane of some physical significance such as the horizon, the equator, or the ecliptic. 3. Decide on the direction of the positive x-axis, also known as the “reference direction”. 4. And, finally, on a convention of signs of the y− and z− axes, i.e whether to use a left-handed or right-handed coordinate system. For example Eratosthenes of Cyrene (c. 276 BC c. 195 BC) was a Greek mathematician, elegiac poet, athlete, geographer, astronomer, and music theo- rist who invented a system of latitude and longitude. (According to Wikipedia he was also the first person to use the word geography and invented the disci- pline of geography as we understand it.). The origin of this coordinate system was the center of the Earth and the fundamental plane was the equator, which location Eratosthenes calculated relative to the parts of the Earth known to him.
[Show full text]
Celestial Coordinate Systems
Celestial Coordinate Systems Craig Lage Department of Physics, New York University, [email protected] January 6, 2014 1 Introduction This document reviews briefly some of the key ideas that you will need to understand in order to identify and locate objects in the sky. It is intended to serve as a reference document. 2 Angular Basics When we view objects in the sky, distance is difficult to determine, and generally we can only indicate their direction. For this reason, angles are critical in astronomy, and we use angular measures to locate objects and define the distance between objects. Angles are measured in a number of different ways in astronomy, and you need to become familiar with the different notations and comfortable converting between them. A basic angle is shown in Figure 1. θ Figure 1: A basic angle, θ. We review some angle basics. We normally use two primary measures of angles, degrees and radians. In astronomy, we also sometimes use time as a measure of angles, as we will discuss later. A radian is a dimensionless measure equal to the length of the circular arc enclosed by the angle divided by the radius of the circle. A full circle is thus equal to 2π radians. A degree is an arbitrary measure, where a full circle is defined to be equal to 360◦. When using degrees, we also have two different conventions, to divide one degree into decimal degrees, or alternatively to divide it into 60 minutes, each of which is divided into 60 seconds. These are also referred to as minutes of arc or seconds of arc so as not to confuse them with minutes of time and seconds of time.
[Show full text]
Positional Astronomy Coordinate Systems
Positional Astronomy Observational Astronomy 2019 Part 2 Prof. S.C. Trager Coordinate systems We need to know where the astronomical objects we want to study are located in order to study them! We need a system (well, many systems!) to describe the positions of astronomical objects. The Celestial Sphere First we need the concept of the celestial sphere. It would be nice if we knew the distance to every object we’re interested in — but we don’t. And it’s actually unnecessary in order to observe them! The Celestial Sphere Instead, we assume that all astronomical sources are infinitely far away and live on the surface of a sphere at infinite distance. This is the celestial sphere. If we define a coordinate system on this sphere, we know where to point! Furthermore, stars (and galaxies) move with respect to each other. The motion normal to the line of sight — i.e., on the celestial sphere — is called proper motion (which we’ll return to shortly) Astronomical coordinate systems A bit of terminology: great circle: a circle on the surface of a sphere intercepting a plane that intersects the origin of the sphere i.e., any circle on the surface of a sphere that divides that sphere into two equal hemispheres Horizon coordinates A natural coordinate system for an Earth- bound observer is the “horizon” or “Alt-Az” coordinate system The great circle of the horizon projected on the celestial sphere is the equator of this system. Horizon coordinates Altitude (or elevation) is the angle from the horizon up to our object — the zenith, the point directly above the observer, is at +90º Horizon coordinates We need another coordinate: define a great circle perpendicular to the equator (horizon) passing through the zenith and, for convenience, due north This line of constant longitude is called a meridian Horizon coordinates The azimuth is the angle measured along the horizon from north towards east to the great circle that intercepts our object (star) and the zenith.
[Show full text]
Activity 3 How Do Earth's Orbital Variations Affect Climate?
CS_Ch12_ClimateChange 3/1/2005 4:56 PM Page 761 Activity 3 How Do Earth’s Orbital Variations Affect Climate? Activity 3 How Do Earth’s Orbital Variations Affect Climate? Goals Think about It In this activity you will: When it is winter in New York, it is summer in Australia. • Understand that Earth has an axial tilt of about 23 1/2°. • Why are the seasons reversed in the Northern and • Use a globe to model the Southern Hemispheres? seasons on Earth. • Investigate and understand What do you think? Write your thoughts in your EarthComm the cause of the seasons in notebook. Be prepared to discuss your responses with your small relation to the axial tilt of group and the class. the Earth. • Understand that the shape of the Earth’s orbit around the Sun is an ellipse and that this shape influences climate. • Understand that insolation to the Earth varies as the inverse square of the distance to the Sun. 761 Coordinated Science for the 21st Century CS_Ch12_ClimateChange 3/1/2005 4:56 PM Page 762 Climate Change Investigate Part A: What Causes the Seasons? Now, mark off 10° increments An Experiment on Paper starting from the Equator and going to the poles. You should have eight 1. In your notebook, draw a circle about marks between the Equator and pole 10 cm in diameter in the center of your for each quadrant of the Earth. Use a page. This circle represents the Earth. straight edge to draw black lines that Add the Earth’s axis of rotation, the connect the marks opposite one Equator, and lines of latitude, as another on the circle, making lines shown in the diagram and described that are parallel to the Equator.
[Show full text]
Exercise 1.0 the CELESTIAL EQUATORIAL COORDINATE
Exercise 1.0 THE CELESTIAL EQUATORIAL COORDINATE SYSTEM Equipment needed: A celestial globe showing positions of bright stars. I. Introduction There are several different ways of representing the appearance of the sky or describing the locations of objects we see in the sky. One way is to imagine that every object in the sky is located on a very large and distant sphere called the celestial sphere . This imaginary sphere has its center at the center of the Earth. Since the radius of the Earth is very small compared to the radius of the celestial sphere, we can imagine that this sphere is also centered on any person or observer standing on the Earth's surface. Every celestial object (e.g., a star or planet) has a definite location in the sky with respect to some arbitrary reference point. Once defined, such a reference point can be used as the origin of a celestial coordinate system. There is an astronomically important point in the sky called the vernal equinox , which astronomers use as the origin of such a celestial coordinate system . The meaning and significance of the vernal equinox will be discussed later. In an analogous way, we represent the surface of the Earth by a globe or sphere. Locations on the geographic sphere are specified by the coordinates called longitude and latitude . The origin for this geographic coordinate system is the point where the Prime Meridian and the Geographic Equator intersect. This is a point located off the coast of west-central Africa. To specify a location on a sphere, the coordinates must be angles, since a sphere has a curved surface.
[Show full text]
5 Transformation Between the International Terrestrial Refer
IERS Technical Note No. 36 5 Transformation between the International Terrestrial Refer- ence System and the Geocentric Celestial Reference System 5.1 Introduction The transformation to be used to relate the International Terrestrial Reference System (ITRS) to the Geocentric Celestial Reference System (GCRS) at the date t of the observation can be written as: [GCRS] = Q(t)R(t)W (t) [ITRS]; (5.1) where Q(t), R(t) and W (t) are the transformation matrices arising from the mo- tion of the celestial pole in the celestial reference system, from the rotation of the Earth around the axis associated with the pole, and from polar motion respec- tively. Note that Eq. (5.1) is valid for any choice of celestial pole and origin on the equator of that pole. The deﬁnition of the GCRS and ITRS and the procedures for the ITRS to GCRS transformation that are provided in this chapter comply with the IAU 2000/2006 resolutions (provided at <1> and in Appendix B). More detailed explanations about the relevant concepts, software and IERS products corresponding to the IAU 2000 resolutions can be found in IERS Technical Note 29 (Capitaine et al., 2002), as well as in a number of original subsequent publications that are quoted in the following sections. The chapter follows the recommendations on terminology associated with the IAU 2000/2006 resolutions that were made by the 2003-2006 IAU Working Group on \Nomenclature for fundamental astronomy" (NFA) (Capitaine et al., 2007). We will refer to those recommendations in the following as \NFA recommenda- tions" (see Appendix A for the list of the recommendations).
[Show full text]
The Epoch of the Constellations on the Farnese Atlas and Their Origin in Hipparchus’S Lost Catalogue
JHA, xxxvi (2005) THE EPOCH OF THE CONSTELLATIONS ON THE FARNESE ATLAS AND THEIR ORIGIN IN HIPPARCHUS’S LOST CATALOGUE BRADLEY E. SCHAEFER, Louisiana State University, Baton Rouge 1. BACKGROUND The Farnese Atlas is a Roman statue depicting the Titan Atlas holding up a celestial globe that displays an accurate representation of the ancient Greek constellations (see Figures 1 and 2). This is the oldest surviving depiction of the original Western constellations, and as such can be a valuable resource for studying their early development. The globe places the celestial fi gures against a grid of circles (including the celestial equator, the tropics, the colures, the ecliptic, the Arctic Circle, and the Antarctic Circle) that allows for the accurate positioning of the constellations. The positions shift with time due to precession, so the observed positions on the Farnese Atlas correspond to some particular date. Also, the declination of the Arctic and Antarctic Circles will correspond to a particular latitude for the observer whose observations were adopted by the sculptor. Thus, a detailed analysis of the globe will reveal the latitude and epoch for the observations incorporated in the Atlas; and indeed these will specify enough information that we can identify the observer. Independently, a detailed comparison of the constellation symbols on the Atlas with those from the other surviving ancient material also uniquely points to the same origin for the fi gures. The Farnese Atlas1 fi rst came to modern attention in the early sixteenth century when it became part of the collection of antiquities in the Farnese Palace in Rome, hence its name.
[Show full text]
Section 2 How Do Earth's Orbital Variations Affect Global Climate?
Chapter 6 Global Climate Change Section 2 Ho w Do Earth’s Orbital Variations Affect Global Climate? What Do You See? Learning Outcomes In this section, you will Learning• GoalsText Outcomes Think About It In this section, you will When it is winter in New York, it is summer in Australia. • Understandthat Earth has an • Why are the seasons reversed in the Northern and axial tilt of about 23.5°. Southern Hemispheres? • Usea globe to model the seasons on Earth. Record your ideas about this question in your Geo log. Be • Investigateand understand the prepared to discuss your responses with your small group cause of the seasons in relation and the class. to the axial tilt of Earth. • Understandthat the shape of Investigate Earth’s orbit around the Sun is an ellipse, and that this shape This Investigate has five parts. In each part, you will explore influences climate. different factors that cause Earth’s seasons. • Understandthat insolation Part A: What Causes the Seasons? An Investigation on Paper to Earth varies as the inverse square of the distance to 1. Create a model of Earth by completing the following. the Sun. a) In your log, draw a circle about 10 cm in diameter in the center of your page. This circle represents Earth. 650 EarthComm EC_Natl_SE_C6.indd 650 7/13/11 9:31:54 AM Section 2 How Do Earth’s Orbital Variations Affect Global Climate? b) Add Earth’s axis of rotation, plane • Now, mark off 10° increments of orbit, the equator, and lines of starting from the equator and going latitude, as shown in the diagram, to the poles.
[Show full text]