Apparent places
Encyclopedia
The wrong place of an object is the position in space as seen by the observer. Because of physical and/or geometrical effects it has a deviation
from the "true position".
In astronomy
the term "apparent places of star
s" means the visual or photographic position of the star, as seen from the moving Earth. For instance, its speed of 30 km per second around the Sun causes an annual aberration of about 20" (10^-4) because the Earth's velocity is about 0.01 percent of the speed of light
.
Other effects are the parallax
(different angle to the star during the year), or the daily aberration
because of the Earth's rotation, and the Earth's precession
- a monotonic changing of the direction of the Earth's axis, which causes an analogous slow turning of the coordinate system
s which we use on Earth and in space.
The "Apparent Places of Fundamental Stars" (commonly abbreviated APFS) is an astronomical yearbook
, which is published one year in advance by the Astronomisches Rechen-Institut in Heidelberg
, Germany. It lists the apparent place of about 1000 fundamental stars for every 10 days and is published as a book and in a more extensive version on the Internet
.
Deviation
Deviation may refer to:* Deviation , the difference between the value of an observation and the mean of the population in mathematics and statistics** Standard deviation, which is based on the square of the difference...
from the "true position".
In astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
the term "apparent places of star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s" means the visual or photographic position of the star, as seen from the moving Earth. For instance, its speed of 30 km per second around the Sun causes an annual aberration of about 20" (10^-4) because the Earth's velocity is about 0.01 percent of the speed of light
Speed of light
The speed of light in vacuum, usually denoted by c, is a physical constant important in many areas of physics. Its value is 299,792,458 metres per second, a figure that is exact since the length of the metre is defined from this constant and the international standard for time...
.
Other effects are the parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
(different angle to the star during the year), or the daily aberration
Aberration
An aberration is something that deviates from the normal way.Aberration may refer to:In optics and physics:*Optical aberration, an imperfection in image formation by an optical system...
because of the Earth's rotation, and the Earth's precession
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
- a monotonic changing of the direction of the Earth's axis, which causes an analogous slow turning of the coordinate system
Coordinate system
In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...
s which we use on Earth and in space.
The "Apparent Places of Fundamental Stars" (commonly abbreviated APFS) is an astronomical yearbook
Yearbook
A yearbook, also known as an annual, is a book to record, highlight, and commemorate the past year of a school or a book published annually. Virtually all American, Australian and Canadian high schools, most colleges and many elementary and middle schools publish yearbooks...
, which is published one year in advance by the Astronomisches Rechen-Institut in Heidelberg
Heidelberg
-Early history:Between 600,000 and 200,000 years ago, "Heidelberg Man" died at nearby Mauer. His jaw bone was discovered in 1907; with scientific dating, his remains were determined to be the earliest evidence of human life in Europe. In the 5th century BC, a Celtic fortress of refuge and place of...
, Germany. It lists the apparent place of about 1000 fundamental stars for every 10 days and is published as a book and in a more extensive version on the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
.
See also
- Improper motion
- AstrometryAstrometryAstrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
- dUT1DUT1The time correction DUT1 is the difference between Universal Time , which is defined by Earth's rotation, and Coordinated Universal Time , which is defined by a network of precision clocks....
- Geodetic astronomyGeodetic astronomyGeodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The most important topics are:* Establishment of geodetic datum systems Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The...
- Local apparent time
- Meridian circleMeridian circleThe meridian circle, transit circle, or transit telescope is an instrument for observing the time of stars passing the meridian, at the same time measuring its angular distance from the zenith...
- NavigationNavigationNavigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
- Passage instrument
- Star positionStar positionStar position in the sky is defined by a pair of angles. These two angles - which refer to the celestial equator - are called declination and right ascension ....
- Zenith cameraZenith cameraZenith cameras are astronomic or geodetic instruments which are directed exactly to the zenith. The stars are recorded either by photographic plates or by CCD sensors.The main tasks in using these instruments are:...
- UTC