Play Video
1
Magnetic Declination Demystified
Magnetic Declination Demystified
::2013/11/10::
Play Video
2
Map and Compass Basics: Magnetic Declination
Map and Compass Basics: Magnetic Declination
::2010/02/02::
Play Video
3
How to Set Compass Magnetic Declination and Declination Error - Compass Tutorial - Lesson 3
How to Set Compass Magnetic Declination and Declination Error - Compass Tutorial - Lesson 3
::2012/08/21::
Play Video
4
How to Use a Compass [Magnetic Declination]
How to Use a Compass [Magnetic Declination]
::2013/05/28::
Play Video
5
The Sun
The Sun's Declination Explained
::2011/05/21::
Play Video
6
Map & Compass 201: Declination
Map & Compass 201: Declination
::2009/12/30::
Play Video
7
Right Ascension and Declination - Sixty Symbols
Right Ascension and Declination - Sixty Symbols
::2011/02/09::
Play Video
8
Com Truise - Declination (feat. Joel Ford)
Com Truise - Declination (feat. Joel Ford)
::2013/12/03::
Play Video
9
Declination
Declination
::2009/09/12::
Play Video
10
Cold As Life - Declination of Independence [Full Album]
Cold As Life - Declination of Independence [Full Album]
::2014/08/09::
Play Video
11
Matric revision: Geography:  Map Work: Calculations (4/7): Magnetic Declination
Matric revision: Geography: Map Work: Calculations (4/7): Magnetic Declination
::2013/08/26::
Play Video
12
Magnetic Declination
Magnetic Declination
::2012/04/15::
Play Video
13
Magnetic Declination Compensation for DJI Naza Flight Controller GPS Fix
Magnetic Declination Compensation for DJI Naza Flight Controller GPS Fix
::2012/08/17::
Play Video
14
Magnetic Declination
Magnetic Declination
::2010/11/07::
Play Video
15
Map Reading Declination Diagram and Scale
Map Reading Declination Diagram and Scale
::2013/05/26::
Play Video
16
Physics Matter & Magnetism part 14 (Magnetic Declination) CBSE class 12
Physics Matter & Magnetism part 14 (Magnetic Declination) CBSE class 12
::2012/09/05::
Play Video
17
DJI F550 Hexacopter NAZA IOC & GPS magnetic declination setup part #4
DJI F550 Hexacopter NAZA IOC & GPS magnetic declination setup part #4
::2012/09/20::
Play Video
18
Right Ascension & Declination
Right Ascension & Declination
::2012/08/18::
Play Video
19
Angle of Declination & Dip
Angle of Declination & Dip
::2013/02/01::
Play Video
20
Multiwii Pro Magnetic Declination Set up
Multiwii Pro Magnetic Declination Set up
::2014/03/22::
Play Video
21
Ossein - Declination (Full Album)
Ossein - Declination (Full Album)
::2013/05/09::
Play Video
22
Darksiders II - Soul Arbiter
Darksiders II - Soul Arbiter's Maze Side Quest - 1: Declination
::2012/08/18::
Play Video
23
Declination and right ascension
Declination and right ascension
::2012/03/01::
Play Video
24
How To Adjust a Compass for Magnetic Declination
How To Adjust a Compass for Magnetic Declination
::2012/04/12::
Play Video
25
How to Adjust Grid to Magnetic Declination
How to Adjust Grid to Magnetic Declination
::2014/03/22::
Play Video
26
DJI NAZA RTH Toilet Bowling Effect and Compass Declination Fix
DJI NAZA RTH Toilet Bowling Effect and Compass Declination Fix
::2014/09/10::
Play Video
27
Map & Compass Declination
Map & Compass Declination
::2014/04/16::
Play Video
28
Land Nav part 8 (Declination Diagram Disected)
Land Nav part 8 (Declination Diagram Disected)
::2010/05/04::
Play Video
29
Com Truise - Declination (live)
Com Truise - Declination (live)
::2014/03/10::
Play Video
30
Mr H
Mr H's Bad Geography Videos - Part 7 Magnetic Declination and Bearing
::2013/09/30::
Play Video
31
Hour Angle, Declination, Upper and Lower Transit
Hour Angle, Declination, Upper and Lower Transit
::2013/08/17::
Play Video
32
Ashes of Existence - Declination [Full EP Stream]
Ashes of Existence - Declination [Full EP Stream]
::2014/11/10::
Play Video
33
Nerium Oleander - Declination [Full CS]
Nerium Oleander - Declination [Full CS]
::2014/09/14::
Play Video
34
Meade LX200GPS Declination Assembly Tour
Meade LX200GPS Declination Assembly Tour
::2012/08/13::
Play Video
35
Learn Albanian with Viola. Declination of (Vajza)
Learn Albanian with Viola. Declination of (Vajza)
::2013/07/28::
Play Video
36
Magnetic Declination curated by Patrick Alken
Magnetic Declination curated by Patrick Alken
::2014/10/15::
Play Video
37
Right Ascension, Declination -  Astronomy
Right Ascension, Declination - Astronomy
::2013/10/07::
Play Video
38
Only The Lightest, Ch 32: Ultralight Backpacking and Finding Your Magnetic Declination
Only The Lightest, Ch 32: Ultralight Backpacking and Finding Your Magnetic Declination
::2010/12/28::
Play Video
39
Example   Right Ascension and Declination and Relationship Between RA and HA
Example Right Ascension and Declination and Relationship Between RA and HA
::2013/08/17::
Play Video
40
Magnetic Declination and How to Use it to Find True North or South
Magnetic Declination and How to Use it to Find True North or South
::2013/10/28::
Play Video
41
Declination and bow offset on the ProStart
Declination and bow offset on the ProStart
::2010/10/27::
Play Video
42
The Declination of Independence
The Declination of Independence
::2011/01/25::
Play Video
43
Social Declination
Social Declination
::2008/05/30::
Play Video
44
Learn Albanian with Viola. Declination of (a girl)
Learn Albanian with Viola. Declination of (a girl)
::2013/07/24::
Play Video
45
Magnetic Declination
Magnetic Declination
::2010/11/17::
Play Video
46
Magnetic Declination (CM14A)
Magnetic Declination (CM14A)
::2012/10/06::
Play Video
47
Suunto MC-2 Compass Review & Declination
Suunto MC-2 Compass Review & Declination
::2011/10/28::
Play Video
48
Stargazing Basics 1: Lean how get oriented in the night sky for stargazing
Stargazing Basics 1: Lean how get oriented in the night sky for stargazing
::2012/07/13::
Play Video
49
Toilet Bowl Effect (TBE) due to Magnetic Declination on DJI Phantom Vision 2+
Toilet Bowl Effect (TBE) due to Magnetic Declination on DJI Phantom Vision 2+
::2014/07/12::
Play Video
50
Learn Albanian with Viola. Declination of (Disa Vajza)
Learn Albanian with Viola. Declination of (Disa Vajza)
::2013/08/13::
NEXT >>
RESULTS [51 .. 101]
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses, see Declination (disambiguation).

In astronomy, declination (abbreviated dec; symbol δ) is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question.[1]

Right ascension and declination as seen on the inside of the celestial sphere. The primary direction of the system is the vernal equinox, the ascending node of the ecliptic (red) on the celestial equator (blue). Declination is measured northward or southward from the celestial equator, along the hour circle passing through the point in question.

The root of the word declination (Latin, declinatio) means "a bending away" or "a bending down". It comes from the same root as the words incline ("bend toward") and recline ("bend backward").[2]

Explanation[edit]

Declination in astronomy is comparable to geographic latitude, projected onto the celestial sphere, and hour angle is likewise comparable to longitude.[3] Points north of the celestial equator have positive declinations, while those south have negative declinations. Any units of angular measure can be used for declination, but it is customarily measured in the degrees ( ° ), minutes ( ' ), and seconds ( " ) of sexagesimal measure, with 90° equivalent to 14 circle. Declinations with magnitudes greater than 90° do not occur, because the poles are the northernmost and southernmost points of the celestial sphere.

An object at the

The sign is customarily included whether positive or negative.

Effects of precession[edit]

Right ascension (blue) and declination (green) as seen from outside the celestial sphere.
Main article: Axial precession

The Earth's axis rotates slowly westward about the poles of the ecliptic, completing one circuit in about 26,000 years. This effect, known as precession, causes the coordinates of stationary celestial objects to change continuously, if rather slowly. Therefore, equatorial coordinates (including declination) are inherently relative to the year of their observation, and astronomers specify them with reference to a particular year, known as an epoch. Coordinates from different epochs must be mathematically rotated to match each other, or to match a standard epoch.[4]

The currently used standard epoch is J2000.0, which is January 1, 2000 at 12:00 TT. The prefix "J" indicates that it is a Julian epoch. Prior to J2000.0, astronomers used the successive Besselian Epochs B1875.0, B1900.0, and B1950.0.[5]

Stars[edit]

A star's direction remains nearly fixed due to its vast distance, but its right ascension and declination do change gradually due to precession of the equinoxes and proper motion, and cyclically due to annual parallax. The declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity.

As seen from locations in the Earth's Northern Hemisphere, celestial objects with declinations greater than 90° − φ (where φ = observer's latitude) appear to circle daily around the celestial pole without dipping below the horizon, and are therefore called circumpolar stars. This similarly occurs in the Southern Hemisphere for objects with declinations less (i.e. more negative) than −90° − φ (where φ is always a negative number for southern latitudes). An extreme example is the pole star which has a declination near to +90°, so is circumpolar as seen from anywhere in the Northern Hemisphere except very close to the equator.

Circumpolar stars never dip below the horizon. Conversely, there are other stars that never rise above the horizon, as seen from any given point on the Earth's surface (except exactly on the equator). Generally, if a star whose declination is δ is circumpolar for some observer (where δ is either positive or negative), then a star whose declination is −δ never rises above the horizon, as seen by the same observer. (This neglects the effect of atmospheric refraction.) Likewise, if a star is circumpolar for an observer at latitude φ, then it never rises above the horizon as seen by an observer at latitude −φ.

Neglecting atmospheric refraction, declination is always 0° at east and west points of the horizon. At the north point, it is 90° − |φ|, and at the south point, −90° + |φ|. From the poles, declination is uniform around the entire horizon, approximately 0°.

Stars visible by latitude
Observer's latitude (°) Declination
of circumpolar stars (°) of non-circumpolar stars (°) of stars not visible (°)
+ for north latitude, − for south   − for north latitude, + for south
90 (Pole) 90 to 0
N/A
0 to 90
66.5 (Arctic/Antarctic Circle) 90 to 23.5 +23.5 to −23.5 23.5 to 90
45 (midpoint) 90 to 45 +45 to −45 45 to 90
23.5 (Tropic of Cancer/Capricorn) 90 to 66.5 +66.5 to −66.5 66.5 to 90
0 (Equator)
N/A
+90 to −90
N/A

Non-circumpolar stars are visible only during certain days or seasons of the year.

The night sky, divided into two halves. Declination (green) begins at the equator (green) and is positive northward (towards the top), negative southward (towards the bottom). The lines of declination (green) divide the sky into small circles, here 15° apart.

Sun[edit]

Main article: Position of the Sun

The Sun's declination varies with the seasons. As seen from arctic or antarctic latitudes, the Sun is circumpolar near the local summer solstice, leading to the phenomenon of it being above the horizon at midnight, which is called midnight sun. Likewise, near the local winter solstice, the Sun remains below the horizon all day, which is called polar night.

Relation to latitude[edit]

When an object is directly overhead its declination is almost always within 0.01 degree of the observer's latitude; it would be exactly equal except for two complications.[citation needed]

The first complication applies to all celestial objects: the object's declination equals the observer's astronomic latitude, but the term "latitude" ordinarily means geodetic latitude, which is the latitude on maps and GPS devices. In the continental United States and surrounding area the difference (the vertical deflection) is typically a few arcseconds (1 arcsecond = 1/3600 degree) but can be as great as 41 arcseconds.[6]

The second complication is that assuming no deflection of the vertical, "overhead" means perpendicular to the ellipsoid at observer's location, but the perpendicular line does not pass through the center of the earth; almanacs give declinations measured at the center of the Earth. (An ellipsoid is an approximation to sea level that is mathematically manageable).[7] For the moon this discrepancy can reach 0.003 degree; the Sun and planets are hundreds of times more distant and for them the discrepancy is proportionately smaller (and for the stars is unmeasurable).

See also[edit]

Notes and references[edit]

  1. ^ U.S. Naval Observatory, Nautical Almanac Office (1992). P. Kenneth Seidelmann, ed. Explanatory Supplement to the Astronomical Almanac. University Science Books, Mill Valley, CA. p. 724. ISBN 0-935702-68-7. 
  2. ^ Barclay, James (1799). A Complete and Universal English Dictionary. , entries for declination, inclination, incline, recline, at Google books
  3. ^ Moulton, Forest Ray (1918). An Introduction to Astronomy. Macmillan Co., New York. p. 125, art. 66.  , at Google books
  4. ^ Moulton (1918), pp. 92–95.
  5. ^ see, for instance, U.S. Naval Observatory Nautical Almanac Office, Nautical Almanac Office; U.K. Hydrographic Office, H.M. Nautical Almanac Office (2008). "Time Scales and Coordinate Systems, 2010". The Astronomical Almanac for the Year 2010. U.S. Govt. Printing Office. p. B2,. 
  6. ^ "USDOV2009". Silver Spring, Maryland: U.S. National Geodetic Survey. 2011. 
  7. ^ P. Kenneth Seidelmann, ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. pp. 200–5. 

External links[edit]

Wikipedia content is licensed under the GFDL License
Powered by YouTube
LEGAL
  • Mashpedia © 2014