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Magnetic Declination Demystified
Magnetic Declination Demystified
Published: 2013/11/10
Channel: survivalresources
How to Use a Compass • Magnetic Declination
How to Use a Compass • Magnetic Declination
Published: 2013/05/28
Channel: Black Owl Outdoors
How To Adjust For Magnetic Declination
How To Adjust For Magnetic Declination
Published: 2016/09/13
Channel: Sierra Trading Post
Declination and Angle of Dip
Declination and Angle of Dip
Published: 2016/03/13
Channel: tick Links
Map and Compass Basics: Magnetic Declination
Map and Compass Basics: Magnetic Declination
Published: 2010/02/02
Channel: safariskills
Learn Map & Compass with Andrew Skurka, Part 1: Adjust for declination & orient a map
Learn Map & Compass with Andrew Skurka, Part 1: Adjust for declination & orient a map
Published: 2016/07/11
Channel: SierraDesigns Gear
Easy basic compass series ( part 4 ) Declination and compass Eagle Jon
Easy basic compass series ( part 4 ) Declination and compass Eagle Jon
Published: 2015/05/22
Channel: Eagle Jon
Angle Of Dip And Declination
Angle Of Dip And Declination
Published: 2015/06/10
Channel: Vikram Singh Physics
Map Reading Declination Diagram and Scale
Map Reading Declination Diagram and Scale
Published: 2013/05/26
Channel: wildernessoutfitters
What is Declination?
What is Declination?
Published: 2014/12/14
Channel: David Cochrane
Easy basic compass series ( part 3 ) Declination explanation Eagle Jon
Easy basic compass series ( part 3 ) Declination explanation Eagle Jon
Published: 2015/04/17
Channel: Eagle Jon
The Sun
The Sun's Declination Explained
Published: 2011/05/21
Channel: TBar1984
Good Vibe Astrology - Learn about Declinations
Good Vibe Astrology - Learn about Declinations
Published: 2014/07/06
Channel: Kim Falconer
Magnetic declination for beginners
Magnetic declination for beginners
Published: 2015/09/09
Channel: Steve Gurney
Magnetic Declination curated by Patrick Alken
Magnetic Declination curated by Patrick Alken
Published: 2014/10/15
Channel: NOAA SOS
02 Altitude, Azimuth, Right Ascension and Declination
02 Altitude, Azimuth, Right Ascension and Declination
Published: 2016/10/05
Channel: Forest Park
Magnetic Declination lead to the Foundations of Heaven and Square flat earth
Magnetic Declination lead to the Foundations of Heaven and Square flat earth
Published: 2016/01/23
Channel: freeanergy
Declination and right ascension
Declination and right ascension
Published: 2012/03/02
Channel: National Museum of Australia
Physics Matter & Magnetism part 14 (Magnetic Declination) CBSE class 12
Physics Matter & Magnetism part 14 (Magnetic Declination) CBSE class 12
Published: 2012/09/05
Channel: ExamFear Education
Map & Compass 201: Declination
Map & Compass 201: Declination
Published: 2009/12/30
Channel: PackRat556
Adjusting for magnetic variation/declination (MikeOut E2)
Adjusting for magnetic variation/declination (MikeOut E2)
Published: 2016/12/12
Channel: MikeOut
Wilderness Navigation #9 - Adjusting Declination on your Compass
Wilderness Navigation #9 - Adjusting Declination on your Compass
Published: 2016/02/09
Channel: Columbia River Orienteering Club
Mapwork magnetic declination and bearing calculations
Mapwork magnetic declination and bearing calculations
Published: 2017/05/18
Channel: Fish
Magnetic Variation or Declination.
Magnetic Variation or Declination.
Published: 2016/04/22
Channel: Trekk Life
Land Navigation (Magnetic Declination)
Land Navigation (Magnetic Declination)
Published: 2017/11/08
Channel: The American Backpacker
Solar Declination
Solar Declination
Published: 2016/12/30
Channel: Robert MacKay
NEET Medical Online Video on Magnetism & Matter: Angle of Declination: Class 12th Physics
NEET Medical Online Video on Magnetism & Matter: Angle of Declination: Class 12th Physics
Published: 2013/04/08
Channel: Aakash iTutor
Stellar coordinate systems
Stellar coordinate systems
Published: 2013/04/11
Channel: Ed Hitchcock
Com Truise - Declination (feat. Joel Ford)
Com Truise - Declination (feat. Joel Ford)
Published: 2013/12/03
Channel: ghostlyintl
Matric revision: Geography:  Map Work: Calculations (4/7): Magnetic Declination
Matric revision: Geography: Map Work: Calculations (4/7): Magnetic Declination
Published: 2013/08/26
Channel: wcednews
Magnetism:-Elements of Terrestrial Magnetism Dip, Declination-04
Magnetism:-Elements of Terrestrial Magnetism Dip, Declination-04
Published: 2017/01/23
Channel: DIGICLASS A
Right Ascension and Declination - Sixty Symbols
Right Ascension and Declination - Sixty Symbols
Published: 2011/02/09
Channel: Sixty Symbols
what is angle of dip- what is declination angle
what is angle of dip- what is declination angle
Published: 2017/03/09
Channel: Yatendra Kumar
Grid to Magnetic Westerly Declination
Grid to Magnetic Westerly Declination
Published: 2015/12/13
Channel: Jarhead Survivor
Declination
Declination
Published: 2009/09/13
Channel: Steven Hoober
Flat Earth • Compass & Magnetic Declination Chart
Flat Earth • Compass & Magnetic Declination Chart
Published: 2016/12/16
Channel: Chippy The Chipmunk
Wilderness Navigation #10 - Deciphering Declination
Wilderness Navigation #10 - Deciphering Declination
Published: 2016/01/12
Channel: Columbia River Orienteering Club
Thrown Into Exile - Declination (Official Album Stream)
Thrown Into Exile - Declination (Official Album Stream)
Published: 2016/10/21
Channel: Urban Yeti Records
Right Ascension & Declination
Right Ascension & Declination
Published: 2012/08/18
Channel: Joe Lalumia
Darksiders II - Soul Arbiter
Darksiders II - Soul Arbiter's Maze Side Quest - 1: Declination
Published: 2012/08/19
Channel: RuymGames
learn German A1: Adjective declination PART 1
learn German A1: Adjective declination PART 1
Published: 2015/04/19
Channel: freeGermanlessons
Declination (feat. Joel Ford)
Declination (feat. Joel Ford)
Published: 2015/08/12
Channel: Com Truise - Topic
Example Declination
Example Declination
Published: 2013/08/17
Channel: IQmates
Meade LX200GPS Declination Assembly Tour
Meade LX200GPS Declination Assembly Tour
Published: 2012/08/13
Channel: meade7lx200gps
What is declination?
What is declination?
Published: 2017/03/27
Channel: Sincere TV
Section III, 10 - Declination
Section III, 10 - Declination
Published: 2014/12/10
Channel: Vandy Astronav
P7 Galactic Sphere, Declination, Right Ascention
P7 Galactic Sphere, Declination, Right Ascention
Published: 2017/06/17
Channel: Gary Whitton
Magnetic Declination for Magnetic Compass and Solar Pathfinder
Magnetic Declination for Magnetic Compass and Solar Pathfinder
Published: 2016/06/20
Channel: tjwiltube
Cold As Life - Declination of Independence [Full Album]
Cold As Life - Declination of Independence [Full Album]
Published: 2014/08/10
Channel: Mosh Pit
Declination (Instrumental) - Com Truise (Hohokum Soundtrack)
Declination (Instrumental) - Com Truise (Hohokum Soundtrack)
Published: 2015/01/20
Channel: Two Turntables and a Microphone
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WIKIPEDIA ARTICLE

From Wikipedia, the free encyclopedia
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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 1/4 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.

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 extremely close to the equator. On flat terrain, the distance has to be within about 2km, but this varies based on observer altitude and surrounding terrain). 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]

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.[6][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.[7]

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).[8] 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. 
  3. ^ Moulton, Forest Ray (1918). An Introduction to Astronomy. New York: Macmillan Co. 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. ^ "Celestial Coordinates". www.austincc.edu. Retrieved 2017-03-24. 
  7. ^ "USDOV2009". Silver Spring, Maryland: U.S. National Geodetic Survey. 2011. 
  8. ^ P. Kenneth Seidelmann, ed. (1992). Explanatory Supplement to the Astronomical Almanac. Sausalito, CA: University Science Books. pp. 200–5. 

External links[edit]

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