Culmination

Source: Wikipedia, the free encyclopedia.

In

transit telescope
.

During each day, every celestial object

geographic poles, any celestial object passing through the meridian has an upper culmination, when it reaches its highest point (the moment when it is nearest to the Zenith), and nearly twelve hours later, is followed by a lower culmination, when it reaches its lowest point (nearest to the Nadir). The time of culmination (when the object culminates) is often used to mean upper culmination.[2][3][4]

An object's

altitude (A) in degrees at its upper culmination is equal to 90 minus the observer's latitude (L) plus the object's declination
(δ):

A = 90° − L + δ.

Cases

Three cases are dependent on the observer's

celestial object:[citation needed
]

  • The object is above the horizon even at its lower culmination; i.e. if | δ + L | > 90° (i.e. if in absolute value the declination is more than the colatitude, in the corresponding hemisphere)
  • The object is below the horizon even at its upper culmination; i.e. if | δ − L | > 90° (i.e. if in absolute value the declination is more than the colatitude, in the opposite hemisphere)
  • The upper culmination is above and the lower below the horizon, so the body is observed to rise and set daily; in the other cases (i.e. if in absolute value the declination is less than the colatitude)

The third case applies for objects in a part of the full sky equal to the

cosine of the latitude (at the equator it applies for all objects, because the sky turns around the horizontal north–south line; at the poles it applies for none, because the sky turns around the vertical line). The first and second case each apply for half of the remaining sky.[citation needed
]

Period of time

See also: Sidereal time, Equation of time, and Perturbation (astronomy)

The period between a culmination and the next is a

solar year, for a culmination to reoccur. Therefore, only once every 366.3 solar days the culmination reoccurs at the same time of a solar day, while reoccurring every sidereal day.[6] The remaining small changes in the culmination period time from sidereal year to sidereal year is on the other hand mainly caused by nutation (with a 18.6 years cycle), resulting in the longer time scale axial precession of Earth (with a 26,000 years cycle),[7][8] while apsidal precession and other mechanics have a much smaller impact on sidereal observation, impacting Earth's climate through the Milankovitch cycles significantly more. Though at such timescales stars themself change position, particularly those stars which have, as viewed from the Solar System, a high proper motion
.

Stellar parallax appears to be a similar motion like all these apparent movements, but has only from non-averaged sidereal day to sidereal day a slight effect, returning to its original apparent position, completing a cycle every orbit, with a slight additional lasting change to the position due to the precessions. This phenomenon results from Earth changing position on its orbital path.

The Sun

Main articles:
Sun transit time and Noon § Solar noon
Further information: Solar zenith angle and Sun path

From the

solar noon) and invisible (below the horizon) at its lower culmination (at solar midnight). When viewed from the region within either polar circle around the winter solstice of that hemisphere (the December solstice in the Arctic and the June solstice in the Antarctic), the Sun is below the horizon
at both of its culminations.

Supposing that the

complementary angle of 70° (from the Sun to the pole) is added to and subtracted from the observer's latitude to find the solar altitudes at upper and lower culminations, respectively.[citation needed
]

Circumpolar stars

Main article: Circumpolar star

From most of the Northern Hemisphere, Polaris (the North Star) and the other stars of the constellation Ursa Minor circles counterclockwise around the north celestial pole and remain visible at both culminations (as long as the sky is clear and dark enough). In the Southern Hemisphere there is no bright pole star, but the constellation Octans circles clockwise around the south celestial pole and remains visible at both culminations.[9]

Any astronomical objects that always remain above the local horizon, as viewed from the observer's latitude, are described as circumpolar.[citation needed][9]

See also

References

  1. ISBN 978-0-521-57600-0
    .
  2. ^
    ISBN 0521449219
    .
  3. ^
    ISBN 978-1438109329
    .
  4. ^ Mackenzie, William (1879–81). "Meridian". The National Encyclopaedia. Vol. 8 (library ed.). London, Edinburgh, and Glasgow: Ludgate Hill, E.C. p. 993.
  5. ^ "Sidereal Time". US Naval Observatory Astronomical Applications Department. 2023-06-02. Retrieved 2023-06-02.
  6. ^ "Calendar - Sidereal Day, Synodic Month, Tropical Year, Intercalation". Encyclopedia Britannica. 1998-07-20. Retrieved 2023-06-02.
  7. ^ "apparent sidereal time". Oxford Reference. 1999-02-22. Retrieved 2023-06-02.
  8. ^ Buis, Alan; Laboratory, s Jet Propulsion (2020-02-27). "Milankovitch (Orbital) Cycles and Their Role in Earth's Climate – Climate Change: Vital Signs of the Planet". Climate Change: Vital Signs of the Planet. Retrieved 2023-06-02.
  9. ^
    OCLC 1085744128
    .
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