Lunar node
This article includes a list of general references, but it lacks sufficient corresponding inline citations. (January 2018) |
A lunar node is either of the two
Motion
The Moon crosses the same node every 27.2122 days, an interval called the
Because the
Eclipses
A lunar eclipse can occur only when the full Moon is near either lunar node (within 11° 38' ecliptic longitude), while a solar eclipse can occur only when the new Moon is near either lunar node (within 17° 25').
Both solar eclipses of July 2000 (on the
An Eclipse of the Moon or Sun can occur when the nodes align with the Sun, roughly every 173.3 days. Lunar orbit inclination also determines eclipses; shadows cross when nodes coincide with full and new moon when the Sun, Earth, and Moon align in three dimensions.
In effect, this means that the "
Names and symbols
The nodes are called by different names in different cultures of the world.
In medieval
In
Extremes
Inclination extremes
Every 18.6 years, the angle between the Moon's orbit and Earth's equator reaches a maximum of 28°36′, the sum of Earth's equatorial tilt (23°27′) and the Moon's orbital inclination (5°09′) to the ecliptic. This is called major lunar standstill. Around this time, the Moon's declination will vary from −28°36′ to +28°36′. Conversely, 9.3 years later, the angle between the Moon's orbit and Earth's equator reaches its minimum of 18°20′. This is called a minor lunar standstill. The last lunar standstill was a minor standstill in October 2015. At that time the descending node was lined up with the equinox (the point in the sky having right ascension zero and declination zero). The nodes are moving west by about 19° per year. The Sun crosses a given node about 20 days earlier each year.
When the inclination of the Moon's orbit to the Earth's equator is at its minimum of 18°20′, the centre of the Moon's disk will be above the horizon every day from latitudes less than 70°43' (90° − 18°20' – 57' parallax) north or south. When the inclination is at its maximum of 28°36', the centre of the Moon's disk will be above the horizon every day only from latitudes less than 60°27' (90° − 28°36' – 57' parallax) north or south.
At higher latitudes, there will be a period of at least one day each month when the Moon does not rise, but there will also be a period of at least one day each month when the Moon does not set. This is similar to the seasonal behaviour of the Sun, but with a period of 27.2 days instead of 365 days. Note that a point on the Moon can actually be visible when it is about 34 arc minutes below the horizon, due to atmospheric refraction.
Because of the inclination of the Moon's orbit with respect to the Earth's equator, the Moon is above the horizon at the
The Moon's light is used by zooplankton in the Arctic when the Sun is below the horizon for months and must have been helpful to the animals that lived in Arctic and Antarctic regions when the climate was warmer.
Declination extremes
The Moon's orbit is inclined about 5.14° to the ecliptic; hence, the Moon can be up to about 5° north or south of the ecliptic. The ecliptic is inclined about 23.44° to the celestial equator, whose plane is perpendicular to the rotational axis of Earth. As a result, once during the 18.6-year nodal period (when the ascending node of the Moon's orbit coincides with the vernal equinox), the Moon's declination reaches a maximum and minimum (northern and southern extremes): about 28.6° from the celestial equator. Therefore, the moonrise or moonset azimuth has its northern- and southernmost points on the horizon; the Moon at culmination has its lowest and highest altitude (when the body transits the meridian); and first sightings of the new moon potentially have their latest times. Furthermore, occultations by the Moon of the Pleiades star cluster, which is over 4° north of the ecliptic, occur during a comparatively brief period once every nodal period.
Effect on tides
The
The U.S.In conjunction with sea level rise caused by global warming, lunar nodal precession is predicted to contribute to a rapid rise in the frequency of coastal flooding throughout the 2030s.[10]
See also
References
- JSTOR 599748.
- ^ Carboni, Stefano (1997). Following the Stars: Images of the Zodiac in Islamic Art. New York: The Metropolitan Museum of Art. p. 23.
- ISBN 9789004129733
- JSTOR 4520926
- JSTOR 43300228
- ^ Godin, G. (2015). The Use of Nodal Corrections in the Calculation of Harmonic Constants. The International Hydrographic Review, 63(2). Retrieved from https://journals.lib.unb.ca/index.php/ihr/article/view/23428
- ISSN 0091-7613.
- NOAA.
- NOAA(Special Publication NOS CO-OPS 1). June 2000.
- S2CID 235497055.
External links
- Sun and Moon Polar Applet, showing moonrise/moonset azimuths
- Astronomy Answers: What are the standstills of the Moon? Retrieved 2016-08-26.
- Eclipses, Cosmic Clockwork of the Ancients
- Lunar and solar periods, about inertial frame of reference for measuring movements of celestial bodies.
- Mean lunar and solar periods