Is the lunar eclipse worth watching

MOON IRIS LEXICON

ANOMALISTIC MONTH:
The anomalistic month is the time that passes before the moon reaches the same position (e.g. the -> perigee) on its orbit around the earth. The length of an anomalous month is 27.55455 days (= 27d 13h 19m).

APHEL:
Aphelion is the point furthest from the Sun on the elliptical orbit of a planet around our central star. The earth is in the aphelion of its orbit 152.1 million kilometers from the sun.

APOGEE:
The apogee is the most distant point on the elliptical orbit of the moon (or an artificial satellite) around the earth. The moon is at the apogee of its orbit, 406,740 kilometers from the earth.

BLUE MOON:
If there is a second full moon in a calendar month, it is referred to as the "blue moon" in English-speaking countries. The term has also found its way into the German language as Anglicism.

BLOOD MOON:
Term used in the media since 2014 for a total -> lunar eclipse.

CRATER TIMINGS:
English term for the measurement of the -> shadow entry times more striking -> moon formations.

DANJON SCALE:
The Frenchman André Danjon (1890 - 1967) developed a five-point scale to classify the color and brightness of the totally eclipsed moon. This Danjon scale is used internationally today. A distinction is made between the following levels:

THE DANJON SCALE
L0: Very dark eclipse, the moon disc appears gray-black, the moon can hardly be seen in the middle of the eclipse.
L1: Dark eclipse, gray or brownish moon disc, surface details are difficult to see.
L2: Moon shines dark red, sometimes rust red, central area of ​​the umbra quite dark, brightening towards the edge of the umbra.
L3: Moon shines brick-red, umbra in the edge zones lightened yellowish.
L4: Moon shows a bright, copper-red color, sometimes orange. The umbra often has a light, bluish border; all surface details are recognizable.

The determination is made with the naked eye to the center of the darkness. However, it is helpful for classification to observe the moon during the entire totality.
The following empirically found relationship exists between the Danjon level L and the brightness M of the totally eclipsed moon:

M = 4 - (2.3 * L)

The determination of the Danjon level can therefore also be used to confirm a -> determination of the brightness of the moon, e.g. with the -> binocular method.

DRAGON POINTS:
In ancient times the -> nodes of the lunar orbit were called dragon points. When the moon is at and at least close to the nodes, solar and -> lunar eclipses occur. Since it was believed in ancient times that a dragon swallowed the sun or moon, the nodes were called dragon points.

DRAKONITIC MONTH:
The draconian month is the time that passes until the moon goes through the same -> node of its orbit again. The length of a draconian month is 27.21222 days (= 27d 05h 06m).

Eclipse:
The ecliptic is the apparent path that the sun draws in the earthly sky over the course of the year. It is nothing more than the projection of the plane of the earth's orbit onto the firmament. Both the Earth's moon and the planets move on orbits that are slightly inclined towards the plane of the Earth's orbit. They are therefore always to be found in the sky close to the ecliptic.

EXELIGMOS PERIOD:
Since a Saros period is 18 years and 10 1/3, 11 1/3 or 12 1/3 days long, successive eclipses of a -> Saros series occur, each shifted by 1/3 of the circumference of the earth to the west. Only after three Saros periods does a MoFi take place again (almost) at the same longitude. This repetition period of 54 years and 31, 32 or 33 days is called the Exeligmos period.

BINOCULAR METHOD:
Probably the most popular method for -> determining the brightness of the eclipsed moon is viewed through inverted binoculars. If you use binoculars with 10x magnification, the apparent diameter of the moon is reduced to a tenth, i.e. about 3 arc minutes, which comes very close to the desired point shape. While one eye is looking at the moon through one of the binoculars, the other eye (without binoculars) takes aim at nearby stars, with which the brightness of the moon is then compared. A correction factor (F) must be deducted from the binocular brightness (m) of the moon determined in this way in star size classes in order to obtain the actual brightness (M, given in star sizes) of the eclipsed moon:

M = m - F

The value of the correction factor depends on the magnification of the binoculars:

F = 4.2 at 6x magnification
F = 4.8 at 8x magnification
F = 5.3 at 10x magnification
F = 5.7 at 12x magnification
F = 6.8 at 20x magnification

For other magnifications (P), the value of F can be calculated using the following formula:

F = 5logP + 0.31

DARK SIZE:
The eclipse size or Magnitude of the darkness indicates in a -> lunar eclipse with what percentage of its diameter the moon enters the -> penumbra or -> umbra of the earth. With a partial lunar eclipse, the umbra magnitude is always less than 1.00, with a total lunar eclipse it is at least 1.00. The theoretical maximum value is 1.889, i.e. at the middle of the eclipse the edge of the moon is 0.889 moon diameter from the inner edge of the umbra. For pure -> penumbral eclipses, in addition to the magnitude of the penumbral eclipse, the umbra magnitude is sometimes also given. The latter then has negative values. For example, an umbra magnitude of -0.09 means that the edge of the moon at the middle of the eclipse is 0.09 lunar diameter from the outer edge of the umbra.

DARK YEAR:
A grouping of 2 or 3 solar and lunar eclipses (-> eclipse season) is followed almost 6 months (173.3 days) later by the next "eclipse season", namely when the other -> lunar orbit node between sun and earth stands. After a further 173.3 days, the eclipse year is then completed with the renewed passage of the first lunar orbit node between the earth and the sun. Since the eclipse year with 346.6 days is 18.6 days shorter than the solar year, the eclipses occur earlier in each calendar year. The situation is complicated by the fact that the lunar year is just under 355 days longer than the eclipse year. Therefore, the eclipses usually occur 10 days earlier for 4 years, but then 40 days earlier in the 5th year. Example: Lunar eclipses on March 14th, 2006, March 3rd, 2007, February 21st, 2008, February 9th, 2009, December 31st, 2009.

DARK SEASON:
In order for a -> lunar eclipse to occur, the full moon must be near a -> lunar orbit node. If this is the case, the other lunar orbit node is logically between the earth and the sun. Now the moon needs about 29.5 days to move from full moon to new moon position and back again. On the other hand, the period in which solar or lunar eclipses can occur before and after a node crossing between the sun and the earth is around 33 days. This means that at least one solar eclipse (S) and one lunar eclipse (M) must occur in this period, but that there can also be 3 eclipses, in the order SMS or MSM. In the latter case, the two lunar eclipses are almost always -> penumbral eclipses. For the periods in which 2 or 3 eclipses take place in quick succession, the term eclipse season has become common.

SEMI-SHADE:
In astronomy, penumbra is a zone from which one celestial body partially obscures another. For an observer who is e.g. on the surface of the moon in the penumbra of the earth, parts of the solar disk are hidden by the earth.

SEMI-SHADOW FINISH:
In a penumbral eclipse, the moon only crosses the -> penumbra of the earth. Most of the time, the moon only enters the penumbra with part of its diameter. In rare cases, however, the moon crosses the penumbra with its entire diameter without touching the umbra. This is sometimes misleadingly referred to as a "total penumbral eclipse".

CORE SHADOW:
In astronomy, umbra is a zone from which one celestial body completely covers another. For an observer who is e.g. on the surface of the moon in the umbra of the earth, the solar disk is completely covered by the earth. The earth's atmosphere, however, refracts long-wave (red) light into the more distant parts of the umbra, which then creates a diffuse twilight on the moon's surface.

CORE SHADOW FINISH:
Umbra eclipses are all -> lunar eclipses in which the moon enters at least part of its diameter in the -> umbra of the earth. So it is a collective term for partial and total lunar eclipses.

BRIGHTNESS DETERMINATION:
To determine the brightness of the eclipsed moon, a comparison with stars of known brightness is useful. Since the moon is not a point of light, but a flat object, it has to be displayed more or less point-like, e.g. by -> silver sphere photometry or by means of the -> binoculars method. The opposite way, namely the two-dimensional display of the comparison stars, is also possible (-> Sidgwick method). Finally, the brightness of a total -> lunar eclipse can also be derived from the -> Danjon scale using an empirical formula.

CORE SHADOW ENLARGEMENT:
Already in 1702 it was Pierre de la Hire noticed that the -> contacts take place earlier than expected when entering the -> umbra and later than expected when exiting. Obviously, the earth's shadow is about 2% larger than it should be based on the geometric relationships. The reason for this is the earth's atmosphere, which increases the shadow diameter. Nowadays, an umbra enlargement of 2% is usually already taken into account when calculating the contact times. Nevertheless, there are still deviations between the calculated and the observed contact times. The magnification of the earth's shadow is a bit different in every eclipse, whereby the state of the earth's atmosphere obviously plays a role. By measuring the -> shadow entry times of striking -> moon formations, the extent of the umbra enlargement for a specific eclipse can be determined quite precisely.

NODES, TRAIN NODES:
All planets and most of their moons orbit the sun in roughly the same plane, but only roughly; their orbits are slightly inclined towards each other. The two points of intersection of the orbital planes of two celestial bodies are called nodes or orbital nodes. Only when two planets or moons reach these points at the same time will they stand in a row with the sun in three-dimensional space and only then are eclipses possible.

CONTACTS:
In eclipses, contacts are the times when two celestial bodies or one celestial body and the shadow of another touch each other for the first time or for the last time. For total -> lunar eclipses, there are 6 different contact times, which are defined as follows:

1. Contact: Coming from the outside, the moon touches the outer edge of the -> penumbra of the earth for the first time.
2. Contact: Coming from the outside, the moon touches the outer edge of the -> umbra of the earth for the first time.
3. Contact: The moon detaches itself from its inner edge after completely entering the umbra.
4. Contact: Coming from within, the moon touches the inner edge of the umbra again.
5. Contact: The moon detaches itself from the outer edge of the umbra after it has completely exited.
6. Contact: The moon detaches itself from the outer edge of the penumbra after it has completely exited.
In the case of partial lunar eclipses, there are only contact times 1, 2, 5 and 6, which are then counted as 1st to 4th contact. Pure penumbral eclipses only have contact times 1 and 6, then referred to as 1st and 2nd contact. For all types of eclipse, the time of the maximum eclipse (= middle of the eclipse) is usually also specified.

Some eclipse tables do not indicate the penumbral contacts for total lunar eclipses; the umbra contacts are then referred to as 1st to 4th contact.
Because of the -> umbra enlargement and the diffuse delimitation of the earth's shadow (both caused by the earth's atmosphere) the 4 contact times cannot be precisely predicted. They can only be determined with an accuracy of a few seconds by observation during the eclipse. In principle, contacts 1 and 6 cannot be observed and therefore cannot be precisely determined.

METONIC CYCLE:
The metonic cycle is the least common multiple of two periods:

1. -> Synodic month
2nd solar year to 365.2425 days

19 solar years correspond to almost exactly 235 synodic months. If, for example, there is a full moon on March 3rd, this is also the case 19 years later. This relationship, known at least since antiquity, but perhaps also to the builders of Stonehenge, is known as the Metonic Cycle. 19 solar years and 235 synodic months coincidentally also correspond to about 20 -> eclipse years. So if there is a -> lunar eclipse on March 3rd at the full moon, this should happen again 19 years later. But because the correspondence between the eclipse year and the metonic cycle is not very precise, such series of eclipses do not last long.
19 years after the MoFi of 03.03.2007 on 03.03.2026 there will be another total lunar eclipse. After another 19 years, a penumbral eclipse will follow on March 3rd, 2045. The next eclipse should therefore occur on 03.03.2064. But this is not the case because the series has now ended. If we look into the past, we encounter another (penumbral) eclipse on 03.03.1988, but not at the beginning of March 1969.

LUNAR ECLIPSE:
A lunar eclipse is the partial or complete entry of the moon into the -> penumbra and / or the -> umbra of the earth. In principle, 3 types of lunar eclipses can be distinguished:

1. Total lunar eclipse:
the full diameter of the moon crosses the umbra of the earth.
2. Partial lunar eclipse:
the moon only crosses part of its diameter through the umbra of the earth.
3. -> penumbral eclipse:
the moon only crosses part of its diameter or (rarely) its entire diameter through the penumbra of the earth.

Total and partial lunar eclipses are always penumbral eclipses as well.
In a calendar year there are at least 2, but no more than 5 lunar eclipses. The maximum number of -> umbra eclipses (partial or total) in a year is 3.

MOON INFORMATION:
Geographic units on the lunar surface such as craters, lunar seas or mountain ranges are called lunar formations. In the case of -> lunar eclipses, the -> umbra enlargement can be determined by measuring the -> shadow entry times of prominent moon formations.

PENUMBRA:
Astronomical technical term for the -> penumbra of a celestial body.

PERIHEL:
Perihelion is the closest point to the Sun on the elliptical orbit of a planet around our central star. The earth is in the perihelion of its orbit 147.1 million kilometers from the sun.

PERIGEE:
Perigee is the closest point to the earth on the elliptical orbit of the moon (or an artificial satellite) around the earth. The moon is in the perigee of its orbit 356,410 kilometers from the earth.

SAROS SERIES, SAROS:
Each -> lunar eclipse belongs to a series of around 75 geometrically similar events, known as the Saros series, which repeat themselves cyclically.
Behind this is actually nothing other than the principle of the least common multiple of the three different lunar months:

1. -> Synodic month
2. -> Draconite month
3. -> anomalous month

18 years and 10 1/3, 11 1/3 or 12 1/3 days (depending on the number of leap years in between) correspond almost exactly to 223 synodic, 242 draconian and at the same time 239 anomalistic months. Therefore, after this time (Saros period, Saros cycle) again a very similar, but not completely identical, lunar eclipse.
Probably the most obvious difference is that successive eclipses of a Saros occur shifted by 1/3 of the earth's circumference to the west, as can be clearly shown in the example of Saros 123: The lunar eclipse on 03/03/2007 was optimally visible in Europe and Africa. The following event of this Saros on March 14th, 2025 will be best observed in America. A Saros period later, after 36.06 years, the lunar eclipse is again visible about 120 degrees of longitude further west, namely on March 25, 2043 over East Asia. The third subsequent eclipse, after 54.09 years (-> Exeligmos period) on 04/04/2061 can then be observed again in Europe and Asia at approximately the same geographical length as the one observed first.

SHADE ENTRY TIMES:
The extent of the umbra enlargement in a -> lunar eclipse can only be precisely determined in retrospect on the basis of observations. For this purpose, with the help of a telescope, both the 4 (or 2 in the case of a partial MoFi) contact times of the umbra and the shadow entry times of more prominent -> moon formations are determined. Usually the 20 formations of an international standard system specially developed for this purpose are used.

SIDGWICK METHOD:
The Sidgwick method was developed to determine the brightness of comets that present themselves as flat and mostly faint objects. But it can also be used for total -> lunar eclipses. To do this, you first look at the eclipsed moon with binoculars or telescope and memorize its brightness. Then you point the instrument at a star or planet of known brightness and defocus so much that the object to be compared reaches about the diameter of the moon. Now compare its brightness with that of the moon, which you have memorized beforehand. This procedure is repeated with differently bright comparison stars until one either finds a star that appears as bright as the moon or until one can at least narrow down the brightness of the moon. In the case of very bright lunar eclipses (-> Danjon level 3 or 4), however, the procedure is not very suitable, because then it is next to the brightest star Sirius only the planets Jupiter, Venus and maybe Mars are available as comparison objects. One should then use the -> binocular method.

SILVER BALL PHOTOMETRY:
An often quoted, but rarely used method to determine the brightness of the totally eclipsed moon. One makes use of the fact that the mirror image of the moon appears almost point-like in a silver Christmas tree ball. This enables direct comparison with point light sources of known brightness (stars, planets). In practice, however, the -> binoculars method is usually used for -> brightness determinations in lunar eclipses.

SUPERMOND:
A term that has been circulating in the media since the end of the 2000s for a full moon near the -> perigee of the moon's elliptical orbit. The apparent diameter of the earth's satellite is then 14% larger than in the furthest position; it also appears 30% brighter.

SYNODIC MONTH:
The synodic month is the time that passes until the moon reaches the same phase again (e.g. new moon or full moon). The length of a synodic month is 29.53059 days (= 29d 12h 44m).

TRIPLE SAROS:
Another name for the -> Exeligmos period.

UMBRA:
Astronomical technical term for the -> umbra of a celestial body.

SOURCE INFORMATION:

ALPO: Observe Eclipses! Excerpts from book by Dr. Michael D. Reynolds and Richard A. Sweetsir

Working group Astronomie Handeloh e.V .: Info lunar eclipse (PDF, 255 kb)

Hans-Ulrich Keller: Kosmos Himmelsjahr 2001, pp. 41 - 46

Philip S. Harrington: Eclipse!

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