Not before tomorrow
Morning first and morning last are astronomical terms for the visibility of bright stars or planets at dawn with the naked eye . There are special terms for the moon.
Overview: morning first and morning last
Tomorrow is the day on which a celestial body rises earlier than the sun over the eastern horizon for the first time and can be seen with open eyes because the sky is not yet outshone by sunlight. On the following days the celestial body will rise earlier than the sun and will be recognizable longer and longer at night. The term is used
- for bright stars , because they are about 4 minutes earlier than the sun from day to day
- for the five freely visible planets of the solar system, which are also regularly "overtaken" by the sun in the starry sky.
The last day of the morning is the day on which the celestial body last rises earlier than the sun over the eastern horizon and can be clearly seen because the sky is not yet outshone by sunlight. After two or more days, the star rises later than the sun and is outshone by its light. The nocturnal period in which the celestial body was above the horizon comes to an end with the end of the morning for a long time. This term is mainly used for the inner planets Mercury and Venus , while the last morning of the moon as a narrow sickle is mostly referred to as old light . There is no last morning for fixed stars and the outer planets Mars to Saturn, because they remain visible for months after the first morning until the last evening .
The morning first of the stars
In its apparent orbit around the earth, the sun lags behind the stars every day. It moves backwards on the ecliptic through the sky once a year . A star that rises at the same time as the sun will rise more and more earlier than the sun on the following days and will be visible longer and longer at dawn.
The first morning of a certain star is a certain day of the year. For example, the first morning of the star Sirius, which appears to us the brightest, was already observed in Mesopotamia and in ancient Egypt and used to plan the agricultural work that depends on the seasons .
(no) morning last of the stars
Because of the retrograde motion in relation to the sun, there is no last morning on the eastern horizon for the stars. In deviation from the definition given above, the term morning last is used for observations on the western horizon when the observed star is not close to the sun, but is in opposition to it. After the day of its last morning, the star that was previously in opposition sets earlier on the western horizon than the sun rises on the eastern horizon.
The morning last of the moon
The moon orbits the earth more slowly than the sun seems to do. It is about 50 minutes late every day compared to the sun. The initially waning moon is overtaken by the sun and overtaken at new moon . One or two days before it is the last of the morning , a narrow sickle that can be seen for the last time, which is also called old light .
Morning first and morning last Venus
The apparent relative movement between the sun and the planets is similar to that of the stars in the upper planets (apart from the retrograde movement during the annual planetary loop ), which is why only one morning can be observed with them.
The situation is quite different for the lower planets Mercury and Venus , of which the latter is more important because of its great brightness. Venus oscillates back and forth in front of the sun on both sides in a 19-month cycle, with the greatest angular difference ( elongations ) being visible for a maximum of about four hours (depending on its position in the ecliptic) alternately in the morning and evening sky , but never in the middle of the night (no opposition to the sun). Your visibility as a morning star is limited by a morning first and a morning last. In the weeks in between, they rise in the last hours of the night before dawn .
The terms heliac and acronic
Heliac (Greek) means "belonging to the sun" and is applicable in the most general case for the rising and setting of celestial bodies that are close to the sun and at the same time rise with it at dawn, but also set with it at dusk. A common, but not consistently applied, restriction only describes the processes at dawn . Heliac is now translated as "belonging to the rising sun". Because rises and sets on the western horizon are included by celestial bodies that are in opposition to the sun, it is no longer true that the celestial bodies are close to the sun. With morning first and morning last could also mean processes on the western horizon in this usage.
Acronychic (Greek) means "at the edge of the night" and denotes the same state of affairs as heliacal with regard to the rising and setting of celestial bodies, i.e. processes at the beginning of the night (dusk) and at its end (dawn). The parallel application of both terms becomes possible by applying the corresponding - also not consistently applied - restriction to acronychic . One now uses acronymically only for dusk , that is, for the "beginning of the night". Evening rises and sets on the eastern horizon of celestial bodies in opposition to the sun are included. With evening last and Abenderst also operations on the eastern horizon could be meant for this usage.
Occasionally, acronym is used exclusively for the rising and setting of celestial bodies that are in opposition to the sun. It must be specified separately whether the events take place in the morning or in the evening.
Because of the ambiguous definition of the terms heliacal and acronic , the use of morning first and morning last is preferable.
See also
Individual evidence
- ↑ Burkard Steinücken: "The use of star phases to determine time in Hesiod" p. 11, Fig. 2, bottom