Evening first
Evening first and evening last are astronomical terms for the visibility of planets or bright stars with the naked eye at dusk . There are special terms for the moon.
Overview: evening first and evening last
The evening is the day on which a planet sets later than the sun on the western horizon for the first time and can be seen with open eyes because the sky is no longer outshone by sunlight . On the following days it sets more and more later than the sun and can be observed longer and longer in the twilight or night. This term is mainly used for the inner planets Mercury and Venus , while the first evening of the moon as a narrow, waxing sickle is mostly referred to as new light . There is no evening first for fixed stars and the outer planets Mars to Saturn, because after their first morning they are visible for months until the end of the evening.
The last day of the evening is the day on which the star sets later than the sun and can be seen with free eyes because the sky is no longer outshone by sunlight. After two or more days, the star sets earlier than the sun. The nocturnal period in which it stood above the horizon and could be seen with the naked eye comes to an end for a long time with the end of the evening . 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 evening 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 later it is evening first , a narrow sickle that can be seen on the western horizon for the first time after sunset, which is also called new light .
The new light of the moon is the first evidence of the beginning of a new lunar period that can be seen with the naked eye . In ancient cultures , the new light from the moon marked the beginning of the new calendar month . It is known from Islam that the beginning and end of the fasting month of Ramadan can still be recognized today by the new light.
The last of the stars
During the apparent daily rotation of the sky, the stars near the ecliptic “overtake” the sun once a year . Because this moves every year - as a mirror image of the earth's orbit - along the ecliptic through the entire starry sky , which amounts to just under 1 ° or 4 minutes per day. When the sun approaches a bright star at around 15 °, it can be seen for the last time on the western horizon at dusk. When it has passed it, it sets earlier than the sun and is below the horizon at night.
The last evening of a certain star is a certain day of the year. For example, the last evening of the star Sirius, which appears to us the brightest, was already observed in Mesopotamia and in ancient Egypt and used to plan agricultural work depending on the seasons .
(no) evening of the stars
Because of the retrograde motion in relation to the sun, there is no evening with the stars . In deviation from the definition given above, the term evening is only used for observations on the eastern horizon when the observed star is not close to the sun, but rather in opposition to it. If the sun is late enough, the star that was previously in opposition rises earlier on the eastern horizon than the sun sets on the western horizon and can be seen with the naked eye for the first time at dawn.
Venus first and last evening
The apparent relative movement between the sun and 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 last evening 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 an evening star is limited by an evening first and an evening last . In the weeks in between, it sinks in the first hours of the night after dusk .
The terms acronymic and heliacal
Acronychic (Greek) means "at the edge of the night" and is applicable in the most general case for the setting and rising of celestial bodies at the edge of the night, i.e. at the beginning of the night (dusk) and at its end (dawn). A frequent but not consistently applied restriction only describes the processes at dusk , ie at 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 evening or at dawn.
Heliacian (Greek) means “belonging to the sun” and is applicable in the most general case for the setting and rising of celestial bodies that are close to the sun and at the same time set with it at dusk, but also rise with it at dawn. A frequent, albeit 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.
Because of the ambiguous definition of the terms heliacal and acronic , the use of evening first and evening last is preferable.
See also
Individual evidence
- ↑ Burkard stone back: The use of star phases to determine time with Hesiod . (PDF) p. 11, fig. 2, above