Loading...

Glossary term: 合

Description: 从地球上的观测者的角度来看,当两个天体在天空中看起来非常接近时,它们被称为处于合相(合)。合相不一定是肉眼可见的——例如,每当新月时,月亮和太阳近似在一条直线上,但在此时,我们看不到月亮,除非发生日食。在这种情况下,或者两个天体非常接近(合)以至于一个天体看起来遮住另一个天体时,天文学家就会将其描述为凌日或食。

Related Terms:



See this term in other languages

Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media


Three bright objects in the sky with one top left, one in the middle and one lower centre.

Jupiter, Venus, Moon Conjunction

Caption: Captured with a smartphone in February 2023, over the skies of Luzerne County, Pennsylvania, USA, this photograph offers a glimpse into a conjunction, an enthralling astronomical phenomenon that occurs when two or more celestial objects are seen in close proximity in the sky from our perspective, despite the objects not being physically near to each other. In this image, the brilliance of Jupiter (top), the allure of Venus (middle), and the familiar glow of our Moon (bottom) dance together against a backdrop of delicate clouds and a treeline silhouette, making it a moment worth treasuring.
Credit: Joslynn Appel/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons


The crescent Moon sits to the left of two bright planets. On the right side the Pleiades star cluster can be seen.

Moon-Mercury-Pleiades Conjunction

Caption: Honourable mention in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This photograph shows the young lunar crescent, some of the nine brightest stars of the Pleiades (with one behind a cloud) on the right, and the planet Mercury, looking slightly red, in the middle of the image. This picture is rather suggestive of the idea that the Pleiades might possibly consist of seven stars. However, the viewer is misled by the clouds; five of the stars form a tiny chariot, one is next to the handle, and three are at the other end of the quadrilateral. Eight stars would be clearly visible if there were no clouds. This configuration of the young Moon next to the Pleiades is visible only in the northern hemisphere spring. Thus it was used by the ancient Babylonians to determine the second month of their year and to judge whether or not an intercalary month was necessary. At least as early as the second millennium before the common era, the Babylonians used several asterisms for each month, with another one of them reappearing every five days after invisibility during daylight. To determine the necessity of intercalation in order to synchronise the solar and the lunar year, the Babylonians used several asterisms, not only the Pleiades. For instance, they also made use of the bright stars Arcturus and Sirius, and they observed a configuration with the Moon as well as heliacal phenomena. The modern Jewish and modern Islamic traditions still make use of some of the Babylonian astronomical rules. However, given that the constellations have shifted as a result of precession, and the fact that nowadays we also have computational means to calculate our calendars, this configuration of the small crescent Moon and the Pleiades is less useful, though it remains exceptionally beautiful. Thus the ancient Babylonian and middle Babylonian tradition survives only rudimentarily. Furthermore, it is unlikely that it is depicted in the Nebra Disc from Bronze Age Europe, as has long been claimed. This image was taken on Elba Island, Italy, in May 2022.
Credit: Giulio Colombo/ IAU OAE

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons