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Glossary term: Leo

Description: Leo, "the Lion", is a constellation in the Zodiac, i.e. the stars that make up this constellation are in the part of the sky that intersects with the ecliptic (the plane defined by the Earth's path around the Sun). Hence, from our point of view here on Earth, we can regularly find the Sun, and also the other planets in our Solar System, in this constellation – in the case of the Sun from August 11 to September 17. (Of course if the Sun is there, we cannot see the constellation's stars.) In the night sky, Leo is easiest to observe in spring. It is one of the 88 modern constellations defined by the International Astronomical Union, and also one of the 48 classical constellations named by 2nd century astronomer Claudius Ptolemy. The brightest of Leo's numerous bright stars is called Regulus.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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 Diagrams


Cancer appears as an inverted “Y” on the sky, with its vertex almost exactly on the ecliptic which runs ESE to WNW

Cancer Constellation Map

Caption: The zodiac constellation Cancer and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Lynx, Gemini, Canis Minor, Hydra, Leo and Leo Minor. The ecliptic (shown here as a blue line) passes almost exactly through the middle of the constellation, this is the path the Sun appears to take across the sky over the course of a year. The Sun is in Cancer from late July to mid August. The other planets of the Solar System can often be found in Cancer. Cancer lies just north of the celestial equator and is thus visible at some time in the year from all of planet Earth except for the most antarctic regions of the world. Cancer is most visible in the evenings in the northern hemisphere spring and southern hemisphere autumn. Two star clusters are visible in Cancer: M44, an open cluster often called the Beehive Cluster, and M46, a denser open cluster with about four times more stars than M44. These clusters are indicated by yellow circles with a dotted border on the map. The y-axis of this diagram is in degrees of declination and with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labelled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Leo resembles a lion standing on the ecliptic (which runs ESE to WNW) with its nose pointed northwest.

Leo Constellation Map

Caption: The zodiac constellation Leo and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Leo Minor, Cancer, Sextans, Hydra, Crater, Virgo and Ursa Major. The brightest star in Leo, Regulus, lies almost exactly on the ecliptic (shown here as a blue line): the path the Sun appears to take across the sky over the course of a year. The Sun spends the period from mid August to mid September in Leo. The other planets in the Solar System can often be found in Leo. Leo spans the celestial equator and is thus part of it is visible at some time in the year from all of planet Earth with some of the constellation obscured for the most arctic and antarctic regions of the world. Leo is most visible in the evenings in the northern hemisphere spring and southern hemisphere autumn. Several objects can be seen in Leo, including M65 and M66 – two galaxies in the Leo Triplet, a trio of galaxies including NGC 3628, not listed here. In addition, M96, a spiral galaxy, can be seen as a fuzzy object using a small telescope, and Messier 105, an elliptical galaxy. Each of these objects are labelled on the map as red ellipses. The y-axis of this diagram is in degrees of declination and with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labelled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Virgo Constellation Map

Caption: The zodiac constellation Virgo and its surrounding constellations. Starting from the top of the diagram and going clockwise, these are Coma Berenices, Leo, Crater, Corvus, Libra, and Bootes. The brightest star in Virgo, Spica, lies just below the ecliptic (shown here as a blue line) in the middle of the map. One way of locating this star in the night sky is to follow the handle of the Big Dipper to the star Arcturus in Bootes and go along a line straight down to Spica (“arc to Arcturus and spike to Spica”). This star lies just below the ecliptic. The ecliptic is the path the Sun appears to take across the sky over the course of a year. The Sun is in Virgo from mid September to late October. The other planets of the Solar System can often be found in Virgo. Virgo spans the celestial equator and is thus part of it is visible at some time in the year from all of planet Earth with some of the constellation obscured for the most arctic and antarctic regions of the world. Virgo is most visible in the evenings in the northern hemisphere spring and southern hemisphere autumn. The constellation Virgo appears as a person lying with their back roughly against the ecliptic, arms outstretched, and feet pointed east. Several deep-sky objects are visible in Virgo, including NGC4697, M49, M87, M86, M84, and M60, all of which are labelled as red ellipses on the map. These are all spiral and elliptical galaxies located several millions of lightyears from Earth. Most notably, M87 is host to the supermassive black hole (Pōwehi) that was imaged by the Event Horizon Telescope in 2019. All of these galaxies are members of the Virgo Cluster, the nearest cluster of galaxies to the Milky Way. The y-axis of this diagram is in degrees of declination and with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labelled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons