Aries Constellation Guide — Stars, the Ram, and How to Find the Golden Fleece

How to Find Aries in the Night Sky

Aries is located in the northern celestial hemisphere, sandwiched between Pisces to the west and Taurus to the east, with Triangulum lying to the north. Its position along the ecliptic makes it one of the 13 zodiac constellations the Sun passes through each year (the Sun is in Aries from approximately April 19 to May 13). Despite being one of the most ancient named constellations, Aries is relatively small — ranking 39th in area — and its stars are modest in brightness.

The easiest way to find Aries is to use the Great Square of Pegasus as a starting point. Look about 20 degrees east of the Great Square's eastern side to find the distinctive arc of three stars that form Aries's most recognisable feature: Hamal (Alpha Arietis, magnitude 2.0), Sheratan (Beta Arietis, magnitude 2.6), and Mesarthim (Gamma Arietis, magnitude 3.9). These three stars form a shallow arc that is distinctly curved, representing the Ram's head. In the northern hemisphere, Aries is best visible in the evening sky from September through December, when it climbs to its highest point around midnight in November.

Key Stars of Aries

Mesarthim (Gamma Arietis) is one of the finest double stars in the autumn sky for small telescopes. Through a 70mm refractor at 60×, the two components — both white, both magnitude 4.7 — are clearly separated by 7.8 arcseconds. This is a true binary system, not a line-of-sight coincidence, and its two nearly identical stars make it a striking sight. The star name "Hamal" derives from the Arabic "ras al-hamal," meaning "the head of the ram" — a direct reference to its position marking the Ram's head. Sheratan comes from "al-sharatan," meaning "the two signs," referring to the star's ancient role as a marker of the vernal equinox.

The Mythology of Aries and the Golden Fleece

In Greek mythology, Aries represents the winged ram that carried Phrixus and Helle, the twin children of King Athamas of Boeotia, to safety when their stepmother planned to sacrifice them. During the journey, Helle fell into the sea at the point now called the Hellespont (modern Dardanelles), but Phrixus completed the journey to Colchis on the Black Sea. In gratitude, Phrixus sacrificed the ram and hung its golden fleece in a sacred grove guarded by a sleepless dragon — the very fleece that Jason and the Argonauts later sought in one of Greek mythology's most famous quests.

Astronomically, Aries holds a special significance in the history of Western astronomy because the vernal equinox — the point where the Sun crosses the celestial equator moving northward — was located in Aries when Hipparchus defined the coordinate system in the 2nd century BC. This point, called the First Point of Aries, is still used as the zero point of right ascension (the celestial equivalent of longitude) even though precession has since moved the equinox into Pisces. The symbol for Aries (♈) is still used to mark this fundamental reference point on star charts and in astronomical coordinate systems, a testament to the constellation's enduring importance in celestial navigation and positional astronomy.

Deep-Sky Objects in Aries

Aries lies away from the plane of the Milky Way, so its deep-sky objects are predominantly galaxies rather than nebulae or star clusters. While there are no Messier objects in Aries, the constellation offers several challenging galaxy targets for observers with moderate to large telescopes.

Aries in Binoculars

Aries is an excellent constellation for binocular observers, though for different reasons than the showpiece binocular targets of the summer Milky Way. The constellation's three brightest stars form a distinctive arc that is easily traced in 10×50 binoculars. The faint background of autumn stars creates a pleasing field that helps orient observers to this region of the sky. The most rewarding binocular observation in Aries is the double star Mesarthim — even at 10× magnification, careful observers with steady hands may detect the split of this 7.8-arcsecond binary.

Mesarthim — One of Autumn's Finest Double Stars

Mesarthim (Gamma Arietis) deserves special attention because it is one of the finest double stars in the entire autumn sky for small telescopes. Discovered by William Herschel in 1778, this binary system consists of two nearly identical white main-sequence stars of spectral type A. Both components shine at magnitude 4.7, separated by 7.8 arcseconds — a gap wide enough that a 60mm telescope at 60× splits them cleanly. The similarity in brightness between the two stars makes Mesarthim a particularly striking sight: where many double stars show a bright primary with a faint companion, Mesarthim presents two equal points of white light, like a pair of celestial headlights.

For observers testing their telescope's optics, Mesarthim is an excellent resolution target. A 70mm refractor at 80× shows a clean split with a thin dark gap between the stars. At 100× in a 130mm scope, the split is wide and obvious, with both stars appearing as sharp, round Airy disks. The position angle of the pair is approximately 360 degrees — meaning the stars are aligned almost exactly north-south. This alignment is slowly changing over centuries as the binary orbits its common centre of gravity, with an orbital period estimated at several thousand years. Observers who sketch the pair and note the position angle contribute to long-term monitoring of this system.

Observing Aries with a Telescope

While Aries lacks bright Messier objects, its galaxies provide excellent challenges for observers with moderate to large telescopes. The constellation's position in a relatively sparse region of the autumn sky makes it a good training ground for star-hopping to faint galaxy targets. Starting from Hamal, the brightest star, locating NGC 772 requires careful use of a finder chart — the galaxy lies about 3 degrees west-southwest of Hamal, near the 5th-magnitude star 7 Arietis.

NGC 772 is the finest galaxy in Aries and a rewarding target for experienced observers. At magnitude 10.3, it requires at least a 6-inch telescope under dark skies and careful star-hopping to locate. Through an 8-inch Dobsonian at 120×, the galaxy appears as an elongated glow approximately 7 by 5 arcminutes in size, with a brighter core that hints at the barred spiral structure visible in photographs. The galaxy's distorted spiral arm — caused by gravitational interaction with its companion NGC 770 — gives it an asymmetric appearance that is noticeable in larger scopes. NGC 770, at magnitude 14.2, is extremely challenging and requires at least a 12-inch telescope under excellent conditions. For astrophotographers, NGC 772 and NGC 770 make a striking pair in long-exposure images, with the larger galaxy's distorted arm pointing toward its smaller companion like an outstretched arm.

For observers interested in variable stars, Aries offers S Arietis, a Mira-type variable that ranges between magnitude 8.5 and 14.5 over approximately 200 days. Monitoring its brightness changes with a small telescope and a comparison chart is a rewarding project that requires no special equipment. The star is located about 3 degrees south of Hamal and is best observed when near maximum brightness, when it is visible in 4-inch telescopes.

The First Point of Aries and Celestial Coordinates

The First Point of Aries (also known as the vernal equinox) is one of the most fundamental reference points in positional astronomy. It marks the location where the Sun crosses the celestial equator moving northward, which occurs at the March equinox each year. When Hipparchus of Nicaea defined the celestial coordinate system in approximately 150 BC, this point lay near the eastern boundary of Aries — hence the name. Today, due to the 26,000-year precession cycle of Earth's axis, the vernal equinox has shifted into Pisces, but the name "First Point of Aries" (symbolised by the Aries glyph ♈) is still used as the zero point of right ascension, the celestial equivalent of longitude on Earth.

This historical accident means that every star atlas, planetarium app, and telescope GoTo system in use today has Aries to thank for its coordinate system. The right ascension of every object in the sky is measured eastward from the First Point of Aries, making the Ram one of the most astronomically significant constellations despite its modest appearance. For amateur astronomers using equatorial mounts or GoTo telescopes, the concept of the vernal equinox is fundamental to understanding how their equipment finds objects — the mount's home position points toward the celestial pole, and its right ascension axis is calibrated to the vernal equinox reference point. When your GoTo telescope asks for "alignment stars," it is effectively using the First Point of Aries as its starting reference.

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