Aries is a relatively inconspicuous constellation of the zodiac representing the Ram—its name literally means “ram” in Latin. Most of its recognizable pattern is formed by only a handful of moderately bright stars, with even its brightest star, Hamal, reaching only magnitude 2.0.
Its modest appearance, however, is deceptive. Aries has played a far larger role in the history of astronomy than its faint stars might suggest, with a story stretching from some of the earliest constellation traditions to the way astronomers still measure positions in the sky today.
Follow the Pleiades and Great Square to Aries
Aries is a northern-sky constellation and is easiest to see on Northern Hemisphere evenings from late autumn through winter, with November through January particularly convenient months. It is visible between roughly 90°N and 60°S, so it can be seen from most inhabited parts of both hemispheres. From northern latitudes it climbs relatively high in the sky, while observers farther south see it lower toward the northern horizon. Because its brightest stars are only moderately bright, a reasonably dark sky makes Aries considerably easier to recognize.
A good way to find Aries is to use two much more conspicuous landmarks. Look for the Pleiades star cluster in Taurus and the large Great Square of Pegasus farther west; Aries lies roughly between them. Once you’re in the right area, look for Hamal, a second-magnitude star with a subtle warm, orange tint. About 4° away is slightly fainter Sheratan, while much fainter Mesarthim sits close beside Sheratan. The result looks less like a ram than a short, crooked line: bright Hamal at one end, with Sheratan and Mesarthim forming a much closer pair at the other.
These three stars traditionally form the Ram’s head, although you’d be hard-pressed to guess that simply by looking at them. Once you’ve found Hamal, Sheratan and Mesarthim, you’ve identified the most recognizable part of Aries; the elaborate animal shown on traditional star charts owes far more to ancient imagination than to an obvious picture drawn by the stars.
Aries’s Modest Stars Hide Some Big Surprises
Hamal’s warm color comes from the fact that it is an evolved orange giant, lying about 66 light-years from Earth. The star has exhausted the hydrogen fuel in its core and expanded well beyond the size it had during the main part of its life. Its name comes from the Arabic for “the ram,” reflecting its traditional position at the head of the constellation.
Hamal also has a planet. Hamal b is a gas giant with a minimum mass around 1.8 times that of Jupiter and takes approximately 381 days to complete one orbit. That makes the brightest naked-eye star in Aries not simply part of an ancient celestial picture, but the center of a planetary system of its own.
Nearby Mesarthim (Gamma Arietis) provides a different surprise. To the unaided eye it appears as a single faint point, but a small telescope reveals two similarly bright stars lying extremely close together.
In 1664, English scientist Robert Hooke resolved Mesarthim while observing a comet, making it one of the earliest double stars discovered telescopically. At a time when telescopes were still transforming our understanding of the night sky, Mesarthim offered a striking example of something astronomers were only beginning to appreciate: a star that looked like a single point of light could actually be two.
Five Stars to Know in Aries
- Hamal (Alpha Arietis) – The brightest star in Aries at magnitude 2.0, about 66 light-years away. This orange giant is the main visual anchor of the constellation and traditionally marks the Ram’s head.
- Sheratan (Beta Arietis) – The second-brightest star in Aries at magnitude 2.6, around 60 light-years away. It is a binary system whose unseen companion is detected through spectroscopy.
- Bharani (41 Arietis) – At magnitude 3.6, Bharani is actually the third-brightest star in Aries, although it isn’t one of the three stars forming the familiar Hamal–Sheratan–Mesarthim pattern. It is a hot blue-white star about 160 light-years away.
- Mesarthim (Gamma Arietis) – Shining at a combined magnitude of about 3.9 from roughly 164 light-years away, Mesarthim is the close pair near Sheratan that can be resolved into two similarly bright stars through a small telescope.
- Botein (Delta Arietis) – A magnitude 4.35 orange giant about 165 light-years away. Its traditional name refers to the belly of the Ram.
Aries also contains several faint galaxies and other deep-sky objects for telescope observers.
Aries’s Closest Star Went Unnoticed Until 2003
One of the nearest stars lying within Aries is also completely invisible to the naked eye. Teegarden’s Star, named after astronomer Bonnard Teegarden, whose team identified it in 2003, lies just 12.5 light-years from Earth yet shines at only around magnitude 15. It is an exceptionally small, cool red dwarf, with roughly one-tenth the Sun’s mass and one-eighth its radius. Because such a small, cool star produces very little visible light, Teegarden’s Star is remarkably faint despite its proximity. That helps explain how such a close stellar neighbor could have escaped recognition until the 21st century.
Despite its tiny size, Teegarden’s Star has three confirmed planets with minimum masses broadly comparable to Earth’s. They orbit remarkably close to the star, taking about 5, 11 and 26 days to complete a year. The two inner planets lie in or close to the star’s habitable zone, where they receive an amount of stellar energy that could allow liquid water to exist if conditions on the planets are suitable. That doesn’t mean either is known to have water or life.
It’s a remarkable contrast with the Aries we see in the night sky. Hamal, Sheratan and Mesarthim form the familiar Ram with stars bright enough for us to trace by eye, while one of Aries’s closest stellar neighbors—and an entire planetary system around it—remains completely invisible to the naked eye.
Daylight Hides One of the Year’s Strongest Meteor Showers
Aries is associated with one of the strongest daytime meteor showers of the year—yet most people never see it. The Daytime Arietids are active during May and June and reach their maximum around early June. Radar and radio observations indicate rates of around 60 meteors per hour near the peak, comparable in underlying activity to some major nighttime showers. But at this time of year Aries lies close to the Sun in our sky, so the point from which the meteors appear to radiate is largely obscured by daylight.
Astronomers can nevertheless detect the Arietids because the meteors leave brief trails of ionized gas that reflect radio signals. A few can sometimes be glimpsed shortly before dawn, when the radiant rises ahead of the Sun, making the Daytime Arietids an unusual case of a major meteor shower studied far more easily by radio than by watching the sky.
Where all this debris comes from is less certain. Much of the stream is thought to consist of ancient material shed by Comet 96P/Machholz, although small sunskirting comets may also have contributed. Whatever its precise origin, the debris hits Earth’s atmosphere at around 38 km/s, producing the same brief streaks of light as the meteors in familiar nighttime showers.
Why Is Aries a Ram?
Nothing about the small group of stars around Hamal and Sheratan obviously resembles a ram. And the Ram wasn’t the earliest known figure associated with these stars. In ancient Babylonian astronomy, this part of the sky was known as the Hired Man, or Agrarian Worker. Over time, however, the constellation also became associated with a ram and with Dumuzi, a shepherd god—a connection that may help explain how the older Hired Man eventually developed into the Ram. Exactly when and how that transformation occurred remains uncertain.
In Greek mythology, the Ram became associated with the story of Phrixus and Helle, a brother and sister whose lives were threatened by their stepmother. They escaped on the back of a miraculous flying ram with a golden fleece, which carried them eastward through the sky. Helle fell into the sea during the journey, giving the Hellespont its legendary name, but Phrixus survived and eventually reached Colchis, on the eastern coast of the Black Sea.
In the best-known versions of the story, Phrixus sacrificed the ram to Zeus as a religious offering and gave its extraordinary Golden Fleece to King Aeëtes, who placed it in a sacred grove. Ancient accounts differ over the details, however, and one tradition has the ram shed its fleece before ascending into the heavens to become the constellation Aries. The Golden Fleece itself later became the treasure sought by Jason and the Argonauts, connecting this faint group of stars with one of the great adventure stories of Greek mythology.
The First Point of Aries Is Where the Sky’s “Longitude” Begins
Aries is considered the traditional first constellation of the zodiac for one simple reason: more than two thousand years ago, the March equinox—the moment each spring when the Sun crosses the celestial equator heading north—happened to fall among its stars.
That crossing point needed a name because the zodiac itself has no natural starting point. It’s a complete circle tracing the Sun’s path through the stars over a year, so ancient astronomers needed to agree on a “zero,” much like the zero-degree line of longitude used to measure position around Earth. The March equinox became that zero point—and because it sat in Aries at the time, it took on the name it still carries today: the First Point of Aries.
That name ended up mattering far beyond the zodiac. Astronomers still use the same point as the zero point of right ascension—the celestial equivalent of longitude, which measures how far east an object lies around the celestial sphere.
There’s just one problem: the First Point of Aries no longer lies in Aries. Earth’s axis slowly wobbles over a roughly 26,000-year cycle called precession, causing the equinox point to drift westward against the background stars. Over the centuries, that drift has carried it out of Aries entirely and into neighboring Pisces, where it sits today.
The name never moved with it. Astronomy’s celestial zero point still carries the Ram’s name more than two thousand years after it actually lay among the stars of Aries—a remarkable legacy for a constellation whose stars are otherwise so easy to overlook.
