Step outside on a clear evening this week, look nearly straight up, and the brightest star you see may well be Vega. Look a little lower toward the south and you will find Altair. Wait until late at night and Aldebaran, Betelgeuse and Rigel climb up in the east. Every one of those names came from Arabic.

That is not a coincidence or a legend. Many of the bright stars that astronomers still call by name today carry names that passed from Arabic into medieval Latin and then into modern English. Here is how that happened, what the names actually mean, and when you can find each star from Massachusetts this fall.

Where the names came from

Long before telescopes, people across Arabia named stars and star groups to keep track of the seasons, the rains and their routes across the desert. In the 9th and 10th centuries, scholars in Baghdad and other cities translated Greek astronomy into Arabic, including Ptolemy's great star catalogue, the Almagest, and then corrected and expanded it.

One of the most important of those works was The Book of Fixed Stars, written around 964 by the Persian astronomer Abd al-Rahman al-Sufi. It combined Ptolemy's catalogue with the older Arabic star traditions and drew each constellation twice: once as you see it in the sky, and once as it appears on a celestial globe. We wrote earlier about al-Sufi's "little cloud," the first written record of what we now call the Andromeda Galaxy.

When European scholars later translated Arabic astronomy books into Latin, they carried many of the star names across, sometimes faithfully and sometimes with spelling mistakes. Those names stuck.

What the names mean

According to the Arabic star-name tables compiled by scholars of the subject, here is what eight familiar names come from:

  • Vega: from an-nasr al-wāqi', "the falling (or swooping) eagle."
  • Altair: from an-nasr aṭ-ṭā'ir, "the flying eagle." Vega and Altair are a matched pair of eagles, one diving and one in flight.
  • Deneb: from dhanab ad-dajājah, "the tail of the hen." Many other stars have "Deneb" in their name for the same reason: dhanab means "tail."
  • Aldebaran: from ad-dabarān, "the follower," because it seems to follow the Pleiades star cluster across the sky.
  • Betelgeuse: from yad al-jawzā', "the hand of al-Jawzā'," the Arabic figure that sits where we picture Orion. The Arabic scholar Paul Kunitzsch concluded that medieval Latin copyists misread the first letter, yā' (written with two dots below), as bā' (one dot below), and that is how yad turned into "Bet."
  • Rigel: from rijl al-jabbār, "the foot of the giant," because it marks Orion's foot.
  • Algol: from ra's al-ghūl, "the head of the ghoul," in the constellation Perseus.
  • Fomalhaut: from fam al-ḥūt, "the mouth of the fish (or whale)."

In 2016 the International Astronomical Union, the body that sets official names in astronomy, set up a Working Group on Star Names and approved a formal list. Vega, Altair, Deneb, Aldebaran, Betelgeuse, Rigel and Algol were all formally approved on June 30, 2016, and Fomalhaut in December 2015. So these Arabic-rooted names are not just old traditions; they are the official names astronomers use today.

Why the sky mattered to Muslim scholars

The night sky was practical knowledge in Muslim civilization. Prayer times, the direction of the qibla and the start of each lunar month all depend on the sun, moon and stars, and travelers by land and sea found their way by them. The Qur'an speaks of this directly: "It is He who placed for you the stars, that you may be guided by them through the darknesses of the land and sea" (Surah Al-An'am 6:97). Another verse says simply, "And by the stars they are guided" (Surah An-Nahl 16:16).

Those verses are about guidance and reflection, not a scientific prediction. What they did do, alongside everyday needs like prayer and travel, was give many Muslim scholars a reason to study the sky carefully, and their careful work became part of the shared heritage of modern astronomy.

When to see them from Massachusetts

These times are for Boston on a clear night in late October and are approximate. Elsewhere in the state they differ by only a few minutes. Remember that clocks fall back on Sunday, Nov. 1, so after that date everything below happens one clock-hour earlier.

Early evening, around 8 PM (7 PM after Nov. 1):

  • Vega is the bright blue-white star high in the west.
  • Deneb is almost straight overhead.
  • Altair is in the southwest, about halfway up. Together, Vega, Deneb and Altair form a big triangle that stargazers call the Summer Triangle, even though it is easiest to see on fall evenings.
  • Fomalhaut sits alone, low in the south. It is the only bright star in that part of the sky, so it is easy to spot if trees and buildings don't block your view.
  • Algol is in the northeast, about a third of the way up.

Late evening, around 11 PM:

  • Aldebaran, orange and bright, is in the east, below the small, tight cluster of the Pleiades.
  • Betelgeuse and Rigel are just rising in the east, on either side of Orion's belt. Betelgeuse looks orange-red and Rigel looks blue-white.

Before Fajr, around 5:30 AM:

  • Orion is high in the south, with Betelgeuse in his shoulder and Rigel in his foot, and Aldebaran is up and to the right. If you are already up for Fajr, step outside for a minute after prayer before it gets light.

Watch Algol wink. Algol is an eclipsing star system: two stars orbit each other, and every 2.87 days one passes in front of the other. For about 10 hours its brightness drops from about magnitude 2.1 to 3.4, so it looks noticeably dimmer, before brightening again. Check it over a few nights and compare it with the stars around it.

You don't need a telescope for any of this. Your eyes are enough, and a star-chart app on your phone can help you confirm which star is which.

See them through a telescope in Boston

Boston University's Department of Astronomy has hosted public open nights at the Judson B. Coit Observatory since 1967. They are held most Wednesday evenings, weather permitting, in the observatory above the Astronomy Department at 725 Commonwealth Avenue. From October to March the program starts at 7:30 PM sharp, and there is no admittance once it begins.

Tickets are free but required, are limited to five per person, and are released on BU's Eventbrite page on Thursday mornings around 11 AM. Clouds, haze or rain cancel the night, and BU decides on the day itself. You can call 617-353-2630 no earlier than two hours before the start to check. The observatory is reached only by stairs, unaccompanied minors are not admitted, and the telescopes are outside, so dress warmly.

A family activity

This is an easy outing with kids. Teach them the two eagles, Vega and Altair, and the hen's tail, Deneb, and let them find the Summer Triangle on their own. Then tell them that the words they just learned were first spoken in Arabic more than a thousand years ago, and are still on every modern star chart.