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Boötes Constellation Guide – The Night Sky Herdsman

In this article, we’ll be sharing with you everything you need to know about the constellation of Boötes, including how to find it and deep space objects contained within it and how to use it to find other night sky objects more easily.

The Constellation of Boötes

Boötes comes from the Greek word for ox-driver or herdsman. The two dots over the second ‘o’ is called a diaeresis and indicates that each ‘o’ is pronounced separately, so Boötes is pronounced bou’ outis or b’oh-OO-Teez.

While the first recorded appearance of this constellation is in Homer’s Odyssey over 3000 years ago, the Ancient Greeks were unclear of this constellation’s origin.

In one myth Boötes represents Arcas, the son of Zeus and Callisto. Hera, Zeus’s wife, transformed Callisto into a bear. An adult Arcas encountered a bear in the woods and began to chase it. That bear was Callisto and Zeus placed them both in the sky to avoid a tragedy.

In another myth, Boötes represents Icarius, a grape grower who had been given the secret of winemaking by Dionysus. Icarius’ friends over-indulged in his wine and when they woke up with hangovers the next day, they assumed Icarius had tried to poison them. They murdered Icarius and a saddened Dionysus placed him in the heavens.

A third myth credits Boötes with inventing the plow. Ceres placed him in the heavens to honor this important invention.

To help you spot Boötes, here’s what SkySafari shows.

The mythical herdsman in the constellation of Boötes
Boötes, the herdsman

Boötes has an area of 907 square degrees and is the 13th largest of the 88 recognized constellations. You may recognize its famous star Arcturus, which is the 3rd brightest individual star in the sky, or its kite-shaped asterism.

The annual Quadrantid meteor shower (peaks ~Jan 4), has its radiant in Boötes.

The whole constellation covers a larger area of sky than just the kite, as you can see in the image below. Click on it for a full screen version.

Map of Bootes constellation showing brightest stars and boundary
The kite of Boötes and its brightest stars (click for full-screen)

In the next section discover how to find Boötes.

How To Find Boötes In The Night Sky

Boötes is part of the Ursa Major family of constellations. It is visible to observers at latitudes between +90° and -50°.

Observers in the Northern Hemisphere have the best views in evenings during spring and summer, while those in the Southern Hemisphere will see it during their autumn and winter months. Boötes is directly overhead when viewed from mid-US latitudes at 10pm in May and June evenings.

The extreme end of the sickle/arm part of the constellation is circumpolar, meaning it’s visible all year around. The main body of the constellation can only be seen between March and September in the evening.

The constellation of Boötes is bordered by the constellations Camelopardalis, Canes Venatici, Coma Berenices, Corona Borealis, Draco, Leo Minor, Lynx, Ursa Major and Ursa Minor. See its brightest stars in the image below, which can be clicked for a full-screen version.

The stars of boötes to magnitude 5.0 (source: SkySafari)

Boötes’ kite-shaped asterism is composed of six stars: Arcturus, Izar, Delta Boötis, Nekkar, Seginus and Rho Boötis.

To find Boötes, carry out a naked-eye hunt for Arcturus (the bottom star of the kite).

If you have trouble spotting Arcturus, you can star hop to Boötes from the Big Dipper. Extend the arc of the Big Dipper’s handle ~30° to Arcturus, otherwise known as the ‘arc to Arcturus’, which you can see in the image below. Use your hand at arm’s length to estimate this distance.

Arc to Arcturus and Spica
See Arcturus a little more than midway along the arc to Spica

To find Boötes’ exact position for your location on any night, use software such as Stellarium (free) or SkySafari.

Boötes’ Brightest Stars

In addition to the stars in its asterism, Boötes has over 20 stars brighter than magnitude 5.0, many of them are lovely binary stars too.

Alpha Boötis (Arcturus) – At magnitude +0.15, Arcturus is the brightest star in Bootes and the brightest star in the northern hemisphere.  It’s located ~37 light-years away. This orange giant lies on the celestial equator. Arcturus means ‘guardian of the bear’ in ancient Greek.

Beta Boötis (Nekkar, Meres) – Magnitude 3.48 Nekkar, is the north star in Boötes’s asterism. This yellow giant is 219 light-years away. The name Nekkar is derived from a miss-translation of the Arabic word for ‘cattle driver’.

Gamma Boötis (Seginus) – This is both a variable star and a double. The main star shines at magnitude 3.0 and its companion at 12.7. Seginus marks the eastern corner of the kite asterism and is 85 light-years away.

Delta Boötis – The fifth brightest star in Boötes is a variable double star. The primary shines at magnitude 3.47 and the secondary shines at magnitude 7.89.

The yellow-giant primary star and main-sequence secondary star are two arcminutes apart. Delta Boötis is one of the stars in Boötes’ asterism and is ~117 light-years away.

Epsilon Boötis (Izar, Mirak, Pulcherrima) –This binary system is an orange giant with a smaller dimmer, blue-green main-sequence companion. They are 3 arcseconds apart, making them a tough spot in smaller scopes.

Izar is Boötes’ second brightest star and has a magnitude of 2.5, while its companion shines with magnitude 4.8. It’s one of the stars in Boötes’ asterism. Izar comes from the Arabic word for ‘veil’ and Pulcherrima means ‘the loveliest’ in Latin.

Zeta Boötis – This 3.77 magnitude binary system contains a pair of nearly identical giant stars. They are just 0.2 arcseconds apart and so can’t be resolved today. However, at their greatest separation, they are easily resolvable… but that’s not due until 2080!

Eta Boötis (Muphrid) – This binary system has a magnitude of 2.68 and is the third brightest star in Boötes. The yellow subgiant primary has a white dwarf secondary shining at magnitude 10. It is not resolvable in a backyard scope because it is too close to the parent star.

Muphrid is ~37 light-years away and its common name is derived from the Arabic phrase ‘the single one of the lancer’.

Kappa Boötis (Asellus Tertius) – This binary system contains a white primary (magnitude 4.5) and a blueish secondary star of magnitude 6.6. The two are 13.4 arcseconds apart and easily seen in a small scope. Kappa Boötis is ~155 light-years away. Asellus Tertius is Latin for ‘third donkey colt’.

Mu Boötis (Alkalurops) – This triple star system has a magnitude of 4.31. The primary yellow-white subgiant and secondary double star (magnitude 7.1) are 1.8 arcminutes apart and easily seen in a small scope.

The secondary star is itself a double, their separation is just over 2.2 arcseconds today, which is just past their maximum distance apart.

All three are naked-eye visible under dark sky conditions. Alkalurops is ~121 light-years away and its common name means ‘the shepherd’s staff’ in Greek.

Pi Boötis – Is yet another binary system, 320 light-years away. This one consists of a blue-white main-sequence primary star shining at magnitude 4.9 and a blueish main-sequence secondary star 5.6 arcseconds away.

Xi Boötis -This binary system consists of a yellow primary and orange secondary anywhere from 2.5” to 7.0” apart over their 151-year orbital period. Right now, they are 5.2″ apart. Both stars are dwarves and ~21.8 light-years away.

Rho Boötis – This variable double star is an orange giant and is one of the stars in Boötes’ asterism. It is ~150 light-years away and has magnitude of 3.58. Rho Boötis has a 12th magnitude line-of-sign companion 42 arcseconds away.

Tau Boötis – This magnitude 4.48 binary system consists of a yellow-white dwarf and a dimmer red dwarf. They are 1.3 arcseconds apart, making them a very tough spot. In 1996 an extrasolar planet was discovered in orbit around the primary. Tau Bootis is ~51 light-years away.

Star Hopping From Boötes

Boötes’ most famous star hop is to Spica.

Spica – Extend the arc of the Big Dipper’s handle ~30° to Arcturus and then another 30° to find the bright star Spica (in Virgo constellation).

Arc to Arcturus and Spica
Use Arcturus in Boötes to find Spica in Virgo

Now let’s take a closer look at the deep sky objects within the Boötes constellation.

Objects To See Within Boötes

Despite its relatively large size, Boötes does not contain any Messier objects. In fact, it is surprising how few small-telescope-worthy deep sky objects this constellation contains.

Boötes Void (Great Void, Supervoid) – The Boötes Void is a spherical region of space ~250 million light-years in diameter and was discovered in 1981.

The average spacing between galaxies is a few million light-years so this area of space should have ~10,000 galaxies… instead of the 60 that have been discovered!

The center of the void is ~700 million light-years away. Look for the void as a ‘blank spot’ between Boötes and Alkaid (at the end of the Big Dipper’s handle) at right ascension 14h 20m and declination +26°.

NGC 5248 – This compact spiral galaxy has a magnitude of 10.14 and an apparent size of 4.1 x 2.4 arcminutes. It is 39 million light-years away and is at right ascension 13h 38m 32s and declination +08° 47’ 03”.

Summary

This big kite-shaped constellation is great to orientate yourself in summer night skies. Ironically, one of its most interesting astronomy facts is the lack of objects it contains.

Its biggest attraction for us backyard astronomer is the large number of double stars it contains.

On a mild, late summer evening, why not see how many of the Boötes doubles you can find with your scope.


Written by Tanya C. Forde