Bo÷tes

Bo÷tes


Transit Date of principal star:
26 April


Bo÷tes may be a hunter, on the tracks of the Great Bear, accompanied by his two dogs Asterion and Chara (the constellation "Canes Venatici").

The constellation was once known as Arctophylax which means the protector of the Bear. Yet the name itself, Bo÷tes, comes from the Greek, as first mentioned in Homer, and means 'ox-driver'. The ÷ is called a diaeresis, and indicates that each 'o' is to be pronounced.

The Romans called him Venator Ursae: the Bear Hunter.

Nowadays Bo÷tes is sometimes considered to be a Herdsman (as in French: Le Bouvier), as he eternally shepherds the stars around the North Pole.

As mentioned above, the first recorded appearance of Bo÷tis is found in Homer's Odyssey. In Book V Odysseus sails his ship by the stars, using the Pleiades, the Bear, and Bo÷tes ("which set late") to reach his destination.


The constellation forms a bright naked eye display, and is quite compact, squeezed between Canes Venatici and Hercules, with Virgo to the south. The northern border touches both Ursa Major and Draco. There is a full complement of Bayer stars.

To find the major star, Arcturus, follow the sweep of the Big Dipper's handle. These stars lead to the brightest star in the northern hemisphere, and the fourth brightest in all of the heavens: alpha Bo÷tis, better known as Arcturus.

Arcturus means "Guardian of the Bear". This orange-red giant is about 20-25 times the size of the Sun, with about the same mass. In fact the Sun will probably take the same path, eventually ballooning to the same size in another five billion years.

The star has an unusually high proper motion (2.281") and a space velocity of 118 km/sec. It is 35.4 light years away.


Some constellations are known for their deep sky objects; others for an interesting variable or perhaps an attractive binary. Bo÷tes has few deep sky objects of any interest. Nor are its variables particularly noteworthy. However the constellation does have one of the finest collection of double stars, some of which are described below.


Double stars in Bo÷tes:

Zeta Bo÷tis is a very fast binary with a highly eccentric orbit of 123.4 years. The companion is currently fairly close (0.9") at PA 301║.

Epsilon Bo÷tis was one of Struve's favourite double star systems: 2.5, 4.9; a bright yellow primary with a blue-green companion. The orbit is so large it may as well be considered fixed: PA 339║, separation 2.8".

Kappa Bo÷tis is a gorgeous double with colour contrast; the primary is yellow and the companion a deep blue. The binary is fixed at PA 235║, separation 13.4".

In the same field is iota Bo÷tis: 4.9, 7.5; PA 33║, separation 38.5"
Mu Bo÷tis is a triple system. AB are fixed: 4.3, 7.0; PA 171║, separation 108". The component B has a close companion C (magnitude 7.6) which is a rapid binary, with an orbit of 246.1 years. The 2000 values are PA 7║, separation 2.1".

Pi Bo÷tis is a pleasant binary of two blue-white stars (4.9, 5.8; PA 108║, separation 5.6").

Xi Bo÷tis is a rapid binary (4.7, 7.0) with orbit of 151 years. The primary is yellow, and the companion a white-pink. Currently the companion is found at PA 321║ and 6.8" separation.

Struve 1785 is another attractive rapid binary, with orbit of 155 years. The companion can now be found at PA 173║, 3.3" separation.

Struve 1909 (44 Boo) is yet another rapid double, with an orbit of 225 years. In the year 2000 the companion will be at its widest separation for the next fifty years. Presently it's located at 54║, 2.2" separation.


Variable stars in Bo÷tes:

The constellation contains three delta Scuti type variables: gamma, iota, and kappa2.

Delta Scuti variables are fairly young stars which pulsate, creating a slight variation in visual magnitude, less than 0.5 magnitude and often considerably less than this, with a short period (from 30 minutes to about eight hours). Thus the stars, while quite numerous, are not of the kind which amateur enthusiasts tend to study.

R Bo÷tis is a long-period variable with a range from 6.2 to 13.1 every 223.4 days. In 2000 the maximum is scheduled to appear in early April.


Deep Sky Objects in Bo÷tes:

There are no Messier objects in this constellation, but for the inveterate deep sky observer there are still a few nice galaxies. Below are two of the better deep sky objects.
NGC 5248 is a very compact spiral galaxy in the southwestern corner of the constellation, ten degrees south of Arcturus and one and a half degrees west. (Two degrees north is the rapid binary BU 612 (6.3, 6.3) with period 22.4 years.)

NGC 5466 is a large but quite dim globular cluster. It's found nine degrees north of Arcturus and one and a half degrees west. (The Messier object M3 is five degrees due west in Canes Venatici.)


For a closer appreciation of Bo÷tes, visit the Binocular Section.


Return to the previous page:

Or go to

the Main Menu


All files associated with The Constellations Web Page are
© Richard Dibon-Smith.