Scorpius


Transit Date of principal star:
29 May


As mentioned regarding Orion, Gaia may have sent the scorpion to kill the mighty hunter, as he had vowed to rid the earth of all wild animals. Or Apollo might have told Gaia of Orion's boast, fearful that Orion had designs on Apollo's sister Artemis.

In any case it was Gaia who sent the scorpion to kill Orion. Later the animal would chase Orion across the heavens, but it could never catch him, for the scorpion was so placed that it would rise in the east only after Orion had safely disappeared over the western horizon.


Scorpius is one of the oldest constellations known - possibly even one of the original six signs of the zodiac. While the sun still traverses Scorpius, it only takes nine days to do so; most of the time is spent in neighbouring Ophiuchus (which is the only constellation that the sun enters but which is not a part of the zodiac).

The asterism of a gigantic skewed "S" was seen in many ancient cultures as a scorpion, possibly handed down by cultural conquest or influence. The two stars lambda and upsilon, both called "The Sting" in Arabic, traditionally form the stinger, although some star maps currently show the nearby "G Scorpii" as one of the stingers. We have recently changed our graphic to reflect the original stingers.

The constellation was once much larger, but the western portion representing the claws of the scorpion was given to Libra.

The star table indicates just how bright many of Scorpius's stars are; in fact the constellation is one of the brightest of the larger constellations.

Alpha Scorpii is better known as Antares ("Rival of Mars"). This is one of the four Royal Stars of the ancients, along with Aldebaran, Regulus, and Fomalhaut. It glitters with an unusual metallic red while the entire region is bathed in a pale red nebula, lit from the same star.

This red supergiant has a visual binary that just might be visible, depending on local conditions and the size of one's scope (see below). The star is estimated to be between 285 sun diameters to about 700 suns. It's 600 light years away.

Due west 1 (about half the distance to sigma Sco) is the bright globular cluster M4, while another globular cluster, M80, is 4 NNW of Antares. See below for these deep sky objects.


Double stars in Scorpius:

[NOTE: See the Binocular Section link at the bottom for updated values.]

Alpha Scorpii is a visual binary which may be difficult to resolve due to the brightness of the primary. Try a moonlight night, which should cut the glare of the brighter star: 1.1, 5.4; PA 274, separation 2.6".

The companion is usually described as green in colour, probably a visual effect created by the red glow of Antares. The star is estimated to orbit its primary every 900 years.

Beta Scorpii. This superb double has a pleasant colour contrast: white and bluish-green. 2.6, 4.9; PA 23, 13.7".

Nu Scorpii is a multiple system, a "double-double". That is, each of the visible components (AC) is also a primary of a closer component; these are termed AB and CD.

AC: 4.4, 6.4; 337, and 41" separation.
AB: 4.4, 5.4; PA 2, 1.3".
CD: 6.3, 8.0; 51, 2.3".

Xi Scorpii is also a multiple system, a system which also includes the next binary system as well (Struve 1999).

Components AB form a close binary with period of 45.7 years. The companion is now gradually drawing away from the primary: PA 308 and separation 0.39".

Sigma Scorpii: a double with faint companion. AB: 2.9, 8.5; PA 273, separation 20".

Struve 1999 is gravitationally attached to the Xi Scorpii system, although at a distance of about 7000 AU (an "AU"--astronomical unit-- being the distance of the earth from the sun).

The binary is found just south of Xi Scorpii, two yellow stars of nearly equal brightness: 7.4, 8.1; 99, 11.6".

Variable stars in Scorpius:

RR Scorpii is the brightest long-period variable in the constellation, with a visual magnitude range of 5.0-12.4 every 281.45 days. In 1999 the maximum should occur around the end of May.


Deep Sky Objects in Scorpius:

There are four Messier objects in Scorpius (some authorities put a fifth in the constellation as well: M62, but usually it is listed in Ophiuchus).

M4 (NGC 6121) is a rather near globular cluster (6000-10,000 light years) but without a large telescope it will not appear very spectacular. There may be as many as fifty RR Lyrae variables in the cluster.

M4 is located just west of Antares, roughly half way to sigma Scorpii.

M6 (NGC 6405) is the second-best cluster of the constellation (after M7). This is an open cluster which sometimes bears the name "The Butterfly Cluster". Its brightest star is BM Scorpii, a sixth-magnitude yellow giant. The cluster is about 1500-2000 light years away.

M7 (NGC 6475) has no name, but is clearly the best deep sky object of the constellation. This magnificent open cluster is extremely large (two full-moon diameters) and quite bright, being visible even to the naked eye under the right conditions.

A scope easily resolves the stars, the brightest twenty-two of which range from 5.6 to 9.0. There are several close visual binaries in the cluster. (See Burnham for these, as well as extensive notes on this cluster.)

M7 is 4 NNE of lambda Scorpii. It's about 800 light years away.

M80 (NGC 6093) is a rather faint, very compact, globular cluster in the vicinity of Antares, between this star and beta Scorpii, and more narrowly speaking, nearly midpoint between two 8th-magnitude stars (which are the brightest stars of the region). The cluster is quite distant, some 36,000 light years away, and it takes a very large telescope to study it in detail.

NGC 6231 is a naked-eye open cluster one half degree north of zeta Scorpii (which is in fact a member of the group). This cluster is certainly worthy of being a Messier; while noticeable to the naked eye, binoculars resolve its various members. It's about 5500-6000 light years from us.

The stars that make up the cluster are generally supergiants that resemble the Pleiades in miniature. Burnham points out that if this cluster were the same distance as the Pleiades, its stars would outshine the Pleiades "by a factor of about 50 times".

The cluster is only part of a much larger, very scattered, cluster called H 12, which is found one degree north. In fact, the stars seen as joining NGC 6231 and H 12 actually form one of the spiral arms of our own galaxy.


For a more detailed appreciation of Scorpius visit the Binocular Section.


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