36
Perseus, The Hero
NAME: Perseus (PERS-ee-us)
SEASON: Autumn
CULMINATION: midnight, 7 November
ABBREVIATION: Per
GENITIVE: Persei (PERS-ee-ee)
NEIGHBORS: Aql, Her, Lib, Sco, Ser, Sgr
BINOCULAR OBJECTS: And, Ari, Aur, Cam, Cas, Tau, Tri
URBAN OBJECTS: NGC 869/884 (Double Cluster), Tr 2, NGC 1039 (M 34), Mel 20, NGC 1342
Perseus is a mid-size northerly constellation that ranks 24th in size among the 88 constellations. Perseus covers 615 square degrees of the celestial sphere, or about 1.5%. Perseus is a moderately bright constellation, containing eight stars brighter than fourth magnitude. Perseus is easily located, lying among the prominent constellations Auriga to the east, Andromeda to the west, Cassiopeia to the northwest, and Taurus to the south. Perseus is home to many fine DSOs, including several fine open clusters—the magnificent Double Cluster and Messier 34 among them—as well as the beautiful planetary nebula Messier 76 and, surprisingly, a bright galaxy and an emission nebula.
In Greek mythology, the Hero Perseus is best known for slaying the Gorgon Medusa, whose face was so ugly that merely looking upon it turned her victims to stone. Equipped with a pair of magic flying shoes provided by the god Hermes and a sword and mirrorlike shield provided by the goddess Athena, Perseus set out to slay Medusa. Turnabout is fair play, so Perseus used his shield to force Medusa to look upon her own image, thereby turning herself to stone. After cutting off Medusa’s head, Perseus set sail for home.
TABLE 36-1.
Featured star clusters, nebulae, and galaxies in Perseus
Object |
Type |
Mv |
Size |
RA |
Dec |
M |
B |
U |
D |
R |
Notes |
NGC 650 |
PN |
12.2 |
167.0" |
01 42.3 |
+51 35 |
|
|
|
|
|
M 76; Class 3+6 |
NGC 869 |
OC |
5.3 |
29.0 |
02 19.0 |
+57 08 |
|
|
|
|
|
Double Cluster; Cr 24; Mel 13; Class I 3 r |
NGC 884 |
OC |
6.1 |
29.0 |
02 22.3 |
+57 08 |
|
|
|
|
|
Double Cluster; Cr 25; Mel 14; Class I 3 r |
Cr 29 |
OC |
5.9 |
20.0 |
02 36.8 |
+55 55 |
|
|
|
|
|
Tr 2; Class II 2 p |
NGC 1023 |
Gx |
10.4 |
8.7 x 2.3 |
02 40.4 |
+39 04 |
|
|
|
|
|
Class SB(rs)0-; SB ??? |
NGC 1039 |
OC |
5.2 |
35.0 |
02 42.1 |
+42 45 |
|
|
|
|
|
M 34; Cr 31; Class II 3 r |
Cr 39 |
OC |
2.3 |
184.0 |
03 24.3 |
+49 52 |
|
|
|
|
|
Alpha Perseii Association; Mel 20; Class III 3 m |
NGC 1342 |
OC |
6.7 |
14.0 |
03 31.6 |
+37 23 |
|
|
|
|
|
Cr 40; Mel 21; Class III 2 m |
NGC 1491 |
EN |
99.9 |
21.0 |
04 03.6 |
+51 18 |
|
|
|
|
|
|
NGC 1528 |
OC |
6.4 |
23.0 |
04 15.3 |
+51 13 |
|
|
|
|
|
Cr 47; Mel 23; Class II 2 m |
NGC 1582 |
OC |
7.0 |
37.0 |
04 31.7 |
+43 45 |
|
|
|
|
|
Cr 51; Class IV 2 p |
TABLE 36-2.
Featured multiple stars in Perseus
Object |
Pair |
M1 |
M2 |
Sep |
PA |
Year |
RA |
Dec |
UO |
DS |
Notes |
26-beta |
n/a |
n/a |
n/a |
n/a |
n/a |
n/a |
03 08.2 |
+40 57 |
|
|
Algol – variable, not multiple |
15-eta |
STF 307AB |
3.8 |
8.5 |
28.5 |
301 |
2002 |
02 50.7 |
+55 53 |
|
|
|
SAO 23763 |
STF 331 |
5.2 |
6.2 |
11.9 |
85 |
2002 |
03 00.9 |
+52 21 |
|
|
|
CHART 36-1.
The constellation Perseus (field width 40°)
On his journey, Perseus happened to sail past the kingdom of Aethiopia, ruled by King Cepheus and Queen Cassiopeia. The vain Cassiopeia’s boasts about her own beauty angered the Nereids, who appealed to Poseidon to punish Cassiopeia. Poseidon sent the sea monster Cetus to wreak havoc upon the kingdom. Cepheus consulted the Oracle at Ammon, who told him that the only way to save his country and his people was to sacrifice his daughter Andromeda to Cetus. Cepheus chained Andromeda to a giant rock near the shore, where she awaited her doom as Cetus approached.
As Perseus sailed past, he noticed Andromeda chained screaming to the rock, with Cetus approaching fast. Perseus whipped out the head of Medusa and showed it to Cetus, who was promptly petrified. Perseus freed Andromeda, and the two of them sailed off together and lived happily ever after.
Perseus culminates at midnight on 7 November, and, for observers at mid-northern latitudes, is best placed for evening viewing from late summer through late winter.
Clusters, Nebulae, and Galaxies
FIGURE 36-1.
NGC 650 (M 76) (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
NGC 650, better known as Messier 76 or M 76, is a large, bright planetary nebula, one of the finest planetaries in the sky. Pierre Méchain discovered M 76 on 5 September 1780, and reported his discovery to Charles Messier. Messier observed M 76 on the night of 21 October 1780 and added it to his catalog.
Although it’s possible to locate M 76 by using a long star hop, it’s much easier to locate it by starting with the bright stars m2.2 Almach in Andromeda and m2.3 Shedir in Cassiopeia, as shown in Chart 36-2. Draw an imaginary 19.5° line between those two stars and look along that line about 40% of the way from Almach to Shedir. You’ll see the m3.6 star 51-Andromedae, which is by far the brightest star in the vicinity. Put 51-Andromedae on the S edge of your finder field and look for the m4.0 star ϕ (phi) Perseii, which is by far the brightest star in the finder field. About 50' dead N of ϕ you’ll see an m6.7 star which is also quite prominent. M 76 lies 12' W of that star (which is visible to the left of M 76 in Figure 36-1), and is easily visible in a low-power eyepiece.
M 76 is often called the Little Dumbbell Nebula for its reputed resemblance to the Dumbbell Nebula, M 27 in Vulpecula. To us, though, it looks more like an elongated rectangle at low magnification and like a peanut or bowtie or figure-eight at medium and high magnification. At 125X in our 10" Dob, M 76 shows two distinct nodes. The SW node is noticeably brighter and has a sharply demarcated border. The dimmer NE node gradually fades into extremely faint tendrils of nebulosity. A narrowband or O-III filter noticeably improves both the contrast and the visible extent of this object.
CHART 36-2.
NGC 650 (M 76) (30° field width; 5° finder circle; 1° eyepiece circle; LM 6.0)
CHART 36-3.
NGC 650 (M 76) detail (10° field width; 5° finder circle; 1° eyepiece circle; LM 9.0)
NGC 869 and NGC 884 are two large, rich, bright open clusters whose centers lie only about half a degree apart. Because it is visible to the naked eye under good conditions, the Double Cluster has been known since at least Babylonian times. No one knows why Charles Messier didn’t add the Double Cluster, individually or together, to his catalog. As we recounted in the Orion chapter, Messier found himself facing a publication deadline with only 41 objects in his catalog. He wanted more, so he added the naked-eye objects M 42/43, M 44, and M 45 to his catalog. Perhaps he was embarrassed at padding out his catalog with these easy objects, or perhaps he was just in such a hurry that he forgot to add the Double Cluster. Either way, the Double Cluster didn’t make it into Messier’s catalog.
The Double Cluster is easy to find, lying about 4.3° WNW of the naked-eye star m3.8 15-η (eta) Perseii on the N edge of the constellation. Put 15-η on the E edge of your finder or binocular field, and you’ll see the Double Cluster near the WNW edge of the field.
With our 50mm binoculars, the Double Cluster is a beautiful sight. Dozens of stars from m6 down to m10 are visible in both clusters, with scores of dimmer stars in each cluster providing a nebulous background glow. At 42X in our 10" Dob (1.6° true field), 100+ stars are visible in each cluster. NGC 869 appears tighter, with a considerable concentration of bright stars near the center and many other stars scattered in knots and chains to the N and S of the central core. The bright stars in NGC 884 are more scattered, with an elongated 3' x 8' WNW-ESE (from west northwest to east southeast) central concentration and a second elongated 4' x 12' E-W concentration lying to the N.
FIGURE 36-2.
NGC 869 (right) and NGC 884 (Double Cluster) (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-4.
NGC 869 and NGC 884 (The Double Cluster) and Collinder 29 (Cr 29) (15° field width; 5° finder circles; 1° eyepiece circle; LM 9.0)
Collinder 29 is a large, bright open cluster that suffers from its close proximity to the Double Cluster. It’s so close, in fact, that all three of these clusters are visible in the same low-power eyepiece field of our 4.5" Orion Starblast richest-field telescope, let alone any binocular or finder. The Double Cluster is so compelling that we’ve found ourselves failing to notice Collinder 29 even when it’s visible in the same field.
Collinder 29 is easy to find, lying just 1.9° dead W of the bright naked-eye star m3.8 15-η (eta) Perseii, about a third of the way along and just S of the line from 15-η to the Double Cluster. With our 50mm binoculars, Cr 29 shows half a dozen m7 through m9 stars embedded in a soft background nebulosity. At 90X in our 10" reflector, about two dozen stars from m7 through m12 are visible. The cluster presents a very loose, scattered, poor appearance.
FIGURE 36-3.
Collinder 29 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
NGC 1023 is a relatively bright galaxy that lies near the border of Perseus with Andromeda. To locate NGC 1023, begin by identifying the bright star 26-β (beta) Perseii (Algol). Algol is a variable star that ranges in brightness from m2.1 at maximum to m3.4 at minimum, but it’s always easily visible to the naked eye. With your finder on Algol, follow the chain of bright stars, 2.2° SSW to m3.4 25-ϱ (rho) and then 2.9° W to m4.2 16-Per. With 16-Per on the E edge of your viewfinder, look for the m4.9 star 12-Per 2.5° NW. NGC 1023 lies 1.2° SSW (south southwest) of 12-Per, where it is visible in a low-power eyepiece.
At 125X in our 10" Newtonian, NGC 1023 presents a bright 1.5' x 5' lenticular halo elongated E-W (from east to west) with an embedded concentrated oval core that surrounds a stellar nucleus.
FIGURE 36-4.
NGC 1023 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-5.
NGC 1023 (10° field width; 5° finder circles; 1° eyepiece circle; LM 9.0)
NGC 1039, better known as Messier 34 or M 34, is a large, very bright open cluster. M 34 has probably been known since ancient times, because under good conditions it’s visible to the naked eye as a faint nebulosity. Charles Messier independently re-discovered and cataloged M 34 on the night of 25 August 1764.
M 34 is very easy to find, lying about 40% of the way along and just N of a line from the bright naked-eye star 26-β (beta) Perseii (Algol) to the even brighter star 57-γ (gamma) Andromedae (Almach). With our 50mm binoculars, M 34 shows about 20 m8 and m9 stars embedded in a nebulous glow. At 90X in our 10" reflector, 50+ stars are visible from m8 to m12, scattered across an area the size of the full moon, with many of the brightest stars concentrated in the central half of the extent. Despite this moderate concentration, the cluster gives the impression of being very loose and scattered because many of its stars are clumped into small groups and chains.
FIGURE 36-5.
NGC 1039 (M 34) (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-6.
NGC 1039 (M 34) (15° field width; 5° finder circle; 1° eyepiece circle; LM 7.0)
Cr 39 |
⋆⋆ |
|
OC |
MBUDR |
Chart 36-1 |
|
m2.3, 184.0' |
03h 24.3m |
+49° 52' |
Collinder 39, also known as Melotte 20 or the Alpha Perseii Association, is a gigantic, bright open cluster that centers on 33-α (alpha) Perseii (Mirphak). We didn’t include an image of this cluster because we couldn’t find one with a wide enough field of view to show the cluster as anything other than just a random collection of field stars. Even in a wide-field binocular, the gigantic size of this cluster—more than 3 full degrees—makes it difficult to take in as a discrete object. Note that the listed visual magnitude of 2.3 is very deceptive. Although you might think that an m2.3 object would be prominent to the naked eye, Cr 39 is anything but. That admittedly large amount of light (which does not include the light of m1.8 Mirphak) is distributed across such a large expanse of sky that the average surface brightness of this object is quite low.
With our 50mm binocular, Cr 39 is a scattering of 50+ stars from m5 down to m10 in small groups and chains across an extent that covers much of the field of view. The boundary of this cluster is not sharply delimited, particularly along the hemisphere of the border from E through S to W, but the density of stars gradually decreases. The border of the N hemisphere is more pronounced, with the star density falling off more rapidly beyond about 1.5° from the cluster’s center at Mirphak. With our 4.5" Orion Starblast richest-field telescope (3.5° true field), it’s very difficult to see this object as a cluster rather than as just a collection of hundreds of random field stars.
NGC 1342 is a bright, medium size, loose, scattered open cluster. It lies far enough from bright stars that locating it by a star hop would take some time. Fortunately, it’s very easy to locate NGC 1342 geometrically. To do so, draw an imaginary line between the bright stars 26-β (beta) Perseii (Algol) and m2.8 44-ζ (zeta) Perseii (Atik). NGC 1342 lies not quite halfway along and just N of that line.
With our 50mm binoculars, NGC 1342 is a relatively large, prominent nebulous patch with half a dozen m8/9 stars snaking along a 15' E-W line and another pair of m8/9 stars lying about 8' NE of center and just outside the nebulosity. At 90X in our 10" reflector, 50+ stars m8 and dimmer are scattered loosely across a 15' extent.
FIGURE 36-6.
NGC 1342 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-7.
NGC 1342 (15° field width; 5° finder circle; 1° eyepiece circle; LM 7.0)
NGC 1491 is a small, moderately bright emission nebula. Although its cataloged size is 21', that’s a photographic extent; visually, NGC 1491 is much smaller.
It’s relatively easy to find NGC 1491. Start by identifying the bright naked-eye star Mirphak. With Mirphak in your finder field, drift the finder about 7° dead E until the prominent group of three m4 stars—47-λ (lambda), 51-μ (mu), and 48-Perseii—come into view. NGC 1491 lies 1.2° NNW of 47-λ. You can judge its exact location by noting the triangle that NGC 1491 makes with 47-λ and m5.3 43-Perseii to the W.
At 125X in our 10" reflector, NGC 1491 is a relatively bright, diffuse 5' triangular nebulosity, elongated NNE-SSW. The SSW apex of the triangle is the brightest, with the nebulosity dimming and becoming more diffused to the NNE. Using our Orion Ultrablock narrowband filter greatly increases the contrast of the nebulosity, and increases its visible extent to 6' or so. With averted vision, the Ultrablock filter reveals extremely faint nebulosity extending 2' E from the SSW apex that is not visible without the filter.
FIGURE 36-7.
NGC 1491 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-8.
NGC 1491 and NGC 1528 (10° field width; 5° finder circle; 1° eyepiece circles; LM 9.0)
NGC 1528 is a large, bright, relatively concentrated open cluster. It’s easy to locate, lying 1.6° NE of the bright star 47-λ (lambda), which can be located as described in the preceding section.
With our 50mm binoculars, NGC 1528 is visible as a moderately bright, moderately large patch of haze without stars about half a degree NW of a prominent m6/7 field star. Averted vision reveals one or two very faint stars, with one or two others flickering in and out on the edge of visibility. At 90X in our 10" reflector, NGC 1528 shows 50+ stars over a 20' extent with considerable central concentration. Several close m10 pairs are visible in the E quadrant of the cluster, and two prominent chains of m9/10 stars extend from the central concentration, one straight W and the other to the SW.
FIGURE 36-8.
NGC 1528 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
NGC 1528 is a very large, moderately bright, loosely scattered open cluster. Although NGC 1582 lies in Perseus, we find it easiest to locate it by starting from Capella in Auriga. With Capella on the NE edge of your finder or binocular field, look SW for m3.0 7-ε (epsilon) and 10-η (eta). With those stars on the E edge of the field, move the field W until the prominent triangle of m6.2 57-, m4.3 58-, and m5.3 59-Perseii comes into view. NGC 1528 lies about 45' NNW of 57-Perseii.
With our 50mm binoculars, NGC 1582 is visible as a moderately large, fairly faint patch of nebulosity centering on a parallelogram of four m8/9 stars. At 90X in our 10" Dob, about two dozen stars down to m11 are visible, with a broad E-SW (from east to southwest) arc containing most of the brighter members. An arc of five m10/11 stars lies on the NW edge of the cluster, anchored by an m9 star at the W terminus. A E-W band of m9/11 stars extends across the S edge of the cluster.
FIGURE 36-9.
NGC 1582 (60' field width)
Image reproduced from Digitized Sky Survey courtesy Palomar Observatory and Space Telescope Science Institute
CHART 36-9.
NGC 1582 (12° field width; 5° finder circles; 1° eyepiece circle; LM 9.0)
Multiple Stars
26-beta |
⋆⋆⋆ |
|
variable star |
UD |
Chart 36-1 |
|
n/a |
03h 08.2m |
+40° 57' |
26-β (beta) Perseii—better known as Algol, the Ghoul Star, or the Demon Star—is not a multiple star in the usual sense, despite the fact that it’s included in the Astronomical League’s Double Star list. Algol is a variable star, and was almost certainly the first variable star to be discovered. Algol made the AL Double Star list because it’s the best-known example of an eclipsing binary variable star—one in which the variance in magnitudes is caused by an invisible companion that orbits Algol, periodically blocking some of its light.
Algol has been known to be variable since antiquity. Its period was first accurately measured and reported in 1782 by the English astronomer John Goodriche, who in an intuitive leap suggested that an invisible companion might be partially eclipsing Algol periodically. The orbital mechanics of stars were not well understood at that time, but as it turns out Goodriche nailed the proper explanation.
During minima, the brightness of Algol falls over a period of about five hours from its usual magnitude 2.1 to magnitude 3.4 as Algol is partially eclipsed by its companion. The eclipse occurs every 2.8674 days, or about 68 hours and 49 minutes. It’s often possible to observe the transition from maximum to minimum or vice versa over the course of one observing session, and it’s sometimes possible to observe the entire cycle maximum-minimum-maximum over one night. For detailed information about forthcoming times for Algol’s cycle, check Sky & Telescope or Astronomy magazine or their web sites.
15-eta (STF 307AB) |
⋆⋆⋆ |
|
MS |
UD |
Chart 36-1 |
|
m3.8/8.5, 28.5", PA 301° (2002) |
02h 50.7m |
+55° 53' |
15-η (eta) Perseii, sometimes called Miram, is one of the best color-contrast double stars other than Albireo. Miram is easy to locate with the naked eye. It lies 7.8° NW of Mirphak and just 3.1° NW of m2.9 23-γ (gamma) Perseii. At 100X in our 90mm refractor, 15-η is a beatiful pair. The primary is golden yellow, and the much dimmer companion is a pretty blue-white.
SAO 23763 (STF 331) |
⋆⋆ |
|
MS |
UD |
Chart 36-10 |
m5.2/6.2, 11.9", PA 85° (2002) |
03h 00.9m |
+52° 21' |
STF 331 comprises the primary, SAO 23763, and its companion, SAO 23765. This double is easy to locate by noting the scalene triangle it forms with the prominent stars 23-γ (gamma) Perseii and 18-τ (tau) Perseii. At 100X in our 90mm refractor, STF 331 is a pretty pair. The secondary is noticeably dimmer than the primary, and both are distinctly blue-white.
CHART 36-10.
SAO 23763 (STF 331) (10° field width; 5° finder circle; 1° eyepiece circle; LM 9.0)
