Objects for October, November and December

Andromeda/Triangulum

Andromeda Galaxy M31

In 1612 Simon Marius observed M31 telescopically and said it looked "like the flame of a candle seen through horn" [1].

M31 is approximately 2.5 [Karkoschka p24] or 2.6 million light-years from the earth [3]. According to Sparrow (pp295-6) the galaxy has a visible diameter of 220,000 light-years. M31 and our Milky Way together gravitationally control a 10 million light-year region of space which contains several dozen galaxies comprising the "Local Group". The Hubble Space Telescope has shown that M31 has two nuclei which suggests the nebula we see today is the result of two individual galaxies merging in the past [2]. As to the future, it used to said that our Milky Way in its turn was going to "collide" with M31 in the far future, and then merge with it. However, the latest research suggests that the chances of such a merger are now considered only 50/50 [4].
 

Triangulum Galaxy M33 - "The Pinwheel"

Distance: 2.7 million light-years, "in binoculars (an) oval glow without a bright core" [Karkoschka p24]. M33 can best be seen by choosing a dark night with the eye allowed to wander generally over the field rather than by seeking a single point. A large ghostly patch will gradually assert itself  [Murden p 137]. "The rotation of the Pinwheel is clockwise... the rotational period in the region of the rim has been measured at about 200 million years" [Burnham p1902]. M33 belongs to our Local Group of galaxies, and is its third largest member (only 60,000 light years across compared to M31 at 200,000 and the Milky Way at 100,000 light years diameter) - The galaxy possesses many bright blue stellar regions showing rapid star formation [5]. In fact "the Triangulum galaxy’s star formation rate is ten times higher than the average found in the Andromeda galaxy" [6].

Cassiopeia

“Cassiopeia lies in a rich part of the Milky Way, and sweeping on an autumn evening is very fine” [Muirden, p115].
 

*Distances in light-years taken from p26 of Karkoschka

Tiansi or Navi

Navi is a subgiant star appearing blue or blue-white in colour [22]. Having almost used up its hydrogen, the star is in the process of evolving into a giant star. This eruptive BE variable has rapid and irregular brightness changes [21]. Muriden describes Navi as "a rapidly spinning star, subject to unpredictable brightenings at long intervals; normally about mag. 2.4, it attained 1.7 in 1937."

Navi rotates every 27 hours [24] and has a strongly oblate shape as it is spinning at a rapid 432 km/sec. This spin rate is so high that material is flung away or erupted into space [21]. Analysis of BE stars (like Navi) show that such eruptions are launched from localized regions on the stellar surface, the emitted material then circularises around the star [29], settling into a decretion disk [21]. Data from the XRISM space telescope establishes that Navi is also orbited by a white dwarf star which draws material from the (decretion) disk producing x-rays as a result [30].

Navi's high mass means that it will end as a supernova in the (astronomically speaking) relatively near future [22]. The name Navi is a modern one, coined by astronaut Gus Grissom, who took his own middle name, Ivan, and reversed it for inclusion on NASA's emergency navigation star charts [23].

Cepheus

Garnet Star or Mu Cephei

Distance: 3000 light-years [Karkoschka p48]. Colour: "a fine claret colour even with binoculars, and it can found by tint alone" [Muirden p117]. "Using x 8 or higher, Mu looks like a glowing coal." [Moore, Binoculars, p76]. According to Crossen, although it is a red supergiant similar to Betelgeuse, it does appear redder from the earth as [p41] "we see Mu Cephei through heavy clouds of interstellar matter which redden its light". He tells us that these clouds also dramatically dim the star.

Mu may well be the largest star visible to the naked eye [12], if it were placed in the middle of our solar system its surface would extend beyond the orbit of Jupiter [13], perhaps almost reaching that of Saturn [14]. The star will die in a huge supernova blast leaving behind a black hole [14].

Cetus

M77

Distance: 50 million light-years [Karkoschka p52]. “… a spiral galaxy visible in good binoculars as a hazy spot. This object … represents, perhaps, the furthest reach of a pair of binoculars” [Muirden, p117]. According to Crossen (p53) M77 is visible in 35mm glasses but only looks like a star.

In the very early hours of the 21st November 2006 I found M77 using 12x42 glasses, the galaxy looked exactly like just another small star, very dim, only visible with averted vision. The experience prompted me to prepare the star chart below:
 

Gemini

Castor

Distance: 51 light years (Karkoschka p66). Castor is a single white star in binoculars, although telescopically it is an interesting multiple system. Castor and Pollux are not associated [Moore, Binoculars p93].

Castor, Vega and Fomalhaut are all members of the Castor Moving Group and as such probably have a common origin [11].

Pollux

Distance: 33.8 light years (Karkoschka p66). Pollux is unmistakeably orange in binoculars [Moore, Binoculars p93].

Open Cluster M35

Distance: 3000 light years (Karkoschka p66). One of the brightest of all open clusters [Moore, Binoculars p94].

Pegasus

The Square of Pegasus

The ancient Sumerians thought of the square as a celestial field, a piece of land [25]. Square mainstay Alpheratz, through an amazing piece of bureaucratic stupidity, is now technically part of Andromeda!
 

Scheat

According to Moore (Binoculars, p118), Scheat is a strikingly orange semi-regular variable with a period of roughly 36 days. Crossen (p36) encourages us to follow Scheat's variability by comparing its brightness to the other three stars of the Square, whose magnitudes conveniently match its range. Moore provides a note of caution, he advises us to allow for differences in altitude when estimating the relative brightnesses. Crossen gives the comparison stars' brightnesses as:
 

Globular Cluster M15

Distance 33,000 light years (Karkoschka p102). This globular is one of the densest known, and hosts a black hole at its core [26]. It is also fabulously ancient at 12.7 billion years old [28]. "Although M15 is small ... it is very bright and for this reason is one of the better globular clusters for small binoculars" [27].

Perseus

Mirphak

Distance: 500 light-years [Karkoschka p28]. A young white/yellow supergiant [16] which used to be a hot blue star but because of its high mass [18] "is evolving toward cooler temperatures with a dead helium core" [17]. Mirphak is the brighest member of the Alpha Persei Cluster [18].

Algol

Distance: 90 light-years [Karkoschka p28]. Muirden tells us [p130] that Algol shines at its maxiumum brightness most of the time, but then dims down in five hours as the large, dim stellar component occults its smaller and brighter companion. The original brightness returns in another five hours.

Stellar Association Melotte 20 - Alpha Persei Cluster

Also known as the Perseus Moving Group - contains 500 young stars (50 to 70 million years old) spread out over 6 degrees of sky. The cluster predominantly contains blue and blue-white stars [16], with the notable exception of white/yellow Mirphak (different because of its high mass and associated advanced stellar evolution [18]). Most of these cluster stars have abundancies of metals similar to that of our own sun, and the cluster we see is therefore reminiscent of the stellar nursery our sun was born in 4.6 billion years ago [15].

Double Cluster - The Sword Handle     

Distance: 7500 light-years, a "splendid view in binoculars" [Karkoschka p26]. The clusters move together through space, and are largely dominated by bright blue stars speckled with a few fine orange ones [19]. The Sword Handle is about 13 million years old [20].

Open Cluster M34

Distance: 1500 light-years, "very nice cluster for binoculars" [Karkoschka p28].

Piscis Austrinus

Fomalhaut

Distance: 25.1 light-years [Karkoschka p100]. Sometimes known as "The Solitary One" [Burnhams, Vol 3, p1485]. Fomalhaut presides over a turbulent system. Back in the 1980s the IRAS orbiting observatory detected an excess of infrared light coming from Fomalhaut. This excess was interpreted as showing that Fomalhaut was surrounded by material left over from the accretion of a solar sytem [7]. The Hubble Space Telescope has since directly imaged this system as a large dust belt with a sharp inner edge surrounding the star [8] and has additionally imaged the dust clouds produced by large objects colliding there [9]. Such collisions were imaged in 2004 and 2023, the colliding planetesimals must have been at least 37 miles across [9].

It appears from Hubble data that Fomalhaut also possesses planets, the star's dust disk contains three belts that extend out to 14 billion miles possibly made by invisible planets [10].

Castor, Vega and Fomalhaut are all members of the Castor Moving Group and as such probably have a common origin [11].