Herschel's Garnet Star

 The constellation Cepheus is a north circumpolar constellation that never sets when viewed from the latitude of Creede (37.8° N), although it may be partially obscured by mountains when low in the night sky of spring and early summer.  It is best viewed in the evening hours of October through December.

Cepheus contains (among other things) one remarkable star known by the nickname "Herschel's Garnet Star".  The nickname comes from a description of the star by the German-English astronomer William Herschel (1738-1822).  It's official name is Mu Cephei.

An outline of the constellation Cepheus high in the evening sky of 05 December.

Mu Cephei is the reddish star at the center left edge of the outlined constellation.  Here is a closer look:

E-M1iii + 75mm f/1.8 + softon filter.  ISO 1600, 60 s.

 Mu Cephei is only a magnitude-4.1 star as seen from Earth, but we now know it to be one of the largest and brightest stars in our galaxy, with a luminosity about 270,000 times that of our sun.  It is a red supergiant similar to Betelgeuse, but larger.

The distance to Mu Cephei is very poorly known, with estimates lying between 1300 and 3100 ly.  The star is so large, however, that its angular diameter has been measured by interferometry as 20.5 mas (milliarcsecond).  The nearest distance estimate of 1300 ly then yields a diameter of 8.2 au (astronomical units).  This would extend well beyond the orbit of Mars (r = 1.52 au) in our solar system.  The larger distance estimate yields a diameter of 19.5 au, which would reach out to the orbit of Saturn (r = 9.6 au) . Compared to our sun these values correspond to a diameter that is from 880 - 2100 times larger.

Our sun's mass divided by its volume gives an average density of 1.4 g/cm³. Mu Cephei has a mass of about 19 suns in a diameter 1000 (roughly) times larger.  This yields an average density of 19 × 10^-9 × 1.4 g/cm³ = 2.7 × 10^-8 g/cm³. This is similar to the density of Earth's atmosphere at an altitude above 100 km, i.e., in space.  Mu Cephei is essentially a red-hot vacuum!

Cepheus without the constellation lines.  E-M5iii + Sigma 30mm f/1.4 + softon filter.  ISO 1600, 30 s.

 

Boxing Day Moon

 The last full moon of 2023 is today, Boxing Day, 26 December.  It is the 13th full moon of the year and is traditionally known as the "Cold Moon".

E-M1iii + AT72EDII.  ISO 200, 1/1600 s.

Not a super moon, not a micro moon, not a blue moon, just a regular old full moon, pretty much indistinguishable from all the superlative-laden full moons.

Polaris on Christmas Eve

 Polaris (Alpha Ursae Minoris), or the North Star,  lies only 0.64° from the North Celestial Pole (NCP).  Unlike the biblical Christmas Star, it is a constant presence in the night sky of the Northern Hemisphere and serves as a convenient guide star for navigation.

Sony A7iii + Asahi SMC Takumar 120mm f/2.8 @ f/5.6.  ISO 1600, 30 s.

 In this 2°-wide image Polaris is the bright six-pointed star top center.  The NCP is marked with a white cross. 

The lens used here is an M42 screw-mount Asahi (Pentax) Super-Multi-Coated Takumar 120mm f/2.8 from the early 1970s, so about 50-ish years old.  I stopped it down two stops to produce the diffraction star effect.  This is the first astrophoto I've taken with a Pentax lens.

Polaris marks the end of the handle of the LIttle Dipper:

credit: SkySafariAstronomy.com

Solstice Sunspots

 Today is the Winter Solstice and the shortest day of the year in the Northern Hemisphere .  There are currently many sunspots and active regions on the sun:

These images were taken with an AT72EDII refractor, Lunt solar wedge + ND-0.9 filter, and E-M5iii camera, ISO 200, 1/800 s.  These are both the same image - the second one has false color added. Sometimes this results in a more interesting picture.

(PSA: Viewing the sun is dangerous.  It requires special filters.  Double-check everything. And then check again.)

Nothing to worry about when photographing the moon (other than dropping things in the dark). Here is the 9.9d-old Solstice moon:

E-M5iii + AT72EDII.  ISO 200, 1/800 s.

The Buck Moon 2023

 According to the Old Farmer's Almanac the full moon on July 3 is (or was, I'm writing this in December) called the "Buck Moon".  I had the idea that I should get a shot of the moon rising over the eastern ridgeline.  The sky was clear except for one solitary cloud that was positioned exactly over the spot where the moon would rise.  It made for a dramatic image:

E-M5iii + AT60ED. ISO 3200, 0.5 s.

I was going to pack up and head back in but then decided to wait and see what happened.  My patience was rewarded.  The cloud dissipated and drifted away.

E-M5iii + AT60mmED. ISO 200, 1/500 s.

The Collinder 65 star cluster

 Collinder 65 (Cr 65) is a wide (about 3.7°) star cluster in Taurus midway between the constellations Orion and Auriga.  It was catalogued by the Swedish astronomer Per Collinder in 1931.  It is not very well known but is easily recognized with binoculars.

The location of Collinder 65 is marked by the red circle. Chart credit: IAU (Creative Commons Attribution 4.0 International license)

Collinder 65 is marked with the white circle.  Sony A7iii + Rokinon 35mm f/1.8 + softon filter.  ISO 1600, 30 s.

A closer look.  E-M1iii + 75mm f/1.8 + softon filter.  ISO 1600, 60 s.

The yellowish star near the center in this image is 119 Tauri, a red supergiant.  The brighter star to the left of center is magnitude-3 Zeta Tauri, and just above that is the Crab Nebula, M1.  Here is a zoomed-in view:

The Crab Nebula, Messier 1, is the small blob in the center of this 3°-wide image.

Here is a closer view of Collinder 65:

E-P5 + Rokinon 135mm f/2 + Kase AstroBlast filter.  ISO 1600, 30s.

In this image 119 Tauri has a cyan or teal hue.  This is a consequence of the photographic color-balance processing used to mitigate red airglow.  There are no green-hued stars in nature.   A similar color-shift is evident in this image of the Hyades cluster:

E-M1iii + Olympus 75mm f/1.8 + softon filter.  ISO 1600, 30 s.

The brightest star in this image is Aldebaran, a magnitude-0.9 orange giant.  Aldebaran is not a physical member of the Hyades cluster - it is a foreground object at roughly half the distance (67 ly).

Mirfak and the Melotte 20 star cluster

Mirfak (Alpha Persei) is the brightest (mag 1.8) star in the constellation Perseus and the brightest member of the Alpha Persei Moving Group, a loose cluster of stars also known as Melotte 20.  This cluster comprises about a dozen bright stars and perhaps several hundred stars total depending on how the boundary is defined. It is about 600 ly distant.  It is an easy sight with binoculars.

credit: IAU (Creative Commons Attribution 4.0 International license)

Mirfak and its associated cluster is on the left.  The Pleiades (M45) is on the right. E-M5iii + Sigma 30mm f/1.4 + softon filter. ISO 1600, 30s.

Mirfak and Melotte 20.  E-M1iii + Olympus 75mm f/1.8 + softon filter.  ISO 1600, 30 s.

Mirfak (left) and Algol (right). E-M1iii + 75mm f/1.8 + softon filter.  ISO 1600, 30 s.

MIrfak and Melotte 20.  Olympus E-P5 + Rokinon 135mm f/2 + Kase starblast filter.  ISO 1600, 30 s.

A 2-deg close-up of Mirfak and surroundings without the softening filter. E-P5 + Rokinon 135mm f/2.  ISO 1600, 30 s.

Mirfak is a yellow-white supergiant with an estimated mass of about 8.5 solar masses.  This is very near the mass threshold that separates future supernovas from future white dwarfs.  Stars more massive than this will eventually collapse and then explode as a supernova.  Less massive stars will shed their outer layers as a planetary nebula and then fade away as a white dwarf.

Winter circles

 Polaris (Alpha Ursae Minoris) is known as the "Pole Star" or "North Star" because it is the nearest naked-eye star to the North Celestial Pole (NCP).  Under casual observation it appears to be motionless while the night sky rotates counter-clockwise around it.

E-M5iii + Leica 15mm f/1.7, live composite mode.

Close examination reveals that it is not quite at the center of rotation.  Polaris is currently 0.63° from the NCP. This is about 1.25 times the width of the full moon.  This distance is slowly changing because of precession of the earth's axis of rotation.  One hundred years ago the separation was 1.1°, and in 1776 it was 1.9°.  According to Belgian astronomer Jean Meeus the closest approach will occur on 24 March 2100, when the NCP will pass within 0.45° of Polaris, just slightly smaller than the width of the full moon.  Mark your calendars!

Polaris has significance beyond just being a navigational aid.  It is also the closest (430 ly) and brightest (mag 2.0) Cepheid variable star.  The brightness variations are too small (about 0.1 mag) to be noticed visually.  Polaris is close enough that its distance has been measured by parallax. This provides an important calibration point for the luminosity versus period relationship of Cepheid variables, which are used to determine the distance scale of the local universe (< 20 Million ly).

In addition to being a variable star, Polaris is also a multiple star, part of a three-star system: Aa, Ab, and B.  One of the companion stars (B) can be seen in small telescopes.  It is a magnitude 9.1 star at a separation of 18".  I have spotted it in a 60mm telescope, but have been unsuccessful with a 50mm scope.  The other companion (Ab) orbits too closely to be resolved easily and was first detected spectroscopically.  It was resolved photographically by the Hubble Space Telescope in 2006.

E-M5iii + Leica 15mm f/1.7 + softon filter.  ISO 1600, 60s.

There are several ways to find Polaris if you are unfamiliar with the night sky.  A magnetic compass will point toward the magnetic north pole, which is currently 8.4° east of true north when measured from Creede.  This is illustrated in the next picture, where I have added an outline of the Little Dipper and two white circles. The circle that intersects Polaris marks the location of the North Celestial Pole.  The circle to the right is the direction that will be indicated by a magnetic compass: 8.4° to the right (east) of the NCP.

Most people are familiar with the asterism known as the Big Dipper, which is part of the larger constellation Ursa Major.  The extension of a line between the two bright stars at the end of the "dipper" will point very close to Polaris.  I have added a line between these two stars (Alpha and Beta Ursae Majoris, aka Dubhe and Merak) in the above image.  Unfortunately, at this time of year (early December) the Big Dipper is skimming the northern horizon in the early evening and is largely obscured by mountain ridges.

 The above images show a yellowish glow along  the northern horizon.  This is what remains after color balancing the night sky.  The original daylight balanced image looks like this:

 I do not know if this pinkish glow is airglow or auroral glow.  It may be a combination of both.  It is not perceivable by eye, but is easily revealed in a long exposure (30-60 s) photograph.  The sky brightness at this time was sqml=21.09, which is considerably brighter than a "normal" dark sky in Creede.  The sun has been very active recently, and reports of auroral activity farther north are very common.  A Hydrogen-alpha image of the sun earlier the same day shows many spectacular prominences along the sun's limb.

Lunt LS50THa double stacked + ZWO ASI178mm camera.  Processed from a stack of 66 video frames.

As usual, click on any image to get access to the full-size version.

A tale of two stars

 Two stars of historical and cosmological significance are currently well situated in the northern evening sky: Beta Persei (Algol) and Delta Cephei.  These stars share two things in common: they are both first-of-kind variable stars and they were both subjects of study by the young English astronomer John Goodricke, FRS.

Algol, aka the "Demon Star", is an eclipsing binary whose variability was likely known as far back as the ancient Egyptians.  Goodricke was the first to determine its regular period of 2.86 days and in 1783 (at age 19)  proposed an eclipsing mechanism as the cause.  For this work he was awarded the Copely Medal by the Royal Society.  The next year he discovered the variability of the the star Delta Cephei. Delta Cephei is the prototype of the class of variable stars known as "Cepheids", which are used to determine the distance scale of the local universe.  Goodricke was elected as a Fellow of the Royal Society in 1786 at age 21, but died of pneumonia only four days later and never learned of the honor.

Algol is marked by the white circle.  The Pleiades star cluster is on the right edge and the star Mirfak (Alpha Persei) is on the left. E-M1iii + Sigma 30mm f/1.4  + softon filter. ISO 1600, 30 s.

 Algol (Beta Persei) varies in magnitude from 2.1 to 3.4, a factor of 3.3 in brightness.  It is easily visible to the unaided eye.

The constellation Cepheus.  Delta Cephei is marked by the white circle.  E-M1iii + Sigma 30mm f/1.4 + softon filter.  ISO 1600, 30 s.

Delta Cephei varies in magnitude from 3.5 to 4.4 over a period of 5.4 days.  The brightness changes are caused by radial pulsations of the star's atmosphere. In 1908 Henrietta Swan Leavitt discovered a relationship between the pulsation period and absolute brightness for this type of star.  Her findings were published in 1912.  This relationship is a crucial tool used to establish the distance scale of the local universe (within 20 million ly).

Another interesting star in the above image is the reddish star about a quarter-frame below Delta Cephei.  This is Mu Cephei, Herschel's "Garnet Star".  It s a red supergiant similar to Betelgeuse and is one of the largest and brightest stars in our galaxy.

As usual, click to get access to the full-size images.

Frosty moon and star trails

 The recent full moon of 27 November, the 11th of the year, has traditional nicknames that differ depending on the source, but the one that seems appropriate this year is "Frost Moon".  According to The Old Farmer's Almanac this name comes from the Cree and Assiniboine cultures.  In the popular press it has been more commonly hyped as the "Beaver Moon", which is the prevailing nickname.  

Full moons with snow on the ground present interesting photographic opportunities.

Olympus E-M1iii + Leica 9mm f/1.7, live composite mode, 1 hour.

 When I retrieved the camera after this exposure the lens was frosting over and the battery was dead.  The outside temperature was 5° F, dropping toward an eventual low of -12° F the next morning.  Frosty indeed.

The Frost Moon.  AT80EDT telescope.

The Frost (aka Beaver) Moon setting over Bristol Head

 

The setting-moon pictures were taken on the morning of the 28th. The temperature was -11° F at the time.  It kept dropping.