The Double Cluster re-visited

 

The Double Cluster - NGC 869 and NGC 884. Modded Canon 200d DSLR with Dual Band Filter and 135mm Samyang Lens.

Map Credit: freestarcharts.com

" Both Kurt and Pip have never believed that they have done the Double Cluster justice. When you look at this pair of open star clusters, through binoculars or a widefield eyepiece on  a telescope at low magnification, it is truly magnificent.  The Double Cluster, viewed through the JPO's tripod mounted 11x80mm.binoculars, is a joy to see in its jewel like appearance. If you have a pair of binoculars and it's a clear night in the Northern Hemisphere, why not try and find it between Cassiopeia and Perseus? - Joel Cairo CEO of the Jodrell Plank Observatory.

"The Double Cluster in Perseus, catalogued as NGC 869 and NGC 884, is a striking pair of young, massive open star clusters located in the Perseus arm of the Milky Way Galaxy. Situated at an approximate distance of 7,500 light-years (2.3 kpc) from Earth, the system lies within the Perseus OB1 association, an active star-forming region rich in hot, luminous stars.

Both clusters are estimated to be relatively young, with ages on the order of 12–14 million years, placing them in a comparable evolutionary stage. Their stellar populations are dominated by early-type B-class main-sequence stars and a notable complement of evolved blue and red supergiants, evidence of rapid stellar evolution in high-mass stars. Integrated spectral analyses indicate a near-solar metallicity, consistent with their origin in a typical Galactic spiral-arm environment.

The clusters are physically separated by only a few hundred light-years, suggesting a common origin from the same giant molecular cloud. Their projected angular separation on the sky is approximately 30 arcminutes (roughly the apparent diameter of the full Moon), making them easily distinguishable yet visually connected in telescopic and binocular observations.

Photometric studies of NGC 869 and NGC 884 reveal high stellar densities in their cores, with mass estimates of several thousand solar masses each, placing them among the most massive open clusters in the Milky Way. Their combined luminosity and concentration of bright, blue stars make the Double Cluster an archetypal laboratory for studying the early dynamical evolution of clustered stellar populations.

Owing to their brightness (apparent magnitudes ~+4.3 and +4.4) and their location near the Perseus–Cassiopeia border, the Double Cluster has been recognized since antiquity, though it was first catalogued systematically by Hipparchus around the 2nd century BCE. Today, the system remains a prominent observational target for both professional astrophysical research and amateur astronomy, offering insight into star cluster formation, stellar evolution, and Galactic structure". - Professor G.P.T. Chat visiting astrophysicist at the Jodrell Plank Observatory.

The Heart of the matter

 

IC 1805 and Melotte 15.

"The above images captured at the Jodrell Plank Observatory and also by the PIRATE robotic telescope on Mount Teide, Tenerife (credit telescope .org, Open Observatories, Open University) show the Heart Nebula, IC1805 in increasing detail and reducing field of vision. The top, widefield image was captured with the JPOs modded Canon 200d Camera with a Dual Band filter and a Samyang 135mm lens. The other two were captured by the PIRATE telescope with SHO filters. Pip Stakkert used a number of processing techniques to emphasise the nebulosity". - Kurt Thrust current Director of the JPO.

"The Heart Nebula (IC 1805) is a large emission nebula located in the Perseus Arm of the Milky Way, within the constellation Cassiopeia. At an estimated distance of approximately 6,000–7,500 light-years from Earth, it extends over nearly 200 light-years in diameter, making it one of the more prominent star-forming complexes in the northern sky. Its common name derives from the overall morphology of its extended H II region, which, in wide-field optical images, presents an outline reminiscent of a stylized human heart.

The nebula is primarily excited by the young stellar population of the open cluster Melotte 15, situated near the nebula’s center. This cluster, containing numerous hot O-type and early B-type stars, serves as the dominant ionizing source for the surrounding gas. The intense ultraviolet radiation emitted by these massive stars ionizes the hydrogen in the surrounding molecular cloud, producing the characteristic red glow of Hα emission. Stellar winds and radiation pressure also drive large-scale feedback processes that shape the morphology of the nebula, generating bright ridges, cavities, and dark, pillar-like structures of dense gas.

Of particular note is the brighter nebulosity concentrated near the nebula’s core. This region surrounds Melotte 15 and exhibits a higher surface brightness due to the proximity of the ionizing sources and the resulting density contrast between ionized and neutral gas. Within this core, the interplay between radiation, stellar winds, and turbulence has carved out intricate filaments and luminous fronts, where shock compression has enhanced local gas densities. These conditions are conducive to ongoing star formation: observations at infrared and radio wavelengths reveal embedded protostars and compact H II regions tracing younger generations of stellar objects still enshrouded in dust.

In summary, IC 1805 exemplifies the dual role of massive stars in galactic ecology: while their radiation and winds sculpt and erode the parent molecular cloud, they also trigger subsequent episodes of star formation. The central bright nebulosity of the Heart Nebula, therefore, represents not only a visually striking concentration of emission but also the dynamic hub of stellar feedback and continuing stellar genesis within the complex". -Professor G.P.T Chat and Karl Segin outreach coordinator at the JPO.

The Iris Reflection nebula in the constellation Cepheus

The Iris Nebula in modified SHO format. The PIRATE Robotic Telescope,Mount Teide, Teneriffe.   Data Credit: telescope.org. Open Observatories, Open University. Image Credit: Kurt Thrust.

" Kurt was feeling a little better today and so he and the JPO engineer, Jolene McSquint-Fleming, were busy remaking a diffraction grating for the Seestar S30. They decided to make a grating, which covers the full aperture of the little scope rather than  partially. It will be interesting to see whether this affects the accuracy of the scope's guidance and goto software". - Joel Cairo CEO at the JPO.

The new-recycled magnetic 50 lines/mm
full aperture grating for the Seestar 30

Spectrum produced by the above grating
using the JPO Visitor Centre door security peep hole
as an artificial star.

" If we get a clear night soon, we will try the new grating out and develop a capture process, which enables the removal of stars and hot spots, which otherwise corrupt the  target and calibration spectra". - Kurt Thrust current Director of the JPO.

" The Iris Nebula, cataloged as NGC 7023, is a bright reflection nebula located in the constellation Cepheus, approximately 1,300 light-years from Earth. It is a striking example of a dust cloud illuminated by starlight rather than by its own emission. At its center lies a young, hot star designated HD 200775, whose intense blue-white radiation reflects off surrounding interstellar dust grains. This scattering process preferentially reflects shorter wavelengths, giving the nebula its characteristic bluish hue, much like the mechanism that makes Earth’s sky appear blue.

The nebula spans roughly six light-years across and is embedded within a larger molecular cloud complex. Its structure reveals striking contrasts: bright filaments and wisps where dust strongly reflects starlight, interspersed with dark lanes where dense concentrations of material obscure illumination. Infrared observations have shown that the dust contains complex carbon-rich molecules, including polycyclic aromatic hydrocarbons (PAHs), which are thought to play a role in interstellar chemistry and may represent building blocks of more complex organic compounds.

Unlike emission nebulae, which glow due to ionized gas, the Iris Nebula remains primarily a reflection nebula because the radiation from its central star is not energetic enough to fully ionize the surrounding hydrogen gas. Instead, the nebula’s beauty lies in the interplay of light and shadow, highlighting the distribution of interstellar dust and providing astronomers with insights into the conditions of stellar nurseries". - Professor G.P.T Chat visiting astrophysicist at the Jodrell Plank Observatory.

Enlarged and cropped view of the spectacular Iris reflection Nebula

IC 5070 or the Pelican Nebula in modified SHO format

Ionization fronts and cold gas in the Pelican Nebula. Data Credit: PIRATE robotic telescope SHO filters. Mount Teide, Tenerife. telescope.org Open Observatories, Open University. Image credit: Pip Stakkert at the JPO..

"The Pelican Nebula is a goto target for Northern Hemisphere  summer astro-imagers and sits next to the North America Nebula NGC7000 in the constellation Cygnus. The above narrowband image shows the delicate interplay of light and shadow: the glowing plasma energized by young stars and the cold dark lanes marking where future stars are gestating. The visible filaments trace the ionization fronts—the boundaries between the ultraviolet-irradiated cavities and the shielded interiors of molecular clouds.

In effect, the above image is a portrait of cosmic evolution in progress: the raw interstellar medium being sculpted into stars, planetary systems, and eventually the building blocks of life itself". - Joel Cairo CEO of the Jodrell Plank Observatory.

The North America and Pelican Nebulae in the Constellation Cygnus. Image credit: Kurt Thrust at the JPO

"Our narrow band SHO image, captured with the PIRATE telescope, depicts IC 5070, more commonly known as the Pelican Nebula, a large emission nebula located in the constellation Cygnus, not far from its companion, the North America Nebula (NGC 7000). Both regions are part of an extended complex of ionized hydrogen gas (an H II region) that lies about 1,800 light-years away in the Orion Arm of our Milky Way galaxy.

What we have imaged is essentially a stellar nursery: a vast cloud of hydrogen, dust, and other trace elements undergoing active star formation. The striking forms in IC 5070—its ridges, filaments, and dark channels—arise from the interaction between intense ultraviolet radiation from nearby massive stars and the dense molecular cloud material.

Ionization and Emission

The gas in IC 5070 glows because young, hot O- and B-type stars in the region emit torrents of ultraviolet light.

This radiation strips electrons from surrounding hydrogen atoms, a process known as photoionization. When the electrons recombine with protons, they emit visible light—most notably in the red H-alpha line (656.3 nm). This is why narrowband astrophotography often reveals IC 5070 with a red or magenta dominance.

Dark Dust Lanes

The jagged black regions cutting through the glowing gas are dense molecular clouds of dust and cold gas.

These clouds absorb and scatter visible light, producing the intricate silhouetted structures that make the Pelican Nebula so recognizable. Within these dark regions, protostars are forming, hidden from optical wavelengths but detectable in infrared.

Stellar Feedback

The radiation pressure and stellar winds from massive young stars push against the molecular material, carving cavities, compressing clouds, and triggering further star formation at the boundaries of these regions.

This feedback loop is a defining characteristic of giant H II regions: they are both destroyers and creators—dissipating the nebula even as they seed new generations of stars.

Overall Context

IC 5070, along with NGC 7000, is part of a giant molecular cloud complex spanning several degrees of sky, visible in wide-field astrophotography, (see Kurt's above  image) as a grand tapestry of glowing hydrogen and sculpted dust.

Astronomers often study it as an analog for stellar nurseries in other galaxies, since its proximity gives us a clearer laboratory for understanding massive star formation and interstellar medium dynamics". -Kurt Thrust current Director of the  JPO and Professor G.P.T Chat visiting astrophysicist .

NGC 281 'The Pac-man' Nebula

 

NGC 281- Part of the Pac-man Nebula. Data Credit: PIRATE robotic telescope, SHO filters, Mount Teide, Tenerife. telescope.org. Open Observatories, Open University. Image Credit: Kurt Thrust.

The Constellation Cassiopeia (The big 'W' asterism in the Northern Sky)
A compilation - 3 pane, widefield image.
Captured with the Jodrell Plank Observatory's mini-rig : Canon 600d DSLR
with a 135mm F2 Samyang Lens all on a Star Adventurer EQ mount.
  - Image Credit: Pip Stakkert

" The weather remains poor on the East Coast and sadly Kurt has been laid low by an auto-immune disorder,consequentially, little astronomy has been pursued at the JPO. Kurt did however, enjoy an hour working upon the Pac-man data obtained via the PIRATE robotic scope on Tenerife". - Joel Cairo CEO of the JPO.

NGC 281 in detail

"The NGC 281 nebula, often nicknamed the Pacman Nebula due to its resemblance to the iconic video game character in optical images, is a large, active star-forming region located in the Perseus spiral arm of the Milky Way. Situated in the northern constellation Cassiopeia, this emission nebula lies approximately 9,200 light-years (2.8 kiloparsecs) from Earth. With an angular diameter of nearly 35 arcminutes—comparable to the size of the full Moon—it corresponds to a physical span of over 100 light-years across.

NGC 281 is classified as an H II region, a vast cloud of ionized hydrogen gas energized by the intense ultraviolet radiation from its embedded young stars. At its core lies the open star cluster IC 1590, which hosts a population of hot, massive O- and B-type stars. Among them, the O6 star HD 5005 is particularly dominant, providing much of the ionizing flux that causes the surrounding hydrogen gas to glow in vivid emission lines, especially the characteristic red Hα radiation.

The nebula’s structure is rich and complex, sculpted by stellar winds and radiation. Prominent features include dense Bok globules—cold, dark molecular clumps that appear as silhouettes against the luminous background. These globules are active nurseries where protostars are forming, their growth regulated by the interplay between self-gravity and external radiation pressure. Infrared observations from the Spitzer Space Telescope and more recent surveys with the James Webb Space Telescope (JWST) have revealed numerous young stellar objects (YSOs) and protostellar disks within NGC 281, highlighting its ongoing role as a cradle of stellar birth.

The nebula is also notable for being the site of significant molecular outflows and stellar feedback processes. Winds from the massive stars in IC 1590 compress nearby gas, triggering sequential star formation along the peripheries of the nebula—a process sometimes described as “collect and collapse.” This makes NGC 281 a textbook example for studying how massive stars regulate the evolution of their parent molecular clouds.

From an observational perspective, NGC 281 is accessible with modest amateur telescopes under dark skies, appearing as a faint glowing patch of nebulosity surrounding a small star cluster. Through long-exposure astrophotography, its intricate structure becomes clear, with reddish emission nebulae, dark dust lanes, and striking cavities carved by stellar activity.

In summary:

NGC 281 in Cassiopeia is a luminous emission nebula and star-forming complex, powered by the young cluster IC 1590. Spanning over 100 light-years, it contains dark Bok globules, active protostars, and striking examples of stellar feedback shaping the interstellar medium. Its combination of visual beauty and astrophysical richness has made it both a popular target for amateur astronomers and a significant object of study for professional astrophysics, particularly in the fields of star formation, stellar feedback, and nebular evolution". - Professor G.P.T Chat visiting astrophysicist at he Jodrell Plank Observatory.

Messier 31 revisited

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Messier 31 The Andromeda Galaxy Group. Altair Lightwave 66mm ED refractor and Canon 600d DSLR.
Image Credit Kurt Thrust.

"Our nearest spiral galaxy neighbour the Andromeda Galaxy is riding high in the Northern Hemisphere autumn sky. The weather has been far from kind and the JPO team has been laid low by a rather nasty virus which may be the latest variant of  Covid. Anyway, as the team has been wrapped up warm for a while, Kurt decided to reprocess this data captured in a previous year.

The above image shows the three galaxies M31 (the large central inclined spiral), M32 the elliptical galaxy (appears as a fuzzy spot on the upper edge of the M31 spiral) and M110 a dwarf elliptical galaxy ( just below and to the centre right of M31). 

So let Professor G.P.T. Chat, our visiting astrophysicist, compare and contrast these nearby galaxies (approximately 2.5 million light years distant) with our home Milky Way galaxy". - Joel Caio CEO of the Jodrell Plank Observatory.

Milky Way – Our Home Galaxy

The Milky Way is itself a barred spiral galaxy, somewhat smaller than M31. Its disk extends ~100,000–120,000 light-years, with a mass of about 1 trillion solar masses and a few hundred billion stars. Structurally, it resembles M31: both have stellar halos, bulges, bars, spiral arms, and satellite galaxies. In cosmic terms, the Milky Way is the second major member of the Local Group, and the future collision and merger of the Milky Way and M31 will reshape them into a single giant elliptical galaxy in several billion years.

M31 – The Andromeda Galaxy

Andromeda is the giant of this quartet. With a disk spanning about 220,000 light-years, it is roughly twice the diameter of the Milky Way. Its stellar population approaches one trillion, compared with the Milky Way’s 200–400 billion. In both size and luminosity, M31 slightly outclasses our own Galaxy, and it exerts enough gravitational pull to dominate the Local Group, which also contains the Milky Way and dozens of smaller galaxies.

• Diameter: ~220,000 light-years (about twice the Milky Way’s diameter).
• Mass: ~1.5 trillion solar masses.
• Stars: ~1 trillion.
• Luminosity: ~2.6 × 10¹⁰ solar luminosities.

Notes: A vast spiral galaxy with an extensive stellar halo and a large, bright disk. It dominates the Local Group both in size and gravitational influence.

M32 – Compact Elliptical

Placed against the scale of the Milky Way, M32 looks minuscule. With only ~3 billion stars in a body just 6,500 light-years across, it is smaller than even some of the Milky Way’s largest globular clusters when measured by diameter. Where the Milky Way’s spiral disk is rich in gas and dust and actively forming stars, M32 is stripped bare, almost entirely quiescent. Its compact, blazing core makes it bright for its size, but compared with the Milky Way, it is less than 1% as luminous.

• Diameter: ~6,500 light-years (tiny compared with M31).
• Mass: ~3 × 10⁹ solar masses.
• Stars: ~3 billion.
• Luminosity: ~3 × 10⁸ solar luminosities.

Notes: Dense and bright, especially in its central regions. Its outer stars and gas are thought to have been stripped by M31, leaving only the compact core we see today.

M110 – Dwarf Elliptical

M110 sits somewhere between M32 and the Milky Way in scale. Its 15,000–17,000 light-year span is still tiny compared with the Milky Way’s disk, and its ~10 billion stars are a mere fraction of the Milky Way’s population. Unlike M32, however, M110 retains some irregular features, dust, and evidence of star formation. It is a faint satellite, thousands of times less luminous than the Milky Way, but still large enough to stand as one of the more substantial dwarf galaxies in the Local Group.

• Diameter: ~15,000–17,000 light-years.
• Mass: ~1–2 × 10⁹ solar masses.
• Stars: ~10 billion.
• Luminosity: ~9 × 10⁸ solar luminosities.

Notes: More diffuse than M32, with some evidence of dust lanes and past star formation. Its structure is irregular compared with typical smooth ellipticals, likely reflecting tidal interaction with M31.

Comparative Perspective

M31 and the Milky Way are the two great spirals of the Local Group, differing mainly in scale (M31 being the larger).

M32 is a stripped-down remnant, a tiny elliptical companion of M31, utterly dwarfed by both the Milky Way and Andromeda.

M110 is a diffuse dwarf elliptical, more extended than M32 but still only a faint shadow of the Milky Way’s scale and richness.

Together, these four galaxies illustrate the hierarchy of galactic forms: two massive spirals shaping the Local Group, orbited by much smaller companions that bear the scars of their gravitational relationship with the giants.

The Approaching Collision

• The Milky Way and M31 are moving toward each other at about 110 km/s.

• In roughly 4–5 billion years, their outer halos will begin to overlap, triggering the first close passage.

• The collision will not be like two solid bodies smashing together; instead, stars will mostly pass by one another because of the vast spaces between them. But gas, dust, and dark matter halos will interact strongly, producing shocks, bursts of star formation, and tidal distortions.

The Merger

• After a series of close encounters, the Milky Way and M31 will merge into a single giant elliptical galaxy — sometimes nicknamed “Milkomeda” or “Milkdromeda.”

• This process will take several billion years to settle into a stable form. The final product will likely resemble today’s giant elliptical galaxies, with a vast stellar halo and little organized spiral structure.

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The Fate of M32

• M32, already stripped and compact, is tightly bound to M31.

• During the merger, it will almost certainly be swallowed whole by the combined Milky Way–Andromeda system.

• Its compact nature means it will survive tidal forces fairly well, likely ending as a dense nucleus or central star cluster within the merged galaxy.

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The Fate of M110

• M110, being larger and more diffuse, will fare differently.

• It may be torn apart by tidal forces during the merger, with its stars spread out into long stellar streams and absorbed into the halo of the new galaxy.

• Some fraction of its stars may survive as a remnant dwarf core, but it will be much more disrupted than M32.

The Long-Term Result

• The Local Group will transform from a system dominated by two spirals into a single elliptical super-galaxy, containing perhaps 2 trillion stars.

• The smaller companions, including M32, M110, and the Milky Way’s own satellites (like the Magellanic Clouds), will either be absorbed into the giant remnant or left orbiting as faint shells and streams.

• From a cosmic distance, the Local Group will eventually resemble a single luminous elliptical galaxy, drifting in relative isolation as the universe continues to expand.

 In short: M31 and the Milky Way will merge into one great elliptical galaxy; M32 will likely become part of its core, while M110 will be torn apart and assimilated into its halo.

Messier 71, the easy to miss Globular Star Cluster.

 

The Globular Star Cluster Messier 71. Data Credit: PIRATE robotic telescope, BVR filters. Mount Teide, Tenerife. telescope.org. Open Observatories, Open University. Image Credit: Kurt Thrust at the JPO.

" Messier 71, sits in the  small constellation Sagitta the arrow. This area of the sky is associated with the plane of the Milky Way's disc and is literally awash with stars when viewed with binoculars or a widefield telescope. Messier 71 being a small globular cluster, is therefore easy to miss within this plethora of stars. As I processed the data and watched the above image materialise, I  was amazed at how many stars I could see!" - Kurt Thrust current Director of the Jodrell Plank Observatory.

A Comparative Report on the Globular Cluster Messier 71

Messier 71 (M71), located in the small constellation Sagitta, is one of the more unusual globular clusters in the Messier catalogue. At a distance of roughly 13,000 light-years, it appears as a loose, irregular grouping of stars through modest telescopes, and for much of the 19th and 20th centuries it was debated whether M71 was in fact a globular or a rich open cluster. Advances in stellar photometry and spectroscopy have since clarified its nature: M71 is a genuine globular cluster, though a relatively low-mass, metal-rich, and loosely concentrated one. Comparison with the more archetypal clusters Messier 13 (M13), Messier 3 (M3), and Messier 4 (M4) underscores the peculiarities of M71.

Messier 13, the “Great Hercules Cluster,” is perhaps the best-known northern globular cluster. It contains several hundred thousand stars in a compact halo over 140 light-years across, with a dense, bright core that exemplifies the globular class. By contrast, M71 contains perhaps only 20,000–50,000 stars spread across a mere 27 light-years. Its lower concentration and modest size explain why early observers mistook it for an open cluster. Whereas M13 presents a dazzling display of densely packed stars and exhibits a well-defined horizontal branch, M71 has only a stubby red giant branch and no extended blue horizontal branch, making its stellar population appear more subdued.

Messier 3 provides another instructive comparison. Situated in Canes Venatici, M3 is among the richest and most extensively studied globular clusters, hosting over half a million stars and more than 200 known variables, including numerous RR Lyrae stars. Its variable population and prominent horizontal branch have made it a cornerstone for calibrating stellar evolution models. M71, on the other hand, lacks a significant RR Lyrae population and is chemically distinct. Its relatively high metallicity ([Fe/H] ≈ –0.8) is atypical for globular clusters, especially when contrasted with the metal-poor stars of M3. This implies that M71 formed later in the Galactic halo’s history, from interstellar gas already enriched with heavier elements, and therefore represents a younger evolutionary epoch within the globular cluster system.

Messier 4, in Scorpius, provides a comparison from the opposite end of the structural spectrum. Though M4 is one of the closest globular clusters to Earth (about 7,200 light-years), and not especially rich in stars compared to giants like M3 or M13, it nevertheless displays a clear globular morphology with a strong central concentration. M4 is notable for its rich population of evolved stars, a well-populated horizontal branch, and chemical peculiarities linked to multiple stellar generations. In terms of mass and richness, M4 is closer to M71 than are M13 or M3, yet it retains the compact, globular appearance that M71 lacks. The difference lies primarily in concentration: M4 is compact and easily recognisable as a globular cluster, while M71 is diffuse, giving it a hybrid appearance that complicated its classification.

In conclusion, M71 highlights the diversity within the globular cluster family. It lacks the immense stellar density and archetypal morphology of Messier 13, the vast population and chemical simplicity of Messier 3, and even the structural clarity of Messier 4. Instead, it is a relatively loose, metal-rich, and moderately populated globular cluster, whose transitional characteristics blur the distinction between open and globular clusters. Its study provides valuable insight into the chemical enrichment of the Galaxy and the lower-mass limits of globular cluster formation.

Professor G.P.T. Chat visiting astrophysicist at the Jodrell Plank Observatory.