Sinus Iridum - The Bay of Rainbows

 

Images captured from the Jodrell Plank Observatory using the 127 mm. Meade Apo Refractor and the Seestar S30. Data and image credit: Pip Stakkert.

"The other evening, our imaging technician Pip was using the  Seestar S30 to photograph the waxing gibbous lunar disc. He noticed that the 'Terminator' or 'daybreak on the Moon' was about to cross the prominent feature Sinus Iridum - The Bay of Rainbows. Sunlight had just touched the peaks of the crater walls creating the effect known as the 'golden handle'. This can just be seen top left in the bottom image". - Joel Cairo CEO of the Jodrell Plank Observatory.

Key features of Sinus Iridum - Lunar notes - from Professor G.P.T Chat visiting astrophysicist at the JPO.

Sinus Iridum (Latin for "Bay of Rainbows") is one of the most striking basalt-flooded impact structures on the near side of the Moon. It forms a broad semicircular embayment on the northwestern margin of Mare Imbrium and is enclosed by the rugged arc of the Montes Jura mountain range. To lunar observers it appears as a near-perfect luminous crescent when illuminated at low solar angles, making it one of the most recognizable features on the lunar disc.

Position on the Lunar Disc

Sinus Iridum lies at approximately 44°N latitude and 31°W longitude on the Moon's near side. Because it occupies the northwestern sector of Mare Imbrium, it appears in the Moon's upper-left quadrant as viewed through most astronomical telescopes that present an upright image. The feature is roughly 240–260 km in diameter and opens southeastward into Mare Imbrium. The enclosing Jura Mountains are remnants of the original crater rim, rising locally several kilometres above the mare floor.

Origin as a Large Impact Basin

Sinus Iridum began as a major impact crater formed during the late stages of the heavy bombardment that shaped much of the lunar crust. The impact excavated a large bowl-shaped basin and produced an elevated rim composed largely of anorthositic highland material. The southeastern portion of the rim was later breached and largely buried when extensive volcanic flooding associated with Mare Imbrium spread into the crater.

The result is not a true bay in the terrestrial sense, but rather the flooded remains of a large impact structure whose interior became connected to the surrounding mare plains. The surviving rim forms the dramatic semicircular wall visible today.

Geological Composition

The floor of Sinus Iridum consists predominantly of mare basalts emplaced during multiple volcanic episodes. Remote-sensing studies using data from the Clementine mission, Chandrayaan-1, the Lunar Reconnaissance Orbiter, and China's Chang'E program show that these lavas vary in composition and age across the basin.

Key geological characteristics include:

• Basaltic mare plains rich in pyroxene-bearing volcanic rocks.
• Progression from low-titanium basalts in older lava units to medium-titanium basalts in younger units.
• Evidence for increasing olivine abundance in some younger volcanic materials.
• Wrinkle ridges, tectonic deformation features caused by contraction of cooling lava plains.
• Small impact craters, crater chains, and rilles recording later geological modification.

The surrounding Montes Jura remain compositionally distinct from the mare floor, consisting mainly of feldspathic highland crust excavated during the original impact event.

Age and Volcanic History

Modern crater-count dating reveals that Sinus Iridum experienced a prolonged history of volcanic resurfacing rather than a single flooding event.

The oldest exposed mare units have model ages of approximately 3.37 billion years, corresponding to the Imbrian period. Younger lava flows continued entering the basin from Mare Imbrium for more than two billion years afterward. Some of the youngest recognized basaltic units have ages near 1.24 billion years, making them among the youngest extensive mare volcanics on the Moon.

The sequence is interpreted as repeated episodes of lava entering the partially enclosed basin from the larger Imbrium volcanic province. Rather than being filled from a single central vent, Sinus Iridum appears to have been resurfaced multiple times by flows arriving from adjacent mare regions.

Tectonic Evolution

Following emplacement of the mare basalts, the region underwent tectonic deformation associated with cooling and subsidence of the volcanic plains.

Researchers using data from the Japanese SELENE (Kaguya) mission and NASA's Lunar Reconnaissance Orbiter identified wrinkle ridges and compressional structures whose formation may have continued into relatively recent lunar history. These structures reflect crustal shortening caused by the weight and contraction of the basaltic fill.

Spacecraft Investigations

Several lunar missions have studied Sinus Iridum in detail.

NASA Missions

• The Lunar Reconnaissance Orbiter has provided high-resolution imagery, topographic measurements from LOLA, and compositional information used in modern geological mapping.
• Earlier missions including Clementine supplied multispectral data that helped determine iron and titanium abundances.

Japanese Investigations

• SELENE obtained detailed terrain and imaging data used to investigate tectonic structures and wrinkle ridges throughout northwestern Mare Imbrium and Sinus Iridum.

Chinese Investigations

• Chang'e 2 produced high-resolution imagery used in detailed geological mapping and age determinations.
• Sinus Iridum was seriously evaluated as a candidate landing area for later Chinese robotic and sample-return missions because of its smooth terrain and geological diversity.

Although no spacecraft has yet landed within Sinus Iridum itself, it remains scientifically attractive because it exposes the interaction between impact-basin formation, mare volcanism, and tectonic deformation in a single locality. 

Captured from the JPO
and previously published on the blog

Messier 3 - New Data and revised data processing methodology.

 

Messier 3 - Globular star Cluster
in the Constellation Canes Venatici.
Seestar S30 in Eq mode.  1 min x 60 subs
Credit: Kurt Thrust at the JPO. 

" Our dedicated team of imagers and data processors has been experimenting with the application of the astro-freeware SIRIL and has used it to good affect in increasing the dynamic range of the M3 data captured on a clear night from the JPO in May this year. 'There is gold in them there 'data reduction' hills'" - Joel Cairo CEO of the Jodrell Plank Observatory.

"These images present the globular star cluster M3 — also catalogued as Messier 3 — suspended against a richly populated stellar background in the constellation Canes Venatici. Captured with a Seestar S30 smart telescope from the grounds of the Jodrell Plank Observatory under the direction of Kurt Thrust, the observation reveals one of the Milky Way’s most celebrated globular clusters: a gravitationally bound sphere containing roughly half a million ancient stars compressed into a region only a few hundred light-years across.

At a distance of approximately 34,000 light-years from Earth, M3 appears as a concentrated stellar nucleus whose luminosity rises sharply toward an intensely radiant core. The cluster's structure is immediately apparent: a dense central condensation surrounded by progressively looser stellar populations that dissolve into the surrounding galactic field. This radial distribution is the visible signature of a system that has remained gravitationally bound for more than eleven billion years, surviving countless passages through the Milky Way's halo while preserving a fossil record of the Galaxy's earliest epochs.

The warm golden and reddish tones scattered throughout the cluster arise predominantly from evolved red giant stars nearing the final stages of stellar evolution. Intermixed among them are hotter blue-white stars, including the enigmatic "blue stragglers" that appear younger than the rest of the cluster population. Their presence suggests a dynamic environment where close stellar encounters, mergers, and mass transfer events continue to reshape individual stars despite the cluster's immense age.

M3 is particularly significant to modern astrophysics because it hosts an extraordinary population of variable stars, including a large number of RR Lyrae variables whose rhythmic pulsations provide a fundamental rung on the cosmic distance ladder. These stars act as standard candles, enabling astronomers to measure distances across the Milky Way and beyond with remarkable precision. More variable stars have been identified in M3 than in almost any other known globular cluster, making it a natural laboratory for studies of stellar evolution and pulsation physics.

The Seestar S30 image demonstrates how modern compact smart telescopes can resolve individual members of a globular cluster once accessible only to larger observatory-class instruments. The cluster's sparkling granularity is evident across the halo, where hundreds of individual stars emerge from what appears visually as a diffuse cloud. Each point of light represents a sun in its own right, collectively tracing a nearly spherical stellar ecosystem orbiting far above the plane of the Milky Way.

Seen in this observation, M3 is not merely a beautiful celestial object but a relic from the early Universe: an ancient stellar metropolis whose stars formed when the Milky Way itself was still young. The image captures a moment in an ongoing cosmic history spanning billions of years, preserving within a single frame both the elegance of gravitational order and the immense scale of galactic time". Professor G.P.T Chat visiting Astrophysicist at the Jodrell Plank Observatory.

Nucleus M3 - Image Credit: night-sky/hubble-messier-catalog

Two Globular Star Clusters for the price of one - M53 and NGC5053

 

The Globular Star Clusters
Messier 53 (top right) and NGC5053 (bottom left)
Seestar S30 Credit: Kurt Thrust.

" Joel is very fond of 'Globular Star Clusters' and Messier 53 in the Constellation Coma Berenices, is his favourite. I spent some time post processing the data from the Seestar S30 to resolve as many stars as close to the centre of M53 as I could. I must try to get the JPO sponsors to purchase a copy of Pixinsight Software, which has a high dynamic range tool." - Kurt Thrust current Director of the JPO the UK's most easterly astronomic observatory. 

Comparison similarities and differences between M53 and NGC5053 - By Professor G.P.T Chat visiting astrophysicist at the Jodrell Plank Observatory. 

The Star Clusters

1. Messier 53 (M53 / NGC 5024)

• Location: The bright, highly concentrated cluster in the upper-right corner.
• Type: Dense Globular Cluster.
• Details: This is a classic, tightly packed cluster consisting of several hundred thousand stars. It sits roughly 58,000 light-years away from Earth. Because its stars are tightly bound by gravity toward a bright central core, it stands out vividly in astrophotography.

2. NGC 5053

• Location: The faint, loose cluster in the lower-left corner.
• Type: Loose (Diffuse) Globular Cluster.
• Details: In stark contrast to its neighbor M53, NGC 5053 is one of the least concentrated and most "ghostly" globular clusters in the Milky Way. It contains far fewer stars (only around 3,500) and lacks a bright, dense core, making it a challenging but rewarding target for astrophotographers.

Notable Stars & Features

• The Bright Red/Orange Star near M53: Just below and slightly to the left of M53's bright core, you will notice a prominent, bright orange-red star (HD 115024 / SAO 100488). This is a foreground star within our own Milky Way galaxy, sitting much closer to us than the background cluster.
• The "Tidal Bridge" (Cosmic Context): Though not visibly obvious without extreme exposure stretching, modern astronomy has revealed that M53 and NGC 5053 are physically close to each other in space (separated by only about 6,500 light-years) and are connected by a gravitational "tidal bridge" of streaming stars. They are essentially interacting with one another!

The globular clusters Messier 53 (M53, NGC 5024) and NGC 5053 form one of the most intriguing paired systems in the Milky Way halo. They lie in the constellation Coma Berenices, are separated on the sky by only about one degree, and are located at nearly the same heliocentric distance (~17–18 kpc, or ~56,000–60,000 light-years). Their proximity is not merely a line-of-sight coincidence; observational evidence suggests tidal interaction and the presence of a stellar bridge or extended envelope connecting the two systems.

Structural Properties

The most striking distinction between the two clusters is their internal stellar concentration.

M53 is a moderately concentrated, classical globular cluster, classified as Shapley–Sawyer class V. It possesses a dense central core and a high central stellar density, giving it a compact, nearly spherical appearance. It contains several hundred thousand stars and is among the more massive outer-halo globular clusters.

NGC 5053, by contrast, is a highly diffuse class XI globular cluster, among the least centrally concentrated globulars known. Its stellar density profile is shallow, it lacks a prominent core, and its stars are distributed over a comparatively large volume. Dynamically, it resembles a cluster that has experienced substantial tidal stripping and mass loss.

In terms of dynamical evolution, M53 appears relatively robust against Galactic tidal forces, whereas NGC 5053 is much more vulnerable to disruption because of its lower mass and weaker gravitational binding. The presence of tidal debris around NGC 5053 supports this interpretation.

Stellar Populations and Metallicity

Both clusters belong to the metal-poor halo population and are among the oldest stellar systems in the Galaxy.

M53 has a metallicity near [Fe/H] ≈ −2.0, indicating that its stars formed from gas enriched by only a few generations of prior stellar evolution. Its age is approximately 13 Gyr.

NGC 5053 is even more chemically primitive, with metallicity estimates ranging from [Fe/H] ≈ −2.1 to −2.3, placing it among the most metal-poor globular clusters in the Milky Way. Its stars therefore preserve an especially early record of Galactic chemical evolution.

The chemical abundance patterns of NGC 5053 are noteworthy because they resemble those observed in the Sagittarius Dwarf Spheroidal Galaxy rather than in typical Milky Way halo clusters. This has led to the hypothesis that NGC 5053 may have originated in an accreted dwarf galaxy and was later incorporated into the Galactic halo. Similar arguments have also been advanced for M53, suggesting that both clusters may share an extragalactic origin.

Variable Stars and Horizontal Branch Morphology

Both clusters are rich in RR Lyrae variables, making them important laboratories for stellar pulsation studies and distance calibration.

M53 contains an unusually large RR Lyrae population and is classified as an Oosterhoff II cluster. Its horizontal branch is predominantly blue, reflecting its low metallicity and old age. The cluster also hosts numerous blue stragglers and at least one millisecond pulsar.

NGC 5053 likewise contains RR Lyrae stars and blue stragglers, but because the cluster is less massive, the total number of such objects is smaller. Nevertheless, its variable-star population has been important in constraining its evolutionary history and distance.

Orbital and Dynamical Context

Both objects occupy the outer Galactic halo and follow highly eccentric orbits around the Milky Way. Their present three-dimensional separation is only a few kiloparsecs, much smaller than typical separations among halo globular clusters.

One of the most interesting current research topics concerns whether the two clusters constitute a physically associated pair. Deep photometric surveys and spectroscopic studies have revealed:

• extra-tidal stars around both clusters,
• a common stellar envelope,
• evidence for a tidal bridge between them,
• overlapping kinematic structures.

While they are not considered a gravitationally bound binary cluster in the strict sense, the data indicate that they have likely undergone past tidal interactions and may have shared a common accretion history.

Scientific Significance

From an astrophysical perspective, M53 and NGC 5053 represent two contrasting outcomes of globular-cluster evolution under similar environmental conditions:

Property	M53 (NGC 5024)	NGC 5053
Concentration class	V	XI
Structure	Compact, dense core	Diffuse, loosely bound
Metallicity	~−2.0 dex	~−2.1 to −2.3 dex
Mass	High	Low
Stellar density	High	Very low
Dynamical state	Relatively intact	Strongly affected by tidal stripping
Variable-star population	Rich RR Lyrae system	Smaller RR Lyrae population
Possible origin	Outer-halo/accreted system	Strong candidate for dwarf-galaxy origin

In essence, M53 is a relatively massive, dynamically resilient halo globular cluster, whereas NGC 5053 appears to be a fragile, chemically primitive remnant that may be nearing the end stages of tidal dissolution. Together they provide a valuable natural experiment for studying globular-cluster formation, Galactic accretion events, stellar dynamics, and the hierarchical assembly of the Milky Way halo. 

Light Fantastic

 

Solar Photosphere 24_05_2026. Seestar S30 with a base filter film Baader White Light OD:5.00 and differing Meade colour filters

"A while ago, whilst capturing some solar video clips with our 66mm Altair Astro Lightwave ED refractor, Kurt doubled up a Baader Film filter he had made with a red filter from his old box of Meade colour filters. He was surprised at how this enhanced the contrast between the photosphere, convection cells and faculae.

From our many posts, I am sure some of you will know how pleased we are at the JPO with the Seestar S30 we purchased over a year ago. It is a great bit of kit particularly for an observatory located next to the sea and subject to fast moving changes in the weather.

I got to wondering, whether Jolene could replicate this 'filter trick' but using a home designed 'Gizmo' for magnetically attaching in front of the Seestar's 30mm diameter objective lens.

We have recently 'invested in a new 3d printer and refurbished the 'Clean Room' so Jolene was set to complete the design and build project.

Yesterday it all came together and Kurt captured some solar video clips using different coloured filters in front of the Baader OD:5.0 white light filter film. 

I was very pleased with the results and suspect different filters in different combinations may provide future surprises for Kurt and the S30.  We shall be posting the 3d Printing files on Thingiverse next week under my name JoelCairo76. Feel free to download and play with this but beware this may damage and/or invalidate your Seestar and its manufacturer's warrantee or guarantee from ZWO.

Jolene's next design and build projects for the Seestar S30 will be ; proper narrow x3  band astrophotography (not dual band) and spectroscopy based. Jolene has a number of new design and build ideas, which we wish to pursue." - Joel Cairo CEO of the Jodrell Plank Observatory.

Supernova SN 2026kid in NGC5907: The Splinter Galaxy, Draco

 

                                      NGC 5907 with SN 2026kid supernova

Data for all images captured with the Seestar S30 smart-scope
from the Jodrell Plank Observatory Lowestoft.
Images Credit: Kurt Thrust

"The continued poor weather, the location of the jet stream overhead and the shortening of night as the summer advances, has reduced astro-imaging at the Jodrell Plank Observatory. The JPO Team determined to capture photons from the newly discovered supernova in the Splinter Galaxy and constellation Draco. Our Director Kurt Thrust wondered whether our smallest aperture telescope, the Seestar S30 would have sufficient light grasp to image the supernova, which at an apparent magnitude of 15, is very faint indeed. The unaided human eye can see stars down to magnitude 6, the scale is logarithmic and gets fainter with increasing positive magnitudes. As a guide, Venus the brightest planet in the sky, varies between minus (-)4 and minus (-)5".  

Unfortunately on the night we captured the data there was some high level thin cloud which was detrimental to image clarity.- Joel Cairo CEO of the Jodrell Plank Observatory.

"The bright stellar point visible against the thin glowing disk of NGC 5907 is a supernova: SN 2026kid, discovered in April 2026 within the edge-on spiral galaxy commonly known as the Splinter Galaxy or Knife Edge Galaxy. The galaxy lies approximately 50 million light-years away in the northern constellation Draco. Kurt wondered whether the

What appears in the Seestar image as a single bright “star” is actually the catastrophic death of a massive star that exploded tens of millions of years ago, long before humans existed. The light from that explosion has only just reached Earth. SN 2026kid is classified as a Type II supernova, meaning the progenitor star retained much of its hydrogen envelope when its core collapsed under gravity.

NGC 5907 itself is an especially striking target because we view it almost perfectly edge-on. Its narrow spindle shape and dark dust lane reveal the structure of a spiral galaxy from the side, offering a perspective similar to how an external observer might see our own Milky Way. The galaxy contains relatively little active star formation compared with many spirals, making the appearance of a bright supernova particularly noteworthy.

Astronomers are especially interested in supernovae because they are fundamental to cosmic evolution. These explosions forge and disperse heavy elements — including oxygen, calcium, silicon and iron — into interstellar space. The material expelled by ancient supernovae eventually becomes incorporated into new stars, planets, and ultimately living organisms. In a very real sense, the atoms in Earth and in our own bodies were created in stars like the one that exploded in NGC 5907.

The images also capture an important aspect of modern astronomy: scientifically useful observations are now possible with compact smart telescopes such as the Seestar S30. Amateur astronomers worldwide have been imaging SN 2026kid and monitoring how its brightness changes over time, contributing valuable observational records of this transient event.

Observed from Lowestoft, Suffolk, UK, the galaxy sits high in northern skies during spring evenings, making it well placed for long integrations even with modest aperture instruments. The combination of the delicate dust lane, the razor-thin galactic profile, and the brief appearance of a supernova creates a scene that connects human observers directly with stellar evolution on a galactic scale".  Professor G.P.T Chat visiting astrophysicist at the Jodrell Plank Observatory.

Widefield view from the Seestar S30 in equatorial mode
 stack of 1 minute lights Image Credit: Kurt Thrust

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Size and apparent size in the night sky

 

Images of the Solar Disc (photosphere) and the full Moon. Seestar S30 from the JPO
Image credit: Kurt Thrust.

"The Sun and the Moon appear to be the same size in the sky, when viewed at the same altitude. If they didn't, a total solar eclipse would not happen when they align in sky.  The Moon would be unable to fully cover the solar disc and an annular rather than full eclipse would occur..

In reality the actual diameter of the Solar disc is x400 that of the diameter of the Moon. At this period in time, the Sun is x400 further away than the Moon and that is why they appear in the sky as the same size.

The Moon is slowly moving further away from the Earth at 3.8cms per year. This is the same rate at which human fingernails grow. 

The Moon is moving away from the Earth because of a transfer of gravitational energy from the Earth to the Moon. The Moon acquires kinetic energy, its orbital velocity increases and its orbit lengthens requiring the Moon to move further away to maintain dynamic equilibrium. Similar gravity transfers of energy between the Earth, the planets and space probes in orbit are used to propel the spacecraft on longer elliptical journeys to other planets in the Solar System. 

It is thought, that last total solar eclipse, due to the Moon' moving further away from the Earth, will happen in 650 million years time. So astro-punters, no need to hurry on the eclipse chasing front!

The next time you look at the Moon, check whether you need a manicure, 'wink' and think of Neil.

For fun and giggles, Pip Stakkert created a 'faux partial eclipse of the Sun' to wile away an hour on a Bank Holiday afternoon". - Joel Cairo CEO of the Jodrell Plank Observatory.

The Plough Asterism

 

The Plough Asterism;
Canon 600d DSLR and EOS 18-55mm zoom lens on a Skywatcher Gti EQ mount.
Image credit: Pip Stakkert.

" The team was out on mass on the night of the predicted meteor maximum, to capture a Lyrid Meteor or two. Unfortunately, we didn't see one but we did get lots of light-subs of the 'Plough Asterism', part of  Ursa Major, the Great Bear Constellation. However, the LVST software defined radio at the JPO, did pick up lots of radar reflections from Lyrid meteor plasma created by friction in the upper atmosphere somewhere over the Southern France" - Kurt Thrust current Director of the Jodrell Plank Observatory.

Screen Capture, using Spectrum Lab Software: of a reflected radar beam generated from Dijon, in France. The plasma, created by the Lyrid meteor, probably no bigger than a grain of sand, is opaque to radar and so reflective. The LVST, via its Yagi Aerial, is able to detect such reflections. Interestingly, we had been picking up reflections from Lyrids for a number of days. All of them showed very little frequency spread, implying little to no doppler effects and implying the Lyrid shower was entering the atmosphere from a consistent direction and not moving towards or away from the Jodrell Plank Observatory.