The stars of the Summer Triangle asterism

The stars of the Summer Triangle: Deneb, Vega and Altair.
All images and spectroscopy captured and processed
by Kurt Thrust at the Jodrell Plank Observatory

" Kurt asked our visiting astrophysicist, Professor G.P.T Chat, to provide some features to look for in the above spectral line profiles and the stellar physics behind them". - Joel Cairo CEO of the JPO.

" An asterism is a recognizable pattern of bright stars in the sky. It may be formed from some of the brighter stars in a constellation, for example the Plough, which includes some of the stars of Ursa Major the Great Bear or a recognizable pattern of bright stars from several constellations, as is demonstrated by the Summer Triangle,which is comprised from the three alpha stars Deneb (Cygnus), Vega (Lyra) and Altair (Aquila). - Karl Segin outreach officer at the JPO.

Big picture

All three are A-type, blue-white stars, so they share strong hydrogen Balmer absorption and relatively sparse molecular features.

They differ mainly in luminosity class and rotation, which change how those same lines look: Deneb is a supergiant (Ia), Vega a near-textbook A0 main-sequence star (V), and Altair a late-A dwarf (A7 V) and extreme rapid rotator.

Where they sit on the HR diagram

Star Spectral type Luminosity class Evolutionary state

Deneb (α Cyg) ~A2 Ia (luminous supergiant) Massive star evolving off the main sequence; on its way through/around the supergiant phases

Vega (α Lyr) A0 V (dwarf) Middle-age main-sequence star, H-burning

Altair (α Aql) A7 V (dwarf) Main-sequence star; very fast rotator (oblate, gravity-darkened)

What your low-res spectra should show

Hydrogen Balmer lines (Hα, Hβ, Hγ, …)

Strongest near A0 → Vega should show the deepest Balmer absorption.

Altair (A7): Balmer lines still strong, but shallower than Vega; metal lines begin to stand out more.

Deneb (A2 Ia): Balmer lines are strong but shaped by low surface gravity—you may notice broad wings with comparatively narrow cores, and in some epochs wind effects (subtle emission infilling or weak P-Cygni signatures in Hα) even at low resolution.

Metal lines (Ca II K at 393.3 nm, Mg II ~448.1 nm, Fe II blends)

Altair: As the latest-type of the three, it should show relatively stronger metal lines than Vega.

Vega: Cleaner A0 spectrum—metals present but less prominent than in Altair; it’s also a mild metallicity-peculiar standard, so don’t be surprised if some metal features look a tad weaker than “textbook.”

Deneb: Despite being only slightly later than Vega by type, the supergiant’s low gravity enhances certain ionized metal lines (e.g., Fe II, Si II) and can make them more conspicuous than in Vega.

Line widths & shapes

Altair rotates extremely fast (period ~9–10 h), so its absorption lines are noticeably broadened even at low resolution.

Vega is also a rapid rotator but seen nearly pole-on, so its projected line broadening is modest—lines look crisper than Altair’s.

Deneb has low gravity and stellar winds; expect less rotational broadening, but broader Balmer wings and occasional wind-affected Hα profiles.

Continuum slope & reddening

Deneb is thousands of light-years away; interstellar reddening can tilt its continuum redward compared with nearby Vega (25 ly) and Altair (17 ly). If the data reduction didn’t fully de-redden Deneb, its spectrum may look slightly warmer/redder than its type alone would suggest.

Physical contrasts that drive those spectral looks

Temperature (rough): Vega ~9,600 K (hottest), Deneb ~8,500 K, Altair ~7,500 K on average (equator cooler than poles from gravity darkening).

⇒ Explains: Vega’s strongest Balmer, Altair’s stronger metal lines, Deneb’s A-type look despite being a supergiant.

Surface gravity (log g): Deneb is very low (supergiant), Vega/Altair are higher (dwarfs).

⇒ Low gravity in Deneb = narrower cores, extended Balmer wings, and stronger ionized metal lines than you’d expect for a dwarf at similar temperature.

Rotation: Altair’s v sin i is huge → rotational broadening across many lines; Vega rotates fast intrinsically but looks sharper because we see it nearly pole-on; Deneb’s spectrum is dominated more by wind + low gravity than rotation.

Luminosity & radius: Deneb is enormously luminous (hundreds of thousands L☉) with a radius of hundreds of R☉; Vega (~40 L☉, ~2.4 R☉) and Altair (~10–12 L☉, ~1.7–2 R☉) are compact by comparison.

⇒ Deneb’s wind features and low-g line morphologies vs. the neat, pressure-broadened dwarf lines in Vega/Altair.

Environments: Vega hosts a well-known debris disk (you won’t see the disk in the spectrum, but it’s part of its story). Altair doesn’t show a comparable far-IR excess. Deneb has a stellar wind and slight α Cygni-type variability, which can subtly change Hα over time.

Quick “at a glance” checklist for the spectral profiles

Deepest Balmer lines? → Vega (A0 V).

Broadened lines overall? → Altair (rapid rotation).

Balmer wings + possible Hα infill, stronger Fe II/Si II for an A-star? → Deneb (A-supergiant, wind + low gravity).

More prominent Ca II K & other metal lines vs Vega? → Altair (later A-type).

Continuum looks a bit redder than expected? → Likely Deneb (distance + interstellar reddening

Epsilon Lyrae 1 and 2

 

Epsilon Lyrae the multiple star system.
Data Credit: PIRATE robotic telescope (Clear and BVR filters).
telescope.org, Open Observatories, Open University.
Image Credit: Kurt Thrust.

"In a dull moment at the Observatory, the JPO Team fell into conversation about the famous double double star, Epsilon 1 and 2, in the constellation Lyra.No one was sure as to whether they had seen the gravitationally bound stellar system through a telescope eyepiece which resolved the target into four stars. Kurt thought that he had once achieved this with the JPO's 127mm refractor at high magnification but if he had it was so long ago that he could not be sure. We looked through the JPO's extensive archive of images but could find none relating to Epsilon Lyrae. As an afterthought, Kurt programmed the PIRATE telescope to capture an image. Clearly the large aperture PIRATE robotic telescope on Mount Teide had sufficient aperture but insufficient magnification to split the star system into four separate stars". - Joel Cairo CEO of the Jodrell Plank Observatory.

" Joel asked me to provide the following overview for the Epsilon Lyrae star system:

Epsilon Lyrae: The Double Double

Situated near the bright star Vega in the constellation Lyra, Epsilon Lyrae is among the best-known multiple star systems in the northern sky. To the unaided eye, it appears as a single faint star of about fourth magnitude, but through even a modest pair of binoculars it is revealed as a close double — two nearly equal stars separated by about 208 arcseconds. These two components are traditionally labeled ε¹ Lyrae (the western pair) and ε² Lyrae (the eastern pair).

What makes Epsilon Lyrae remarkable is that each of these stars is itself a tight binary. Thus, the system has earned the nickname the Double Double. Through a telescope of about 100 mm (4 inches) aperture under steady seeing, each component can be resolved into two stars. The separations are small:

ε¹ Lyrae (STF 2382) splits into a pair of magnitude 5.1 and 6.1 stars, separated by only 2.6 arcseconds.

ε² Lyrae (STF 2383) splits into a slightly wider pair of magnitude 5.4 and 5.5 stars, with a separation of 2.3 arcseconds.

Both pairs orbit each other over timescales of centuries, and the wider ε¹–ε² pairing is gravitationally bound, though the orbital period is measured in tens of thousands of years. The geometry of the system gives observers a striking contrast: ε¹’s stars are aligned roughly north-south, while ε²’s pair is oriented nearly east-west. This nearly orthogonal arrangement makes the system especially pleasing to amateur astronomers who succeed in splitting all four stars.

From a physical standpoint, the Epsilon Lyrae stars are main-sequence A-type stars, somewhat hotter and more massive than the Sun, shining white due to their surface temperatures of around 8,000–9,000 K. They lie at a distance of about 162 light-years (49.6 parsecs).

In observational astronomy, Epsilon Lyrae is often used as a test of both atmospheric seeing and optical resolution. Smaller telescopes may split the wide pair (ε¹ vs ε²), but only instruments of sufficient aperture and magnification under steady skies will reveal the close binaries that make the system a true Double Double". - Professor G.P.T Chat visiting astrophysicist at the Jodrell Plank Observatory. 

The Realm of Galaxies

 

The Realm of Galaxies in the Constellation Virgo. Seestar S30 402x10 sec subs in Alt-Az mode. Data captured from Suffolk in spring 2025. Image Credit: Pip Stakkert.

"The above image depicts a deep-sky view of the Realm of Galaxies in the constellation Virgo, a region that is one of the richest nearby concentrations of galaxies observable from Earth. This area is dominated by the Virgo Cluster, the central component of the larger Virgo Supercluster, of which the Local Group (containing the Milky Way and Andromeda) is a small part. The line of galaxies (running vertically centre right) is known as Markarian's Chain.

The Realm of Galaxies

The term "Realm of Galaxies," introduced by Edwin Hubble in the mid-20th century, refers specifically to the Virgo Cluster of galaxies, situated at a distance of about 54–65 million light-years from Earth.

This cluster contains more than 1,300 confirmed galaxies, with estimates of up to 2,000 members. The population includes giant ellipticals, spirals, irregular galaxies, and numerous dwarf ellipticals.

The Virgo Cluster is gravitationally bound and exerts significant dynamical influence on the motions of galaxies in the Local Supercluster.

The image above shows a wide-field survey view of the Virgo Cluster core region. Several important galaxies can be identified :

Elliptical Giants (Center-right, glowing regions)

Bright, extended objects with smooth light profiles correspond to giant elliptical galaxies such as M84 (NGC 4374) and M86 (NGC 4406).

These galaxies dominate the dense cluster core and are rich in globular clusters and hot X-ray gas.

M87 (Virgo A)

This supergiant elliptical galaxy is among the most massive galaxies in the local universe, containing a supermassive black hole of ~6.5 billion solar masses, famously imaged by the Event Horizon Telescope.

Spiral Galaxies

Edge-on streak-like structures visible across the field correspond to spirals, such as NGC 4388 or NGC 4438, which are undergoing gravitational interactions and ram-pressure stripping due to the intracluster medium.

Intracluster Medium & Dwarfs

The faint reddish diffuse glow represents background stars, dust, and possibly intracluster light produced by stripped stars from past galactic interactions.

The field is peppered with dwarf ellipticals and irregular galaxies, which are abundant in the cluster but often difficult to discern individually without deep surveys.

Scientific Importance

The Virgo Cluster serves as a laboratory for galaxy evolution, as interactions and environmental effects (tidal stripping, ram-pressure stripping, and mergers) can be directly studied.

It provides an anchor point for the extragalactic distance scale, with Cepheids and surface brightness fluctuations used to refine measurements of the Hubble constant.

The cluster's gravitational well shapes the Local Velocity Field, influencing the peculiar motions of nearby galaxies, including the Milky Way".- Professor G.P.T Chat visiting astrophycist at the JPO.

Comet K1 (ATLAS) in the constellation Hercules

 

Comet K1 (ATLAS) powering through Hercules.
Seestar S30 image credit: Kurt Thrust

" This comet is not to be confused with interstellar Comet 31 (ATLAS) which is currently in the constellation Libra. Comet K1 is on a parabolic orbit around the Sun and is a visitor from the Oort Cloud. Comet 31 is on a hyperbolic course from well beyond the Oort Cloud and the Solar System". - Joel Cairo CEO of the JPO.

"Comet C/2025 K1 (ATLAS) is a newcomer from the farthest reaches of our solar system, making its very first visit close to the Sun. Discovered in late May 2025, it's shooting in on a highly eccentric, tilted orbit, taking it closer to the Sun than Mercury ever gets.

In August, it's still faint—only visible through strong amateur telescopes. But by early October, as it dives toward the Sun, it might brighten enough to be seen with binoculars or small telescopes.

The big question: will it survive the solar heat? With a small nucleus and unusual orbit, it's quite possible the comet may break apart as it zips past the Sun. If it holds together, late November might offer another viewing opportunity when it's closer to Earth but dimmer.

We can think about this comet's “age” in two ways:

Formation Age

• Like most comets, K1 (ATLAS) formed about 4.5 billion years ago, during the birth of the solar system.

• It’s made of the same primordial ices and dust that went into forming planets, but it was ejected outward by the giant planets’ gravity early in solar system history.

Dynamical Age (Time in the Oort Cloud)

• It’s considered a dynamically new comet, meaning this is likely its first ever passage into the inner solar system.

• That implies it has spent essentially its entire existence (billions of years) stored in the cold, dark Oort Cloud, preserved in nearly pristine condition.

Sad to think that its first journey to the centre of the Solar System may be its last". -  Professor G.P.T Chat visiting astrophysicist  at the JPO.

34 Cygni an unusual star in Cygnus the Swan

 

34 Cygni aka P Cygni in the constellation Cygnus.
PIRATE robotic telescope with BVR filters, Mount Teide, Teneriffe.
Data credit: telescope.org. Open Observatories, Open University.
Image Credit: Pip Stakkert at the JPO.

Annotated Image credit Astrometry .net.

Why is 34 Cygni unusual:

• 34 Cygni is unusual because it is not a single star, but a symbiotic binary system. That means it’s made of two very different stars orbiting each other:
• A cool red giant, which has a very extended, bloated atmosphere.
• A hot companion (likely a white dwarf), which shines with intense ultraviolet light.
• The giant loses gas, and the hot companion excites and ionizes this gas, producing a glowing nebula-like envelope around the system. Because of this, 34 Cygni shows features of both a cool star and a hot star mixed together in its spectrum.

34 Cygni is classified as a symbiotic star of type S. Its peculiarities arise from the interaction between its components:

Binary Composition

• M-type red giant donor: contributes strong molecular bands (TiO, VO, CN), characteristic of a cool photosphere (T_eff ≈ 3200–3600 K).
• Hot compact companion (white dwarf): provides ionizing radiation (T_eff > 50,000 K) that excites emission lines in the red giant’s wind.

Spectral Profile Features

• Cool star absorption spectrum:
• Broad molecular bands (TiO, VO) dominating the optical.
• Strong continuum slope toward the red.
• Superposed emission spectrum:
• Hydrogen Balmer lines (Hα, Hβ, Hγ, etc.) in strong emission.
• Helium lines (He I, sometimes He II) from higher excitation regions.
• Forbidden lines ([O III] 5007 Å, [Ne III], [N II]) from the ionized nebular gas around the binary.
• Occasionally, Raman-scattered O VI lines around 6825 Å and 7082 Å, which are diagnostic of symbiotic systems.

Why Kurt Thrust and his team want to capture 34 Cygni's spectrum as a 'try out' for the new diffraction grating affixed to the Seestar S30.

• Most stars show either an absorption spectrum (normal stars) or an emission-line spectrum (nebulae, hot stars with winds).
• 34 Cygni shows a hybrid spectrum, with both molecular absorption and nebular emission simultaneously.
• Its spectral variability over time reflects mass transfer episodes, changes in the red giant wind, and accretion activity on the white dwarf.
• The JPO team has not captured spectral data for this star before and Kurt loves a challenge.

 Summary:

• 34 Cygni is unusual because it is a symbiotic binary, displaying both red giant absorption bands and nebular emission lines. In a low-resolution spectrum you’d see molecular TiO absorption from the cool star, plus bright emission lines of hydrogen, helium, and forbidden ions, giving it a “mixed identity” unlike normal stars.
• Prof  G.P.T Chat has theoretically constructed the following spectral profile simulation for a binary star system like 34  Cygni. We shall compare the theoretical profile with the actual profile captured at the JPO."

- Joel Cairo CEO of the Jodrell Plank Observatory.

Stop press: 

• The clouds cleared and the Seestar S30 plus diffraction grating captured zero and first order spectra for 34 Cygni together with a calibration set for Vega. Yet to see if we can create meaningful profiles from the data using BASS software. This will be the subject of a future post. Jolene, has used the feedback from the performance of the prototype, to make some minor modifications to the design of the grating holder, in order to reduce the overall length of spectra on the Seestar S30's sensor.

"Astronomy is temporarily on hold at the JPO as its sponsor, Anita Roberts will be 75 years old this week and she is the JPO Team's favourite star. There will be much jollity and partying in the JPO Visitor Centre this week!! Give Comet the Cat another 'goldfish'! " - Kurt Thrust current Director of the Jodrell Plank Observatory.

Aurora October 2024 - visible to the naked eye over the Jodrell Plank Observatory.

 

Aurora Borealis -visible from Latitude 52 degrees North
-Taken with a handheld Canon 600d DSLR in the early hours, October 2024.
Image Credit: Kurt Thrust.

"What causes the aurora ?

• The aurora borealis (also called the northern lights) happens when tiny charged particles from the Sun — mostly electrons and protons — reach Earth.

• The solar wind: The Sun constantly releases a stream of these charged particles, called the solar wind.

• Earth’s magnetic field: Our planet has a magnetic field, shaped a bit like a bar magnet, with field lines curving out from the north and south poles. This field usually shields us from most of the solar wind.

• Particles guided to the poles: Some solar wind particles get caught in Earth’s magnetic field and are funneled down toward the poles along those field lines.

• Collision with the atmosphere: When these particles collide with gases high up in the atmosphere (mostly oxygen and nitrogen), the gases become “excited.” As they calm down, they release light — that glowing curtain of green, red, or purple we call the aurora.

• So, the aurora is basically the Earth’s atmosphere lighting up because of a storm of solar particles guided in by the magnetic field.

Why is it usually only near the Earth's North and South poles?

• The Earth’s magnetic field directs incoming solar particles toward the polar regions. This creates a kind of “auroral oval” — a ring-shaped zone around the magnetic poles where auroras usually appear.

• Most of the time, this oval sits well within the Arctic Circle (for the north), meaning the northern lights are a common sight in places like Norway, Sweden, Finland, Canada, and Alaska.

• Why only rarely in the UK at Latitude 52°N?

• The UK is much farther south than the usual auroral oval. For people at that latitude to see the aurora, something special must happen:

• Solar storms: Occasionally, the Sun produces a particularly powerful burst of particles, such as from a coronal mass ejection (CME).

• Solar storms can cause an expansion of the auroral oval: When such a strong storm reaches Earth, it pushes the auroral oval outward, expanding it farther from the poles. During big storms, it can stretch far enough south that the lights become visible from northern England or even further south.

• That’s why the aurora in the UK is rare — it takes unusually strong solar activity to push the lights down that far.

The Solar Disc captured in white light from the JPO in Summer 2024.
The Sun's Photosphere shows lots of dynamic activity with, sunspots and faculae on display. Image Credit: Kurt Thrust.

Imagine the Sun as a great ball of energy, constantly sending out streams of tiny charged particles, like sparks from a bonfire. This stream is called the solar wind. Most of the time, Earth’s magnetic field shields us from the particles, deflecting them away. But near the north and south poles, the field acts like a funnel, guiding some of them down into our atmosphere.

When the particles finally reach the thin air high above Earth, they crash into atoms of oxygen and nitrogen. Those atoms get “excited” for a moment, then calm down by releasing energy as light. That light is what we see as the aurora.

The color depends on which gas is struck and at what height. Oxygen high up glows a soft red, lower down it shines bright green — the most common color. Nitrogen adds streaks of purple or pink. Together, they paint the sky like nature’s neon sign.

Energised atmospheric Oxygen and Nitrogen atoms releasing photons at differing wavelengths creating the red, green, purple and pink auroral colours.
Credit: Pip Stakkert at the JPO.

The shape of the aurora — those tall shimmering curtains — comes from Earth’s magnetic field lines. Charged particles flow along those invisible lines, lighting them up like glowing threads. And because the solar wind is gusty and Earth’s magnetic field quivers under the strain, the aurora doesn’t sit still. It flickers, ripples, and waves, as though the sky itself were alive and dancing.

The Aurora Borealis dancing over the JPO
- Credit: Anita and George Roberts

Usually, this show stays tucked safely within the Arctic Circle, because that’s where the magnetic funnel is strongest. But when the Sun sends a particularly powerful blast — a storm of particles — the glowing oval around the pole expands. On rare nights, it stretches far enough south that people in the United Kingdom, even at latitude 52° north, can look up and catch the northern lights painting their skies". Professor G.P.T Chat visiting astrophysicist at the Jodrell Plank Observatory.

Low resolution Stellar Spectroscopy and the Seestar S30

 

Two 3d printed grating holders with iron dust doped epoxy resin.
(The Seestar S30 uses magnetism to affix external filters).
- Credit: Jolene McSquint-Fleming.

The SolidCad generated grating holder model for 3d printing. 
- Credit: Jolene McSquint-Fleming

The 50 lines/mm transmission grating
(sourced 'off the shelf' from China via the Internet for less than £10)
sitting on a laptop next to a 3d printed grating holder.
- Credit: Jolene McSquint-Fleming 

Ken Harrison's Excel Spreadsheet (SimSpec V4_4a)
- Credit K.M. Harrison

The completed Seestar S30 compatible objective lens mounted
50 lines/mm. transmission grating glued to the
3d printed iron dust doped holder
awaiting attachment (upper face down) and
magnetically to the Seestar smart telescope. 
Credit: Jolene McSquint-Fleming
(distantly related by marriage to Bob Fleming).

"Our ever resourceful engineer at the JPO, Jolene Mc Squint-Fleming, has been beavering away in the JPO's 'Clean-room' to make a Mark 4 prototype objective lens mounted slitless low resolution transmission grating spectrometer for the Observatory's Seestar S30 smart telescope. Previous prototypes have been partially successful in that they delivered stellar spectra using an 80 lines/mm grating. Unfortunately the star (zero order) and its first order spectrum could not be contained within the longest side of the Seestar's deepsky imaging sensor. This is not essential but it does aid spectrum calibration by having a zero point together with the first order spectrum, blue through red, in one field of vision. The JPO team recommend, to anyone wishing to develop an interest in stellar spectroscopy, Ken Harrison's excellent book 'Astronomical Spectroscopy for Amateurs' (The Patrick Moore Practical Astronomy Series) Paperback – 9 Feb. 2011

by Ken M. Harrison (Author). 

The next to last of the above images shows Mr Harrison's Excel spreadsheet which given the application inputs of a telescope, camera and diffraction grating calculates a number of useful spectral related features and confirms whether or not the zero to red first order spectrum will fit on the camera sensor. 

The night sky may be appreciated in many ways. For some, just looking up at the  beauty of the stars and planets is enough but for others finding out how the Universe works is a strong driving force. 

In the distant past, astronomers and scientists believed that all humanity could ever know about stars were their position in the sky, their colour and their apparent and relative brightness. It is no exaggeration to say that the science and practice of spectroscopy changed this severely limited expectation and has provided not only comprehensive information about galaxies, stars, and other cosmic matter but also about the space between them. It might be said that 'Spectroscopy' provided both the foundation and prime tool for  the development of the science of  'Astrophysics'.

The early days of 'Spectroscopy' 

The “fathers” of astronomical spectroscopy are generally considered to be:

Joseph von Fraunhofer (1787–1826)

He built some of the best early spectroscopes and discovered the dark absorption lines in the solar spectrum (now called Fraunhofer lines) around 1814.

His work laid the foundation for using spectra to study the Sun and stars.

Gustav Kirchhoff (1824–1887) & Robert Bunsen (1811–1899)

In the 1850s–1860s, they showed that each chemical element produces a unique spectral “fingerprint” of emission and absorption lines.

They were the first to identify chemical elements in the Sun and stars using spectroscopy, proving that the stars are made of the same elements found on Earth.

Together, Fraunhofer, Kirchhoff, and Bunsen are usually credited as the founders of astronomical spectroscopy.

So what are the Jodrell Plank Observatory goals for the use of spectroscopy and what tools can we use to achieve them?

Kurt and his team have already designed and made a 500 lines/mm spectrometer and have captured and processed stellar spectra for a number of stars using the JPO 127mm Meade refractor. The results have been quite encouraging but capturing and processing data using this telescope-spectrometer  is very resource and time hungry. As a consequence the number of stars for which spectra have been obtained from the JPO is quite small. 

Comparative Spectral Profiles for the Stars Altair, Alshain and Tarazed captured with the 500 lines/mm spectrometer attached to the JPO's 127mm Meade refractor. (three we did earlier)

500 lines/mm. Spectrometer
utilising the QHY5-11 mono camera.
Credit: J.McS-F and Kurt Thrust.

The team would like to do more spectroscopy combined with standard imaging using kit that can be quickly and easily deployed. If the Seestar S30 can be converted for spectroscopy by the addition of an external objective mounted transmission grating, quite wide star-fields might be first imaged and then have selected star spectra captured. Hopefully, if we can get this bit of kit to work we will be able to work faster and smarter. 

A Seestar objective lens spectrometer using a 50 lines/mm set up will  provide lower resolution spectra than the 500 lines/mm spectrometer attached to the eyepiece end of 127mm refractor but working smarter will result in the spectral investigation of more stars! 

Both spectrometer set ups, however, work at  'low resolution'. Much more expensive equipment is required to undertake 'high resolution' spectral work which puts such activity outside JPO budgetary constraints.

What, in general terms, is the difference between the spectrum of a star and a spectral profile?

A stellar spectrum is the diffracted light from a star displaced  and spread out by wavelength (from blue to red)  in a number of bands (orders) which decrease in brightness as the orders  increase (displacement from the star increase). The spectrum is the raw image captured by the camera and visible to the eye. You will notice that spectra are created on either side of a star by the grating. More expensive gratings direct more light to one side than the other. These gratings are referred to as being 'blazed'. It is usual to work with the right hand first order spectrum when creating the spectral profile.

The spectral profile is a graph of the intensity of the spectrum's light (photon counts by the camera sensor) (plotted on the Y axis) plotted against wavelength ( x axis). The profile is derived from the spectrum which requires careful calibration and processing. At the JPO we have traditionally used bright stars such as Vega in the constellation Libra, which have strong Hydrogen absorption lines, for calibration of target stars under investigation. For processing the spectral profile we use the excellent software BASS Project 1.9.9.

 https://britastro.org/2017/guide-to-processing-spectra-using-the-bass-software

The useful information relating to a star is derived from the  spectral profile. A profile may be best obtained from a black and white spectrum and for this reason our 500 lines/mm. spectrometer uses a mono QHY5-11 camera.   The Seestar S30 by default captures colour datas.

What "low resolution" in stellar spectroscopy means

A low-resolution spectrum is one where fine details in the spectrum are blurred together. Instead of seeing very sharp, narrow absorption lines, you mostly see broad dips and bumps in the rainbow of starlight. So, you don’t get fine chemical fingerprints, but you do still capture the overall shape and large spectral features.

What we can learn from low resolution spectral profiles:

• Stellar temperature (the star’s “color” in detail)

The overall slope of the spectrum tells us how hot the star’s surface is.

Hot stars (like O and B types) peak in the blue/ultraviolet, while cool stars (K and M types) peak in the red/infrared.

Even at low resolution, the shape of the spectrum across visible light gives a good estimate of the star’s effective temperature.

• Spectral type and classification

Big molecular bands (e.g., TiO in cool M-type stars) or hydrogen Balmer lines (prominent in A-type stars) are broad enough to show up even in low resolution.

That lets astronomers assign a star to a spectral class (O, B, A, F, G, K, M).

• Surface gravity (giants vs dwarfs)

The strength and width of certain broad features are sensitive to whether a star has high gravity (main sequence dwarf) or low gravity (giant or supergiant).

For instance, pressure broadening is stronger in dwarfs, so hydrogen or calcium features look different.

• Metallicity in broad strokes

While you can’t measure detailed abundances, the overall strength of metal absorption blends can suggest whether a star is “metal-poor” (like in old halo stars) or “metal-rich” (like stars in the disk).

Extremely metal-poor stars stand out because their spectra look much smoother.

• Reddening and interstellar dust

Comparing the expected spectral shape (from the star’s type) to the observed shape tells how much starlight has been reddened by dust.

This helps estimate extinction and distance effects.

• Radial velocity (roughly, if the resolution is not too low)

At very low resolution, Doppler shifts are hard to measure precisely.

But with moderate low-res data (say R ~ 1000), you can still detect bulk shifts of broad features to see if a star is moving toward or away from us at tens of km/s accuracy.

• Special features or stellar activity

Strong emission lines (like H-alpha) show up even at low resolution.

This can reveal things like chromospheric activity, accretion (in young stars), or stellar winds.

What you cannot do with low resolution spectral profiles:

You can’t measure fine chemical abundances (like “this star has 0.2 times the Sun’s iron content”).

You can’t detect narrow line profiles that reveal rotation, turbulence, or precise radial velocities.

You can’t see isotopic ratios or subtle line blends.

Why low resolution spectroscopy is still powerful:

Even though it blurs the details, low-resolution spectroscopy is fast and efficient. Large surveys (like SDSS or LAMOST) have gathered millions of low-res spectra, which let us classify stars, map stellar populations across the Milky Way, and study galactic evolution.

So, in summary: 

Low-resolution spectroscopy can reliably tell you a star’s temperature, general spectral type, luminosity class, approximate metallicity, effects of dust, and presence of strong emission features. It gives a broad but still very physical picture of the star, even if the fine chemical “fingerprints” are lost.

 We are now ready to test the prototype and await a clear night to undertake first light for this home-made bit of kit". - Karl Segin outreach coordinator at the Jodrell Plank Observatory.