All posts by A. Anfuso

Hunting down Planet Nine

It has been nearly a decade since researches at California Institute of Technology (Caltech) noticed irregularities in the orbit of some extreme trans-Neptunian objects (ETNOs) -bodies orbiting the Sun in the outermost region of our Solar System, well beyond Neptune. What was causing the strange behaviour? Have we cracked the mystery?

When Caltech astronomers Konstantin Batygin and Mike Brown first published their research showing evidence of a giant planet in the outer Solar System in 2015, they certainly made the headlines. The announcement came nearly 170 years after the discovery of Neptune, the latest planet to be found orbiting the Sun.

The two researchers had used detailed mathematical modelling and complex computer simulations to explain the odd orbital behaviour of some dwarf planets and other smaller icy bodies in the Kuiper Belt, the outskirts of the Solar System. The explanation, they proposed, was the gravitational pull of an elusive planet, which they dubbed “Planet Nine”.

Read also: The Mysteries of Outer Space.

Other possible explanations were considered, too. In fact, the debate in the scientific community about whether Planet Nine exists is still ongoing. The most sceptical astronomers tend to minimise, calling out some “ghosts” or biases in the data. A more moderate wing believes we should be looking for a primordial black hole instead, or perhaps some new physics. The enthusiast astronomer, on the other hand, is still out there looking for Planet Nine.

But what is it that they’re looking for exactly? According to scientists, the mysterious world has a mass about 5 to 10 times that of Earth, and it could look anything from a rocky super-Earth to a gaseous mini-Neptune, perhaps sharing characteristics with Uranus or Neptune.

Artist impression – Planet Nine

One thing we know for sure is that spotting a celestial body in the vastness of space is not exactly a straightforward task. Besides, Planet Nine is believed to be orbiting the Sun in a highly elongated orbit far beyond Pluto, and considering its elusive nature, it may well be at the far edge of its enormous orbit, meaning it would move quite slow (relative to us) and reflect little to no sunlight.

While this most certainly adds difficulty to the quest, astronomers are confident that modern telescopes around the world are powerful enough to at least spot the elusive world, thus the hunt continues. New data is being acquired and paired or compared with old data: in fact, the truth may hide somewhere in there.

Will we find Planet Nine? And if we do find it, will tradition be followed, and the planet be named after a mythological roman god?*

Personally, I would be delighted to know there really is a Planet Nine lurking in the outskirt of the Solar System. This would be a sensational discovery, with a lot of new science to come! At the same time, I would be even more thrilled if we finally found evidence for a primordial black hole, and right in our backyard!

Spotting one, of course, would be way more problematic.


* Konstantin Batygin and Mike Brown dubbed their predicted object “Planet Nine,” and the name has been used ever since (along “Planet X”). However, it is the person who actually discovers the planet to get the right to name it (pending approval from the International Astronomical Union).

The long wait is over…

Dear friends of The Lonely Photon,

I’m sure by this time you will have noticed the marvellous colours all around, the slightly cooler temperatures and progressively longer, darker nights. And I’m sure you know what this means: yes, Autumn is back!

Apart from being my favourite season, this is also the best time of the year for astronomers and astrophotographers as the sky plumes with magnificent jewels and breath-taking sights.

Some of the largest galaxies (including Andromeda and Triangulum) are climbing up quickly, the planets keep on dancing with the Moon and other objects while vibrant nebulas take over the sky again.

And speaking about nebulas, I want to introduce you to my latest projects and possibly my best works so far.

The North America and Pelican nebulas

This is a large emission nebula located some 2,600 light years from Earth, in the constellation Cygnus.

The left part of the nebula is informally known as the North America Nebula, due to its resemblance in shape to the continent. The region equivalent to the area between Mexico and Central America is known as the Cygnus Wall, the area of the nebula with the highest star formation rate.

More info here: North America and Pelican

The Cygnus Loop

The Cygnus Loop is what astronomers call a large supernova remnant (SNR) -the leftovers of a massive stellar explosion that occurred 15,000 to 20,000 years ago. As the blast was enormous, the gas and dust that form this nebula are still expanding at incredible speed.

More info here: Cygnus Loop

The Elephant Trunk nebula

The Elephant Trunk  is a “globule”, or a region of interstellar dust and gas, that takes its peculiar name from the resemblance to the proboscis of an elephant. This is part of a large but faint emission nebula (IC 1396) that lies around 2,400 light years from Earth, in the constellation Cepheus

More info here: Elephant Trunk

I hope you enjoyed the view, stay tuned for more.

Clear skies!

IC 1101 – The supergiant galaxy

Lurking around at the centre of the Abell 2029 galaxy cluster, in the constellation Virgo, is IC 1101 -a monster galaxy that makes our Milky Way look like a grain of sand. The galaxy was discovered on 19 June 1790 by British astronomer William Herschel and is still one of the largest galaxies we know of.

Of course, in 1790 these objects were still believed to be nebulas within our own galaxy. The discovery of other galaxies outside the outskirts of the Milky Way only came in 1920, when Edwin Hubble demonstrated that Andromeda was a body outside the Milky Way by measuring Cepheid variable stars, changing our concept of the universe forever.

It soon became clear that there are countless other galaxies out there. And among these, IC 1101 is one of the most interesting. Classified as a supergiant elliptical galaxy, IC 1101 boasts a diameter of about 400,000 to 550,000 light years, which makes it one of the largest galaxies ever found. In fact, this has been for years the largest-known galaxy in the universe!*

The galaxy spans around 4 million light years across and has an extensive, diffuse halo that stretches up to 2 million light years from the core. The enormous size of IC 1101 leads most astronomer to believe that the galaxy formed from the merger of several smaller galaxies; a hypothesis supported by the scarcity of interstellar matter, which results in a low star-formation rate.

Read about the Andromeda Galaxy: Andromeda.

IC 1101’s distance from Earth is still unclear as different calculation methods across different wavelengths give different results. Initial estimations in 1980 assessed the distance from Earth at approximately 850 million light-years but more recent calculations suggest a distance of 1.2 billion light-years.

At such distance, the number of stars in the galaxy can’t be estimated accurately but astronomers believe that IC 1101 contains around 100 trillion stars, which could contribute to the galaxy’s astounding luminosity. However, the lack of interstellar matter indicates a low star-forming rate, leaving the galaxy with mostly old, metal-rich stars that give IC 1101 its distinctive yellow hue.

The galaxy’s core is one of the largest ever observed, if not the largest, with an apparent size of 2.77 arcseconds or 13,700 light years. Several radio burst have been observed from there, suggesting IC 1101, like most large galaxies, has a supermassive black hole at his core.

Hubble Space Telescope – Credit: Wikipedia

Read more about black holes: Black holes: the dark side of gravity.

The black hole’s mass is uncertain but ranges between 50 to 70 billion or 40 to 100 solar masses, depending on the calculation method used. In both cases, this is one of the largest and most massive black holes ever detected.


* After being the largest known galaxy for decades, IC 1101’s record was broken in February 2022, with the discovery of a gigantic radio galaxy dubbed Alcyoneus. Alcyoneus is located in the constellation of Lynx, about 3.5 Billion Light Years away, and spans approximately 16 Million Light Years across.

UY Scuti – Meet a hypergiant star

Do you ever wonder about the size of the universe? Looking up at the sky, at all those stars, gives a pretty good idea, but can our brain even process how vast it really is?

Take the Sun for example. It is massive compared to our home planet, to the point that “it would take 1.3 million Earths to fill the Sun’s volume”, according to NASA. And yet in terms of size and volume the Sun is just a regular star in the cosmos.

Read more about the Sun here: The Sun, our host star.

Especially if we consider that there are countless stars in the universe (with the current technology we can only take a good guess), and around 100 billion in the Milky Way alone, according to NASA’s latest estimations.

The Sun with a large prominence and the Earth in scale – Credit: A. Anfuso ®

Among these is UY Scuti, a bright red hypergiant star located near the centre of our galaxy, approx. 9,500 light years away from us, in the small but rich constellation Scutum.

Despite being very luminous, it has a relatively low magnitude oscillating between 8.3 and 10.5 as seen from Earth, mainly due to its distance and its position in the Zone of Avoidance (ZOA), an area of the sky obscured by the Milky Way.

The fluctuation in UY Scuti’s magnitude indicates that UY Scuti is as a semiregular variable star. First catalogued in 1860 by astronomers at the Bonn Observatory, in Germany, the following observations in fact showed an approximate pulsation period of 740 days.

Rather than its magnitude though, it’s the size of UY Scuti that caught the eye of astronomers. It has nearly five billion times the volume of the Sun (yes, it means that around 5 billion Suns would fit within it!) and latest assessments suggest the star has a radius around 1,700 times larger than that our star, which makes UY Scuti the second largest star by radius, behind Stephenson 2-18 (2,150 solar radii).

Credit: Wikipedia

At the time of writing, astronomers have not discovered any companion stars or planets orbiting UY Scuti although it is widely believed that the radiations emitted by the enormous star would make life as we know it impossible, even if there were indeed some tenacious planets in its orbit.

Besides, UY Scuti is believed to be nearing the end of its cycle. Stars typically spend 90% of their life on main sequence, converting hydrogen into helium in their core, and according to current stellar evolution models, UY Scuti has already completed its main sequence phase and has started fusing helium in its core. This means the star is somewhere within the last 10% of its life cycle.

Once it runs out of helium, it will start fusing heavy elements. This will disrupt the balance the star needs to sustain itself against gravity, causing a gravitational collapse and ending into a spectacular, powerful supernova.

According to some models, the core left behind by the explosion would then become a black hole or a neutron star.

UY Scuti – Credit: NASA

Observing UY Scuti is quite easy. Despite being located in the Zone of Avoidance, in fact, the star is so large and bright that can be observed from Earth, even with amateur telescopes.

It is located just northeast of the Eagle Nebula and can be seen even with a pair of binoculars or a small telescope.

While UY Scuti’s significant size is perhaps not enough for understanding how big the universe is, it is definitely helpful to put things into perspective and to realise how small we are in the scale of the universe.

After all, “we are just a slightly advanced breed of monkeys on a minor planet orbiting an average star” as Stephen Hawking once said.

As bold as it sounds, it’s an undisputable truth.

Lunar imaging

Peering at the Moon through a telescope or a pair of binoculars is an incredible experience. I will never forget the first time I pointed my scope at our natural satellite: as I approached the eyepiece with my eye, I became speechless, and my jaws slowly dropped…it was love at first sight!

I soon became addicted as I went on for months observing the Moon, tracking its craters, valleys, maria, and all of its beautiful features. Until one day that wasn’t enough anymore: I wanted some cool pictures to show to my friends and family, and that’s when my astrophotography journey began.

Read my article about the Moon by following this link: The Moon.

For many like me, in fact, Lunar imaging was the first dive into astrophotography. This is because it is quite straightforward, it requires simple gear, and can be done literally from everywhere, including heavily light-polluted cities. There are a few things that you need to know about the Moon, however.

First, from Earth we only see one side of the Moon. This is due to the fact that the time the Moon takes to complete a spin on its axis equals the time to complete an orbit around Earth, which always leaves the same side of the Moon facing us. This phenomena is called “tidal locking“ and it’s more common than you’d think in the universe.

Another important aspect to consider is that our satellite is observed in phases: depending on where it is positioned compared to the Sun and Earth, we see a different portion of its surface lit.

While pictures of a Full Moon are quite suggestive, the best time to image the Moon is actually when around half or less of the disc is lit. This is because the contrast increases, and more details and features are revealed.

Now let’s see in detail the technique I use to image the Moon, using only free software. For clarity, I divided the process in three phases.

Phase 1 – Capturing

In astrophotography this is the most crucial step of the process, for obvious reasons: there’s little you can do in post-processing to fix a dull image, so focus is paramount and must be spot on.

Take all the time you need to reach perfect focus, or anywhere near that anyway, and your efforts will be rewarded. Using a Bahtinov mask (focus mask) on a bright star is usually the more efficient way to do that.

The second vital aspect is “seeing” – the effect of fast-changing, turbulent airflows in Earth’s atmosphere that can make an image look blurred or distorted. Sadly, there isn’t much you can do about this apart from sitting tight with you finger ready to hit the record button as soon as the live-view image on your screen gets clear.

Imaging the Moon in infrared (IR) using an IR-pass filter and a mono camera helps you reduce the effects of bad seeing. Also, recording more than one video obviously increases your chances to get a good image out of your session, after all it’s called “lucky imaging” for a reason.

For planetary and lunar/solar photography the most widely used software is SharpCap or FireCapture. Both are free, work great and have pretty much the same functionalities. Personally, I started with SharpCap and never changed thereafter.

I record my videos in *SER format, which is more complete and easier to work on than *AVI or other formats. I typically keep gain and exposure low (but not too low) to avoid “burning” the image. Remember: you can increase exposure and brightness in post-processing, but you can’t fix an overexposed image!

Depending on the atmospheric conditions and camera performance, I generally capture various videos of several minutes each, to get somewhere between 10,000 and 20,000 frames. This should guarantee good results.

Note: Whether or not you can fit the Moon in your field of view depends on your gear. Using a telescope with a long focal length or a camera with a small resolution (or both), you may get only a portion of the Moon in your field of view. Don’t worry though: luckily there’s a way to get around this, thanks to a free Microsoft software called ICE (Image Composite Editor). All you have to do is capture some more videos, one for each area of the Moon and continue as usual (more on this below).

Phase 2 – Stacking

Once done with the capturing phase, I load the videos one by one into AutoStakkert!3, a free stacking software that analyses the video’s individual frames, giving as a result a diagram with the overall quality of the video.

Based on this graph, I choose the percentage of total frames that I want to stack (usually somewhere between 5% and 20%). The software then chooses the single best frame (the reference frame) to which all other frames are aligned a stacked upon.

When the job of AutoStakkert!3 is over, the result is a single final image made of the video’s best frames. Generally, these images look a little blurred and certainly nowhere near the amazing picture you were expecting; nothing to worry about, this is where post-processing works its magic.

Note: If you weren’t able to fit the Moon in your field of view and you had to take several panels, all you need to do now is repeat this process for each video you took. You’ll be then left with several stacked images that you can load into ICE, which will stitch them together for you using its advanced AI and will give you a final image made of all the individual panels. Look at the photo gallery below to get a sense of the process.

Phase 3 – Post-processing

When it comes to Lunar imaging, I do most of the post-processing in GIMP, a free software that looks a lot like PhotoShop, but first I use Registax and its wavelets functionality to sharpen the freshly-stacked image and bring out as many details as possible. Watch out this step though, it is very easy to get carried away and oversharp an image!

Once done, I load the sharpened image in GIMP and crop it to leave out any stacking artefacts and to position the Moon exactly at the centre of the image. Then I adjust the exposure and add some contrast before I play gently with shadows, mid-tones, and highlights to bring out some more subtle features.

If you used a colour camera, you may also want to balance and align the RGB. I usually adjust the colour curves to get a grey-metal surface.

Now your image of the Moon is finally ready to be shared on social media with friends and family!

I hope this guide will get you started into lunar imaging as a first step into astrophotography. Bear in mind that there are many other techniques out there, my advice is to try over and over, being creative and experimenting with settings and software until you find your own method.

To download the software mentioned in this guide, go to the “Downloads” section on this blog and follow the links.


Lunar Gallery


Sagittarius A* – Our backyard’s black hole

There’s nothing in the whole universe as mysterious and fascinating as black holes. First theorised by John Michell in 1783, and also predicted by Einstein’s Theory of General Relativity in 1916, these dense, dark and elusive objects have been researched and studied for decades, capturing the interest of some of the world’s greatest physicists.

Among these, are three laureates who shared a Nobel Prize in physics in 2020 for their studies on black holes. Roger Penrose, one of the most brilliant minds of our times, demonstrated mathematically that black holes are indeed a direct consequence of the Theory of General Relativity, whereas Reinhard Genzel and Andrea Ghez predicted the existence of the supermassive black hole at the centre of the Milky Way and calculated its mass with fair precision: about 4.3 million solar masses!

Now, the idea of having such a supermassive black hole right at the core of our galaxy could be for many a cause of nightmares but in reality, there is nothing to fear. In fact, this is very common in the universe: it is estimated that there is a supermassive black hole in the centre of virtually every large galaxy.

Do you want to know more about black holes? Read my article: Black Holes: The dark side of gravity.

The supermassive black hole at the core of the Milky Way is called Sagittarius A* (abbreviated as Sgr A* and pronounced “Sagittarius A star”) and is located near the border of the constellations Sagittarius and Scorpius; it has a diameter of around 23.5 million km (14.6 million miles), and it is mostly dormant as it only occasionally feeds on nearby objects.

In May 2022, Sgr A* has made the headlines after its first-ever picture was produced and released to the public by the Event Horizon Telescope (“EHT”), a combination of eight large, ground-based telescopes that had already produced the first image ever of black hole in 2019 (in that case it was the black hole at the core of the Galaxy M87).

First ever image of Sagittarius A*

But how did they manage to achieve this? Obviously, imaging a black hole is a very complex business: while these objects have huge densities, in fact, they are very tiny regions of space. Besides, to observe Sgr A* one must look into the centre of the Galaxy through thick lines of dust, so the best options for observing the Galactic centre are in radio waves and in infrared light.

That is why the EHT used a technique known as Very Long Baseline Interferometry, which allowed astronomers to combine data from eight radio telescopes across the world as though they were one large telescope. Owing to this configuration, the EHT’s maximum baseline — the equivalent to a telescope’s aperture — for observing Sagittarius A* was 10,700 km (6,650 miles) across, effectively making the EHT the largest telescope on Earth!

The Event Horizon Telescope

Since the observation of Sgr A* and M87 were made, three more telescopes have been added to the network, but is it enough to get sharper images or even capture farther away black holes? After all, Sgr A* and M87 were the EHT’s top two targets especially because of their relatively large angular size in the sky whereas supermassive black holes in other galaxies appear far smaller from our viewpoint.

For higher resolution and more imaging power the EHT would need to widen its aperture even further. But how to achieve that given Earth’s limited size? Well, one solution would be to have a space-based addition to the EHT, which would significantly increase the overall angular resolution. How cool would that be?

Black holes: the dark side of gravity

When Galileo Galilei first pointed his homemade telescope toward the sky in 1610, he couldn’t have possibly imagined that he was about to change astronomy forever. His discovery of Jupiter’s moons in particular had two major effects: it provided compelling evidence for the Copernican theory, and it recognised the use of the telescope as a key element in unravelling the mysteries of the universe.

In the centuries following Galileo’s discovery we have built larger and ever-more powerful telescopes, some of which are conveniently placed in space, and have come to map the cosmos with a fair degree of precision. And although there are plenty of things that we still don’t know about the universe, one thing we can be absolutely certain of is that it is an extremely intriguing place.

A place crammed with beautiful galaxies, colourful nebulas and hot stars that are often orbited by planets, which in turn are revolved by rings and moons. A home to fast-spinning pulsars, ultra-compact neutron stars, wandering comets, icy asteroids, and countless other treasures.

But hidden among these jewels is a swarm of elusive, almost invisible objects: black holes, the most mysterious and fascinating objects that we know of, certainly the most feared. After all science fiction has frequently depicted them as evil monsters wandering in the universe vacuuming everything they encounter. But is that really what black holes are?

Well, not exactly. Technically, a black hole is a region in space where a massive amount of matter is compressed into a very tiny area, and its gravitational pull is so strong that nothing, not even light, can escape! Black holes, however, do not roam through the universe, randomly swallowing things. Just like any other celestial body, they obey the laws of gravity: they follow precise orbits and are orbited by other bodies.

It is true though that anything swallowed by a black hole is gone for good. This is because at the “event horizon,” the so called “point of no return” or the boundary of the black hole, gravity is so strong that in order to escape, matter would have to travel faster than the speed of light. As this is physically impossible, nothing can escape!

The idea of black holes (initially called “frozen stars”) has been around for centuries although the term “black hole” was first used only in 1967 by the American astronomer John Wheeler. It was in these years that scientific attention shifted back to black holes, with some of the greatest minds such as Wheeler, Oppenheimer, Penrose, Hawking and many others making significant contributions.

Today we are fairly confident that most black holes form from the remnant of large stars. The idea is that when a massive star consumes all its fuel and dies, all it leaves behind is a dense core. If this core has a certain mass (over three times the mass of the Sun), it collapses on itself under the effect of gravity to become a black hole.

But while the theory is elegant and widely accepted, the direct observation of a black holes remained fairly complicated, considering that not even light can escape to reveal them. Astronomers, however, are very clever people and eventually figured out a way: to spot a black hole all they needed to do was observing its effects on nearby matter.

Imagine a black hole passing through a region of interstellar dust or crossing paths with a close star: the extreme gravitational pull would draw matter toward the event horizon and in doing so the matter would accelerate and heat up, emitting fancy x-rays that can be easily observed by astronomers.

That is precisely what astronomers did in 2019 when the Event Horizon Telescope (EHT), a combination of eight ground-based radio telescopes, captured the image of the supermassive black hole at the centre of the galaxy M87 interacting with nearby matter. The first image ever recorded of a black hole was served.

The first image ever of a Black Hole – Credit NASA ®

Black holes are quite common in the universe and, according to recent studies, there may be billions of them in our own galaxy alone. In fact, a supermassive black hole called Sagittarius A* sits at the core of the Milky Way, and astronomers estimate that there is one at the heart of virtually every large galaxy.

So far, scientists and astronomers have identified three types of black holes whereas a fourth type, primordial black holes, is still only theoretical although scientific evidence of their existence is mounting. These are the main classes of black holes:

  • Primordial – While these black holes are still only theoretical, scientists believe they formed in the initial stages of the universe, a fraction of second after the Big Bang. At this stage, the universe was not homogeneous and areas that were denser and hotter than others may have quickly collapsed into black holes.
    According to some theories, primordial black holes may even explain one of the biggest mysteries of the universe: dark matter. Such theories suggest that primordial black holes may in fact be a type of dark matter called MACHOs (MAssive Compact Halo Objects,), the glue that keep galaxies together.
  • Stellar mass (5 to 100 solar masses) – These are the “ordinary” black holes, which form when a star more than thirty times the mass of the Sun explodes into a supernova at the end of its cycle, leaving behind a dense core. This new core than collapses on itself under the effect of gravity and a stellar mass black hole is formed. They are relatively small but incredibly dense, with an impressive gravitational force.
  • Intermediate mass (100 to 10,000 solar masses) – As the name suggest, these black holes represent a midway between stellar mass and supermassive black holes. Scientists ignored their existence for decades until in March 2020 Hubble spotted what it is believed to be a 50,000 solar mass black hole. Intermediate black holes could form when stars in a cluster collide in a chain reaction or from the merger of two or more stellar mass black holes.
  • Supermassive (greater than 1 million solar masses) – These black holes are millions or even billions of times as massive as the Sun and are found at the core of major galaxies: they are the seeds around which the galaxies are constructed. For instance, Sagittarius A*, the supermassive black hole at the core of our galaxy, is roughly four million times the mass of the Sun whereas the black hole photographed in 2019 weighs a billion solar masses. Supermassive black holes are thought to be formed from the merger of hundreds or thousands of tiny black holes.

Luckily for us, the nearest black holes are thousands of light-years away from Earth. At such distance there is no danger for us or our planet; as we saw, black holes obey the law of gravity like any other celestial body. If we were to replace the Sun with an equal-mass black hole, our orbit and that of all planets in the Solar System would remain unchanged.

On the other hand, if someone, say a curious astronaut, was to wander too close to a black hole, this would have catastrophic consequences. As the astronaut approached the black hole, he would be stretched head-to-toe into a long string of particles before even reaching the event horizon, in a process known as “spaghettification.”

So, the bottom line is: unless you want to become spaghetti, better stay away from back holes!

Spaghettification – Source: Wikipedia ®

A deeper look into Solar Imaging

Since I began my journey into astronomy and astrophotography, I’ve always been fascinated by the idea of photographing the Sun. Yes, galaxies or nebulas are perhaps more intriguing objects with their incredible shapes and dramatic colours but think about the Sun for what it represents.

Our beautiful host star, that governs the Solar System and provides life to our planet, that seems so far away above our heads and yet is so close that we can feel its warmth. Besides, what better opportunity to learn about stars than studying one so close to us?

Below is a graphic from NASA displaying the Sun’s structure and layers:

The internal structure is not relevant for photographing purposes, but it is worth mentioning that this is where the thermonuclear fusion happens (in the core precisely) and hydrogen is turned into helium. The energy produced in the process is than released in the form of visible light (yes, lonely photons!).

The atmosphere, on the other hand, is where fun stuff happens; stuff that we can actually see, if we have the right equipment of course. As we will see, different layers emit light in different wavelengths, and each can be observed with a dedicated filter.

Choosing the right one that matches your needs (and your telescope) is therefore very important and requires some research. For instance, if you get one of those cheap yellow filters, similar to those for observing eclipses, all you’ll see is a red-yellowish disc with sunspots as black dots and virtually no details.

A high-quality filter, on the other hand, not only will ensure safety to you and your instruments but will also provide sharper images through the eyepiece or camera.

These are some of the most common filters in amateur solar imaging:

  • White light (WL): A white light filter shows the Sun’s photosphere, where sunspots are best observed, at a reasonable price. If you own a refractor telescope, the best option is a Herschel wedge or prism, which is placed at the bottom of the telescope, replacing the standard diagonal.
    For other types of optics there are white light filters, such as the Baader Astrozap or Thousand Oaks’ Solarlite film, which can be mounted in front of the telescope.
  • Calcium K line (CaK): With these filters we enter a pricier category, but the costs are fully justified by enchanting views of sunspots and granularity on the lower chromosphere, in the violet part of the spectrum.
    CaK filters work best through dedicated modules placed between the (refractor) telescope and the eyepiece or camera. For different telescope designs you can get a CaK filter that can be screwed directly into the eyepiece or camera and can be used in combination with a Herschel wedge (WL).
  • Hydrogen-alpha (H-a): These very expensive filters reveal stunning, sharp features of the Sun’s upper chromosphere with flares and filaments in spectacular detail (see the gallery at the bottom of this article).
    The best way to observe or photograph the Sun in H-alpha is through a dedicated H-a telescope, such as Lunt or Coronado, although these generally come with an extremely big price tag. A valid alternative is provided by H-a filters, such as the Daystar Quark, which are screwed in the diagonal just before the eyepiece or camera. This solution, however, works only with refractors and provides better images at long focal lengths (> F/10).

As an avid solar photographer, I own several tools to photograph the Sun in nearly all wavelengths though I find myself using mostly the H-a filter, which I believe delivers the most dramatic images.

Solar photography, particularly in H-a, works best with monochrome cameras as they are more sensitive to light compared to colour cameras. Generally speaking, for solar imaging you want a monochrome camera with a CMOS sensor (with high dynamic range) and a high frame rate capability.

This is because, like the Moon and planets, the Sun is photographed through a technique called “lucky imaging”. Some of the most popular cameras for solar photography are the ZWO ASI174MM and ASI290MM.

Now let’s see in detail the technique I use to image the Sun. For clarity, I divided the process in three phases.

Phase 1 – Capturing

In astrophotography this is the most crucial step of the process, for obvious reasons: there’s little you can do in post-processing to fix a dull image, so focus is paramount and must be spot on. Take all the time you need to reach perfect focus, or anywhere near that anyway, and your efforts will be rewarded.

The second vital aspect is “seeing” – the effect of fast-changing, turbulent airflows in Earth’s atmosphere that can make an image look blurred or distorted. Sadly, there isn’t much you can do about this apart from sitting tight with you finger ready to hit the record button as soon as the live-view image on your screen gets clear.

Imaging the Sun in the early hours of the morning (9-12am), when the Sun is high enough, helps mitigating the effects of seeing whereas places surrounded by water tend to have less turbulence in the low layers of the atmosphere.

Also, recording more than one video obviously increases your chances to get a good image out of your session, after all it’s called “lucky imaging” for a reason.

For planetary and lunar/solar photography the most widely used software is SharpCap or FireCapture. Both are free, work great and have pretty much the same functionalities. Personally, I started with SharpCap and never changed thereafter.

I record my videos in *SER format, which is more complete and easier to work on compared to *AVI or other formats. I adjust gain and exposure to be anywhere between 70-90% of the histogram, depending on seeing conditions. Over this range, the image is overexposed and will appear as a bright patch with no details.

Bear in mind that the higher the exposure time is, the lower the frame per second (FPS) gets, meaning you’ll need longer videos during which the seeing could turn bad or clouds may roll in (a classic!). On the other hand, higher gain means more noise, so it’s important to find a good balance between exposure time and gain.

For solar photography, capturing around 2000-3000 frames is generally enough, as you only need between 300-500 good frames for a quality image. In bad seeing conditions I go as far as 5000 frames per video, hoping that at least 5-10% turn out to be good.

It is also recommended to take flat frames to remove signs of dust from the optics or camera sensor and to minimise any vignetting effect.

Phase 2 – Stacking

Once I have my set of videos, I load them one by one in the stacking software AutoStakkert!3 (also free), which analyses them by evaluating each single frame and giving as a result a diagram with the overall quality.

It’s based on this graph that I choose the percentage of total frames that I want to stack (usually between 10% and 20%). The software then chooses the single best frame, the reference frame, to which all other frames are aligned. If you took any flats, this is the right moment to use them.

When the job of AutoStakkert!3 is over, the result is a single final image made of the 10-20% best frames of the video. The stacked image generally looks a little blurred and certainly nowhere near the amazing picture you were expecting; nothing to worry about, this is where post-processing works its magic.

Phase 3 – Post-processing

The first thing a stacked image needs is some sharpening to bring out as many details as possible. This step can be done in any image-processing software although (free) astronomy tools such as ImPPG or Registax do an exceptional job, in my view.

While for planetary and lunar photography I usually work with Registax, for solar imaging I prefer the functionalities in ImPPG, which uses Lucy Richard deconvolution technique.

Here I adjust the Sigma and Amount parameters to sharpen the image and based on the histogram, I carefully move the Tone curve to bring out prominences while also trying to keep surface detail.

Once I’m done with ImPPG, I do the final adjustments in GIMP, a free software that looks a lot like PhotoShop. The first thing I do is crop the image to leave out any stacking artefacts, then I adjust exposure and contrast and play slightly with shadows, mid-tones, and highlights to bring out some more subtle details.

Now, this final step may come as a surprise to you, but I can assure it is common practice. As monochrome cameras represent the best option for solar imaging, the final image is of course black and white and as such it must be coloured artificially.

To do that I convert the image from grayscale to RGB, and with the use of curves in the red, green, and blue channels I give my solar image the colour I like. As we saw before, Calcium operates in the violet part of the spectrum so I would give the Sun taken with a CaK filter a bluish, violet tint.

Hydrogen-alpha, on the other hand, operates in the red-orange part of the spectrum so my H-a pictures generally have a reddish, gold or orange hue, depending on my mood.

To achieve that I push up the curve in the red channel and move down the curves in the blue and green channels. I know, I know…it sounds like cheating, but this is solar photography!

I hope this guide will get you started into solar imaging. Bear in mind that there are many other techniques out there, my advice is to try over and over, being creative and experimenting with settings and software until you find your own method.

The Sun is a dynamic, ever-changing target that never ceases to amaze; whether in a maximum or minimum solar cycle, there is always something going on with our star!

Remember: NEVER EVER point your telescope toward the Sun without using a proper, safe solar filter. Looking directly at the Sun can and will damage your eyes and your instruments irreversibly! Also, always ensure that the solar filter is well attached and stable before pointing your telescope toward the Sun.


Solar Gallery


The James Webb Space Telescope

Since the human race emerged on Earth several hundreds of thousands of years ago, men have been looking up at the sky in wonder, asking some very big questions. Why are we here? What are stars? What is the Universe made of? Are we alone out there?

In the past centuries we made sensational discoveries, pushing the boundaries of our knowledge to unimaginable levels and thanks to some brilliant, visionary minds today we’ve got a fundamental understanding of the Universe.

For instance, we know what stars are, how they form, evolve and die; we built tools that helped us mapping the Universe, with its billions of galaxies, quasars, black holes and so on. We sent probes and humans into space…even a dog once, poor little thing!

So do we have all the answers now? No, we most certainly do not but we are still driven by our curious nature and thanks to a joint effort among NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA), we are now ready to send into space the most advanced telescope ever built, which will help unravel some of the unresolved mysteries of the cosmos.

This is the James Webb Space Telescope (JWST), a 6.5-tonne telescope with a cost tag of nearly 10 billion dollars (8.9 billion euro), which is set to be launched aboard the European Ariane 5 rocket on December 25, 2021 and begin its science observations 6 months after.

Having a telescope in space helps with the two main problems that ground-based astronomers have to face: the weather (clouds are astronomers’ worse nightmare) and the Earth’s atmosphere, which acts like a protective blanket letting only some light through while blocking or distorting some wavelengths. Besides, a space telescope doesn’t have to wait for the Earth to spin to be able to point toward the desired target.

Currently there are several telescopes in space, the most famous being Hubble, which has been orbiting Earth since more than 30 years, delivering iconic images and contributing to more than 15 000 scientific papers.

As the JWST is widely considered the successor of Hubble, regardless of some major differences, it is understandable why the excitement around the new observatory grows by the hour within the scientific community.

Credit: NASA ®

The JWST is a powerful observatory, brimming with innovation and complexity. It boasts an impressive primary mirror with a diameter of 6.5 meters, composed of 18 adjustable, gold-plated beryllium segments, which has six times the light-collecting capability of Hubble, and a roughly 15 times wider field of view.

It will be equipped with four main scientific instruments, collectively known as the Integrated Science Instrument Module (ISIM):

  • A near-infrared spectrograph (NIRSpec) that can observe 100 objects simultaneously
  • A near-infrared camera (NIRCam)
  • A combined mid-infrared camera and spectrograph (MIRI) with a cryocooler to keep its temperature at –266˚C
  • A fine guidance system and wide-field imager (FGS/NIRISS) that includes a mode for exoplanet spectroscopy

The JWST’s main goal is to look back to 100–250 million years after the Big Bang, when the first stars and galaxies formed, to shed some light on the so-called “end of the dark ages”.

According to the Big Bang theory, this is when the Universe began to fill with “first light” from newly ignited stars. By comparison, Hubble was “only” capable of looking back 500 million years after the Big Bang.

Moreover, the mid- and near-infrared cameras will allow the new observatory to peer into the birth of new stars and solar systems and will be sensitive enough to detect oxygen and other so-called biomarkers in the atmosphere of exoplanets (planets orbiting stars outside the Solar System).

The JWST will also study the effects of black holes and the origins of life; it will provide a better calculation of the Universe’s size and geometry, getting some insights on dark matter and dark energy, and helping us understand the ultimate fate of the cosmos.

The capabilities of the James Webb Space Telescope are huge but so are its risks. The JWST, in fact, will be folded down to fit inside the Ariane 5 rocket and, once deployed, it will unfold itself, cool down and calibrate in a process that will likely make all those involved in the project lose their sleep.

The JWST folded into the Arian 5 rocket – Credit NASA ®

On top of that, the JWST will position itself beyond the reach of manned repair missions as it will be orbiting the Sun at the Lagrange point 2 (L2), approximately 1.5 million km from us where it will have unobstructed views of the Universe.

Keeping the JWST in orbit around L2, however, requires an astonishing amount of energy and the on-board fuel will guarantee a limited lifetime (5 to 10 years), which should still be enough for some sensational discoveries.

So brace yourself and be ready for the main scientific event of the 21st century!

The Pleiades

Located some 440 light years from Earth, in the constellation Taurus, the Pleiades is one of the most beautiful sights in the night sky: whether through the naked eye, an eyepiece or a camera sensor, this unmistakable celestial object never ceases to amaze!

The Pleiades is what astronomers call an “open cluster” or a group of stars formed from the same cloud of gas and dust: under the effect of gravity, these particles are pressed together pushing the temperature up to extreme levels. As the new stars take shape and increase in size, their own gravity becomes stronger, mutually bounding them together.

The cluster contains over three thousand stars (mostly hot B-type stars) although only a handful is visible to the naked eye as a consequence of increasing light pollution.

Today, in fact, from most cities it is possible to recognise around 6 or 7 stars, thus the cluster is often referred to as “The Seven Sisters”.

The Pleiades has been known for centuries and there is no shortage of legends about it. According to the Greek mythology, the Pleiades were the seven daughters of the Titan god Atlas who rebelled against Zeus and was thus sentenced to hold up the heavens on his shoulders. Moved by compassion, however, Zeus allowed the seven daughters a place in the sky so they could stay close to their father.

In Japan, the cluster is known as Subaru and was chosen as the name of the 8.2-meter (320 inches) telescope of the National Astronomical Observatory of Japan. It is also the brand name of the famous car manufacturer Subaru, which has 6 stars in its logo.

The Pleiades is arguably the most famous star cluster in the sky, prominent and unmistakable to the naked eye, but who was the first astronomer to resolve the Pleiades through a telescope?

Well, Galileo Galilei of course. The Italian astronomer was the first to discovered that the cluster contains way more stars than those visible to the unaided eye. He published his observations and a sketch of the Pleiades in his “Sidereus Nuncius” in 1610.

However, the nebulosity around the Pleaides was only discovered in 1859 by the German astronomer Ernst Tempel who described it as “a faint stain like a breath on a mirror”, when gazing at the Pleiades through his 4-inch (10cm) telescope.

The nebulosity is not directly connected to the star cluster, but it rather seems that the latter is passing through a particularly dusty region, which reflects the light from the brighter stars.

Depending on the observer’s latitude, the Pleiades cluster is visible from late September to May and it is best observed in November, when is up the whole night.

As mentioned before, the Pleiades is clearly visible to the naked eye but have a look at it through a pair of binoculars or a telescope and I assure you your jaws will drop!