Zoom in to explore this high resolution image

The Milky Way from Lepus to Aquilla

Our home in the Universe, the Milky Way galaxy, is a vast disk of stars and gas. We are inside this disk, about 1/2 way from the centre. On a clear night the Milky Way appears as a hazy band in the night sky because as we look out through this disk, the nearly uncountable stars blend together into a hazy cloud.

Orion is perhaps the most easily recognized constellation in the sky, and for good reason. Its main stars are very bright, and the constellation actually looks like something!

When looking towards Orion, we are looking away from the centre of the Milky Way galaxy, out towards the edge. There’s no shortage of things to see towards this edge, as this region contains the closest star-forming region, the brightest star in the sky, two of the closest star clusters to Earth, numerous nebulae, over a dozen bright star clusters, and millions of stars. It’s a stunning sight under these fantastically dark skies!

By luck, Sirius, the brightest star in the sky, is just poking through the gap between the peaks to the south-west, and is reflecting beautifully off the lake ice. The sky rotates quite quickly, but I’m able to capture this reflection before Sirius moves to the right and disappears behind the peak.

Lots to explore here…

Stars and Nebulae of Orion

One of largest nebula in the sky is Barnard’s Loop, covering over 10 degrees of the sky (20x the size of the full moon!) as it curves around the central belt region of Orion. Too dim to be seen with the naked eye, it was named after the pioneering astrophotographer E.E. Barnard, who published a description of it in 1894. It is not known exactly what created this graceful arc, but it is possible that one or more supernova explosions, several million years ago, are responsible for creating the vast arch of ionized hydrogen.

The brightest star in Orion is Rigel, at the bottom-right foot. Rigel is a young, blue super-giant star, only 10 million years old and 772 light-years away. It appears very blue/white to the naked eye, weights in at 17 times the mass of our Sun and emits 85,000x as much light.

In contrast, Betelgeuse, on the top-left corner of Orion, appears very red to the naked eye, and is classified as a red super-giant star. It is a variable star, with its luminosity varying between 90,000 and 150,000x our sun. It is also one of the largest known stars, and would easily engulf both Earth and Mars, reaching roughly out to the orbit of Jupiter, if it replaced our Sun. It is also very young, less than 10 million years, is consuming its fuel very quickly and will explode as a supernova in the (relatively) near future, likely within one million years.

The three brilliant stars of Orion’s Belt, Alnitak, Alnilam and Mintaka, are all young blue giant stars, with luminosities between 90,000x and 375,000x our Sun’s output.

The brightest stars in the sky all have traditional names that date back 1000s of years, and the names we use today in English are phonetic translations of the ancient names, many Arabic, with Greek and Latin names as well.

Generally, the more massive a star is, the hotter it is, the more quickly it burns through its supply of hydrogen fuel, and the shorter its life. Just like the hot filament in an old incandescent light bulb, colour of a star is determined by its surface temperature. The relationship between a star’s mass, lifetime, luminosity and surface temperature (colour) was first characterized around 1910 and summarized in the Hertzsprung-Russell diagram, which drove the understanding of the physics of stellar evolution for decades.

Photography notes: after capturing the wide-field mosaic, I decide to photograph Orion in more depth, and capture 8 frames of the lower half, and 8 frames of the upper half. Each of the 8 frame sets will be stacked together, a process which reduces image noise and reveals dimmer, more subtle features like the nebulosity.

The Belt and Sword of Orion

Zooming in to focus on the belt and sword region of Orion reveals numerous clouds of glowing gas, including the Great Orion Nebula, M42, the closest star-forming region to Earth and by far the brightest nebula in the northern sky.

The Orion Molecular Cloud complex is the entire region of nebulosity around Orion’s Belt, 100s of light-years wide, which includes M42, M43, M78, the Flame nebula, Barnard’s loop, and the intense blue/white stars formed by this vast cloud, including Orions belt stars. It is the nearest star-forming region to Earth and has spawned 1000s of stars over the last 10 or so million years. Observations by the Hubble and other telescopes have revealed 100s of infant stars that are still shrouded in gas but have already ignited their nuclear fusion cores and are spewing out radiation and stellar winds.

Stars are formed from the gravitational collapse of vast clouds of gas and dust. As these clouds collapse, the gas density increases until the pressure and temperature are enough to initiate nuclear fusion, and new stars are born. The young stars start pumping out electro-magnetic radiation (light) and particles (solar wind), eroding the surrounding gas clouds. This tug-of-war between gravity and radiation shapes the gas clouds, with the young stars carving out bubbles of relatively empty space and spectacularly illuminating their birth-clouds from within.

The Orion Nebula is so large and close to Earth that it is visible to the naked eye, appearing as the blurry middle “star” in Orion’s sword. At around 1340 light-years away, M42 is the closest star-forming region to Earth, it is one of the most photographed and studied by both amateur and professional astronomers. Numerous discoveries have been made in this region, including around 700 stars being formed, and the first image of solar-system formation around a new-born star.

Photography notes: This image is a 10-frame stack taken with a 200mm lens at f/4.0. Eight frames have identical 120-second exposures, and the other two are shorter exposures, because the core of the Orion Nebula contains an extremely bright cluster of stars that over-expose the surrounding nebulosity. A little more work processing, but the result is a deep, High Dynamic Range (HDR) image of this incredible region of our galaxy.

Horsehead and Flame nebulae

The left-most star in Orion’s belt is Alnitak, which is surrounded by bright and dark nebulosity. On one side is the Horsehead nebula, which is famous for the same reason that Orion is famous – it looks like something familiar to us here on Earth. It is a (relatively) dense cloud of interstellar gas and dust, thick enough to block the light of the glowing gas behind it so that it stands out as a dark silhouette.

In infrared light, the nebula looks very different, with the dark gas glowing from the heat of newly forming stars embedded in the dust. This stunning composite image is made from VISTA and Hubble telescope data and reveals the new-born stars embedded in the dust.

The Horsehead lies only 100 light-years from the Orion Nebula, and is part of the same massive dust and gas cloud, called the Orion Molecular Cloud Complex.

The Flame Nebula, NGC 2024, the orange and black region just below the brilliant star Alnitak, is another beautiful portion of the Orion Cloud complex, and is often photographed together with the Horsehead nebula. In it, a dark band of interstellar gas is silhouetted against a more distant, brightly glowing emission nebula.

This entire region around Orion contains stunning examples of the major types of nebulae: emission nebulae glowing red from ionized hydrogen, dark nebula that revealed as silhouettes, and reflection nebula that appear blue as the light of blue giant stars is reflected off nearby clouds.

Here are the Flame and Horsehead nebulae in infrared light by the 4m VISTA telescope.

M78 nebula

Through the giant optics of professional telescopes, the relatively small blue blob between Orions belt and Barnards loop is revealed to be a maelstrom of dust, gas, brilliant young stars and dim, still-forming stars buried in gas.

A reflection nebula glows from the reflected light of stars, often appearing blue / white because that is the colour of the brilliant young stars that are nearby or embedded in the nebulous clouds. The La Silla Observatory visible-light image clearly shows the blue reflected starlight.

The 4m VISTA telescope is equipped with an infrared camera, and infrared light penetrates much of the dust and gas. The resulting stunning image of M78 revealing dozens of still-forming stars buried inside the clouds.

Taurus, the bull

Above Orion in the zoomable image is the constellation of Taurus, the Bull. One of the oldest constellations, its association with a bull dates back to the early Bronze age, 3000-5000 BC.

Taurus is easily recognizable by the distinct V-shaped group of stars called the Hyades cluster, which is the nearest star cluster to Earth at about 153 light-years. There are hundreds of stars in this cluster, with about 10 bright ones visible to naked eye.

The brightest star in Taurus, Aldebaran, is not an actual member of the Hyades cluster, but just happens to be in the line of sight, and is much closer to Earth than the cluster stars. Aldebaran is an old, giant star that has exhausted its hydrogen core. It’s only about 16% more massive than our Sun, but has expanded to 44x the diameter and outputs 400-500x the energy.

Dark nebula

There are many dark nebulae in the zoomable image, visible as dark patches against the dense fields of stars. A dark nebula is simply one of the many vast clouds of interstellar dust and gas present in our galaxy, that has not yet collapsed to form stars. Without intense, bright young stars nearby, the gas cloud is not lit up or glowing, and is visible only because it blocks the light of the stars behind it.

Under pristine dark skies, these dark clouds are visible to the naked eye, silhouetted against the innumerable stars of the Milky Way.

These dark clouds may look thick and dense, and obviously are dense enough to block the light of the stars behind them, but compared to our atmosphere they are nearly a perfect vacuum. However, they have 1,000,000 times more molecules as “empty” interstellar space, which contains on average only one single molecule per cubic centimetre.

Crab Nebula, M1

Just above Tianguan, the lower-left star in Taurus, is a small fuzzy spot with an incredible history. In July of 1054 an extremely bright star suddenly appeared in the sky. Chinese astronomers of the Song Dynasty noted the appearance of this “guest star”, which was so bright that it was visible in daylight for 23 days and visible in the night sky for almost two years. The most detailed record from Japan describes a guest star that was as big as Jupiter, and accounts from Persia talk of a spectacular new star in that year.

In 1758, the French astronomer Charles Messier was watching for the return of Halley’s Comet when he observed a fuzzy patch in the constellation Taurus. After noting that the object did not move or change brightness over several nights, Messier concluded that this was not a comet, and thereby started his famous catalog of non-comets with Messier 1. That catalog eventually grew to include over 100 of the most interesting objects in the night sky.

Starting the in 1920s, astronomers first noticed that the M1 nebula appeared to be expanding, by comparing images taken many years apart. This was still the very early days of astrophotography, and the earliest photographs of M1 were from 1909. In 1928 Edwin Hubble suggested that the expanding nebula was the remains of a stellar explosion, and also suggested that the “guest star” of 1054 was the culprit. It wasn’t until 1942, however, that the link between the guest star of 1054 and the expanding M1 nebula was confirmed beyond reasonable doubt.

The stunning Hubble image really reveals what happened here: the “guest star” was actually the explosive death of a star, now known as Supernova 1054, and the fantastic web of dust and gas is the exploding debris itself.

The remnants of this incomprehensibly powerful explosion are still expanding, at roughly 1500 kilometres per second (0.5% of lightspeed). In the nearly 1000 years since the explosion the debris cloud has grown to about 11 light-years in diameter: that fuzzy little spot in the sky is immense: 11 light-years is about 100,000 billion kilometres.

At its centre is a neutron star called the Crab Pulsar, only 28-30km in diameter and spinning at an incredible 30 revolutions per second. This means that the surface of this star is moving at around 2700 km/s, or nearly 1% of light speed! This neutron star is the strongest persistent source of X-ray and gamma ray energy in the sky.

NGC 2174

This distant but spectacular nebula is located around 6400 light-years away, just to the east of Orion’s raised arm, on the edge of the constellation Gemini.

Through the 85mm lens used for the mosaic image, it appears as a roughly round red blob, but in 2001 and 2014 the Hubble space telescope focused it’s 57,600mm focal length optics on it. Those images, zoomed in to the inner edge of the nebula and captured in visible and infrared light, reveal complex pillars of gas that are being eroded by the torrential light of massive, young stars. Infrared light travels is not blocked as much by dust and gas, revealing the still-forming stars buried in the gas.

This image compares two views of the same detailed area in the star-forming nebula NGC 2174 from the Hubble Space Telescope. On the left is a visible-light image made by WFPC2 observations taken in 2001 — and released in 2011 — and on the right is an image made by the WFC3 infrared camera. Infrared light penetrates more dust and gas than visible light, allowing details to become visible. A jet of material from a newly forming star is visible in one of the pillars, just above and left of centre in the right-hand image. Several galaxies are seen in the infrared view, much more distant than the columns of dust and gas.

Rosette nebula

East of Orion is the rather dim constellation Monoceros (the unicorn), and this is where the brilliant Rosette nebula resides. This is a massive star-forming complex, nearly 130 light-years across, and if it was visible to the naked eye, it would appear almost 3x the size of the full moon. It is about the same apparent size as the Orion Nebula, but at 5000 light-years it is over 3x further away, which means that it is a much larger structure in space.

At the core of this bright star-forming region is the cluster NGC 2244, only a million years old. Formed from the dust and gas of the nebula, this cluster contains hundreds of stars, and a few of the most massive stars, each hundreds of thousands of times brighter than our sun, are pouring out such a torrent of light and stellar wind that they have evacuated a cavity in the centre of the nebula and have ionized the remaining hydrogen in the cloud, causing it to glow red.

As the original dust cloud is carved out and eroded by the massive young stars, higher-density clumps are left behind, which is spectacularly shown in this image, captured by the VLT telescope in Chili.

Auriga

At the top of the zoomable image, sharing the star Alnath with Taurus, is the constellation of Auriga, “the charioteer” in Latin. Looking towards Alnath you are looking through the plane of the Milky Way, but exactly opposite it’s centre.

Auriga is also one of the ancient constellations of western culture, and was included in the 2nd century Almagest by Ptolemy.

Clusters M36, M37, and M38

In the constellation Auriga are several star clusters of varying ages. Through binoculars or a moderate telephoto lens they appear as small clumps of stars against a background already dense with stars.

Messier 36 is a small, young cluster about 3600 light years away 25 million years old containing approximately 60 stars in a ball about 14 light-years across.

Messier 37 is much older, around 500 million years, and farther away, about 4500 light-years. With an estimated 2000 stars in a diameter of about 30 light years it is much bigger and denser than M36.

At 220 million years, M38 is about half-way between the ages of M36 and M37. 220 million years ago, Earth was at the beginning of the Triassic age, the dawn of the dinosaurs. These are ‘young’ clusters compared to the age of our Sun, 4.6 billion years.

Flaming star nebula

In Auriga is the Flaming Star nebula, which glows due to the torrential energy output of a single star, AE Aurigae. This brilliant star both ionizes the gas, causing the hydrogen to glow red, and illuminates the gas, causing it to shine blue with reflected light of the star.

But this is no ordinary star – this massive blue star is a runaway star that is sailing through the galaxy at around 100 km/second, relative to us on Earth. By tracing its observed motion backward, it appears to have originated in the Orion Nebula around 2 million years ago. Two other stars were also ejected from the nebula (53 Arietis and Mu Columbae), and all three stars are moving away from each other at 200 km/second.

Stars in a cluster are moving relative to each other, orbiting the centre of mass of the cluster. A close encounter with another star, often within its birth cluster, can slingshot a star out of a cluster and send it careening across the galaxy. This is how star clusters fall apart, slowly losing their original stars, over 100s of millions of years, out into the galaxy.

M45, Pleiades cluster

At the very top-right of the mosaic image, and easily visible to the naked eye, is the famous Pleiades cluster, from Ancient Greek, also known as the the Seven Sisters, Subaru in Japan, and dozens of other names to dozens of ancient cultures. The first likely depiction of this star cluster is on a bronze disk from the 16th century BC.

Around seven stars are visible to the naked eye, but the cluster contains many than that, with Galileo Galilei counting 36 stars when he first viewed the cluster through his telescope in 1610 and modern analysis showing over 1000 stars, at distances of between about 350 to 435 light-years.

M79 globular

At the very bottom of the mosaic image, just above the mountains in the constellation of Lepus, is the globalar cluster M79, a completely different type of star cluster.

Most of the star clusters in the Milky Way contain a few hundred stars, are relatively young (100s of millions of years) and lie within the disk of the Milky Way. The stars have formed together, from a collapsing gas cloud, and are loosely bound by gravity, usually breaking up and dispersing after a few 100 million years.

Globular clusters, however, are completely different beasts, as they are much bigger, much, much older, and much further away. The globular M79 is about 42,000 light-years from us, contains around 150,000 stars, and is 11.7 billion years old, which is almost as old as the Universe itself (13.8 billion years). The clusters orbit our Milky Way (as opposed to being within it) and are often in retrograde orbits (reverse direction from the rest of the galaxy), which suggests that these globulars were captured by our galaxy.

Optics, small, large and huge

I love the wide-angle view that captures the vast structures of our Milky Way galaxy plus several constellations. There is infinite detail in the Universe, and zooming in to distant objects reveals their incredible structure. But, zooming in requires larger, more cumbersome and expensive optics – telescopes! – and it doesn’t take long before they are too big to move.

Soon after the invention of the telescope in 1608, it became apparent that bigger telescopes reveal more details, and already by the late 1600s there were telescopes over 100m long. 400 years later, the history of telescopes has shown that every bigger and better telescope enabled new scientific discoveries.

The two primary parameters of any optical system are aperture, which determines how much light is gathered, and focal length, which determines the field of view. F/stop, the ratio between them, determines the brightness of the optics.

Focal length	Camera lens	Notes
22mm, f/2.1	Human eye	140 degree field of view with each eye
28mm, f/1.8	Wide angle	75 degree field of view
50mm, f/1.4	Normal lens	47 degree field of view
100mm, f2.0	Small telephoto	23 degree field of view, Orion fills the frame
200mm, f/2.8	Medium telephoto	12 degree field of view
400mm, f/4.0	Long telephoto	6 degree field of view
Focal length	Amateur telescopes
1000mm, f/7	Small reflector	6″ aperture=150mm
2000mm, f/10	Medium reflector	8″ aperture=200mm, the moon fills the frame
4000mm, f/11	Large reflector	14″ aperture=355mm
Focal length	Professional telescopes
12,100mm, f/3	VISTA survey telescope	2009, 4m aperture, Paranal Observatory, Chile
16,760mm, f/3.2	Hale telescope	1948, largest in the world until 1976, 5.1m aperture=200in
27,940mm, f/11	Hooker telescope	1917, largest in the world until 1949, 2.5m aperture=100in
57,300mm, f/24	Hubble space telescope	1990 launch, 2.4m aperture
120,000mm, f/15	Very Large Telescope	1998, 8.2m aperture, Paranal Observatory, Chile
131,400mm, f/20	James Webb Space Telescope	December 2021 launch, 6.5m aperture, infrared wavelengths

There is always more to see, all you need to do is to look.

– Darren Foltinek, February 2022