Tag: Astronomy Essentials

The dark of the night!

This recent post from EarthSky is a fascinating read!

By some amazing luck when we came to Merlin, Oregon some eight years ago we found these acres distant from any form of light pollution. Frankly, light pollution at night never crossed our mind at the time.

But almost every evening, when it is dark, I go outside to call in the dogs and look up at the night sky. At this time of the year the Big Dipper is high in the sky. Also the Milky Way can be seen as a faint ‘smudge’ of light. It is a glorious sight and one that I will never, ever tire of seeing.

Which is my introduction to today’s post Why we need darkness.

And, please watch this TED Talk given by Paul.


Paul Bogard on why we need darkness

Posted by in ASTRONOMY ESSENTIALS, October 29, 2020

Light at night may be a sign of life on Earth, but the darkness will proclaim our true intelligence. Check out this video on why we need darkness, from Paul Bogard. In his captivating talk Paul describes what we call “light pollution,” the overuse and misuse of artificial light at night. In cities and towns, in suburbs and villages all over the world, we are using more light than we need, and we are using it ways that waste money and energy, harm our physical health, harm the environment, and yes — rob us of the stars. What are the solutions for this problem? A native Minnesotan, Paul Bogard loves night’s natural darkness. So much so that he wrote two successful books about it. He is author of The End of Night: Searching for Natural Darkness in an Age of Artificial Light and editor of Let There Be Night: Testimony on Behalf of the Dark. He also likes to walk through the woods, surrounded by the trees and birds and hidden animals. For 15 years he had a dog who would come with him on these walks. Her name was Luna, like the moon. He misses her a lot. He loves coffee in the morning and red wine at night. Paul is now an assistant professor at James Madison University in Harrisonburg, Virginia, where he teaches creative writing and environmental literature.

The dark is good for our sleep, our biology, and the health of our ecosystems. It’s good for our creativity and our spirits, and, yes, it’s even good for our safety and security. That’s the message of Paul Bogard, who has written extensively on the importance of darkness. His book is titled “The End of Night.” His TEDx Talk – above – focuses on why we need darkness. I’ve spent time mulling over both the book and this video and recommend them highly. In this pandemic year – as many wondered whether lockdowns gave us darker skies – you might enjoy thinking about it, too.

Bogard researched night-shift workers, those who are exposed to light during the hours that most bodies crave darkness and sleep. Humans have a circadian trough from approximately midnight to 6 am. The absence of darkness and sleep during this trough contributes to night-shift work being labeled a probable carcinogen, with workers more likely to suffer from obesity, diabetes, cardiovascular issues, depression, substance abuse, and especially breast and prostate cancer. Light at night disrupts the body’s production of melatonin, which is thought to be needed to keep these types of cancers at bay.

But it’s not just night-shift workers who suffer from exposure to lights at night. Any quick look at a photo of the Earth at night shows the great glows of cities and suburbs spilling across the land and down highways into the edges of the countryside. Even when we keep the lights dark outside our own home, the light from our neighbors’ homes seeps around the cracks in our blinds and splashes across our back patio.

Earth at night, via NASA.

The light we see on maps of Earth at night isn’t just interrupting our sleep or blinding us on a late-night walk with our dog. It’s also wasting money. Bogard claims that billions of dollars are wasted each year throughout the world on light that illuminates nothing on the ground, but instead points straight up.

He points out that proper lighting directs illumination toward the ground, away from the sky and out of the eyes of those nearby. Bright lights near someone’s front door create an illusion of safety, but not true safety, according to Bogard. That’s because the glare shining into our eyes makes it difficult to impossible to see what is hiding in the deep shadows cast by the light.

Policing in some communities has been made much easier with the replacement of constant lighting by motion lights. For example, Bogard recounts how Loveland, Colorado, changed their schoolyard lighting to motion detectors, which made it simple for patrols to see if someone was present or not determined by whether or not the area was dark or light.

The issue with safety and lighting isn’t black or white, or darkness or light. It’s choosing proper lighting for each situation, which helps to make an area safer, saves money, preserves sleep, and protects the dark night sky.

When we protect the night sky, Bogard says, we’re also protecting not just ourselves and our biology but those of the ecosystem around us. In his book “The End of Night,” Bogard writes:

I remember Pierre Brunet arguing in Paris that the presence of an astronomer was the sign of a healthy ecosystem; that when the sky grows too bright for astronomy and the astronomers go away, you know you have a light-polluted sky, and whatever has polluted that sky will eventually pollute other resources, given time.

Countless animals are dependent on darkness, Bogard points out. More than 60% of invertebrates and 30% of vertebrates are nocturnal, having evolved to find food and mates in uninterrupted darkness.

Sea turtles are a well-known example of animal life that needs darkness to survive. Anyone who has been to the oceanfront has seen the lighting adapted to help the sea turtles find their way back to the sea. At my parents’ condo in Florida, the ocean-facing side of lamps have been blacked out so that the newly-hatched sea turtles, upon leaving their nests, are not lured onshore by false light but find their right paths into the water.

When you examine the night sky map of the United States and consider where most of the population lies, it’s not hard to believe, as Bogard tells us, that more than 80% of Americans can no longer see the Milky Way from their home. I live in the suburbs of a large city, for example, and my location on a map of light pollution is nearly bright white.

Recently, I spent some time about three hours west of Chicago in a quiet patch of countryside that is a rare blue shade of darkness on light pollution maps. When I stepped out onto the deck on a crystal-clear evening, I looked up at the stars and was immediately lost.

I’ve been observing and writing about the night sky for two decades, but my familiarity with the sky is linked to recognizing what I see nightly above me, which is usually a dim cousin to the depth and wonder of a truly dark sky. None of the conventional patterns were popping out at me like I was used to: the Big Dipper, the Summer Triangle, the V-shape of Taurus’s head. Instead, a brilliant orange Mars was bright enough to wash out the stars around it, yet the lush Milky Way held her own and a thousand normally unseen stars twinkled in a chorus.

For the first time ever, I witnessed the fuzzy oval glow of the Andromeda Galaxy with nothing more than my eyes. I saw star clusters dig out patches of sky and anchor their surroundings instead of having to hunt them down with binoculars. Cassiopeia and Perseus were nearly swallowed up by the sea of stars flowing from the Milky Way behind them.

We need darkness for moments like that. We need darkness to feed our spirit, protect our health and protect the health of our planet. Light at night may be a sign of life on Earth, but the darkness will proclaim our true intelligence.

Bottom line: A video on why we need darkness from Paul Bogard, author of the book “The End of Night.” The video explains why light pollution is detrimental and why darkness is good for our bodies, our world and our spirits.

Via Paul Bogard

Via YouTube


Yes, we need darkness!

So, please, take a moment to view the night sky. If you are somewhere where there is excessive light pollution then plan at some point to get away to the darkness. Also make sure you sleep in a dark room. It’s too easy to let a light or two get in the way of a properly darkened room.

Finally, amongst my many photographs I do not have is one of the night sky. And, frankly, if I did it wouldn’t be as fantastic as the one below. So let me close with a Pexels photograph of the Milky Way by Sam Kolder.

Photo by Sam Kolder from Pexels

Stunning and what a brilliant photograph.

Simply in awe!

It’s both beautiful and yet beyond comprehension.

When we have a clear night there are two occasions for me to gaze upwards and become lost in thought. One is in the evening when the dogs are outside just before going to bed. The other is in the morning because we are usually awake well before sunrise.

We are very lucky in that there is no light pollution locally.

So, in the evening, while I look at the broad expanse of stars, my eyes are drawn to the Big Dipper and to Orion.

In the morning, when we look to the East there is Venus sparkling bright in the night-sky over the hills.

I still vividly remember all those years ago when I was sailing in the Western Mediterranean coming on deck in the middle of the night to find the stars down to the horizon all 360 degrees about me. I am sure it will be one of the last memories of mine just before I die! I hope so!

But I speak of the solar system. Here’s an article that was recently published by EarthSky that goes way beyond the solar system. It is a wonderful essay and almost mystical.


What is a galaxy?

Posted by in ASTRONOMY ESSENTIALS, September 25, 2020

We live in a galaxy called the Milky Way. But there is so much more to know about these grand and glorious star islands in space! Click in here, and prepare to have your mind expanded.

This is a giant galaxy cluster known as Abell 2744, aka Pandora’s Cluster, located in the direction of the constellation Sculptor. The cluster is about 4 million light-years across and has the mass of 4 trillion suns. It appears to be the result of a simultaneous pile-up of at least 4 separate, smaller galaxy clusters that took place over a span of 350 million years. Read more about this image at HubbleSite. Image via NASA/ ESA/ J. Lotz/ M. Mountain/ A. Koekemoer/ the Hubble Frontier Fields Team.

A galaxy is a vast island of stars in an ocean of space. Galaxies are typically separated from one another by huge distances measured in millions of light-years. Galaxies are sometimes said to be the building blocks of our universe. Their distribution isn’t random, as one might suppose: galaxies are strung out along unimaginably long filaments across the universe, a cosmic web of star cities.

A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, nearly a million trillion kilometers.

Galaxies are of widely varying sizes, too.

There are an estimated two trillion galaxies in the universe.

Illustration showing snapshots from a simulation by astrophysicist Volker Springel of the Max Planck Institute in Germany. It represents the growth of cosmic structure (galaxies and voids) when the universe was 0.9 billion, 3.2 billion and 13.7 billion years old (now). Image via Volker Springel / MPE/ Kavli Foundation.

Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, for example: a cluster comprising 55 galaxies that we know of so far.

In turn, galaxy clusters themselves group into superclusters. Our Local Group is part of the Virgo Supercluster.

The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity, the universe’s construction worker, which sculpts all the structures we see in the cosmos.

Distances from the Local Group for selected groups and clusters within the Local Supercluster, which is called the Virgo Supercluster.

There are several basic types of galaxy, each containing sub-types. Galaxies were first systematically classified, based on their visual appearance, by the famous astronomer Edwin P. Hubble in the late 1920s and 30s, during years of painstaking observations. Hubble’s Classification of Galaxies, as it is known, is still very much in use today, although, since Hubble’s time, like any good classification system it has been updated and amended in the light of new observations.

Before Hubble’s study of galaxies, it was believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw in their telescopes were in fact nebulae within our own galaxy and not, as Hubble discovered, galaxies in their own right. It was Hubble who demonstrated, by measuring their velocities, that they lie at great distances from us, millions of light-years beyond the Milky Way, distances so huge that they appear tiny in all but the largest telescopes. Moreover, he demonstrated that, wherever he looked, galaxies are receding from us in all directions, and the further away they are, the faster they are receding. Hubble had discovered that the universe is expanding.

A diagrammatic representation of Edwin Hubble’s “tuning fork diagram.” In the late 1920s and 30s, Hubble conducted the laborious observations needed to begin to classify galaxies. His original classification scheme was published in 1936 in a book called “The Realm of the Nebulae.” His original scheme is – like all scientific work – continually being modified. But his idea of a “tuning fork diagram” has continued to be useful. Image via Las Cumbres Observatory.

The most common type of galaxy is the one most people are familiar with: the spiral galaxy. The Milky Way is of this family. Spiral galaxies have majestic, sweeping arms, thousands of light years long, made up of millions upon millions of stars. Our solar system is situated about 2/3 of the way out from the galactic center towards the periphery of the galaxy, embedded in one of these spiral arms.

Spiral galaxies are also characterised by having a bright center, made up of a dense concentration of stars, so tightly packed that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge. At the center of the Milky Way – within the galactic bulge – the density of stars has been calculated at 1 million per 34 cubic light-years, for example.

Meanwhile, in the vicinity of our sun, the stellar density has been estimated as 0.004 stars per cubic light-year. Big difference!

A stunning view of the center of our Milky Way galaxy as seen by the Murchison Widefield Array (MWA) telescope in Australia in 2019. Image via Natasha Hurley-Walker (ICRAR/ Curtin)/ GLEAM Team/ Phys.org.

The Milky Way is, in fact, in one of Hubble’s spiral galaxy sub-types: it’s a barred spiral, which means it has a bar of stars protruding out from either side of the center. The ends of the bar form the anchors of the spiral arms, the place from where they sweep out in their graceful and enormous arcs. This is a fairly recent discovery: how the bar forms in a galaxy is not yet understood.

Also established recently is the fact that the disk of the Milky Way is not, as most diagrams depict, flat: it is warped, like a long-playing vinyl record left too long in the sun. Exactly why is not known, but it is thought to be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.

Artist’s illustration of our warped Milky Way. Image via Ogle/ Warsaw University/ BBC.

Elliptical galaxies are the universe’s largest galaxies. They are huge and football-shaped.

They come to be because – although most galaxies are flying apart from each other – those astronomically close to each other will be mutually gravitationally attracted. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years, eventually forming a single, amorphous elliptical galaxy. Such mergers may result in the birth of new generations of stars as gravity’s shock-wave compresses huge clouds of interstellar gas and dust.

The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years from now. However, both galaxies are surrounded by huge halos of gas which may extend for millions of light-years, and it was recently discovered that the halos of the Milky Way and M31 have started to touch.

The two galaxies have had their first kiss.

Galaxy mergers are not uncommon: the universe is filled with examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.

Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can see only “snapshots” of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed The Mice because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via Wikimedia Commons.

At the lower end of the galactic size scale, there are the so-called dwarf galaxies, consisting of a few hundred to up to several billion stars. Their origin is not clear. Usually they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 20 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.

The two most famous dwarf galaxies for us earthlings are, of course, the Small and Large Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.

Eventually, these and other dwarf galaxies will be ripped apart by the titanic maw of the Milky Way’s gravity, leaving behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.

Lynton Brown captured this beautiful image of the Milky Way over Taylor’s Lake near Horsham, Australia, on April 22, 2019. The 2 objects on the right are the Magellanic Clouds. Thank you, Lynton!

It is believed that all galaxies rotate: the Milky Way takes 226 million years to spin around once, for example. Since its birth, therefore, the Earth has travelled 20 times around the galaxy.

At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. The record holder, TON 618, has a mass 66 billion times that of our sun.

The origin and evolution of supermassive black holes are not well understood. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship is, but its existence seems to indicate that the growth of a galaxy’s stellar population and that of its supermassive black hole are inextricably linked.

This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy: the copious amounts of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole, known as the accretion disk, may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as a throttle on the galaxy’s ability to give birth to new stars. Ultimately, the emergence of life itself may be tied to the activity of supermassive black holes. This is an area of much ongoing research.

While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent forms existing only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.

Less than a hundred years after it was realized that other galaxies beside our own exist, we have learned so much about these grand, majestic star cities. And there is still much to learn.

Bottom line: What is a galaxy? Learn about these starry islands in space.


There are an estimated two trillion galaxies out there. It is beyond comprehension. Well it is to this mind sitting in front of his Mac in a rural part of Oregon. Two trillion! I can’t even get my mind around the fact that our local galaxy, our Milky Way, is 100,000 light years across. Although some would say that it is even larger; about 150,000 light years across. And what is a light year?

Here’s NASA to answer that:

A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.

Why would you want such a big unit of distance? Well, on Earth, a kilometer may be just fine. It is a few hundred kilometers from New York City to Washington, DC; it is a few thousand kilometers from California to Maine. In the universe, the kilometer is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is 21 quintillion km. That’s 21,000,000,000,000,000,000 km. This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.

In our solar system, we tend to describe distances in terms of the Astronomical Unit (AU). The AU is defined as the average distance between the Earth and the Sun. It is approximately 150 million km (93 million miles). Mercury can be said to be about 1/3 of an AU from the Sun and Pluto averages about 40 AU from the Sun. The AU, however, is not big enough of a unit when we start talking about distances to objects outside our solar system.

For distances to other parts of the Milky Way Galaxy (or even further), astronomers use units of the light-year or the parsec . The light-year we have already defined. The parsec is equal to 3.3 light-years. Using the light-year, we can say that :

  • The Crab supernova remnant is about 4,000 light-years away.
  • The Milky Way Galaxy is about 150,000 light-years across.
  • The Andromeda Galaxy is 2.3 million light-years away.

So here we are. In a remote part of our galaxy, the Milky Way, far, far from everywhere, on a pale blue dot. As Carl Sagan put it in his talk from The Age of Exploration given in 1994:

On it, everyone you ever heard of… The aggregate of all our joys and sufferings, thousands of confident religions, ideologies and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilizations, every king and peasant, every young couple in love, every hopeful child, every mother and father, every inventor and explorer, every teacher of morals, every corrupt politician, every superstar, every supreme leader, every saint and sinner in the history of our species, lived there on a mote of dust, suspended in a sunbeam. …
Think of the rivers of blood spilled by all those generals and emperors so that in glory and triumph they could become the momentary masters of a fraction of a dot.

Carl Sagan, Cornell lecture in 1994

It all seems impossible for us mortals to understand.

But it won’t stop me from peering up into the night sky and wondering about the universe with total awe.

And thank goodness for dogs!