# What would the night sky look like if the Milky Way were the only galaxy in the universe?

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I'm curious to know what the sky would look like without any other galaxies out there. How much do other galaxies factor into the stars we see? Does the Milky Way account for most of them? Would the night sky look normal? Or would it be very empty?

I feel sure this is a repeat, but couldn't immediately find it. The only things in the night sky we can see (with the naked eye) that are not part of our own Galaxy are (on a good night) the Andromeda galaxy and the Large and small Magellanic clouds. Every individual star brighter than $V=6$ and visible to the naked eye is in the Milky Way.

So it would hardly look any different.

It wouldn't be too apparent, but there are a few objects that you can see in good viewing conditions with the naked eye that would disappear.

Here they are in order of brightness. I marked the objects in a reddish color.

1. The Large Magellanic Cloud, apparent magnitude 0.9, located in the constellation Dorado. Only visible from the southern hemisphere.

2. The Small Magellanic Cloud, apparent magnitude 2.7, located in the constellation Tucana. Only visible from the southern hemisphere.

3. The Andromeda Galaxy, apparent magnitude 3.4, located in the constellation Andromeda.

And that's it. Seriously. Sure, there are a few others, but they're exceedingly difficult to see.

## The Andromeda Galaxy’s Discovery

Ancient skygazers have probably pondered the nature of this blurry spot for many thousands of years. However, the oldest known discovery of the Andromeda Galaxy dates to 964 A.D., when a Persian astronomer named Abd al-Rahman al-Sufi wrote a book about “Fixed Stars.” In it, he called out Andromeda, and also noted the position of the Large Magellanic Cloud , a much more petite satellite galaxy of our Milky Way. The Andromeda Galaxy was referred to as a “small cloud” in the heavens.

But it wasn’t until the 1800s that astronomers started realizing just how special Andromeda was. That's because until roughly a century ago, scientists thought our Milky Way was the entire universe.

For some time, observers using their telescopes to hunt comets had been turning up “nebulae” — a term that described basically any fuzzy night-sky object that was not a comet. Ones with spiral shapes, like Andromeda, were called spiral nebulae. But in 1864, an English astronomer named Sir William Huggins used a prism to break apart and analyze the various colors of light from a variety of nebulae. When he did, Huggins noticed that the light spectra of M31 was very different from some of these other nebulae.

## A challenging viewpoint

It wasn’t easy getting to this point. The Murchison Widefield Array had to be built more than 300km from the nearest town, Geraldton, to ensure a radio-quiet environment.

The array consists of thousands of radio antennas, similar to TV aerials and somewhat resembling an army of mechanical spiders. These observe low-frequency radio waves, from the lowest end of the FM (72MHz) up to the highest end of the digital TV band (300MHz).

View of about 1% of the Murchison Widefield Array, showing the tiled dipoles used to receive astronomical signals, and a ‘beam former’, aggregating the signals and controlling the pointing of the instrument. MWA Collaboration

To build the survey, a team of 20 astronomers across Australia and New Zealand has painstakingly knitted together more than 45,000 images of the sky, inventing new algorithms at every turn in order to deal with the unique challenges of these data.

For instance, while the wide field-of-view of the MWA makes an all-sky survey possible, the ionosphere distorts the signals of every observation, sometimes creating giant plasma tubes that render a night unusable.

While the wide frequency coverage yields astronomers a scientific goldmine, it also makes source-finding and analysis more difficult. And of course, an all-sky survey isn’t small - nearly half a petabyte of data and several million CPU-hours on cutting-edge supercomputers went into its making.

The first data release was published this week in Monthly Notices of the Royal Astronomical Society. It comprises a catalogue of more than 300,000 radio galaxies and images spanning 25,000 square degrees, all of which is freely accessible to the world.

There are yet more astronomical wonders lurking in the images such as collisions between galaxy clusters - some of the largest structures in the universe - to mysterious transient radio sources, and serendipitous discoveries that will take many eyes on the data to find.

A great place to start looking is the GLEAM-o-scope, an easy-to-use interactive viewer that gives anyone in the world the power to see the sky with radio eyes.

## Make the Milky Way

In this activity learners will make a model of the Milky Way. They must come up with the best materials they can think of and obtain for their models. For example, they can use cardboard, cotton wool balls and glitter. This can be done as a group model, where learners are given the task a couple days before the lesson and they must collect the materials, or else you can supply a selection of materials in class which they can then use to build the model. Encourage learners to be creative when thinking about the materials to use to represent the different components.

The aim of this activity is to give learners a three dimensional view of the Milky Way, including the structure of the central bulge and the disk containing the spiral arms. The glitter is used to represent the distribution of stars and the colours are used to demonstrate how old and young stars are distributed in the galaxy. The life cycle of stars in not covered until Grade 9. Therefore, although you may want to mention that the stellar populations in the bulge and the disk of our galaxy are different, it is not essential to do so.

• thick piece of black cardboard at least 30 cm across
• other materials for your model, either collected by you or supplied by your teacher

Examples of other materials to supply are:

• a bag of cotton balls or pillow stuffing
• glue
• string
• pencil
• red, blue, gold and silver glitter
• star sticker

We will learn more about the life cycle of stars in Gr 9. Younger stars are hotter and bright white or blue in colour, while older stars are cooler and more yellow and red in colour.

INSTRUCTIONS:

1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will either need to collect the most appropriate materials for your model beforehand, or else your teacher will supply you with a selection of materials to use in class.
2. Cut out a circle of radius 15 cm from the black card and use this to build your 3D model.
3. You must show the central bulge, the spiral arms and the different coloured stars.
4. Mark the position of our Sun on your model.
5. Using your model, view it from different angles and compare the view you have with the images of the Milky Way in this chapter.

Learners must come up with their own model designs. An example design is included here if you would prefer to make one which you then use to demonstrate to learners, instead of them making their own:

1. Build a dome of cotton balls in the centre of one side of the cardboard. Use glue to keep the cotton balls in place. The dome should be about 8 cm across and 4cm high.
2. Repeat on other side of the board. The cotton ball dome represents the bulge of our galaxy.
3. Pull the outer cotton balls into six spirals around the cotton ball dome. These represent the five major spiral arms found in the disk of our galaxy, in addition to the minor spiral arm that our Sun is found in.
4. Dribble glue on the spiral arms and sprinkle blue and silver glitter on the glue. These represent hot newly forming stars.
5. Dribble glue all over the cotton wool dome ball in the middle and sprinkle this glue with gold and red glitter to represent cooler, older stars.
6. Mark a position 8 cm from the centre inside one of the spiral arms.
7. Stick the star sticker on the spiral arm at the marked position. This marks the position of our Sun.
8. Make a hole in the centre of the model and thread it with a string so that it can be hung up.

What are the two main parts that make up our Milky Way Galaxy?

Where are the spiral arms located in the disk or the bulge of our galaxy?

Is our Sun found in the central bulge or in a spiral arm in the disk?

Our Sun is located in a spiral arm.

How far from the centre of the galaxy is our Sun located?

Just over half way out from the centre.

## Milky Way: A Night Sky Wonder

The same new moon that sets up the total solareclipse Aug. 1 will create dark night-sky conditions for stargazing, makingthis a great time to check out the beautiful midsummer Milky Way.

Campers and rural residents should have littletrouble spotting it, weather permitting.

As soon as darkness falls, the Milky Way becomesevident as a wide glowing arch of variety and beauty, stretching high acrossthe sky from the northeast to southwest.

Sweep with binoculars up from the tail of theconstellation Scorpius, low in the southwest through the Summer Triangle,almost overhead and down toward Cassiopeia and Perseus in the northeast. You'llfind concentrations of stars, clusters, large apparent gaps such as the GreatRift in Cygnus, and more stars than you thought existed.

Never visible from large cities with their bright lights,smoke and haze, the Milky Way canstill be readily viewed from distant suburbs and rural locations. Visually itappears as a faint, albeit distinct ghostly band of light it almost looks more"smoky" than "milky" in appearance. From a truly dark site,however, it appears in full glory: The brightest portions can cast faintshadows, and it appears highly complex and structuredto the unaided eye and like veined marble when viewed with ordinary binoculars.

Before the invention of the telescope, the true nature ofthe Milky Way Galaxy ("Gala" is Greek for milk) was a mystery. Now weknow it's a concentration of stars in our own galaxy.

The galaxy's center is about 26,000 light-years away towardthe Sagittarius star cloud. From where we sit, the galaxy's outer edge is about20,000 light-years in the opposite direction (toward Auriga and Taurus). We resideon a spur of the Orion arm, and what we see as we look at the Milky Way in ournight sky is just a portion of nearest stars between us and the galactic center.

The sun and all the outer stars of the galaxy revolve aroundthe galacticcenter at the rate of 155 miles per second. It apparently requires about225 million of our earthly years to make one complete revolution, or one "cosmicyear," around the center of our galaxy.

When we began to realize that there were other suchvast collections or aggregation of stars, we called them "islanduniverses," but this was an obvious misnomer since universe meanseverything there is, it can hardly have a plural. So we've seemed to havesettled on "galaxies," which is a compromise as a new meaning for an old word.

What was that eerie cloud?

Unfortunately, because of the tremendous increase in lightpollution over the past quarter century, the majority of our current generationhave never seen the night sky in allits grandeur.

In his book "Nightwatch," the well-known Canadianastronomer Terrence Dickinson comments that in the aftermath of the predawn1994 Northridge, California earthquake, electrical power was knocked out over awide area. Tens of thousands of people in southern California rushed out oftheir homes looked up and perhaps for the first time in their lives saw a dark,starry sky. In the days and weeks that followed, radio stations andobservatories in the Los Angeles area received countless numbers of phone callsfrom concerned people who wondered whether the sudden brightening of the starsand the appearance of an eerie silvery cloud (the Milky Way) might have causedthe quake.

"Such reaction," notes Dickinson, "can comeonly from people who have never seen the night sky away from city lights."

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and otherpublications, and he is also an on-camera meteorologist for News 12 Westchester, New York.

## When were the top 25 Milky Way images taken?

Most of the images in the article were taken during the 2019 and the current 2020 “Milky Way season”, which stretches from about March to November each year. “While fresh and new photographs is one of the most important factors to include the image in the collection, there are other factors to consider like the originality of the place and the technical difficulties for taking the picture,” Zafra told me. “As an example, in this year’s edition, the Milky Way image from Antarctica was taken in 2018, but it’s a unique image and the author Jorgelina Álvarez posted it this year for the first time.”

Here is that image—complete with “shooting stars.”

“The same happens with Miles Morgan’s photo of erupting volcanoes and the Milky Way, which are very rare shows with very inspiring stories behind them,” said Zafra.

## Our Work

Center for Astrophysics | Harvard & Smithsonian astronomers use many methods to study the Milky Way:

Measuring precise distances and 3-dimensional motions for massive star-forming regions in the disk of the Milky Way in order to map out its spiral structure and determine its overall size and rotation speed. CfA astronomer Mark Reid is leading an international team of astronomers on the BeSSeL project, which uses Very Long Baseline Interferometry to measure extremely precise trigonometric parallaxes and proper motions for maser sources within massive star forming regions.
Measuring the Distance to the Far Side of the Galaxy

Looking for the remnants of the galaxies the Milky Way is built from. We know our galaxy grew by merging from smaller galaxies, because traces of that history are visible. That process continues today as the Milky Way strips stars from its satellite galaxies, producing “tidal streams” and other measurable effects.
Farthest Stars in Milky Way Might Be Ripped from Another Galaxy

Tracing the history of Sgr A* and the way it affects the rest of the galaxy. While our supermassive black hole is quiet today, astronomers have found signs it hasn’t always been that way. Studying the cycles of activity in Sgr A* helps us understand the behavior of supermassive black holes in other galaxies.
Milky Way Had a Blowout Bash 6 Million Years Ago

Capturing the first image of a black hole’s “shadow”: a dark region surrounded by a ring of light. The Event Horizon Telescope is a globe-spanning virtual observatory monitoring Sgr A*, designed to study the shape of the black hole’s event horizon, the boundary beyond which nothing can escape.
Event Horizon Telescope Reveals Magnetic Fields at Milky Way's Central Black Hole

Hunting for hidden structures in the Milky Way that reveal its history. Astronomers using NASA’s Fermi Gamma Ray Observatory discovered two huge bubbles of hot material extending from the center of the galaxy. These are likely either relics of a more active period in the life of Sgr A*, or the outbursts from rapid star formation earlier in the Milky Way’s history.
Astronomers Find Giant, Previously Unseen Structure in our Galaxy

Observing hypervelocity stars flung out by the supermassive black hole. These stars, which are moving at very high speeds, were probably once part of a binary system that drifted too close to Sgr A*. The gravitational interaction pulled the binary apart, kicking one of the pair out of the Milky Way entirely. Studying these runaways reveals important clues about the stars in the galactic center, including how often they are affected by the black hole.
Hyperfast Star Was Booted From Milky Way

## What is the Milky Way? (with pictures)

The Milky Way is a cluster of stars bound together by gravity in the shape of a spiral. This type of arrangement of stars is known as a galaxy. Many people are familiar with the concept of the Milky Way, since it hosts our own solar system on one of its spiral arms. During especially clear conditions, the Milky Way is visible as a faint band of light in the sky. The stars in this band of light stretch across hundreds of thousands of light years to collectively form our galaxy, which is merely one among billions in the universe.

The name was directly lifted from the Latin via lactea, which means “Milky Way.” It is probably a reference to the appearance of the galaxy in the night sky, since it does look rather like a large puddle of spilled milk. The fact that our galaxy was an interconnected system of stars was posited as early as the 1750s, when observers realized that the white blur in the sky was actually composed of millions of stars.

Astronomers who have studied the origins of our galaxy have determined that it is almost as old as the universe. The galaxy has six spiral arms which emerge from a clear center, marked with a bar of stars. The combination of spirals and a bar has led to the classification of the Milky Way as a barred spiral galaxy. It is estimated that our galaxy holds between 200 and 400 billion stars.

When viewed on its side, the Milky Way has a large central bulge surrounded by a disk of stars and dust. When viewed from above, the arrangement of the spirals around a central bar can clearly be seen. Our solar system is found on the Orion Arm, one of the shorter arms in the Milky Way. The entire galaxy is surrounded by a halo of small star clusters and dust, which would make the galaxy appear murky to outside observers.

The entire galaxy is slowly rotating around the central bar. Given the size of the galaxy, this rotation is so gradual that casual observers do not notice it. It takes the sun between 200 and 230 million years to complete an orbit of the galaxy. The next closest galaxy is the Andromeda Galaxy, another spiral galaxy which is sometimes referred to as our “sister galaxy.” Both galaxies are found in the Virgo Supercluster, a large group of galaxies which includes the “local group,” an assortment of galaxies which includes the Milky Way.

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a InfoBloom researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a InfoBloom researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

## Here's What The Night Sky Would Have Looked Like 10 Billion Years Ago

Our sun has only been around for 4.5 billion years — which means it missed the cute early years of the Milky Way galaxy. If you were standing on a planet 10 billion years ago, when the Milky Way was relatively young, the night sky would have looked very different.

#### Top image: NASA/ESA/Z. Levay (STScI)

The above image is an artist's impression of the night sky on a planet in a young Milky Way-type galaxy, the way ours was 10 billion years ago. You can see "the sky are ablaze with star birth. Pink clouds of gas harbor newborn stars, and bluish-white, young star clusters litter the landscape," as NASA explains .

A new survey of young galaxies like our own shows that as these galaxies slow down making stars, they also stop growing as quickly in general. Which makes sense. NASA explains:

Astronomers don’t have baby pictures of our Milky Way’s formative years to trace the history of stellar growth so they studied galaxies similar in mass to our Milky Way, found in deep surveys of the universe. The farther into the universe astronomers look, the further back in time they are seeing, because starlight from long ago is just arriving at Earth now. From those surveys, stretching back in time more than 10 billion years, researchers assembled an album of images containing nearly 2,000 snapshots of Milky Way-like galaxies.

The new census provides the most complete picture yet of how galaxies like the Milky Way grew over the past 10 billion years into today’s majestic spiral galaxies. The multi-wavelength study spans ultraviolet to far-infrared light, combining observations from NASA’s Hubble and Spitzer space telescopes, the European Space Agency’s Herschel Space Observatory, and ground-based telescopes, including the Magellan Baade Telescope at the Las Campanas Observatory in Chile.