By the time you have completed the 2.6. Introduction & Exploration Activities, you should be able to:
Understand the meaning of the following terms/concepts and be able to identify examples of each: Universe, Planet (rocky, gaseous, and icy), planetesimal, solar/planetary system, star, normal star, giant star, mini star, nebula(ae), galaxy (spiral, elliptical, & irregular), galaxy cluster, galactic voids.
Use a scale model of the Solar System (the Sun as a 12” ball) to describe 1) the relative sizes of the Sun, Mercury, Earth, & Jupiter, 2) the distances from the Sun to Mercury, Earth, & Jupiter, 3) the relative distance between the Sun and other nearby stars, and 4) the size of the Milky Way Galaxy.
Use a scale model of our galaxy (the Milky Way as a DVD) to identify the relative distance to the Andromeda galaxy, relative diameters of the largest and smallest galaxies, the size of the Universe, and the distribution of galaxies in the Universe.
Scientific Terms/Concepts
Terms: Universe, Planet (rocky, gaseous, and icy), Planetesimal, Solar/Planetary System, Star, Normal Star, Giant Star, Mini Star, Nebula(ae), Galaxy (spiral, elliptical, & irregular), Galaxy Cluster, Galactic Voids.
Define and give an example of each term:
Term:
Universe
Definition:
Answer: All the aspects of the physical world that humans can possibly interact with or observe constitute the universe.
All the aspects of the physical world that humans can possibly interact with or observe constitute the universe.
Example:
Answer: Image 483529342 (this is the Hubble Ultra Deep Field)
This is the Hubble Ultra Deep Field
Term:
Planet
Definition:
Answer:Relatively large spherical objects (~100 km) that orbit a star and can be rocky, gaseous, or icy.
Relatively large spherical objects (~100 km) that orbit a star and can be rocky, gaseous, or icy.
Example:
Answer:Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, and Uranus are all examples of planets. There are also planets outside our solar system, such as Proxima b, which orbits Proxima Centauri.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune, and Uranus are all examples of planets. There are also planets outside our solar system, such as Proxima b, which orbits Proxima Centauri.
Term:
Rocky Planet
Definition:
Answer: A planet that is composed primarily of silicate rocks or metals.
A planet that is composed primarily of silicate rocks or metals.
Example:
Answer:The four inner planets of Mercury, Venus, Earth, and Mars.
The four inner planets of Mercury, Venus, Earth, and Mars.
Term:
Gaseous Planet
Definition:
Answer: A planet that is composed primarily of hydrogen and helium.
A planet that is composed primarily of hydrogen and helium.
Example:
Answer:The four Jovian planets of Jupiter, Saturn, Uranus, and Neptune.
The four Jovian planets of Jupiter, Saturn, Uranus, and Neptune.
Term:
Icy Planet
Definition:
Answer: A giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur with their constituent compounds being solids during formation, either directly in the form of ices or trapped in water ice.
A giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur with their constituent compounds being solids during formation, either directly in the form of ices or trapped in water ice.
Example:
Answer:Uranus and Neptune are really far from the sun and are thus very cold. While they are gaseous, the methane, sulfur and ammonia in their atmospheres can freeze. They can be icy planets as well as gaseous planets.
Uranus and Neptune are really far from the sun and are thus very cold. While they are gaseous, the methane, sulfur and ammonia in their atmospheres can freeze. They can be icy planets as well as gaseous planets.
Term:
Planetesimal
Definition:
Answer: Planetesimals (tiny planets) are relatively solid and irregularly shaped planetary objects that are smaller than planets. Rocky planetesimals are called asteroids and icy planetesimals are called comets.
Planetesimals (tiny planets) are relatively solid and irregularly shaped planetary objects that are smaller than planets. Rocky planetesimals are called asteroids and icy planetesimals are called comets.
Example:
Answer:Many moons that orbit planets are considered planetesimals. A good example would be Phoebe, one of the moons of Saturn. (Saturn moons since there wasn’t just one of Phoebe)
Many moons that orbit planets are considered planetesimals. A good example would be Phoebe, one of the moons of Saturn. (Saturn moons since there wasn’t just one of Phoebe)
Term:
Solar/Planetary System
Definition:
Answer: Solar/planetary systems consist of a star(s) and all the objects and matter that orbit it, including all the planets, planetesimals, dust, and gas.
Solar/planetary systems consist of a star(s) and all the objects and matter that orbit it, including all the planets, planetesimals, dust, and gas.
Example:
Answer:Our planet, Earth, is in the solar system. There are many other similar systems in the Milky Way Galaxy.
Our planet, Earth, is in the solar system. There are many other similar systems in the Milky Way Galaxy.
Term:
Star
Definition:
Answer: A star is a gaseous object large enough to fuse (or have fused) elements in its interior.
A star is a gaseous object large enough to fuse (or have fused) elements in its interior.
Example:
Answer:Our sun is a star. Much of the light we see in the night sky would constitute a star. This image is of the HR diagram (Hertzsprung-Russell) because it shows all of the stars!
Our sun is a star. Much of the light we see in the night sky would constitute a star. This image is of the HR diagram (Hertzsprung-Russell) because it shows all of the stars!
Term:
Normal Star
Definition:
Answer: A normal star is called a main sequence star by astronomers. It is a star that currently fuses hydrogen to helium in its core.
A normal star is called a main sequence star by astronomers. It is a star that currently fuses hydrogen to helium in its core.
Example:
Answer:Our sun is a normal star.
Our sun is a normal star.
Term:
Giant Star
Definition:
Answer: A giant star is a large star that fuses hydrogen to helium in shells outside its core and may fuse heavier elements in its core.
A giant star is a large star that fuses hydrogen to helium in shells outside its core and may fuse heavier elements in its core.
Example:
Answer:The star Aldebaran in the constellation Taurus is a good example of a giant star.
The star Aldebaran in the constellation Taurus is a good example of a giant star.
Term:
Mini Star
Definition:
Answer: A mini star, or dwarf, is a small, extremely dense star produced at the end of a star’s life cycle. As such, it is a remnant of normal & giant stars.
A mini star, or dwarf, is a small, extremely dense star produced at the end of a star’s life cycle. As such, it is a remnant of normal & giant stars.
Example:
Answer:Proxima Centauri, the star closest to us, is a mini star.
Proxima Centauri, the star closest to us, is a mini star.
Term:
Nebula
Definition:
Answer: Nebula(ae) are large clouds of gas and dust and are usually several light years across and contain mostly hydrogen and helium gas.
Nebula(ae) are large clouds of gas and dust and are usually several light years across and contain mostly hydrogen and helium gas.
Example:
Answer:
*
Term:
Galaxy
Definition:
Answer: A galaxy is an enormous agglomeration of planets, stars, and nebulae, organized into massive glowing aggregates, and held together by mutual gravitational attraction and glow by the combined light from their stars, planets, gas, & dust.
A galaxy is an enormous agglomeration of planets, stars, and nebulae, organized into massive glowing aggregates, and held together by mutual gravitational attraction and glow by the combined light from their stars, planets, gas, & dust.
Example:
Answer:We live in the Milky Way Galaxy. Andromeda (our closest neighbor) is a great example as well. There are billions of galaxies you could use as an example. Andromeda: *image 1920413984
We live in the Milky Way Galaxy. Andromeda (our closest neighbor) is a great example as well. There are billions of galaxies you could use as an example. Andromeda: *image 1920413984
Term:
Spiral Galaxy
Definition:
Answer: Spiral galaxies consist of a relatively thin, pinwheel shaped disk orbiting a central bulge composed of older stars and fewer nebulae.
Spiral galaxies consist of a relatively thin, pinwheel shaped disk orbiting a central bulge composed of older stars and fewer nebulae.
Example:
Answer:Our Milky Way galaxy is a spiral galaxy.
Our Milky Way galaxy is a spiral galaxy.
Term:
Elliptical Galaxy
Definition:
Answer: An elliptical galaxy is a spherical- to football-shaped galaxy that contains few nebulae but many stars. In elliptical galaxies, the stars orbit the center in all directions.
An elliptical galaxy is a spherical- to football-shaped galaxy that contains few nebulae but many stars. In elliptical galaxies, the stars orbit the center in all directions.
Example:
Answer:
Term:
Irregular Galaxy
Definition:
Answer: An irregular galaxy is when the shapes of spiral and elliptical galaxies are distorted by collisions or near misses, irregular galaxies are formed.
An irregular galaxy is when the shapes of spiral and elliptical galaxies are distorted by collisions or near misses, irregular galaxies are formed.
Example:
Answer:
Term:
Galaxy Cluster
Definition:
Answer: A galaxy cluster is a large group of galaxies. Clusters can be clusters and superclusters.
A galaxy cluster is a large group of galaxies. Clusters can be clusters and superclusters.
Example:
Answer:Watch this video (4 minutes) about the Laniakea Supercluster:
Watch this video (4 minutes) about the Laniakea Supercluster:
Term:
Galactic Voids
Definition:
Answer: Galactic voids are large regions of the Universe that contain few, if any, galaxies.
Galactic voids are large regions of the Universe that contain few, if any, galaxies.
Example:
Answer:An example would be anywhere in the universe where nothing seems to be there.
An example would be anywhere in the universe where nothing seems to be there.
Solar System Scale
Use a scale model of the Solar System (the Sun as a 12” ball) to describe 1) the relative sizes of the Sun, Mercury, Earth, & Jupiter, 2) the distances from the Sun to Mercury, Earth, & Jupiter, 3) the relative distance between the Sun and other nearby stars, and 4) the size of the Milky Way Galaxy.
Scale Model 1. The Sun as a 12" ball (30.5 cm)
The Sun is so large that is is hard for us to comprehend, so let's shrink it to something we do understand. Imagine making the Sun about 4.6 billion times smaller. If we did, the Sun would be about the size of a 12" ball (a little bigger than a basketball and nearly twice as big as a soccer ball). At this scale, what size would the planets be? ...and how far apart would they be?
The Size of the Planets
In the box below, enter estimates for the scaled sizes of 1) Mercury (the smallest planet in our solar system), 2) Earth (our home), and 3) Jupiter (the largest planet).
If you'd like, you can also estimate the sizes of the other planets. Remember, you're estimating the size these planets would be if they were 'scaled down' in the same way we scaled the Sun. Number your estimates (as above).
Answer
At this scale:
Mercury would be the size a grain of sand (0.05 in or 1.3 mm)
Venus would be a little smaller than a BB (0.11 in or 2.8 mm)
Earth would also be a little smaller than a BB (0.12 in or 3 mm)
Mars would be the size of a grain of sand (~0.06 in or 1.5 mm)
Jupiter would be the size of a ping pong ball (~1.2 in or 3 cm)
Saturn would be the size of a ping pong ball, with rings! (~1 in or 2.6 cm)
Uranus would be the size of a small marble (0.44 in or 1.1 cm)
Neptune would also be the size of a small marble (0.42 in or 1 cm)
Pluto would be the size of a very sharp pin (~0.02 in or 0.5 mm)
Mercury, Earth, and Jupiter are useful scale sizes to remember. With those memorized, you only need to remember the relative sizes of the other planets to have an accurate model for the relative sizes of the planets and Sun. (The relative sizes are as follows: Mars is a little bigger than Mercury, Venus and Earth are about the same size, Jupiter & Saturn are about the same size, and Uranus and Neptune are about a third the size of Jupiter.)
The Distances between the Planets
In the box below, enter estimates for the scale distances from the Sun to 1) Mercury, 2) Earth, and 3) Jupiter.
If you'd like, you can also estimate the distances to the other planets. Number your estimates (as above).
Answer
At this scale:
Mercury would be 41.6 feet away from the Sun (12.7 m)
Venus would be 78 feet away (24 m)
Earth would be 106 feet away (32 m)
Mars would be 162 feet away (49 m)
Jupiter would be 555 feet away (~0.1 mi or ~0.16 km)
Saturn would be 1019 feet away (~0.2 mi or ~0.3 km)
Uranus would be 2032 feet away (~0.4 mi or ~0.6 km)
Neptune would be 3200 feet away (~0.6 mi or ~1 km)
Pluto would be 4200 feet away (~0.8 mi or ~1.3 km)
The edge of the solar system would be ~2 miles (~3.2 km) from the Sun.
The image below is a satellite image of the campus of BYU-Idaho, showing the scale distances between the Sun and planets of our solar system. The uppermost blue dot (representing the location of the Sun, Mercury, Venus, & Earth) lies in the Romney Building, home to the physical sciences, and the lowermost blue dot (representing the location of Pluto) lies in the field just southwest of the Rexburg Temple. In this image covered all of Rexburg, the edge of the solar system would be a circle (with the Romney Building at the center) that nearly passes through the Walmart north of town. If you've never been to campus, use the ruler feature in Google Earth (or equivalent) to help you imagine where the planets would be located if the Sun were sitting next to you.
As above, focusing on patterns can help you keep the model straight. For example, remembering these facts is not challenging: the terrestrial planets all lie at scale distances between ~40 & 160 feet from the Sun, the gas giants are located at 0.1, 0.2, 0.4, & 0.6 miles, and the edge of the solar system lies at about 2 miles.
The Distances between Stars (Solar Systems)
In the box below, enter an estimate for the scale distance from the Sun to the nearest star, which is a little over 4 light years away.
Answer
The image below shows the scale distance between our solar system and our nearest neighbor, which would be located near the Eiffel Tower! At this scale, each solar system would be several miles wide but the two solar systems would be separated by more than 5500 miles! Are you surprised? Most people are. Space is tremendously vast... and empty!
In case you were wondering, the solar system nearest our own is called Alpha Centauri. It consists of three stars and one confirmed exoplanet. That planet is not much larger than Earth and orbits in the habitable zone of Proxima Centauri, the smallest and nearest of the three stars. To the naked eye, this three star solar system looks like a single star—the third brightest in the night sky and the brightest in the southern constellation Centaurus. Powerful telescopes can resolve individual stars, as shown in the image below.
The Size of the Milky Way Galaxy
With the scale size of a star (~0.02 in or 0.5 mm), scale width of a solar system (~4.3 in or 11 cm), and scale distance between stars (0.25 mi or 0.4 km) established, we are prepared to consider the size of a galaxy in this model.
In the box below, enter your estimate for the scale width of the Milky Way Galaxy.
Answer
At this scale, the galaxy would be about twice as big as North America, as illustrated in the image below. Note the location of our star, the Sun—which we placed near the BYU-Idaho campus. Consider that this scale model of the Milky Way would be about 5,000 miles (~8,000 km) wide, about 80 miles (129 km) thick, and consist of several hundred billion candy-sprinkle-sized stars spaced about 4 football fields apart—across an area about twice as big as North America. Isn't that a cool model, one worth carrying around in your head? We think so!
Galaxy Scale
Use a scale model of our galaxy (the Milky Way as a DVD) to identify the relative distance to the Andromeda galaxy, relative diameters of the largest and smallest galaxies, the size of the Universe, and the distribution of galaxies in the Universe.
Scale Model 2. The Sun as a Candy Sprinkle
The Size of Our Solar System & The Distance between Stars
Our first scale model becomes unproductive if we try to extend it beyond the nearest stars. In order to understand distances in galaxies, we need a new scale. For our new model, we make the Sun even smaller: we scale it down to the size of a very small, round candy sprinkle (about 0.02 in or 0.5 mm across). At this scale, the solar system would be about the size of your palm (~4.3 in or 11 cm)—as shown in the image below. (FYI: The green dot representing the candy sprinkle is larger than the Sun would be. We made it that size so you could see it.)
At this new scale (Sun is a small candy sprinkle), where would you place the next star (solar system)? Enter your estimate below.
Answer
If our Sun was the size of a cake sprinkle, the next closest solar system would be about 4 American football fields away. Imagine laying a tiny cake sprinkle at the end of a field and then walking across four football fields to see the next cake sprinkle. That is a really big distance.
The Number of Stars in Our Galaxy
We mentioned above that there are several hundred billion stars—say 200 billion—in our Galaxy. Does the number 200 billion mean anything more than 'A FREAKIN LOT!' to you? It doesn't to most people. So, that's next on our list of things to understand. In order to do that, we want you to estimate how much space 200 billion small candy sprinkles would fill. Would it fill a bucket? a car? a bedroom? ... ?
In the space below, enter your estimate of the space that 200 billion small candy sprinkles would fill.
Answer
200 billion candy sprinkles would fill one extra-large yellow school bus... and 14 more just like it, as shown below! Kind of boggles the mind, doesn't it?!
By the way, 200 billion is a reasonable estimate for the number of galaxies in the Universe. So, how many stars are there in the Universe? A reasonable estimate based on today's knowledge would be about 200 billion times 200 billion stars, or about 40,000,000,000,000,000,000,000 stars. Um ... that's a really big number. In fact, with that number of small candy sprinkles, you could cover the entire continent of North America (from Panama to the Arctic, Alaska to Florida, and from Nova Scotia to Baja California) nearly one football field deep in candy sprinkles.
Is it any wonder that the Lord described His creations to Moses as 'without number'? Remember, Moses lived in a culture where even a small number like 1,000 didn't usually mean '999 + 1'; it typically meant 'AN IMMENSE NUMBER!'
Scale Model 3. The Milky Way is the Size of a DVD
As we extend our view beyond galaxies, our second scale model also becomes unproductive. In order to understand distances between galaxies in the Universe, we need a new scale. Our new model is based on scaling the Milky Way down to the size of a DVD. In this model, the ~100,000 light year diameter of the Milky Way becomes the 5 inch (13 cm) diameter of a DVD.
How Big are Galaxies?
At this scale, the very smallest galaxies would be a little smaller than BBs, large galaxies such as the Milky Way and Andromeda would be about the size of a DVD, and the largest galaxies would be about the size of a car or merry-go-round (~8 feet or 2.5 m across). The scaled size range of galaxies in the Universe is illustrated by the images below. Small galaxies, which can contain as few as several hundred thousand stars, are far more abundant in the Universe than large galaxies. And the largest galaxies, which can contain as many as 1 trillion stars, are quite rare.
The Distances between Galaxies
Andromeda is the nearest large galaxy to the Milky Way. Using our current scale model, estimate the scaled distance to Andromeda.
Record your estimate in the box below.
Answer
If our galaxy was the size of a DVD, the next closest galaxy (Andromeda) would be 8 feet away. If a 6 foot man reached his arms up high , we would have to put the first DVD (the Milky Way) at the top of his reach, and the second DVD (Andromeda) below his feet. At this scale, that is how far apart these two galaxies are.
On this same scale, where the sun is the size of a soccer ball, let’s look at how far the planets will be from the sun. Keep in mind that if the sun was about the size of a soccer, this would be how big Mercury, Earth, and Jupiter would be:
But for the purposes of this next image, we are just looking at distance. Planets are not to scale. If the sun was about the size of a soccer ball, how far away would Mercury, Earth, and Jupiter be from the sun?
If we assume a standard size bus is about 45 feet, this would give us a rough idea of the distance between the Sun and Mercury, Earth, and Jupiter.
The Size of the Universe
The Universe contains all existing energy, matter, and space. As we'll discuss later in this unit, the Universe does not exist inside 'something else', like Earth exists inside our solar system and galaxy. As a result, it's inappropriate to think about the dimensions of the Universe in the same way we think about the size of objects that exist inside the Universe. For now, we'll leave this issue alone and simply provide an answer. Later, we'll explore some introductory ideas regarding how to think about the geometry of the Universe. At the scale of model three the Universe would be about 70 miles (113 km) in diameter. In southeast Idaho, where BYU-Idaho is located, the distance between Rexburg and Pocatello is about 70 miles. Can you think of a city or location that is about that distance from you? Now, image a 70-mile-wide sphere (that doesn't exist inside something larger) containing several hundred billion galaxies ranging in size from BBs to merry-go-rounds and spaced up to about 80 feet apart. Finally, consider that these galaxies and not evenly spread throughout the sphere but are instead concentrated at nodes and along sheets and filaments, as illustrated in the image below. Recognize that each dot of light in that image is a galaxy, galaxy cluster, or galaxy supercluster. In other words, each dot of light represents billions of stars. Note also the large voids that contain few, if any, galaxies. That's our Universe! It looks a little like foam, neuron networks, or cell boundaries, doesn't it?
