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What is that?–COMET-a ball of ice and rock orbiting the sun that leaves a ‘flaming’ trail of particles behind it

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Image: 2013 image of Comet Ison on its path towards the Sun. Source: NASA/MSFC/Aaron Kingery

Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:

Comet – an object orbiting the sun made of rock and ice that grows a “tail” of vapor and dust when it approaches the sun

Dirty Snowball

Comets are sometimes described as “dirty snowballs” because they are made of a mixture of both ice and rock and dust.  They orbit the sun in an elongated, oval path that can take hundreds or even millions of years to  complete.  They may spend much of their time traveling through the Kuiper Belt, a region of space beyond Neptune, the furthest planet from our sun.  

Flaming Tail

Comets are different from asteroids, which tend to be composed of rock and/or metals, because they contain large amounts of ice–frozen water and other frozen gases.

This image of Comet Ison, published in 2013, was made from combined photos taken through blue and red filters. Source: NASA/ESA/Hubble Heritage Team (STScI/AURA).

“When frozen, they are the size of a small town.  When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets,” according to NASA.

When a comet’s orbit brings it near to the Sun, the Sun’s warmth heats up the comet’s ice.  The melted ice boils off and the comet’s ice, dust, and rock surface make a cloud around the comet.  As the cloud trails behind the comet it leaves a wide path of particles millions of miles long.  The sun lights up this tail, sometimes making it visible on Earth.

Parts of a comet

Source: NASA
  • Nucleus–the main body of the comet, which is made of frozen gases, rock and dust
  • Coma–the cloud of particles and gases that form around the comet nucleus when it is heated by the Sun
  • Head–when a comet is traveling near the sun, and a coma forms, the head is the nucleus and coma, which may be 600,000 miles (1 million kilometers) across.  The head is a bright cloud of particles and gases lit by the sun.
  • Tail–when the comet is near the sun and the coma forms, the tail is the long trail of particles and gases left behind the head as it hurtles through space.  Tails can stretch for millions of miles.

How many comets are there in our solar system?

Scientists estimate there are billions of comets orbiting the Sun in paths that pass far outside Neptune’s orbit.  They travel in the far distant portions of our solar system called the Kuiper Belt and the Oort Cloud.

Although scientists think there are billions of comets, we have only discovered and named less than 4,000 comets.

The European spacecraft Giotto took this photograph of the nucleus of Halley’s Comet in 1986. Image Credit: Halley Multicolor Camera Team, Giotto Project, ESA.

How are comets named?

A comet is usually named after the person that discovered it.  Halley’s Comet, perhaps the most famous comet, is named after Edmond Halley, an English astronomer.  He studied historical reports of other astronomers and suggested that reports of a comet appearing every 75 years might be the same comet.  He predicted it would appear again in 1758.  He was right and the comet was named after him.  But he did not live long enough to see its return and his theory proven.

Halley’s comet will not appear to us on Earth again until 2061.

Many comets now have the names of spacecraft in their names–names like Linea, Soho and Wise–because spacecraft (and their operators) are very good at finding comets.

Design your own comet!

Imagine you discovered a comet flying through space and it was named after you. What would it look like? What types of ices and rock would it be made of? How long would it take to orbit the Sun? What year would we see it next in Earth’s nighttime sky?

Please post your comments below.

Be stellar!

Matthew Cross

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Quick and easy explanation of ASTEROIDS

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Image Headline: What is that Asteroid--A tiny planet, a rock, a lump of metal--any one of these--floating in space without gravitry and without air

Asteroid – lump of rock or metal that orbits the sun

An asteroid, a word also meaning “like a star,” is a lump of rock or metal–and sometimes ice–that orbits the sun. Some orbit the sun directly, some orbit other planets, and some orbit our entire solar system.

Asteroid Belt

What is the Asteroid Belt and where is it located?

Millions of asteroids orbit the sun just like the Earth and the planets do. Most of the asteroids scientists have found are located in the Main Asteroid Belt, which is a band of asteroids 140 million miles wide. The Main Asteroid Belt starts just outside the orbit of Mars and is well inside the orbit of Jupiter, which is the next planet out from Mars.

Image of the asteroid Bennu and other asteroids in the distance
The asteroid Bennu likely formed in the Main Asteroid Belt, maybe two billion years ago, but its path brings it much closer to Earth now. Source: NASA.

See an amazing image of the Main Asteroid Belt here at Space.com. (The Main Asteroid Belt is shown in green.)

If you have ever seen a model of the solar system, you know the eight planets all travel in the same plane around the sun. Their orbits–the paths they take–look like a disc (or flat plate) of rings around the sun. The Main Asteroid Belt creates a thick ring on this same plane, like its part of the same disc or plate. The asteroids in the Main Asteroid Belt also travel in the same direction around the sun as all the planets of our solar system.

What are asteroids made of?

Most asteroids in the Asteroid Belt are made of rock. Some asteroids are made of metal–mostly iron and nickel. These metal asteroids are shiny and reflect the sun’s light. Some asteroids are made of a mix of rock and metal. And some more distant asteroids are made of ice. Some asteroids may even contain ice made from water, which could be useful to support astronauts if we colonize the Asteroid Belt.

Image of the asteroid Psyche showing two large craters
Artist’s concept of the asteroid 16 Psyche, a metallic asteroid composed of iron and nickel, like the Earth’s core. Psyche may be the stripped core of an ancient planet. Image credit: Maxar/ASU/P. Rubin/NASA/JPL-Caltech.

Some asteroids are solid. Some asteroids are just “piles of rubble held together by gravity,” according to an article by Nola Taylor Redd on Space.com. “Most asteroids aren’t quite massive enough to have achieved a spherical shape and instead are irregular, often resembling a lumpy potato.”

How big are asteroids?

Asteroids range from the size of specks of dust to moonsize. The largest asteroid in the Asteroid Belt is the dwarf planet Ceres. It is almost 590 miles across (diameter). That is small compared to Earth’s moon, which has a diameter of 2,158 miles. But it’s much bigger than one of Mars’s moons, Deimos, which is only seven miles across.

Ceres comprises 25 percent of the mass in the Main Asteroid Belt.

There are a number of other asteroids that are 100 and 200 miles long.

What about other asteroids?

Image of the asteroid Arrokoth, which looks like a sphere stuck to a slightly larger sphere, giving the impression of a two-ball snowman
Here is a photo of Arrokoth taken by the New Horizons spacecraft. Image grabbed from NASA’s website.

Beyond Neptune is an even wider ring of asteroids called the Kuiper Belt. The Kuiper Belt includes the dwarf planet Pluto, which astronomers once used to count among the nine planets in our solar system. There is even a snowman-shaped asteroid in the Kuiper Belt named Arrokoth.

NASA has a great interactive web page dedicated to the Kuiper Belt.

Eros

The asteroid Eros has made history both in astronomy and science fiction.

Discovery of Eros

Two astronomers discovered Eros independently on the same day, August 13, 1898–Gustav Witt in Berlin, Germany and Auguste H.P. Charlois in Nice, France. It was the first near-Earth asteroid ever discovered.

Image of the asteroid Erros, which looks like an oblong shape with a crater near the center
This image of Eros was created from four images taken by NEAR on February 14, 2000, immediately after taking orbit. The crater in the center is four miles wide. Source: NASA/JPL/JHUAPL.

NASA’s visit to Eros

Eros was also the first asteroid on which we have landed a spacecraft. Eros, named after the Greek god of love, was first orbited by a spacecraft, the NEAR spacecraft, on Valentine’s Day, February 14, 2000. After nearly a year orbiting and studying Eros, the NEAR spacecraft landed on Eros on February 12, 2001.

Astronomers have also used Eros to determine the distance between the sun and the Earth and to determine the combined mass of Earth and the Moon.

See a NASA’s 3-D rendering of Eros that you can move and manipulate on your own screen.

Ender’s Game

Eros also entered the annals of Science Fiction in the novel Ender’s Game, which won both the Hugo and Nebula awards.

Cover of Ender's Game by Orson Scott Card

In Ender’s Game, the hero Ender Wiggin travels to the asteroid Eros, which has been turned into I.F. Command, a military base and training center, to finish his military training.

“The tug reached Eros before they could see it. The captain showed them the visual scan, then superimposed the heat scan on the same screen. They were practically on top of it–only four thousand kilometers out–but Eros, only twenty-four kilometers long, was invisible if it didn’t shine with reflected sunlight.”

“The captain docked the ship on one of the three landing platforms that circled Eros. It could not land directly because Eros had enhanced gravity, and the tug, designed for towing cargoes, could never escape the gravity well.”

. . . .

“Ender hated Eros from the moment he shuttled down from the tug. He had been uncomfortable enough on Earth, where floors were flat; Eros was hopeless. It was a roughly spindle-shaped rock only six and a half kilometers thick at its narrowest point. Since the surface of the planetoid was entirely devoted to absorbing sunlight and converting it to energy, everyone lived in the smooth-walled rooms linked by tunnels that laced the interior of the asteroid. The closed-in space was no problem for Ender–what bothered him was that all the tunnel floors noticeably sloped downward. From the start, Ender was plagued by vertigo as he walked through the tunnels, especially the ones that girdled Eros’s narrow circumference. It did not help that gravity was only half of Earth-normal–the illusion of being on the verge of falling was almost complete.

[E]veryone lived in the smooth-walled rooms linked by tunnels that laced the interior of the asteroid.

Ender’s Game

“There was also something disturbing about the proportions of the rooms–the ceilings were too low for the width, the tunnels too narrow. It was not a comfortable place.”

By the end of Ender’s Game, we learn the secret of the unusual construction of the base inside Eros. But I won’t spoil author Orson Scott Card’s surprise. So read Ender’s Game and find out for yourself.

Design your own asteroid!

Image: Artist's concept of an asteroid.
Artist’s concept of an asteroid. Source: NASA.

As we’ve seen, asteroids can be any shape you want. What shape would you make your asteroid? Would you create a military base or a shopping mall inside it? Or would you make a theme park or a factory on the outside?

Would you add your own gravity–like I.F. Command did in Ender’s Game? Or would you let visitors enjoy the fun of zero-grav?

What would you name your asteroid?

Please post your comments below.

Be stellar!

Matthew Cross

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Weird science that makes giant arthropods impossible

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Some of Sci Fi’s most interesting aliens look like or share traits with Earth’s arthropods.  Arthropods include insects (like, ants), centipedes and millipedes, arachnids (like, spiders) and crustaceans (like, crabs and lobsters).  Think of the giant sandworms of Arrakis in Dune, the spider-like buggers of Ender’s Game, and the Bugs of Starship Troopers, which are very cool alien space bugs.  All of these aliens are human-size or larger.

But on Earth, physics and genetic history have kept arthropods much smaller than humans.  The largest arthropods alive are certain crabs and lobsters, and even the largest of these, the American Lobster, does not grow to 50 pounds.  Yes, that’s big for a lobster, but not exactly the match of a human in a gladiator ring or in a space battle.  It’s certainly not large enough to develop the large, complex brain needed for sentience.

Photo of crayfish. Crayfish exoskeletons form natural armor. Photo by Anton Ahlberg (https://unsplash.com /@anton_ahlberg).
Crayfish exoskeletons form natural armor. Photo by Anton Ahlberg (https://unsplash.com
/@anton_ahlberg).

On Earth, arthropods developed exoskeletons (skeletons on their outsides), which provide great protection from enemies and allow the evolution of an amazing range of weapons and tools.  Consider the giant claws of a crab or the sting of a scorpion.  But exoskeletons restrict how large arthropods can afford to grow.  Molting — the process of replacing an exoskeleton as the animal grows — takes longer the larger the animal grows.  Some crabs take an entire month to climb out of their old skeleton and allow the new one to harden up.  Exoskeletal legs are also basically tubes filled with muscle and tissue.  If an arthropod grew to human size, the exoskeleton would not be strong enough to hold up the ‘pod’s weight.  And the arthropod’s muscles would not be strong enough to move the exoskeleton around.

Arthropods also evolved in a way that their cells get oxygen through gills, their skin, or tubes in their bodies, called tracheae, that open directly to the outside air.  Humans and other vertebrates have lungs and feed oxygen to the cells through the blood.  As ‘pods grow larger, it becomes harder and harder to get enough oxygen through their skin or tracheae to every cell.  A ‘pod as large as a human might easily suffocate.

As ‘pods grow larger, it becomes harder and harder to get enough oxygen to every cell.

But a ‘pod-like animal that evolved on another planet might not have those limits.  For example, we can imagine an alien “Pod” that evolved from simpler ancestors with both an internal and external skeleton.  Such creatures might have an internal skeleton in their arms and legs to support the weight of a large body.  But with a partial exoskeleton, the Pod might have a natural helmet for its head, giant claws, or possibly a scorpionlike tail.  With lungs instead of tracheae, the Pods could breathe like we do.  Finally, on an alien world with different elements in the rocks and soil, the Pods might evolve with exoskeletons made from lighter, stronger materials that would allow them to grow mighty armor and still move quickly.

Photo of two red crab claws clasping. Could a Pod with giant crablike claws evolve on some distant planet? Photo by Joshua Théophile (https://unsplash.com@nunchakouy).
Could a Pod with giant, crablike claws evolve on some distant planet?
Photo by Joshua Théophile (https://unsplash.com@nunchakouy).

Check out this great University of California at Berkeley website that explains the reasons that limit the size of arthropods on Earth.

Photo of bee. Bees and wasps can fly AND sting. Photo by USGS (https://unsplash.com /@usgs).
Bees and wasps can fly and sting.
Photo by USGS (https://unsplash.com
/@usgs).

Design a Pod

Let’s design our own alien Pod.

What two features that exist on Earth’s arthropods would you add to your Pod?  Would they make it a fearsome foe?  Would it have any weaknesses?

Please post your comments below.

Be stellar!

Matthew Cross

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What is that?–LIGHT YEAR-a measure of distance–not a measure of time

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Image: Prism refracting white light into a rainbow. Text: LIGHT YEAR--A measure of distance--not a measure of time--the light year helps astronomers describe the vast distances between the stars.

Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:

Light Year – a unit of length used to measure great distances in space

Light Year is a confusing term.  We all know what a year is.  A year is the length of time from your birthday to your next birthday.  It is also the length of time it takes the Earth to travel around the sun one time.  That idea may help us.


A year measures time.  It is how long the Earth takes to travel around the sun.  We could make up a term called an Earth Year.  It would mean how far the Earth travels in one year — or how far that trip around the sun is.  By the way, that is about 584,000,000 miles.  (If you live anywhere besides the United States, then that is about 940,000,000 kilometers.)


If an “Earth Year” (my made up term) is how far the Earth travels in one year, then a Light Year is how far a beam of light travels in one year.  Light travels very, very fast.  It can travel from the sun to the Earth in about 8 minutes.  That is about 92,960,000 miles (149,600,000 kilometers).  It takes me more than 8 minutes just to run one mile.

Sunlight on the Earth. Image: NASA.

According to scientists, light is the fastest traveler in the universe.  In fact, there is a rule of physics that says nothing in the universe can travel faster than light.

Light travels slower through glass and water than through air or a vacuum. Source: NASA.

Light also travels at a constant speed in the vacuum of space.  (It does slow down when it passes through air, a window, or water.  But even then, it travels super fast.  Michael Phelps is fast in water, but light is still faster.)  In the vacuum of space, light does not get tired and stop flying along.

A digital version of the Sun’s spectrum created from observations captured by the Fourier Transform Spectrometer at the McMath-Pierce Solar Facility at the National Solar Observatory on Kitt Peak, Arizona. Source: N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF.
Proxima Centauri. Image: NASA.

Because light travels so fast, it travels very far in one year.  That makes a Light Year–a measure of distance–very useful for measuring the vast distances between stars.  For example, the nearest star to our sun is Proxima Centauri.  It is about 25,000,000,000,000 miles away (40,000,000,000,000 kilometers).  It’s much easier to say (and to write) 4.25 light years.

So, when someone says “That is light years away,” they mean it is very far.  They are not talking about time or how quickly a human could travel that distance.  They are just talking about how large the distance is.

Invent your own measurement!

Let’s invent our own measurement of distance.

First, decide what you will use to set your measurement length. Will it be the length of an object? (To measure small distances, we could use the length of a twig we found.) Will it be the distance that something travels? (Like how far you can ride your bike in five minutes?)

  • Tape Measure
  • Bug on Stick
  • Bicycle
We can use measuring tools, objects we find, or even distances we can travel in a certain amount of time as ways to measure lengths and distances.
Photos by Brett Jordan, Elegance Thika, and Fachy Marin from unsplash.com.

What will you use your new measurement length to measure? The length of your hand? Then length of a car? The length of your neighborhood?

Finally, what will you name your measurement length? An “twig unit”? A “bike in 5”? Will you name it after yourself? (A “Matthew Mile”?) Or create a shiny, brand-new name you made up yourself? (A “plenth”?)

Please post your comments below.

Be stellar!

Matthew Cross

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Star Clusters–Trumpler 14

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This star cluster–called Trumpler 14–contains some of the brightest stars to be seen in the Milky Way. The Milky Way is the galaxy where we live.

Trumpler 14 lies in the Carina Nebula, about 8,000 light years away. The Carina Nebula is known for being a major star birthplace or nursery.

What if we called it a Star Farm?

Can you imagine a Sci Fi story set in a Star Farm like Trumpler 14? The seeds have already been planted and the crops of stars are already springing up.

What would the star farmers do?

  • Operate massive solar arrays to collect energy?
  • Siphon off hot gases–like hydrogen and helium?
  • Operate orbiting plant farms?

Please post your comments below.

Be stellar!

Matthew Cross

P.S. The small, dark shape just left of center is the silhouette of a nodule of gas. But it looks like a ship full of eager star farmers to me. MC