Maggie A's Meanderings




 Nov 10, 2013

My Illustrated Astronomy Definitions

This is my 100th piece. For number 100, I wanted to do something special --- something that I would really love, something that would definitely be "me" yet, hopefully be interesting or enjoyable to others.

This piece was inspired as I was taking my cat, Trilby Kitty, for his nightly walk. It was a beautiful, clear night with a star-filled sky (well, as many stars as the light pollution allows). There in the sky was the familiar hourglass of Orion which I hadn't seen in months. It got me contemplating the difference between asterisms and constellations and this piece was born..........

Asterism What a constellation ought to be. An asterism is the part of a constellation that actually looks like what you call it. Examples: Big Dipper (of Ursa Major), Teapot (of Sagittarius), "W" (of Cassiopeia), Hourglass (of Orion)
Teapot asterism of the constellation Sagittarius
Teapot asterism in Sagittarius
By Eoghanacht (Own work) [Public domain], via Wikimedia Commons
Black Hole Not the most dangerous thing in the universe. A black hole is something you basically have to be sitting on top of (in astronomical terms) before you can get sucked in. See "Last Stable Orbit" for more details. Also see "Gamma-ray Burst" for comparison.
Earth and Black Hole
The Earth would have to be quite close to a black hole to be sucked in.
If the Sun were turned into a black hole, the Earth's orbit wouldn't even be disturbed.
From my piece "The Black Hole that (Didn't) Devour the Galaxy"
Blazar Not to be confused with blazer, an item of clothing. A blazar is an active galaxy tilted in such a way we can see the disk and the jet.
Blazar, showing the viewing angle
By Mrbrak ([1]) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons
Bolide A really boring word to describe a meteor so awesome it turns into a fireball and makes a sonic boom as it blasts through the atmosphere. A bolide is what happened in Russia in 2013. It was also a bolide that devastated 830 square miles of Siberia in the Tunguska event. Calling it a bolide is a lame term for something so powerful it can cause such massive destruction. Now Calvin of "Calvin and Hobbes" would have come up with a name with some punch like a Super-Kablooier.
Bolide video
Meteor Russia 2013 Sonic Boom SOUND by George Dominik
Circumpolar One of those highly specialized, technical terms astronomers like to throw around to describe stars instead of just saying it's stars that never set so are always in the night sky. Heaven forbid they come up with a term like "perma-view" or something equally intuitive to describe that characteristic. No, they use a word you have to look up and then memorize the meaning of. Circumpolar depends on your latitude ---- at the North or South Poles every star is circumpolar; at the equator no star is circumpolar.
How to find Polaris, the North Star
Circumpolar is why the time honored instruction of how to find Polaris, the North Star, is friggin' useless for much of the northern hemisphere. Because the instruction starts with finding the Big Dipper........except the Big Dipper is only circumpolar (always in the night sky) if you happen to be 42║ north in latitude or higher which excludes most of the United States. So if you're ever lost and looking for the North Star you'd better either hope you're way up north or that the Big Dipper just happens to be out.
42nd parallel in the United StatesThe line from the Big Dipper leads to Polaris
By Filip em (Own work) [GFDL or
CC-BY-SA-3.0], via Wikimedia Commons

42nd latitude line
By Bazonka (Based on Image:Blank US Map 48states.svg)
[CC-BY-SA-3.0], via Wikimedia Commons
Constellation Those imaginary figures in the sky that our ancestors must have been experimenting with some interesting botanicals to come up with because a lot of the patterns of stars don't look a thing like the figures they're supposed to be. If these were connect-the-dots drawings, you still wouldn't know what it was supposed to be when you finished.
Constellation drawings -- Click image for full size
By Frederi(c)k de Wit (Koninklijke Deense Bibliotheek) [Public domain], via Wikimedia Commons

Gamma-ray BurstUnlike black holes, you don't have to be near a gamma-ray burst to take a hit ---- these can kill from thousands of light-years away. The most intense explosions of electromagnetic radiation there are, these bursts travel for galaxies. Lasting from milliseconds to a few minutes, while they do last they're the brightest thing in the universe. The long--duration bursts (2 or more seconds) are thought to be caused by supernovas so powerful that a term came into use to describe them, "hypernova." The short-duration bursts are now thought to be caused when two massive bodies like neutron stars or black holes collide. The radiation from gamma-ray bursts is so intense, it's speculated that one mass extinction on Earth was caused by us getting hit by a gamma-ray burst. But I still wouldn't worry about it.........even though a gamma-ray burst happens about once a day, almost all of them originate from so far away (as in way out of this galaxy) that they can't do any harm when they reach us. And gamma-ray bursts are rare in the Milky Way, so even if it did happen once in the history of Earth, my non-statistician's estimate of you dying from one of these is about as likely as you getting struck by lightning as you go to claim your Powerball winnings. 
Artist’s impression of a gamma-ray burst shining through two young galaxies in the early Universe
Artist’s impression of a gamma-ray burst shining through two young galaxies in the early Universe
By ESO/L. Calšada [CC-BY-3.0], via Wikimedia Commons
Idiot Anyone who's seriously doubted there's other life in the universe since we figured out those points of lights in the sky are suns too. Incidentally, that time period covers the 20th century when I heard a lot of speculation about if there was life "out there" or if Earth was the only planet in the universe with life. Idiots. (The concept that the Sun and the stars were the same dates all the way back to 450 BC when it was suggested by the Greek philosopher, Anaxagoras. However, it took another 2287 years, until 1838, to finally prove it.)
Observable Universe
The Observable Universe. We're in the Local Superclusters (marked in red) -- Click image for full size
By Andrew Z. Colvin (Own work) [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons
Lagrange Point The favorite of 1970s science-fiction writers ---- even had an organization, the L5 Society, named for it. Lagrange 4 and Lagrange 5 are spots at equal distance from the Earth and the Moon and, in theory, any object like a space station at L4 or L5 would stay in place without using any fuel. In actuality, it doesn't work quite that simply.
Lagrange Points
The five Lagrange points calculated by the French mathematician, Lagrange, in 1772. L1, L2 and L3 are unstable.
By Anynobody [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons
Last Stable Orbit The closest distance an object can orbit a black hole without being pulled in. In astronomical terms, pretty darn close. See "Can I safely orbit a black hole?"
orbit around a black hole
A safe orbit around a black hole.
Notice how close to the event horizon it is.
NASA and STScI [Public Domain] from
Light-year Incredibly useful and intuitive term meaning the distance that light travels in a year. See "Parsec" for comparison.
light year illustration
Light-year depiction
From StarChild site at NASA/ GSFC which should make this image Public Domain.

Three terms you have to be an astronomy buff to distinguish.....
The rock when it's flying around in space 
The same rock when it enters Earth's atmosphere. A meteor only exists for seconds or minutes.
Whatever's left of the rock when it hits the ground.
If you really want to remember how to distinguish among the three, try this:
For meteroid, think asteroid 
Meteors have a short lifespan and "meteor" is the shortest of the three terms
For meteorite, it was "rite" lucky to have made it all the way to the ground. (Hey, that's no sillier than the stalactite/stalagmite mnemonic.)
Meteoroid to meteor to meteorite
Anynobody [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons



Two terms that show the danger of naming something before you know what the hell it is because a supernova isn't a really large nova.

The sudden temporary brightening of a star but the star stays intact, caused when a white dwarf in a binary star system sucks material off the other star and nuclear fusion happens with this new material.
Binary System Nova
A white dwarf in the process of taking matter from its neighboring star
By NASA/CXC/M.Weiss [Public domain], via Wikimedia Commons

The explosion of a star leaving behind either a neutron star or a black hole
Supernova to neutron star animation
A star going supernova leaving behind a type of neutron star called a pulsar
By Simynazareth at ml.wikipedia ( [Public domain], via Wikimedia Commons

Neutron Star The answer to the question I asked myself way back in elementary school the first time I saw a drawing of atoms with all that empty space, "What would happen if you squashed the atoms so tight there wasn't any empty space?" The answer is it would turn into a neutron star. Under the tremendous pressure as the atoms are squeezed, the negatively charged electrons and the positively charged protons would combine to become uncharged neutrons.
Neutron Star
The theorized interior of a neutron star. 
A teaspoonful would weigh approximately 10 million tons.
By NASA [Public domain], via Wikimedia Commons
Oort Cloud A theorized source of comets. Something only astronomy buffs and fans of Anne McCaffrey's "Dragonriders of Pern" novels had ever heard of.
Oort Cloud
The Oort cloud relative to the Solar System.
By Jedimaster (Own work) [CC-BY-SA-3.0], via Wikimedia Commons
Parsec Totally useless and non-intuitive term for distance in space that astronomers are using instead of light-year because they think it sounds cool. Technically, "an abbreviated form of 'a distance corresponding to a parallax of one arcsecond'" (wikipedia)......yeah, cause everyone immediately understands what that is. One parsec equals 3.26 light-years.
Parsec drawing
Illustration of how to calculate a parsec.
The black dot at the end of the solid red line is exactly 1 parsec from the Sun.
By jd (Own work) [Public domain or Public domain], via Wikimedia Commons
Pulsar All pulsars are neutron stars, but not all neutron stars are called pulsars ---- even though they might be. A neutron star is only called a pulsar if we can detect the beams of electromagnetic radiation from it because they're being sent in our direction. It's the astronomer's version of "If a tree falls in a forest and no one can hear it, does it make a sound?"
Vela Pulsar jet seen by Chandra Observatory
By NASA/CXC/Univ. of Toronto/M. Durant, et al. [Public domain], via Wikimedia Commons
However, the Wikimedia file kept crashing this page, so I converted the file and transferred it to YouTube.
Millisecond pulsar and accretion disk
A neutron star in a binary system pulls in material from its neighboring star, causing the neutron star to spin faster until it becomes a pulsar with a rotational period from 1-10 milliseconds (called a millisecond pulsar).
By NASA (animator: Dana Berry) [Public domain], via Wikimedia Commons
However, the Wikimedia file kept crashing this page, so I converted the file and transferred it to YouTube.
Red Dwarf Not the really funny cult British TV show, but the most common star in the Milky Way galaxy with a mass smaller, and a temperature cooler, than the Sun.
Red dwarf star in comparison with other stars
left to right: Red Dwarf, Yellow Dwarf, Blue Dwarf, 300 solar mass star 
By ESO/M. Kornmesser ( [CC-BY-3.0], via Wikimedia Commons
Shepherd Moon Not the full moon after the Harvest Moon or any of the special names given to the full moons or that album by Enya. It's a moon that orbits near or in a planet's ring system and whose gravity "shepherds" the ring, helping to keep its shape.
Shepherd moons of Uranus
Two shepherd moons of Uranus' rings.
By NASA [Public domain], via Wikimedia Commons
Spaghettification One of the best, most descriptive terms in astronomy. The stretching (or spaghettifying) of a body falling into a black hole.
Body being stretched or spaghettified as it falls into a black hole
An unfortunate astronaut being spaghettified while drawn into a black hole.
By Cosmocurio  [CC-BY-SA-3.0], via Wikimedia Commons
Synchronous rotation Different from the synchronized rotation seen in pairs figure skating where two bodies rotate at the same speed and in the same direction. This type of synchronous rotation is the reason why we only see one side of the Moon. The moon rotates on its axis in the same length of time it takes to go around the Earth. Also known as tidal locking. 
Rotation of the Moon around the Earth
On the left is a demonstration of synchronous rotation. On the right is non-synchronous rotation.
By Stigmatella aurantiaca (Own work) [CC-BY-SA-3.0], via Wikimedia Commons

Terminator When you type in "terminator definition" in Google, what comes up is going to make you think of Arnold Schwarzenegger. But in astronomy, a terminator is the line between day and night (light and dark).
Terminator lines on the Earth and the Moon
Terminator lines on the Earth and the Moon
Image taken by Galileo at a distance of 4 million miles
By NASA [Public domain], via Wikimedia Commons
Zenith Frankly, I still think TV if someone says "Zenith" to me. But it's the highest point that is directly overhead of the observer.
drawing showing the zenith
The "Z" is zenith. "Alt" is altitude. "Az" is azimuth.
"S" is the south point on the horizon. "N" is north.
By haade (Own work) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons
Zodiac Don't be fooled by the common usage. This definition has nothing to do with that most inane of all belief systems, astrology. It's the constellations within 8║ of the ecliptic path through which the Sun, the Moon and visible planets seem to move as viewed from the Earth.
Ecliptic path showing the 12 constellations
The outer red ring is the ecliptic path -- Click image for full size
By Tauʻolunga (Own work) [GFDL, CC-BY-SA-3.0 or CC-BY-SA-2.5-2.0-1.0], via Wikimedia Commons

Astronomy Definitions Book

For more of my astronomy pieces, read "The Black Hole That (Didn't) Devour the Galaxy" or "Star Wars, Einstein and When Lucas Got It Right" and its addendum "Difficulty Levels of Death Star Versus Various Astronomical Bodies." Another science piece is on the topic of population growth,"As Dumb as Deer."

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