ABC Game

tessu

X (in the box for multiple choice tests)

Kaption

yearbooks, yells (cheering, not teachers), youngsters

Mominator

zero (for not handing in work)

zoo field trip

Zoom (popular kid TV show with learning mixed in)

Mominator

New topic: things in space: stars, planets and species (real or imagined), space ships, constellations

Alpha Centauri (closest real star to our solar system)

Andoria and Andorians (planet and species in Star Trek universe)

Alderaan (Princess Leia's home planet, in Star Wars universe)

Andromeda (constellation: the chained lady or the Princess)

Aquarius (constellation: the water-bearer)

Aries (constellation: the ram)

I hope that's enough flexibility for an interesting topic

ruthbru

Aurora Borealis (which gives us both an 'A' and 'B'), Black Hole, Binary Star,

M0mmyof3

Caprica (planet on Battlestar Galactica)

Mominator

Dwarf planets, dark nebulae, diffuse nebulae

Denobulans are a Humanoid species who hail from the planet of Denobula  (Star Trek)

Count Dooku (a.k.a. Darth Tyranus), Darth Vader, (Star Wars)

Constellations Delphinus, Dorado, and Draco (also a Harry Potter character)

Kaption

Earth

Evening sky

ruthbru

flares, fly, full moon

Mominator

Galaxies of all sorts!

Gas giant planets

Gemini, a constellation

Gemini, the second manned NASA space program (conducted between projects Mercury and Apollo)

Gravity, which holds it all together.

tessu

helium

Hubble space telescope

Kaption

interstellar

Ionosphere

International Space Station

ruthbru

Jupiter, Jet Stream, Jar Jar Binks (Star Wars)

PattyPeppermint

stuck ????

M0mmyof3

Kessel (planet in Star Wars)

ruthbru

Mars, moon, Mecury

M0mmyof3

Leo (constellation)

Libra (constellation)

I noticed that L got skipped so I fixed it.

On to the letter N since we have M thanks to Ruth

ruthbru

oops!

Neptune, Nebula, Night Sky

M0mmyof3

It's no biggie Ruth.

Orion (constellation)

ruthbru

photopshere, planet, phases, Pluto (which is still a planet to me )

M0mmyof3

Quasars

Kaption

rocket, radiation,

PattyPeppermint

satelite

Mominator

Tantalus – A Federation prison colony is located on planet Tantulus, where the warden conducted cruel psychological experiments on the inmates in Star Trek (TOS).

Talax/Talaxian - Neelix from Star Trek: Voyager is from planet Talax in the Delta Quadrant and his people are Talaxians

Tatooine is the home planet of Luke Skywalker in Star Wars

Takodana is a Forest planet in The Force Awakens

Taurus, Triangulum, and Tucana are constellations

Terrestrial   

Pheasantduster

Uranus......... (hear all of us tittering !!!)

M0mmyof3

(not going there, trying to be mature, aww to heck with it, roflol)

Venus

Virgo (constellation)

Kaption

Venus

PattyPeppermint

zenith and zodiac

I'll let someone else pick next topic

Mominator

Just for fun, here's W, X, and Y

weightlessness, worlds, wrinkle in time,

Warp engines, warp speed, Battle of Wolf 359, Wesley Crusher in Star Trek

Wookies and Mace Windu (Samuel Jackson's character) in Star Wars

X-ray pulsars;

Xendi, Xerxes, and Xindi are planets in Star Trek universe;

X-wing fighters in Star Wars

Yellow stars

Yadera, Yalidia, Yalosia, Yonada, Yridian are planets in Star Trek universe 

Yoda in Star Wars

Mominator

I picked the last topic: things in space: stars, planets and species (real or imagined), space ships, constellations; many of which are very big

New topic: things that are small

amoeba, atom

edited to improve clarity (I hope)