"S" words
Number, please
Outer Space
"A" in Science
Finish the phrase
100

A store lowers prices in a "clearance" one 

Sale

100

Number of sides on an octagon

8

100

The ringed planet is sixth from the sun

Saturn

100

Smaller earthquake felt "after" a larger one

Aftershock

100

Time flies when you're

having fun

200

Shhh! It comes before  "partner" and "majority"

Silent

200

Number of days in the month of April

30

200

The leonids are among thee annual "showers"

Meteor showers

200

Protons are found in its nucleus

Atom

200

a picture is worth

a thousand words

300

It's the highest female  singing voice

Soprano

300

Most people are born with this many ribs

24

300

Telescope launched by NASA in April 1990

Hubble Space Telescope

300

Toads and salamanders belong to this class

Amphibians

300

still waters run

deep

400

A short burst: kids can have a "growth" one

Spurt

400

Electoral votes needed to win the presidency

270

400

The Sea of Tranquility is on it's surface

The Moon

400

It describes something with a ph more than 7

Alkaline

400

brevity is the soul of 

wit

500

4-letter word that can mean "cozy" or "tight"

Snug

500

It shares a computer key with a dollar sign

4

500

It's "The Dog Star"

Sirius

500

Seaweed is in this diverse group of organisms

Algae

500

Chickens come home to 

roost