Which of the following analogies best describes how the structure of the galaxy's spiral arms is maintained?
A) Like military jets flying in formation above a football stadium, the stars in the spiral arms keep a spiral-shaped formation as they orbit the galaxy.
B) Like cars slowing in traffic to look at an accident, stars slow as they pass through the spiral arms.
C) Like a coiling rope, the spiral arms wind up tighter with every galactic rotation.
D) Like the fins of a giant pinwheel toy, the spiral arms carry a set of bright stars around as they sweep through the galaxy.
Question 2
How did Eratosthenes estimate the size of Earth in 240 B.C.?
A) by observing the duration of a solar eclipse
B) by measuring the size of Earth's shadow on the Moon in a lunar eclipse
C) by comparing the maximum altitude of the Sun in two cities at different latitudes on the summer solstice
D) by sending fleets of ships around Earth
E) We don't know how he did it since all his writings were destroyed.
The three dimensions of stream structure.
Overview of protein structure and function
Structure of a myofiber (muscle cell)
The Structure of an Artery
Structure of immunoglobulin molecules
Typical bacterial size and structure