How Do We Know That the Milky Way Has a Spiral

question 46

Multiple Choice

How do we know that the Milky Way has a spiral structure?

• A)By plotting the distances and directions of objects known to be in spiral arms
• B)By viewing the galaxy from a point well above its plane
• C)By observing the changing conditions as the sun enters a spiral arm
• D)By observing the gravitational influence of the arms on nearby galaxies

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Definitions:

Erectile Problems

Issues related to achieving or maintaining an erection sufficient for satisfactory sexual performance.

Impotence

A term often used to describe erectile dysfunction, which is the inability to achieve or maintain an erection suitable for sexual intercourse.

Erectile Disorder

A dysfunction characterized by difficulties with obtaining an erection during sexual activity, maintaining an erection until the completion of sexual activity, and/or a marked decrease in erectile rigidity in about 75 to 100 percent of sexual occasions over a period of at least six months, leading to distress.