One Way to Distinguish a Star from a Planet, Particularly

question 149

Multiple Choice

One way to distinguish a star from a planet, particularly when they appear near the horizon, is that stars appear to twinkle and planets shine steadily. Which of these statements is a reasonable explanation for this phenomenon?

• A) Stars actually do twinkle-shine with a light that flickers bright and dim-whereas planets shine with a steady, unwavering light.
• B) The light from planets is so much brighter than the light from stars (when they are observed from Earth) that it is unaffected by air movement in Earth's atmosphere.
• C) The disk of a planet, as observed from Earth, appears larger than the disk of a star. Thus, if refraction through moving air in Earth's atmosphere makes the planet's disk appear to move about slightly, there will normally be a central part of the disk that shines steadily and does not appear to twinkle.
• D) Because light from planets is reflected, it is unaffected by the refraction in Earth's atmosphere.

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Definitions:

Absolute Refractory

A period immediately following the transmission of a nerve impulse when a neuron cannot be stimulated to transmit another impulse, regardless of the strength of the incoming signal.

Relative Refractory

A phase following the absolute refractory period during which a neuron or muscle cell requires a stronger than normal stimulus to respond.

Period

An interval of geologic time that is a subdivision of an era; each period is divided into epochs.

Humanitarian Concern

Refers to the care, empathy, and actions taken to improve the welfare and happiness of people, especially those in crisis or need.