Astronomy Practice Exam

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What is parallax used to measure in astronomy?

The brightness of a star
The distance from Earth to a celestial object
An apparent shift in a star's position
The speed of light particles

The correct answer is: An apparent shift in a star's position

Parallax is a fundamental concept in astronomy used to measure the distance from Earth to a celestial object. This technique relies on the apparent shift in a star's position as observed from different points in Earth's orbit. By measuring this slight shift, astronomers can calculate the distance to the star using trigonometry, with the base of the triangle formed by the Earth’s orbital diameter. When a nearby star is observed at two different times in the year (six months apart), it appears to move against the more distant background stars. This apparent displacement is what is known as parallax. The angle of this shift can then be used in conjunction with the distance from the Earth to the Sun to derive the distance to the star in parsecs. While the brightness of a star, the speed of light particles, or the direct measurement of the star's position might involve various astronomical techniques and effects, they do not utilize parallax directly. The beauty of parallax lies in its straightforward geometric nature, making it a powerful tool for mapping the cosmos.