Questions and Answers
The point in the sky directly above your head at any given time is called the ___
zenith
The celestial sphere turns once around each day because ______.
the planet is rotating
The south celestial pole and the north celestial pole lie in the sky directly above the _____.
Earth's axis
Halfway between the celestial poles lies the _____.
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In the Northern Hemisphere, the altitude (height in degrees above the horizon) of the North Star is always roughly equal to the ____.
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The star that is currently closest to the North Celestial Pole is ______.
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As seen from the continental United States, the Big and Little Dipper _____.
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Where on Earth do stars always circle the zenith (and never rise and set)?
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From horizon to opposite horizon, the sky takes up how much angular distance?
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The Sun's apparent path around the celestial sphere is called _____.
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If the Earth goes around the Sun, why is the ecliptic not lined up with the celestial equator?
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Every celestial object appears to go around the Earth once a day. In addition to this motion, which celestial object has the fastest apparent motion in the sky?
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The strip of the sky through which the Sun, Moon, and bright planets appear to move in the course of a year is called ____.
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The 88 sectors into which astronomers today divide the celestial sphere (the whole sky) are called ______.
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Which ancient Greek thinker suggested (long before Copernicus) that the Earth is moving around the Sun?
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How did Eratosthenes measure the size of the Earth?
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When a planet temporarily moves westward in the sky over the course of several weeks or months (instead of eastward, as it typically does), we call it _____.
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The slow tipping of the Earth's axis in a circle with a period of about 26,000 years is called_______.
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The great astronomer of ancient times who summarized and improved a system of circles upon circles to explain the complicated motions of the planets (and published the system in a book now called The Almagest) is: ______.
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In Ptolemy's system, how did the planets explain the retrograde motion of planets like Jupiter?
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Study Notes
Celestial Concepts
- The zenith is the point directly above an observer's head in the sky.
- The celestial sphere rotates daily due to Earth's rotation.
- North and south celestial poles align with Earth's axis.
- The celestial equator lies halfway between the celestial poles.
Observational Astronomy
- In the Northern Hemisphere, the altitude of the North Star (Polaris) equals the latitude of the observer.
- Big and Little Dipper constellations are circumpolar in the northern sky throughout the year.
- At the North Pole, stars circle the zenith, never rising or setting.
Angular Measurements
- The sky from horizon to horizon spans an angular distance of 180 degrees.
- The ecliptic is the Sun's apparent path across the celestial sphere.
Celestial Mechanics
- The ecliptic does not align with the celestial equator due to Earth's axial tilt.
- The Moon exhibits the fastest apparent motion among celestial objects, completing its journey across the sky daily.
- The zodiac is the band of the sky where the Sun, Moon, and bright planets appear to move annually.
Constellation and Historical Figures
- The celestial sphere is divided into 88 constellations by astronomers.
- Aristarchus of Samos proposed the heliocentric model long before Copernicus.
- Eratosthenes calculated Earth's circumference by comparing the Sun's angle at two different latitudes.
Motion Dynamics
- Retrograde motion refers to a planet's apparent westward movement over weeks or months.
- Precession is the gradual change in Earth's axial tilt that occurs over approximately 26,000 years.
Ancient Astronomical Systems
- Ptolemy enhanced a geocentric model that utilized circular orbits to explain planet movements and retrograde motion.
- In Ptolemy’s system, planets are thought to move along small circles (epicycles) while circling near Earth.
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Test your knowledge of key astronomy terms and concepts with these flashcards. Each card presents a fundamental idea related to celestial mechanics and the structure of the sky. Ideal for students preparing for an astronomy exam or anyone interested in the field.