Astronomy Celestial Sphere Flashcards

Celestial Sphere Concepts

• Celestial Sphere: An imaginary sphere surrounding Earth, historically thought to hold all celestial objects.
• Celestial Pole: The projection of Earth’s North and South poles onto the celestial sphere.
• Celestial Equator: Represents the projection of Earth’s equator on the celestial sphere.
• Celestial Meridian: A line extending from the North to South Celestial pole, traversing directly overhead.

Solar and Celestial Events

• Ecliptic: Describes the Sun's apparent annual path against the backdrop of stars on the celestial sphere.
• Zodiac: Comprises 12 constellations that the Sun appears to traverse throughout the year.
• Vernal Equinox: Marks the Sun’s northward crossing of the celestial equator, occurring around March 21.
• Autumnal Equinox: Occurs when the Sun crosses the celestial equator moving southward, around September 21.
• Winter Solstice: The point where the Sun reaches its southernmost position below the celestial equator, around December 21.
• Summer Solstice: The point where the Sun is at its northernmost position above the celestial equator, around June 21.

Astronomical Phenomena

• Precession: The gradual shift in the orientation of a spinning object's rotation axis, influenced by gravitational forces.
• Circumpolar Stars: Stars that are permanently visible above the horizon throughout the year.
• Celestial Horizon: The boundary separating the visible and invisible halves of the celestial sphere.

Celestial Navigation

• Right Ascension: A coordinate system for measuring longitude on the celestial sphere.
• Declination: A coordinate for measuring latitude above or below the celestial equator.
• Latitude: Indicates how far north or south a location is relative to the equator.
• Longitude: Indicates how far east or west a location is relative to the prime meridian.

Time Measurement and Motion

• Sidereal Day: The duration between successive risings of a specific star, relating to the stars' position.
• Solar Day: The time interval from one solar noon to the next, based on the Sun's position in the sky.
• Retrograde Motion: The apparent east-to-west movement of a planet against the fixed stars in the night sky.

Planetary Classification

• Inferior Planets: Planets that orbit closer to the Sun than Earth does.
• Superior Planets: Planets that orbit farther from the Sun than Earth.
• Planetary Opposition: A configuration where a planet is positioned opposite the Sun in the sky at midnight.

Astronomical Structures

• Constellation: A recognized pattern formed by a group of stars in the night sky, based on human interpretation.
• Lunar Phase: The different appearances of the Moon as it orbits Earth.
• Lunar Planetary: Similar to lunar phases, this refers to the visibility of Venus, typically as a crescent.

Transits

• Transit of the Sun: Occurs when Mercury passes directly in front of the Sun from Earth's perspective.

Celestial Sphere and Components

• Celestial Sphere: Imaginary sphere encompassing Earth, where all celestial objects are projected.
• Celestial Pole: Earth's North and South poles extended onto the celestial sphere.
• Celestial Equator: Projection of Earth's equator onto the celestial sphere, dividing it into northern and southern hemispheres.
• Celestial Meridian: Imaginary line connecting the North and South Celestial poles, passing directly overhead.

Key Astronomical Concepts

• Ecliptic: The pathway the Sun appears to trace among the stars throughout the year.
• Zodiac: A belt of 12 specific constellations through which the Sun travels annually.
• Vernal Equinox: Occurs around March 21st when the Sun crosses the celestial equator moving north.
• Autumnal Equinox: Occurs around September 21st when the Sun crosses the celestial equator moving south.
• Winter Solstice: Around December 21st, the Sun reaches its southernmost point below the celestial equator.
• Summer Solstice: Around June 21st, the Sun reaches its northernmost point above the celestial equator.

Celestial Mechanics

• Precession: Gradual shift in the orientation of the rotation axis of a spinning object due to gravitational forces.
• Circumpolar Stars: Stars that are always visible in the night sky and never set below the horizon.
• Celestial Horizon: Imaginary line distinguishing the visible celestial dome from the unseen hemisphere.

Celestial Coordinates

• Right Ascension: Longitude-like celestial coordinate, measuring the east-west position on the celestial sphere.
• Declination: Latitude-like celestial coordinate, measuring how far an object is above or below the celestial equator.

Earth-Based Coordinates

• Latitude: Measures North-South position on Earth.
• Longitude: Measures East-West position on Earth.

Time Measurement

• Sidereal Day: Time taken for a star to return to the same position in the sky; relates to the stars.
• Solar Day: Period between two successive solar noons where the Sun is directly overhead.

Planetary Movements

• Retrograde Motion: Apparent backward movement of a planet against the backdrop of fixed stars.
• Inferior Planets: Planets that orbit closer to the Sun than Earth; example includes Mercury and Venus.
• Superior Planets: Planets that are located further from the Sun than Earth; examples include Mars, Jupiter, Saturn.

Additional Concepts

• Planetary Opposition: Configuration when a planet is directly opposite the Sun in the sky at midnight.
• Constellation: Recognizable patterns formed by grouping stars in the night sky.
• Lunar Phase: Changing appearance of the Moon as it orbits Earth, resulting from its position relative to the Sun.
• Lunar Planetary: Refers to Venus as seen in its phases, appearing only as a crescent.
• Transit of the Sun: Occurs when Mercury passes directly between Earth and the Sun, appearing as a small dot moving across the Sun.