Q.E. Reviewer - AST01-AST15-part-4.pdf

AST04 - Observational Astronomy I Celestial Sphere - an imaginary sphere of arbitrary large radius centered on the Earth. It is a useful tool for astronomers to visualize the positions and movements of stars and other celestial objects in the sky. Key Features: 1. Celestial P...

AST04 - Observational Astronomy I Celestial Sphere - an imaginary sphere of arbitrary large radius centered on the Earth. It is a useful tool for astronomers to visualize the positions and movements of stars and other celestial objects in the sky. Key Features: 1. Celestial Poles: ○ North Celestial Pole: The point in the sky directly above Earth's North Pole. It is currently close to the star Polaris. ○ South Celestial Pole: The point in the sky directly above Earth's South Pole. 2. Celestial Equator: ○ An imaginary circle that is the projection of Earth's equator onto the celestial sphere. It divides the celestial sphere into the northern and southern celestial hemispheres. 3. Ecliptic: ○ The apparent path that the Sun follows over the course of a year against the backdrop of the stars. It is inclined at about 23.5 degrees to the celestial equator due to the tilt of Earth's axis. 4. Horizon: ○ The plane that separates the visible sky from the part of the sky that is blocked by the Earth. It changes depending on the observer's location. 5. Zenith and Nadir: ○ Zenith: The point on the celestial sphere directly above an observer. ○ Nadir: The point on the celestial sphere directly opposite the zenith, beneath the observer. 6. Right Ascension (RA) and Declination (Dec): ○ These are the celestial equivalents of longitude and latitude on Earth. ○ Right Ascension: Measured in hours, minutes, and seconds, it is the celestial equivalent of longitude and measures east-west positions on the celestial sphere. ○ Declination: Measured in degrees, minutes, and seconds, it is the celestial equivalent of latitude and measures north-south positions on the celestial sphere. 7. Equinoxes ○ The two points in the year when the Sun crosses the celestial equator, resulting in nearly equal day and night durations across the Earth. They occur twice a year: the vernal equinox and the autumnal equinox. Positional Astronomy Opposition ○ A planetary position in which the Sun, the Earth and a superior planet are aligned in that order and in a straight line. ○ This is also the best time to observe a planet because: it is at its closest approach to Earth. The planet rises just as the Sun is setting, allowing observation any time during the night. Quadrature ○ A planetary position in which the Sun, the Earth and a superior planet form a right angle with the Earth at the vertex. ○ At sunset during eastern quadrature, a superior planet is overhead and is overhead at sunrise during western quadrature.  Conjunction ○ A planetary position in which the Earth, the Sun and the planet are aligned in that order and in a straight line. ○ A conjunction is the worst time to observe a planet because it is lost in the Sun's brilliance. Inferior Conjunction ○ A planetary position in which the Earth, an inferior planet and the Sun are all in a straight line. Superior Conjunction ○ A planetary position in which the Earth, the Sun and a superior planet are all in a straight line. Greatest Elongation - Point at which an inferior planet has the greatest visual distance from the Sun. (Mercury 28º, Venus 47º) ○ During Greatest Eastern Elongation an inferior planet is visible at sunset and is visible before sunrise during Greatest Western Elongation. Messier Catalog Messier Catalog - 110 objects listed by Charles Messier Important/Relevant/Popular Messier Objects: # Common Name Image Object Type Constellation M1 Crab Nebula Supernova Remnant Canis Major M31 Andromeda Galaxy Spiral Galaxy Andromeda Triangulum Galaxy M33 Spiral Galaxy Triangulum Pinwheel Galaxy M42 Great Orion Nebula Planetary Nebula Orion M44 Beehive Cluster Open Cluster Cancer M45 Pleiades Open Cluster Taurus M57 Ring Nebula Planetary Nebula Lyra M81 Bode’s Galaxy Spiral Galaxy Ursa Major  M82 Cigar Galaxy Starburst Galaxy Ursa Major M101 Pinwheel Galaxy Spiral Galaxy Ursa Major M104 Sombrero Galaxy Spiral Galaxy Virgo Constellations Constellations refer to a certain region of the sky. Every star located in that specific region is included in the constellation where it belongs. There are a total of 88 constellation regions both in northern and southern hemispheres. Apparent Magnitude The apparent magnitude (m) is a measure of the brightness of a celestial object as seen from Earth. It depends on the object's intrinsic brightness (luminosity), distance from Earth, and any interstellar material that may dim its light. The scale is logarithmic and inversely proportional—lower numbers mean brighter objects. For example, a star with an apparent magnitude of 1 is brighter than a star with an apparent magnitude of 6. Absolute Magnitude The absolute magnitude (M) is a measure of the intrinsic brightness of a celestial object. It is defined as the apparent magnitude the object would have if it were located at a standard distance of 10 parsecs (about 32.6 light-years) from Earth. It only depends on the object's intrinsic luminosity and does not vary with distance or interstellar absorption. Asterisms Asterisms are parts of a constellation but are too recognizable due to its prominent stars or it may be composed of two or more stars from different constellations. Examples: