Mapping the Celestial Sphere & Human Perception of the Sky

Human Interaction w/ the Sky

Light

  • The sun rises in the east

    • Shadows are cast to the west

  • The sun sets in the west

    • Shadows are cast to the east

  • Most light we see is from the sun

    • atmospheric scattering = the redirection of sunlight (or other electromagnetic radiation) by air molecules and particles in the atmosphere

    • The amount of scattering depends on the density in the amount of molecules in the atmosphere around the viewer

      • The more molecules in the atmosphere around the viewer, the more light can be reflected, while less molecules mean less light can be reflected

    • The central point in the sky where the sun is will always be stronger than reflected light from other sources

    • Space appears black because its molecular density is too low for any significant light to scatter towards a viewer

  • The atmosphere ends only ~60miles above the Earth’s surface

    • Because the atmosphere fades slowly away as height in relation to the earth increases, this definition is where 99.9% of molecules are condensed

Division of the Sky

  • The whole sky is divided into parcels

    • Each region of sky is called a constellation

      • There are 88 constellations

  • asterisms = individual patterns of noticeable stars that are not officially part of any constellation

    • Asterisms are celestial projections, meaning that only in 2d do the stars within them look related

    • The objects and pictures associated with asterisms are cultural and often have no real relation to the stars themselves

Mapping the Sky

  • The Celestial Sphere is a sphere of infinite radius centered around Earth

    • By using the Celestial Sphere coordinates can be applied to objects and bodies around the Earth

    • From Earth, only half of the celestial sphere can be observed at one time

      • The end of the half which can be observed is called the horizon line

      • relative motion = the motion of one object with respect to another object

    • celestial projections = objects which all appear equally on a spherical plane around Earth, regardless of their true distance from Earth or eachother

      • The North Celestial Pole is a celestial projection

        • Polaris is very close to the North Celestial Pole

      • The Equator is a celestial projection

      • The South Celestial Pole is a celestial projection

    • The Celestial Sphere is anchored by the connecting line between the North Celestial Pole and the South Celestial Pole

      • The points on this line never appear to move

Understanding Coordinates

  • zenith = the imaginary point on the celestial sphere directly above an observer's head

  • meridian = the line connecting crossing through zenith due North and South

  • altitude = how many degrees above the horizon a star is, ranging from 0°–90°

    • Zenith sits at 90°

    • The horizon line is at 0°

  • azimuth = how many degrees along the horizon a star is in correspondence with compass direction

    • North = 0

    • East = 90

    • South = 180

    • West = 270