Observing
the Sky
LECTURE 2
, I. BASICS
HORIZON
A flat tangent to the Earth’s
surface where the observer is
standing (line that connects
the sky to the ground/sea). ZENITH
Appears as a straight line in Point on the celestial
human perspective. sphere directly above the
observer’s position on Earth
(point of where you are).
Point over your head.
If looking up into the sky,
the zenith is the point
NADIR
where your line of sight
Opposite of zenith.
intersects with the celestial
Point directly below the
sphere.
observer’s position on Earth
(directly beneath your feet).
Lowest point in the sky.
CELESTIAL SPHERE
Giant, imaginary spherical
dome that surrounds the
Earth.
Rotates as Earth does on its
axis.
A reference point for
measuring and calculating
positions of celestial
objects.
the Sky
LECTURE 2
, I. BASICS
HORIZON
A flat tangent to the Earth’s
surface where the observer is
standing (line that connects
the sky to the ground/sea). ZENITH
Appears as a straight line in Point on the celestial
human perspective. sphere directly above the
observer’s position on Earth
(point of where you are).
Point over your head.
If looking up into the sky,
the zenith is the point
NADIR
where your line of sight
Opposite of zenith.
intersects with the celestial
Point directly below the
sphere.
observer’s position on Earth
(directly beneath your feet).
Lowest point in the sky.
CELESTIAL SPHERE
Giant, imaginary spherical
dome that surrounds the
Earth.
Rotates as Earth does on its
axis.
A reference point for
measuring and calculating
positions of celestial
objects.
