Chapter 2
The tilt of Earth's spin axis to the direction perpendicular to the ecliptic plane (known as the ecliptic pole) is
23.5 degrees
In modern astronomy, the constellations are
88 regions of sky, covering the entire sky
The direction of Earth's rotation about its axis is the same as teh direction of its revolution about the sun. How does a solar day compare to a sidereal day on Earth?
A solar day is always longer
The lowest amount of solar energy per square meter is incident on the surface of Earth in the northern hemisphere on or about
December 21, the beginning of winter
A sundial isn't considered to be a good timekeeper because the
Earth's orbital speed around the ecliptic is variable
What is the primary cause of Earth's seasons?
Earth's rotation axis tilts with respect to the plane of its orbit around the sun
The celestial equator is defined as the
Line in the sky that is perpendicular to Earth's spin axis
The two angles used by astronomers to define the position of a star in the sky and define a coordinate system applicable anywhere on Earth are
Right ascension and declination
Diurnal motion of objects in the sky is caused by the
Rotation of Earth on its axis
Polaris, the "pole star", is at present
Within 1 degree of the north celestial pole
Precession is
a very slow conical motion of Earth's axis of rotation
By observing the sky closely night by night, you would note that a particular star rises
about 4 minutes minutes earlier every night
The arctic circle is defined as a line on Earth where the sun
can be seen for 24 hours on at least one day of the year
constellations are generally made up of stars which are
merely located along more or less the same line of sight as viewed from Earth
The phenomenon of precession of Earth's spin axis is caused by the
gravitational pull of Moon and Sun on Earth's equatorial bridge
The ecliptic is defined as the
line traced in our sky by the sun over one year against the background stars
For an observer at a fixed location on Earth, the angle between the north celestial pole and an observer's horizon depends on the
observer's latitude
If the daytime sky were not bright, in which direction would we see the sun move along the ecliptic over the course of a year, relative to the background stars?
toward the east
The ecliptic crosses the celestial equator at
two points, known as equinoxes
The zenith defines a direction
vertically above an observer