1. ROTATION The Earth is a sphere that
rotates on its axis that
passes through the North
and South poles. The
time it takes for the Earth
to make a complete
rotation is approximately
24 hours (exactly 23.934
hours). This rotation
results in daytime when
an area is facing the Sun
and nighttime when an
area is facing away from
the Sun.
2. Mean sidereal day: the period during which
Earth makes a complete rotation on its axis
(absolute rotation). The time interval of the
mean sidereal day is 86164.0905382 seconds.
Mean solar day: The period of time
between two successive transits of the mean
sun; the standard for the 24-hour day
measured from midnight to midnight
3.
4.
5. HOW FAST IS THE EARTH SPINNING AROUND ITS AXIS?
At the equator, the Earth's surface moves 40,000
kilometers in 24 hours. That is a speed of about
1040 miles/hr (1670 km/hr or 0.5 km/sec).
This is calculated by dividing the circumference of
the Earth at the equator (about 24,900 miles or
40,070 km) by the number of hours in a day (24).
As you move toward either pole, this speed
decreases to almost zero (since the circumference
of the spinning circle at the extreme latitudes
approaches zero).
6. REVOLUTION
The Earth revolves around the Sun
once every 365.25 days. Its velocity
in space in its orbit is about 18.5
miles per second. The shape of the
orbit is an ellipse
7.
8. A tropical year (also known as a solar year) is the
length of time that the Sun takes to return to the
same position in the cycle of seasons, as seen
from Earth; for example, the time from vernal
equinox to vernal equinox, or from summer
solstice to summer solstice.
The sidereal year is the time taken for the Sun to
return to the same position with respect to the
stars of the celestial sphere. It is the orbital period
of Earth, equal to 365.25636042 The sidereal year
is 20 minutes and 24 seconds longer than the
tropical year.
9. HOW FAST IS THE EARTH REVOLVING AROUND THE SUN?
The Earth orbits, on average, 93 million miles
(149,600,000 km) from the Sun (this distance is
defined as one Astronomical Unit (AU)), taking
one year to complete an orbit.
The Earth revolves around the Sun at a speed of
about 18.5 miles/sec (30 km/sec).
11. One consequence of precession is
that the north star Polaris is
drifting. It is only "north star" by
coincidence today. Vega will be
our north star for a time in the
distant future.
Another consequence is that precession introduces a
difference between a sidereal (real) year and a tropical
(by the sun) year because during the course of one year
the position of the equinox changes slightly.
"precession" was discovered by Greek astronomer
Eratosthenes when he compared his own circa 200 BC
records with older charts
12.
13. HOW FAST IS OUR SOLAR SYSTEM MOVING WITHIN THE
MILKY WAY GALAXY?
The sun is about 26,000 light-years from the center of
the Milky Way Galaxy, which is about 80,000 to 120,000
light-years across (and less than 7,000 light-years thick).
We are located on one of its spiral arms, out towards
the edge
It takes the sun (and our solar system) roughly 200-250
million years to orbit once around the Milky Way. In
this orbit, we (and the rest of the Solar System) are
traveling at a velocity of about 155 miles/sec (250
km/sec).
14. HOW FAST IS THE MILKY WAY GALAXY MOVING WITHIN
THE LOCAL GROUP OF GALAXIES?
The Milky way Galaxy is just one galaxy in a
group of galaxies called the Local Group. Within
the Local Group, the Milky Way Galaxy is moving
about 185 miles/sec (300 km/sec).
