CELESTIAL NAVIGATION I
Perihelion and Aphelion
Motion of Bodies of the Solar System
SUBMITTED BY: SUBMITTED TO:
Tagupa, Vincent Dores N. Capt. Bernabe Lim
Tinson, Melchen M. Instructor
Trinidad, Robert Jr. M.
Vistar, Oscar III M.
PERIHELION and APHELION
The distance that the Earth is from the Sun is vital to life on the planet. Too close and
the heat of the entire planet would increase. Too far and the Earth would turn into a frozen
world. The distance Earth is from the Sun during perihelion and aphelion does not make
enough of a difference to affect the planet's climate. If it had an orbit shaped such as Mercury
does, with a perihelion of 28 million miles and an aphelion of 44 million, the drastic change
would be disastrous.
Astronomers use the terms perihelion and aphelion to describe the points of an object's
orbit around the Sun when they are closest to and farthest away from the Sun, respectively. In
the case of the planet Earth, with the Sun as the focal point around which it orbits, the
difference between the distances at perihelion and aphelion are much less than some of the
other planets. Here are some facts about Earth's perihelion and aphelion.
The word perihelion comes from the Greek, with "peri" meaning near and "helios"
meaning the Sun. Conversely, "apo" in Greek means away from. When the Earth is its farthest
from the Sun it is said to be at apogee. When it is closest it is at perigee.
The sun, although it is in the middle of the Earth’s orbit, it is not in the exact center of
the Earth’s orbit. The distance of the Earth from the sun varies as the Earth revolves around the
sun. At its closest point the Earth is about 91,000,000 miles from the sun, and 95,000,000 miles
from the sun at its farthest point. This makes the mean distance of the Earth from the Sun
about 93,000,000 miles. What may seem strange to people in the Northern Hemisphere of the
Earth is that the Earth is closest to the sun in the winter and farthest from the sun in the
Perihelion is the closest point to the sun in a planet’s orbit. Perihelion is one of the two
points of apsis on elliptical orbit. The closest point is generally called a periapsis and the
farthest point apoapsis. These changes depending on the object being orbited. For orbiting
satellites around the Earth, these two points are called the perigee and the apogee. For other
object the suffix changes to match that
object being orbited.
An elliptical orbit has two centers or
foci. The apsis are the points furthest or
closest to one of these points. In the case of
the Solar System, the main focus is the Sun
so that is why we use the terms perihelion
Aphelion is the farthest point of a
planet’s orbit around the Sun. This occurs
because orbits around stars are normally
elliptical. That is, they have an ovoid shape.
Originally astronomers thought that the
orbits of the planets were perfectly circular. However the observations of the planets never
quite matched the calculations the astronomers did. This was eventually remedied by two
major discoveries. First was the work of Copernicus who disproved the standard theory of the
geocentric or Earth Centered model of the classical universe that was proposed by the Hellene
philosopher Ptolemy. This radically changed our understanding of how planets and other
celestial bodies in the observable region of space move.
The aphelion has many interesting effects on the earth. For one, the orbital velocity of
the Earth slows down as it reaches its aphelion. It also has an effect on the climate. Due to the
point in its orbit the Earth climate is made cooler and warmer in the Northern and Summer
Hemisphere creating milder or more severe seasons. Some scientist hypothesize that major
climate shifts like the Ice Ages are caused in part by major shifts in the Earth’s Orbit which can
alter its apsis points.
MOTION OF BODIES OF THE SOLAR SYSTEM
The axis of the Earth is an imaginary line on which the Earth rotates. It links up the two
poles. Both the axis and the Earth are tilted at an angle of 23.5° during a revolution. The tilting
of the axis results in direct sunlight falling on different places during different seasons. These
cause variations in the duration of days, nights and seasons.
Relationship between the location of the
overhead sun and the seasons. Similarly, the
revolution of the earth and the tilting of its axis
results in different angles of the sun during
different periods. When the sun is directly
overhead, we call this the overhead sun. At this
time, the earth’s surface and the midday sun
forms 90° angle. Different locations of the
overhead sun results in variations in the amount
of solar radiation received in different areas under
Earth's rotation is the rotation of the solid
Earth around its own axis. The Earth rotates
towards the east. As viewed from the North Star Polaris, the Earth turns counter-clockwise.
As the Earth revolves around the sun, it also rotates or spins around its axis. One
rotation of the Earth takes about 24 hours and is equal to one day. The spinning of the Earth on
its axis causes daytime and nighttime.
The earth belongs to the
solar system. This is the system
of planets, asteroids,
meteoroids, comets, stellar dust
and gases that orbit the sun.
Each orbit by a member
of the solar system is its
revolution. A revolution is also
called a year. The Earth takes
365.25 day to revolve around
the sun. It is during this year or
revolution that brings Earth its