Perigee is the closest point a satellite gets to Earth. The apogee is the furthest point. Perihelion is the point in a planet's orbit closest to the sun. The aphelion is the furthest point. In the Northern Hemisphere, the Earth's aphelion occurs during the summer. In the Southern Hemisphere, the Earth's perihelion occurs during winter.
Satellites move around the Earth in elliptical orbits. At any given time, some satellites are closer to the Earth than at another. These are called "in-range" satellites. Others are farther away and not within range. Satellites cannot communicate with each other unless they are within range of at least one other satellite.
The distance between a satellite and the Earth determines how much energy it needs to stay in orbit. If the distance becomes too large, then the satellite will fall into Earth's atmosphere where it will be destroyed. At the other extreme, if the distance becomes too small, then gravity from Earth will cause the satellite to crash back down toward its home planet.
In-range satellites follow tracks across the sky as the Earth rotates. When they reach their highest point above the horizon they are at their most distant from Earth. When they drop below the horizon they are getting closer. Occasionally, a satellite will pass directly over a station on the ground; these are known as direct broadcasts.
The Earth's aphelion happens during the summer in the Northern Hemisphere. The period of a satellite is the amount of time it takes to complete one full orbit. Earth, for example, has an orbital period of one year. A lunar month is 29 or 30 days. The moon does not follow exactly the same path around the earth each month, so its orbit is an ellipse rather than a circle.
Lunar perigee occurs when the moon is at its closest approach to the Earth, which is about 384,000 miles (624,000 km). At this distance, the gravitational pull of the Earth and moon together is greatest. All other things being equal, objects in lunar perigee will experience 9% less gravity than at the surface of the Earth.
Lunar apogee occurs when the moon is at its most distant approach to the Earth, which is about 363,000 miles (590,000 km). At this distance, the gravitational pull of the Earth and moon together is least. Objects in lunar apogee experience 14% more gravity than at the surface of the Earth.
The mean radius of the Earth is 6,371 miles (10,000 km). It can be calculated by averaging the distances from the center of the Earth to the various land masses.
The man-made satellite that is now the furthest away from Earth (and is orbiting anything) is most likely the Juno (spacecraft), which is orbiting Jupiter at a distance of 4.67 AU from Earth. Its mission is to explore whether Jupiter's atmosphere and magnetic field can protect its interior from asteroids and krypton-87, which may be used as fuel for nuclear power generators in future space vehicles.
The closest orbiting satellite is probably either the International Space Station or a component of it. It is called the Bait Satellite because one of its main objectives is to attract attention and increase funding levels for further research on animal behavior in space. It is operated by NASA and was launched on 24 August 2006. At the time of writing, it was around 730,000 km from Earth and orbiting at an altitude of 3953 km.
The record for a satellite orbiting another body is held by the HOPE spacecraft, which is flying past both Venus and Mars. It is expected to arrive at Venus in 2034 but might be captured by the planet's gravity and end up orbiting it for several more centuries.
Another example is the EPO Satellite, which is orbiting Earth every 90 minutes at an altitude of about 36,000 km. It carries experiments related to environmental protection studies.
Because of the planet's elliptical orbit, there will be a time each year when it is closest to the sun, known as perihelion, and a period when it is farthest away, known as aphelion. At its most distant point from the sun, if it were possible for us to see it, the earth would be beyond the orbit of Mars.
During a perihelion passage, the temperature on earth will be hot enough to melt ice and rock, causing natural disasters. All around the world people will celebrate with fireworks and light shows because they believe that this is how the sun remembers them every year at perihelion.
At its closest approach to the sun, the earth travels around it in 10 months but due to gravitational forces between the earth and moon, which are equal in magnitude but opposite in direction, the earth's axis tends to tilt at an angle where it takes 26,569 miles (43,000 km) to go from one side of its orbit to the other.
The reason why we have seasons is because the earth's axis is not fixed, but instead it wobbles like a spinning top. This means that at any given moment the north pole is pointing either toward or away from the sun.
During its 27-day orbit around Earth, the Moon reaches both its perigee, which is about 226,000 miles (363,300 km) from Earth, and its apogee, which is roughly 251,000 miles (405,500 km) from Earth. These are the closest points to our planet that it will ever get, and they can be reached within one lunar month.
The Moon's orbit is elliptical, not circular; thus, it has two different distances from Earth at any given time: a minimum distance of about 363,300 miles (590,900 km), and a maximum distance of about 405,500 miles (660,200 km).
These ranges occur because of the influence of Earth's gravity. The closer the Moon comes to Earth, the stronger its gravitational pull becomes, so it needs less speed to stay in orbit. As it moves away from us, the force of gravity decreases, and it needs more speed to remain in orbit. Over the course of one full orbit, the Moon travels about 394 million miles (639 million km).
However, due to tidal forces, both the water under the Moon's surface and the water inside Earth itself rise in temperature during this motion. This is why tides are higher when the Moon is near Earth than when it is far away - about 73 inches (183 cm) on average.
Every year in early January, when the Northern Hemisphere is in winter, Earth is closest to the sun. During our Northern Hemisphere summer, we are the farthest away from the sun in early July. NASA provided the image. As you can see, there isn't a tremendous space between perihelion and aphelion.
Perihelion is the point in an object's orbit where it is closest to the Sun. Aphelion is the point in an object's orbit where it is farthest from the Sun. The term perihelion comes from Greek words meaning "around" or "near" the Sun and refers to the fact that an object is closest to the Sun at this time of year. Aphelion comes from a Greek word meaning "far" or "away" and refers to the fact that an object is farthest from the Sun at this time of year.
So, close to home for January but far away in July!
The distance between these points on Earth's surface varies depending on where you are located. If you're near the equator, then you'll be closer to perihelion in January than aphelion in July. If you're near the poles, then you'll be closer to aphelion in January than perihelion in July.
These distances change over time as well.