Mercury is 0.4 astronomical units distant from the Sun at an average distance of 36 million miles (58 million kilometers). The distance between the Sun and Earth is measured in astronomical units (abbreviated as AU). One astronomical unit is the mean distance between the Earth and the Sun, about 150 million miles (241 million km).
Thus, mercury orbits the sun every 88 days at a distance of about 60 million miles.
The radius of mercury's orbit around the Sun is 508 thousand miles (800 thousand km), which means that it completes one orbit in 87 days. This means that it travels around the Sun at a speed of 582,000 miles (942,000 km) per day. It follows that one mile on Mercury is equal to 1561 feet or 4840 centimeters.
A solar eclipse occurs when the Moon passes between Earth and the Sun, obscuring the sunlight directly behind it. The total lunar eclipse happens when all of Earth is within the path of totality for the eclipse. For a total eclipse, anyone anywhere on Earth could see the eclipse, but only those located where no clouds are present will see all of the moon darken during a total eclipse. A partial eclipse is seen over a portion of Earth.
Total eclipses of the Moon happen in either its first or third quarters.
The astronomical unit (or AU)—the measurement used for the Earth-sun distance—is no longer always in flux, depending on the duration of a day and other shifting circumstances, according to the new definition. It is now a definite number: 149,597,870,700 meters, or approximately 92.956 million miles. This may seem like a very large number, but it is actually quite small compared with the size of the universe. The average density of matter in the universe is about 0.0011 g/cm3, so if you packed all the atoms in the observable universe into a cube one meter on each side, that stack of cubes would be only 2.5 millimeters high.
The astronomical unit was first defined by French astronomer Urbain Le Verrier in 1873. He based his calculation on the known positions of the Earth and the Sun at any given time and on their predicted movements over several years. The result was less than 1 percent off from the current value.
The astronomical unit has been changing over time as well. In 1753, Johann Bode discovered that the distances between the planets then known ranged between 3.47 and 5.52 times the distance between the Earth and the Sun. Today, this range is estimated to be between 4.39 and 5.83 times.
These days, the most common way to estimate the distance between the Earth and the Sun is by using light signals.
An astronomical unit (AU) is equal to 150 million kilometers (93 million miles), and the Sun is one AU distant from Earth. The Sun is 0.00001581 light-years distant in light-years, and 8.20 light-minutes or 500 light-seconds away in light-minutes from Earth.
The speed of light is about 300,000 km/s, so a signal sent out from Earth at the speed of light would reach the Sun in 5 minutes and 20 seconds.
The distance between Earth and Sun varies over time. If we looked up in the night sky and saw that the Sun was farther away than it usually is, this would mean that the Earth was moving toward it towards mid-summer. If we saw it closer than it usually is, then the Earth would be moving away from it, going through its winter.
This distance changes by about 4 percent every 100,000 years as the Earth's orbit around the Sun changes orientation with respect to the other planets in our solar system. When this happens, we call it an "orbital revolution". Each time the Earth makes one full orbit around the Sun, it travels about 15 million km. At the end of each year, the Earth is on the opposite side of the Sun from where it started, but at the beginning of each month it is back where it started again.
Mercury is about 46.0 million km from the Sun at "perihelion" (the orbital point closest to the Sun), and 69.8 million km at "aphelion" (the orbital point furthest from the Sun). Its average distance from the Sun is 57.9 million km.
The perihelion and aphelion distances are important parameters in understanding how planets orbit the sun. They also play a role in determining Mercury's climate. A planet's distance from the Sun affects how much radiation it receives, which in turn influences its surface temperature. Radiation is measured in units called "gray", and the closer a planet is to the Sun, the more grayness there is to it experience during a year at the equator. Grayness increases as you go farther from the Sun. Earth's average annual grayness is 10 millimeters, or about 0.4 inches; for comparison, sunlight at noon on a clear day in July in Los Angeles is about 60 mm gray.
Radiation is one factor that determines a planet's climate. Another is axial tilt. Because Earth orbits the Sun at an angle, most of its surface is not exposed to direct sunlight for part of the year. The amount of darkness this brings about causes differences in animal behavior between the seasons, which in turn affects their evolution.
The grey line represents the Earth-Sun distance, which is around 1 astronomical unit on average. The astronomical unit (symbol: au, or AU, or AU) is a unit of length equal to around 150 million kilometers (93 million miles) or 8 light minutes from Earth to the Sun. It is used as a standard measure for the distance between the Earth and other parts of the Solar System.
There are approximately 365 days and 6 hours between one new moon and the next, but because of the eccentric orbit of the Moon, this period varies over time. At its most distant point, about 236,000 km (150,000 mi) from Earth, the Moon takes about 29 days to complete one full orbit around our planet; at its closest approach, about 63,000 km (40,000 mi) away, it takes about 27 days to make one trip around Earth. The average distance of the Moon from the Earth is about 384,400 km (236,900 mi), which means that it covers an average area of surface of 4π radians² (1 radian is about 57.3°).
The radius of the Moon is about 7,476 km (4,650 mi), so it covers an average area of surface of 15.8 square kilometers (6 square miles).