Then, six months later, when the Earth is on the other side of its orbit around the Sun, the astronomer will line up the distant star with the known star. Thus, 1 parsec = 1 AU / tan(1 arcsecond).Īt some given time of the year, an astronomer can line up a distant star or galaxy with a nearby star of known distance from the Earth. This is because measurements are made in two parts of the Earth's orbit around the Sun, in order to get as great a distance for the base as possible. In defining the parsec, the distance from the Earth to the Sun (1 AU) is used as the base of the right triangle and the arcsecond is used as the angle. Astronomers can measure angles as small as 0.001 arcsecond. An acrsecond is equal to 1/60 of an angular degree. Tangent of angle used to determine length of sideįor distant objects in space, the angle becomes very small. That angle, in turn, is used to calculate the distance.įor example, knowing the distance A and the angle a in the illustration below, you can find the distance B using simple trigonometry. This effect can be used to determine the resulting angle from moving side-to-side as compared to the distant object. The object seems to move or change position. Parallax effect determines angleĪs an explanation of the geometric method used to measure distance with the parallax effect, consider the situation when you observe a distant object and move side-to-side. It is 1 AU divided by the tangent of an arcsecond. Parsec stands for parallax of one arcsecond. ParsecĪstronomers prefer to use the parsec to designate extremely great distances in space, because it relates to the geometric method they commonly use to establish distance. You could say that 1 AU equals 8.33 light minutes. The time it takes light to travel from the Sun to the Earth (1 AU) is approximately 499 seconds or 8.32 minutes. The size of the Universe is estimated to be between 93 billion and 156 billion light years across.The Andromeda Galaxy is approximately 2,500,000 light years away.The Milky Way galaxy is about 100,000 light years across.Proxima Centauri, the nearest star in our Milky Way galaxy, is 4.22 light years away.Common large distancesĬommon large distances in space, measured in light years, include: Thus, a light year is about:Ī light year is also equals 63,241 AU. One year equals 365 days × 24 hours in a day × 60 minutes in an hour × 60 seconds in a minute, which equals 31,536,000 seconds. The speed of light is approximately 300,000 kilometers per second or 186,000 miles per second. Instead, the light year is used as a unit of measurement.Ī light year is the distance light travels in one year and can be calculated as the speed of light in kilometers/second or miles/second multiplied times the number of seconds in a year.
Light yearĪlthough the astronomical unit is fine for our Solar System, it is not sufficient to designate the greater distances to other stars and galaxies. Mars can be between 2.52 AU and 0.53 AU from Earth, depending on their relative positions.Īs of 2009, the American spacecraft Voyager 1 had traveled over 108 AU from the Sun, the furthest a man-made object has traveled.
The distance between planets depends on their orientation in their orbits. By definition, the Earth is 1 AU from the Sun.Some distances within the Solar System in AU are: That distance is approximately 150 million kilometers (150,000,000 km) or 93 million miles (93,000,000 mi). It is defined as the distance from the Earth to the Sun. The unit of measurement that is convenient for stating the large distances within our Solar System is the astronomical unit (AU).
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