The Size and Distance Scale Of The Solar System EARTH AND THE SOLAR SYSTEM The Size and Distance Scale Of The Solar System Our Earth is just one of several Planets that revolve around our Sun, the primary and central object of our Solar System. Since the entire Solar System, including our Earth, was created about the same time (about 4.6 billion years ago), our understanding of the origin and properties of the Solar System, the Sun, and its other members are important to our understanding of Earth itself. We consider the size of our Earth to be very large, in comparison with most sizes and distances we deal with in our daily lives. However, the size of the Earth is very small compared to the size of the Solar System, which consists of the Sun and its family of planets, of which our Earth is only about average in size.

The Size and Distance Scale Of The Solar System In turn, the size of our Solar System is very large compared to the size of our Earth, or even the largest planet, Jupiter. The distance from our Earth to the Moon is about 238,000 miles or 384,000 kilometers (nearly 100 times Earth’s diameter, or about 30 times the distance around the Earth at its equator). The distance from our Earth to the Sun is about 93,000,000 miles or 149,600,000 kilometers (more than 390 times the distance to the Moon). The most distant major planet from the Sun, Neptune, is 30 times Earth’s distance from the Sun. The nearest stars in our Galaxy, the star system of Alpha Centauri, is 9,000 times Neptune’s distance from the Sun!

SIZES AND DISTANCES IN THE SOLAR SYSTEM Diameters of Solar System Members: Sun = 1,392,000 km Mercury = 4,878 km Venus = 12,104 km Earth = 12,756 km Mars = 6,794 km Jupiter = 142,984 km Saturn = 120,536 km Uranus = 51,118 km Neptune = 49,530 km Pluto = 2,304 km Mean Distance from Sun 57,900,000 km = 0.387 AU 108,200,000 km = 0.723 AU 149,600,000 km = 1.000 AU 227,900,000 km = 1.524 AU 778,300,000 km = 5.203 AU 1,427,000,000 km = 10.07 AU 2,871,000,000 km = 19.19 AU 4,497,000,000 km = 30.06 AU 5,914,000,000 km = 39.53 AU Earth’s Moon = 3,476 km Mean Distance from Earth = 384,400 km

Earth and Moon to Scale

Sizes and Distances in the Earth-Moon System

Relative Sizes of Planets in Our Solar System

The Planets of Our Solar System The Inner Planets Sizes to Scale Mercury Venus Earth and Moon Mars

The Planets of Our Solar System The Outer Planets Jupiter Saturn Earth Included for Scale. Uranus Pluto Neptune

Size Comparisons In Our Solar System

THE SIZE AND DISTANCE SCALE OF THE SOLAR SYSTEM The distances between the members of our Solar System are much larger than the sizes of the members (even the Sun). The distance from the Earth to the Sun is about 150,000,000 km (about 93,000,000 miles) in comparison to the Sun’s diameter of about 1,392,000 km (about 110 times that of Earth). The largest planet, Jupiter, is 5 times Earth’s distance from the Sun, and 11 times Earth’s diameter (1/10 of the Sun’s diameter). The most distant major planet, Neptune, is 30 times Earth’s distance from the Sun. The region beyond the orbit of Neptune, called the Kuiper Belt, contains a large number of smaller objects (including Pluto and at least one recently discovered slightly larger object), all (as yet known) smaller than our Moon. The Kuiper Belt objects known to date can reach distances of more than 90 times Earth’s distance from the Sun.

SIZES AND DISTANCES IN THE SOLAR SYSTEM Diameters of Solar System Members: Sun = 1,392,000 km Mercury = 4,878 km Venus = 12,104 km Earth = 12,756 km Mars = 6,794 km Jupiter = 142,984 km Saturn = 120,536 km Uranus = 51,118 km Neptune = 49,530 km Pluto = 2,304 km Mean Distance from Sun 57,900,000 km = 0.387 AU 108,200,000 km = 0.723 AU 149,600,000 km = 1.000 AU 227,900,000 km = 1.524 AU 778,300,000 km = 5.203 AU 1,427,000,000 km = 10.07 AU 2,871,000,000 km = 19.19 AU 4,497,000,000 km = 30.06 AU 5,914,000,000 km = 39.53 AU Earth’s Moon = 3,476 km Mean Distance from Earth = 384,400 km

Orbits of the Inner Planets

Orbits of Jupiter and Saturn

Orbits of the Outer Planets

The Kuiper Belt The Kuiper Belt is a zone beyond the outermost major planet, Neptune, in which many of the comets that pass through the inner part of the solar system travel, and may have originated in the early years of our solar system. Surveys of the outer part of the solar system, beyond the orbit of Pluto, have recently found several additional objects comparable to Pluto in size. Most recently, an object apparently larger than Pluto has been found, which would (if verified) make it the 10th planet of our solar system. The detection of this (as yet un-named) object, called (temporarily) UB313, was made using the ground-based 48-inch Samuel Oschin telescope at Palomar Observatory. The object is 97 times Earth’s distance from the Sun, or more than twice Pluto’s greatest distance. It is likely that, with continuing very deep sky surveys with both ground-based and space-based telescopes, that more objects of these types will be discovered.

Orbit of the newly discovered object, 2003 UB313, compared to those of Pluto and the giant outer planets. Note, the orbits of Pluto and UB313, in red, are tilted relative to the plane of the inner giant planet orbits.

The Size and Distance Scale of The Solar System The size of our Solar System, if defined by the diameter of Pluto’s orbit, is about 40 times the diameter of Earth’s orbit around the Sun. If we consider also the most distant Kuiper Belt objects discovered to date, up to 90 times Earth’s distance from the Sun, the diameter of our solar system would be increased accordingly. However, the distance to the nearest star other than our Sun is vastly larger than the size of our Solar System. The distances to stars can be estimated by comparing their observed brightnesses with that of our Sun, if they are known to be similar to our Sun in other respects (as determined, for example, by spectroscopic measurements). The nearest stars to our solar system, the star system Alpha Centauri, is at a distance about 9000 times Neptune’s distance, or 6800 times Pluto’s maximum distance, from our Sun! If our solar system were scaled to the size of a quarter (with Pluto’s orbit about 1 inch in diameter) the Alpha Centauri system would be at a distance of about 285 feet!