What does the Sun's orbit within the Solar System look like?

What does the Sun's orbit within the Solar System look like?

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Everything in the Solar System revolves around the "barycenter": the overall center of mass. This barycenter is not in the center of the Sun. Some articles and essays I've read go so far as to suggest that the position of the barycenter does not have a set of fixed coordinates within the System: it fluctuates.

Well. Since everything, including the Sun, revolves around this barycenter, the Sun must have its own orbit around it. What does it look like? How large is it? How elliptic?

(In my research, I have tried and failed to establish whether the barycenter is within the Sun or outside it. Either way, an orbit is an orbit).

In case anyone can't follow the links in my comment (above), here are the two pictures I mentioned. From: here and here.

The first claims to show the track of the solar system barycentre in the heliocentric reference frame. The outer yellow circle marks the photosphere of the Sun. The second plot claims to show the track of the centre of the Sun in the barycentric reference frame. The yellow circle shows the photosphere of the Sun to scale. As you can see, the plots are actually (almost) the same! Given that to go from one frame to the other is just a translation, I suppose they can both be right providing the x and y axes are defined appropriately.

To answer the questions posed: "What does it look like" - it looks like these two pictures. "How large is it?" As you can see, the maximum separation between the barycentre and the solar centre appears to be about 2 solar radii over the timescale covered by these plots, but is as small as a tenth of a solar radius (e.g. in 1950). "How elliptic?" Not at all really, it is a complicated superposition caused by the orbits mainly of Jupiter and Saturn, but all the planets contribute to a greater or lesser extent.

The barycenter is calculated from the instantaneous positions of all the discrete masses in the solar system. I do not know for sure, but I assume that it includes all of the planets, and that everything else is negligible at the scale of the thickness of the line.

How long to orbit Milky Way’s center?

Our sun is located about two-thirds of the way out from the center of the Milky Way. Illustration via Caltech.

The planets in our solar system orbit around the sun. One orbit of the Earth takes one year. Meanwhile, our entire solar system – our sun with its family of planets, moon, asteroid and comets – orbits the center of the Milky Way galaxy. Our sun and solar system move at about about 500,000 miles an hour (800,000 km/hr) in this huge orbit. So in 90 seconds, for example, we all move some 12,500 miles (20,000 km) in orbit around the galaxy’s center.

Our Milky Way galaxy is a big place. Even at this blazing speed, it takes the sun approximately 225-250 million years to complete one journey around the galaxy’s center.

This amount of time – the time it takes us to orbit the center of the galaxy – is sometimes called a cosmic year.

Artist’s concept of solar system with the Milky Way galaxy in the background.

By the way, in the past when we’ve talked about this subject, people have commented on the difference between the words rotate and revolve. The word revolve means to orbit around another body. Earth revolves (or orbits) around the sun. The sun revolves around the center of the Milky Way galaxy.

On the other hand, rotate means to spin on an axis. The Earth rotates every 24 hours. The sun rotates, but not at a single rate across its surface. The movements of the sunspots indicate that the sun rotates once every 27 days at its equator, but only once in 31 days at its poles.

What about the Milky Way galaxy? Yes, the whole galaxy could be said to rotate, but like our sun, the galaxy is spinning at different rates as you move outward from its center. At our sun’s distance from the center of the Milky Way, it’s rotating once about every 225-250 million years – defined by the length of time the sun takes to orbit the center of the galaxy.

Illustration of a rotating galaxy, with different parts of the galaxy revolving around the center at different rates. Scientists call this “differential rotation.” Stars near the center revolve around the center faster than those farther out. This diagram is from Nick Strobel’s Astronomy Notes. Go to his site at for updates and more info.

Bottom line: The planets in our solar system orbit (revolve) around the sun, and the sun orbits (revolves) around the center of the Milky Way galaxy. We take about 225-250 million years to revolve once around the galaxy’s center. This length of time is called a cosmic year.

Solar System Map of Current Planetary Positions

Both apps show a solar system map - a "plan view" of the planets laid out in the plane of the ecliptic (the flat plane in which all the main planets move about the Sun).

Dwarf planet positions are also shown - but it should be realised that these objects often rise far above and below the plane of the ecliptic. This is because their orbital planes are tilted with respect to the ecliptic - by more than 40 degrees in some cases. So be aware that just because the app may occasionally show a planet and a dwarf planet to be very close to each other in the plan view, they may, in fact, be separated by a large perpendicular distance.

10 Need-to-Know Things About the Solar System

One of Billions

Our solar system is made up of a star, eight planets and countless smaller bodies such as dwarf planets, asteroids and comets.

Meet Me in the Orion Arm

Our solar system orbits the center of the Milky Way Galaxy at about 515,000 mph (828,000 kph). We&rsquore in one of the galaxy&rsquos four spiral arms.

A Long Way Round

It takes our solar system about 230 million years to complete one orbit around the galactic center.

Spiraling Through Space

There are three general kinds of galaxies: elliptical, spiral and irregular. The Milky Way is a spiral galaxy.

Good Atmosphere(s)

Our solar system is a region of space. It has no atmosphere. But it contains many worlds&mdashincluding Earth&mdashwith many kinds of atmospheres.

Many Moons

The planets of our solar system&mdashand even some asteroids&mdashhold more than 150 moons in their orbits.

Ring Worlds

The four giant planets&mdashand at least one asteroid&mdashhave rings. None are as spectacular as Saturn&rsquos gorgeous rings.

Leaving the Cradle

More than 300 robotic spacecraft have explored destinations beyond Earth orbit, including 24 astronauts who orbited the moon.

Life as We Know It

Our solar system is the only one known to support life. So far, we only know of life on Earth, but we&rsquore looking for more everywhere we can.

Far-Ranging Robots

NASA&rsquos Voyager 1 is the only spacecraft so far to leave our solar system. Four other spacecraft will eventually hit interstellar space.

Diameter of the Solar System

Defining the diameter of the Solar System is a matter of perspective and characterization. You can look at the Solar System’s diameter as ending at the aphelion of the orbit of the farthest planet, the edge of the heliosphere, or ending at the farthest observable object. To cover all of the objective bases, we will look at all three.

Looking at the aphelion(according to NASA figures) of the orbit of the farthest acknowledged planet, Neptune, the Solar System would have a radius of 4.545 billion km and a 9.09 billion km diameter. This diameter could change if the dwarf planet Eris is promoted after further study.

Sedna is three times farther away from Earth than Pluto, making it the most distant observable object known in the solar system. It is 143.73 billion km from the Sun, thus giving the Solar System a diameter of 287.46 billion km. Now, that is a lot of zeros, so let’s simplify it into astronomical units. 1 AU(distance from the Earth to the Sun) equals 149,597,870.691 km. Based on that figure, Sedna is nearly 960.78 AU from the Sun and the Solar System is 1,921.56 AU in diameter.

A third way to look at the diameter of the Solar System is to assume that it ends at the edge of the heliosphere. The heliosphere is often described as a bubble where the solar wind pushes against the interstellar medium and edge of where the Sun’s gravitational forces are stronger than those of other stars. The heliopause is the term given as the edge of that influence, where the solar wind is stopped and the gravitational force of our Sun fades. That occurs at about 90 AU, giving the Solar System a diameter of 180 AU. If the Sun’s influence ends here, how could Sedna be considered part of the Solar System, you may wonder. While it is beyond the heliopause at aphelion, it falls back within it at perihelion(around 76 AU).

Those determinations of the diameter of the Solar System may seem about as clear as mud, but they give you an idea of what scientists are trying to place a definitive value on. The distances involved are mind boggling and there are too many unknowns to place a absolute figure. Perhaps, an exact number will be determinable as the Voyager probes continue their outward journey.

Here’s an article on Universe Today about the closest star to Earth, and another about how long it would take to travel to the closest star.

Here’s an article from the Physics Factbook about the diameter of the Solar System, and a cool way to visualize it using the Earth as a peppercorn.

We have recorded a whole series of podcasts about the Solar System at Astronomy Cast. Check them out here.

Egyptian astronomy, Sirius mythology, and ancient calendars.

The Greeks weren’t the first or only culture to use Sirius to begin the calendar year. The Egyptian calendar was also based on Sirius. In fact, the Greeks in all likely-hood acquired the method from Egypt.

In ancient Egypt, New Year’s Day was signaled by the annual heliacal rising of the star Sirius. In Egyptian, it’s known as Sothic. For a long time, it was thought this longer cycle was calibrated to the rise and fall of the river Nile. However, the tidal flooding of the Nile is highly unpredictable.

Sirius in Egypt could be observed on the eastern horizon just before dawn on the summer solstice. The timing of its rise would determine whether an extra month with a few days would be employed that year. The rise of Sirius determined the calendar year.

This method allowed for incredibly accurate date-keeping. The various lunar calendars governed by a 365-day civil calendar moved forward through the season without ever being corrected throughout the entire Egyptian history. Unlike the Gregorian calendar, the seasons stayed alongside the important first day of the first month of the solar year.

Across the globe, ancient cultures would use this system. In ancient Mesopotamia, to the Dogon tribe in Mali, to the Hindu Yuga traditions across India, to the ancient Mayans in Mexico, New Zealand, and China, Sirius would set the beginning of the year. They all had Sirius mythology outlining its importance.

By the time the Roman calendar was employed it lost the calibration point. Without setting the year to the rise of Sirius, the imperfect leap year method was needed to stop drifting of the seasons.

Ancient calendar systems could be evidence that our solar system is rotating around its binary partner Sirius.

What does the Sun's orbit within the Solar System look like? - Astronomy

  • Mass: 333 thousand times the mass of Earth
  • Diameter: 109 times the diameter of Earth
  • Temperature: 5,500 degrees C (10,000 degrees F) on the surface
  • Distance from Earth: 150 million kilometers (93 million miles)
  • Age: 4.5 billion years

The Sun is a yellow dwarf star at the center of our Solar System. All the planets of the Solar System orbit around the Sun. The Sun and the Solar System orbit around the center of our Galaxy, the Milky Way.

Although the Sun is a relatively small star in the universe, it is huge in relation to our solar system. Even with massive gas planets like Jupiter and Saturn, the Sun contains 99.8% of all the mass in the solar system.

The Sun is made up of superheated hydrogen and helium gas. Hydrogen makes up about 74% of the mass of the Sun. At the center of the Sun, hydrogen atoms, under intense pressure from gravity, undergo a process called nuclear fusion and get converted into helium atoms. The process of nuclear fusion generates a tremendous amount of heat causing radiation and eventually the sunlight that reaches the Earth.

Cross Section of the Sun. Source: NASA

The Sun is the main source of energy in the Solar System and life on Earth. Plants use photosynthesis in order to harness energy from the Sun. Even energy that we get from fossil fuels like oil originally came from the Sun. We can also use solar cells to convert energy from the Sun directly into electricity.

An eruption from the surface of the Sun. Source NASA.

How do we know about the Sun?

The Sun has been studied by humans, scientists, and astronomers for as long as people have been around. In the 16th and 17th centuries astronomers like Galileo and Isaac Newton began to study the Sun and learned that planets orbit the Sun due to gravity. In the early 1900's Albert Einstein used the formula E=MC^2 to explain how the Sun generated so much energy. In 1920 Arthur Eddington explained how the intense pressures at the center of the Sun could produce nuclear fusion and, in turn, great amounts of heat and energy. Since 1959 many space missions have observed and studied the Sun, its solar winds, and sun spots to give us more and more information about the Sun and this giant center of the Solar System.

The Sun as seen from the International Space Station.
Source NASA.


The first evidence that the Sun changes came from studies of sunspots, which are large, dark features seen on the surface of the Sun caused by increased magnetic activity. They look darker because the spots are typically at a temperature of about 3800 K, whereas the bright regions that surround them are at about 5800 K ([link]). Occasionally, these spots are large enough to be visible to the unaided eye, and we have records going back over a thousand years from observers who noticed them when haze or mist reduced the Sun’s intensity. (We emphasize what your parents have surely told you: looking at the Sun for even a brief time can cause permanent eye damage. This is the one area of astronomy where we don’t encourage you to do your own observing without getting careful instructions or filters from your instructor.)

Sunspots. This image of sunspots, cooler and thus darker regions on the Sun, was taken in July 2012. You can see the dark, central region of each sunspot (called the umbra) surrounded by a less dark region (the penumbra). The largest spot shown here is about 11 Earths wide. Although sunspots appear dark when seen next to the hotter gases of the photosphere, an average sunspot, cut out of the solar surface and left standing in the night sky, would be about as bright as the full moon. The mottled appearance of the Sun’s surface is granulation. (credit: NASA Goddard Space Flight Center, Alan Friedman)

While we understand that sunspots look darker because they are cooler, they are nevertheless hotter than the surfaces of many stars. If they could be removed from the Sun, they would shine brightly. They appear dark only in contrast with the hotter, brighter photosphere around them.

Individual sunspots come and go, with lifetimes that range from a few hours to a few months. If a spot lasts and develops, it usually consists of two parts: an inner darker core, the umbra, and a surrounding less dark region, the penumbra. Many spots become much larger than Earth, and a few, like the largest one shown in [link], have reached diameters over 140,000 kilometers. Frequently, spots occur in groups of 2 to 20 or more. The largest groups are very complex and may have over 100 spots. Like storms on Earth, sunspots are not fixed in position, but they drift slowly compared with the Sun’s rotation.

By recording the apparent motions of the sunspots as the turning Sun carried them across its disk ([link]), Galileo , in 1612, demonstrated that the Sun rotates on its axis with a rotation period of approximately 1 month. Our star turns in a west-to-east direction, like the orbital motions of the planets. The Sun, however, is a gas and does not have to rotate rigidly, the way a solid body like Earth does. Modern observations show that the speed of rotation of the Sun varies according to latitude, that is, it’s different as you go north or south of the Sun’s equator. The rotation period is about 25 days at the equator, 28 days at latitude 40°, and 36 days at latitude 80°. We call this behavior differential rotation.

Sunspots Rotate Across Sun’s Surface. This sequence of photographs of the Sun’s surface tracks the movement of sunspots across the visible hemisphere of the Sun. On March 30, 2001, this group of sunspots extended across an area about 13 times the diameter of Earth. This region produced many flares and coronal mass ejections. (credit: modification of work by SOHO/NASA/ESA)

The Planets and the Moon

Planets seen in the sky are always near the ecliptic, which means that their orbits are never too far from the plane of the ecliptic. In other words, the solar system is rather flat, with all its major parts moving in nearly the same plane.

What about the connection between "ecliptic" and eclipses?

The moon's orbit cuts the ecliptic at a shallow angle, around 5 degrees, which means that on the celestial sphere the Moon, too, follows a path through the zodiac. Half the time the Moon is north of the ecliptic, half the time south of it. If the shadow of the moon hits the Earth, the Sun is eclipsed in the shadow area if on the other hand the shadow of the Earth covers the moon, the moon goes dark and we have an eclipse of the moon.

Either of these can only happen when the Sun, Earth and Moon are on the same straight line. Since the Sun and Earth are in the plane of the ecliptic, the line is automatically in that plane too if the moon is also on the same line, it must be in the plane of the ecliptic as well.

It takes close to a month for the Moon to go around the Earth ("month" comes from "Moon") and during that time its orbit crosses the ecliptic twice, as it goes from one side to the other. At the time of crossing, the Sun may be anywhere along the ecliptic usually it is not on the Earth-Moon line, and therefore an eclipse usually does not take place. Occasionally, however, it is on that line or close to it. If it then happens to occupy exactly the same spot on the celestial sphere, we get an eclipse of the Sun, because the moon is then between us and the Sun. On the other hand, if it occupies the spot exactly opposite from that of the Moon, the Earth's shadow falls on the Moon and we have an eclipse of the Moon.

A new distant planet far from the Ecliptic

They first photographed it in October 2003, but only discovered its motion by comparing that picture with one from January 2005. One reason no one had discovered it until now seems to be that previous searches examined the vicinity of the ecliptic, whereas the new planet (nameless, so far) was about 44° away from the ecliptic. For more, see here and here .

As reported in the " New Scientist " (6 August 2005, p. 10) the planet's orbit is also rather eccentric, approaching the Sun within 36 AU--though its orbital period of 560 years means this would not happen very soon. Like Pluto, it seems to be an extreme member of the Kuiper Belt , a population of small planets outside the orbit of Neptune. Most such objects are the size of large asteroids, but according to the same article, two recent additions (one of them announced just a day before the new planet) are about 0.7 time the size of Pluto and have inclination of 28°.

For anything else you may want to know about the new planet and its moon (it seems to have one) and those two runners-up, look here , on a web page by Mike Brown , one of the discoverers.

(Concerning Sedna , another newly discovered planet, see here and here .)

Watch the video: Jupiter does not orbit the sun (September 2022).