The plane (or equator) of the Milky Way is tilted by about 60º to the plane of the ecliptic, the plane of the Earth's orbit around the sun.
The plane of the Earth’s orbit around the sun is called the ecliptic. The plane of the ecliptic projected onto the stellar sphere marks the sun’s annual path in front of the background stars. Although the sun appears to move eastward through the stars at about one degree per day, this apparent motion is really a reflection of the Earth orbiting the sun.
The ecliptic is an important reference and is often highlighted on sky charts. Because the planets of the solar system circle the sun on nearly the same plane that the Earth circles the sun, the planets are always found on or close to the ecliptic. The plane of the moon’s orbit around Earth is only somewhat askew to the plane of the ecliptic, so the moon is always found on or near the ecliptic, too. When the new moon aligns with the ecliptic, we have a total eclipse of the sun. When the full moon aligns with the ecliptic, we have a total lunar eclipse.
Where is the ecliptic in relation to the Milky Way?
The plane (or equator) of the Milky Way galaxy is tilted by about 60 degrees to the plane of the ecliptic. Quite by coincidence, the ecliptic intersects the galactic plane on or near the June and December solstices. But does that mean the Earth literally crosses the plane of the Milky Way galaxy at these times? The answer is no!
The ecliptic as marked on sky charts represents an outward projection of the Earth’s orbital plane onto the distant stellar sphere. By galactic standards, the Earth’s orbit around the sun is so puny that it shrinks to the size of a point. Earth’s orbit is about 16.5 light-minutes in diameter, whereas the diameter of the Milky Way disk is a whopping 100,000 light-years wide.
The vastness of the Milky Way dwarfs our solar system to almost nothingness. If the solar system, from the sun out to Pluto, were shrunk to the size of a quarter, the Milky Way galaxy would be the size of North America.
By galactic standards, The Earth and solar system reside right next to the galactic plane. But by solar sytem standards, we’re far from the plane of our Milky Way galaxy. Astronomers estimate that we’re several dozen light-years north of the galactic plane.
There’s no such thing as a coincidence.
Last I heard, the sun (and every other star in the Milky Way Galaxy) orbits the center of the galaxy. If it\’s true that \”we’re several dozen light-years north of the galactic plane\”, it\’s also true that the sun/solar system will be several dozen light-years SOUTH of the galactic plane after half an orbital period. Perhaps you\’d like to explain how we can do that without passing THROUGH the galactic plane…
Given that we\’ve crossed the plane twice in each galactic orbit for as long as the sun\’s been in existence, I guess it\’s safe to assume that nothing catastrophic happens at the stellar scale. Hell, galaxies are so sparse that \”interesting\” events are rare even during galactic COLLISIONS!
On the other hand, what about galactic debris? If there is roughly the same amount of \”stuff\” above the galactic plane as below, and everything changes sides in half an orbit- wouldn\’t it seem reasonable that collision probability is maximum at the equator?
Something the size of a small asteroid hitting the sun might be but a blip on the stellar scale, but on the planetary scale it could ruin your whole day!
Hi Chip.
Yes, the sun and the stars of our galaxy revolve around the center of the Milky Way. The astronomer Ken Croswell (in his article The Brightest Red Dwarf in the July 2002 issue of Sky & Telescope magazine) reports, “As they orbit the Milky Way, stars bob up and down through the galactic plane like horses on a merry-go-round.” Our sun stands as no exception. According to the astronomer Karen Masters, the sun crosses the galactic plane in periods of about 35 million years. One revolution of the sun around the galactic center takes an estimated 230 million years.
Presently the sun lies north of the galactic plane. Moreover, the sun is continuing to travel northward from the galactic plane at some 7 kilometers per second. The sun last crossed the galactic plane several millions of years ago, and isn’t expected to cross the galactic plane again for many millions of years to come.
Bruce
That being said, our sun is 4.5 billion years old, we complete a revolution every 230 million years, and cross a plane every 35 million years, that makes no sense unless you realize the center of the center of the galaxy rotates faster the we do some 27K miles light years away, like how the milk in the center of your coffee spins faster that the milk our near the edge of the rim…
We have crossed the plane 128.57 times and are due to actually cross again in about 15 million years, then will visually cross on a map about 27 thousand years later.
I don’t think these calculations are even close to being correct since I believe light slows without relation to time as it exits the gravitational center of our galaxy therefore our visual representations of the universe based on photos are completely incorrect without proper correction for time/speed based compensations of the visual light we can see and plot on paper with regard for the actually true current locations based on time and assumed directions of travel.
Computer based extrapolations around the world have all calculated the actual true physical crossing a plane to occur in December of 2012.
Siempre,
Given that the solar system resides north of the galactic plane and is traveling north of the galactic plane at the rate of 7 kilometers per second, that means we’ll be farther out from the galactic plane in 2012 than we are at present.
Bruce