What Do We Encounter Going Straight Up Out Of The Solar System?

So if our solar system is more or less flat in terms of the planetary rotations around the sun (I’m using typical pictorial depictions of the solar system), what is up and down from our solar system and galaxies? It doesn’t seem like above and below of light years in space is ever explored. Or are the (for example) constellations examples of up and down in space?
"Draco and Ursa Minor", plate 1 in Urania's Mirror, a set of celestial cards accompanied by A familiar treatise on astronomy. Jehoshaphat Aspin,  Public domain

"Draco and Ursa Minor", plate 1 in Urania's Mirror, a set of celestial cards accompanied by A familiar treatise on astronomy. Jehoshaphat Aspin, Public domain

Originally posted on Forbes! 

The solar system is indeed pretty much a flat sheet, with the major planets all orbiting in a very thin plane surrounding the Sun. Part of the reason we don’t tend to send spacecraft in the 'up' direction, out of this thin plane, is simply that there’s not very much...

The solar system is indeed pretty much a flat sheet, with the major planets all orbiting in a very thin plane surrounding the Sun. Part of the reason we don’t tend to send spacecraft in the 'up' direction, out of this thin plane, is simply that there’s not very much there! Now, that’s not to say that there isn’t anything out that direction, but you have to travel for a while before you reach it.

Closest to the solar system, but at its outermost fringes, the orbits of the objects in the Kuiper Belt deviate from this extremely flat plane, but still tend to orbit mostly in a disk surrounding the Sun. Instead of an extremely flat plane, you have something more like an inner tube - inflated, with some vertical height to it, but still mostly lining up along the plane of the rest of the major planets. This area is where Pluto falls - its orbit is tilted out of the plane of the major planets by 17 degrees, but it’s not so far tilted out of the plane of the rest of the planets that it’s really traveling overhead the other planets.

A drawing of the solar system shows Pluto's tilted orbit. Pluto's path is angled 17 degrees above the line, or plane, where the eight planets orbit. Pluto's orbit is more elliptical than the planets’ paths. Image credit: NASA

A drawing of the solar system shows Pluto's tilted orbit. Pluto's path is angled 17 degrees above the line, or plane, where the eight planets orbit. Pluto's orbit is more elliptical than the planets’ paths. Image credit: NASA

What you do get overhead the planets is a much more distant object, the Oort Cloud. This is a reservoir of comets, incredibly distant from the Sun, which are arranged in a roughly spherical distribution around the Sun. The objects out here are small, dimly lit chunks of ice and rock, and so far from the Sun that they are extremely difficult to observe, even with high end telescopes.

If we travel further away, and look for even more distant objects, then suddenly we run into a proliferation of stars within our own galaxy which are 'up' above the plane of our solar system. Part of this is that the galaxy is much thicker than the solar system, and so even if the plane of the galaxy and the plane of the solar system were perfectly aligned, we would see stellar neighbors of our Sun, both above and below our solar system. However, our solar system isn’t perfectly well aligned with the Milky Way galaxy- those two are off from each other by 63 degrees. What this means is that we see far more stars 'up' or 'down' out of our solar system, as we look through part of the densely populated disk of the galaxy, than we would if we were looking directly 'up' out of the plane of the galaxy.

A star chart oriented so that the center of the image is directly perpendicular to the plane of the solar system. The constellation Draco falls in the center of the image, with the Little Dipper slightly to the right of center. Image credit: Tom Ruen, public domain

A star chart oriented so that the center of the image is directly perpendicular to the plane of the solar system. The constellation Draco falls in the center of the image, with the Little Dipper slightly to the right of center. Image credit: Tom Ruen, public domain

The constellations are a good example of things that exist 'above' our solar system. Our planet spins on an axis that’s tilted by 23 degrees relative to the plane of the solar system, so looking at the stars at the exact North Pole isn’t quite pointing us in the right direction, but it’s pretty close! If you find the North Star, Polaris, and then wander about twenty degrees (about two fists, held at arm’s length at the sky) away from the path the Moon travels, now you’re pointing 'up' out of the solar system. The constellations in this region of the sky are plentiful. This is roughly where the cup of the Little Dipper is, though exactly 'up' is in the much fainter constellation Draco (illustrated at the top of the article). The stars that hang 'above' our planet remain roughly stationary in our night skies as our planet rotates beneath them - if you’re far enough North these stars will never set.

Since the direction of 'up' away from the solar system doesn’t also point you directly out of the Galaxy, if you want to face a direction that aims you at the center of the galaxy or 'up' out of the Galaxy, you need to point yourself in a different direction.  The center of the galaxy is in the direction of the Sagittarius constellation, which looks a bit like a very pointy teapot in the sky. To point your face out of the galaxy, you must aim yourself at the lesser-known constellation Coma Berenices, which is surrounded by other constellations you’ve probably heard of - Virgo and Leo border it, as does Ursa Major (which contains the Big Dipper). If you take the last three stars in the curve of the handle of the Big Dipper, and imagine them creating a long, pointy pizza wedge, you’ve gotten pretty close to Coma Berenices. What's in that direction? Not much that's visible to the naked eye, but if you have a well-equipped telescope, you run into the Coma Cluster, a very dense collection of galaxies - an environment very unlike the galaxy our own Milky Way finds itself within. 

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Is there a universal addressing scheme?

Is there a universal addressing scheme for the universe? (e.g. Quadrants… etc.) If so, what is the central reference point, or zero?

We’ve come up with a few different coordinate systems for the Universe, but none of them are really “universal”. By that, I mean that you wouldn’t be able to use them no matter where you are in the universe - most of them only work conveniently from Earth.

Starting small, we’ve got one coordinate system to describe our solar system, with our sun at the center. This coordinate system is easiest to visualize as if you had a birds eye view of our solar system, watching all the planets go around the sun. Every coordinate system needs three coordinates to describe a location - normally we think of up/down, right/left, and forward/back. The three coordinates here are distance outwards from the sun (in any direction), the position of the object in a circle around the sun at that distance (usually measured as an angle from a line drawn from the position of the Earth in September to the sun), and distance away from the plane described by the orbits of the planets. Perhaps unsurprisingly, this is only really a useful coordinate system for objects in our solar system.


We also have a galactic coordinate system, which is not centered on the center of the galaxy as you might expect, but instead, it’s still centered on the location of the sun. The second coordinate here is the distance “up” out of the disk of the Milky Way, and the third is distance from the sun once again. The disk of the Milky Way is not in line with the disk of our solar system, which you can spot if you go outside in a dark sky. The Milky Way usually goes North-South in the sky, and all the planets (and the moon) will always be found in a line that goes East-West. This coordinate system is generally considered to be confusing to work with, and is mostly not used, unless you’re trying to map the Milky Way itself.

By and large, what astronomers use to describe the locations of things in the sky is actually a projection of the Earth’s latitude and longitude lines onto the sky. Take the line between the north and south poles, and extend them out into the sky - those are the northern and southern celestial poles. (The north celestial pole points almost exactly to the North Star.) The equator, expanded outwards in a plane from the surface of the earth, describes the Celestial Equator. The units we then use to describe the positions of objects are right ascension, declination, and distance (if we have it). Declination is similar to latitude - it describes the angle above or below the celestial equator. Right Ascension is like longitude, but instead of being measured in degrees, is measured in hours, minutes, and seconds. We do this because we know how fast the earth rotates - 360 degrees in 24 hours. This means that the earth rotates through 15 degrees in an hour, and we can easily tell how long we need to wait for another object to be overhead. If an object at the 0 hour coordinate is overhead right now, objects at the 3 hour line will be overhead in three hours. This coordinate doesn’t tell you anything about the absolute position of an object in the Universe, but it’s very good at describing where that object appears to be placed in the sky.



Using the earth as the zero point starts to make more sense once you start looking at things that are very far away, because at that point, you start looking increasingly far back in time. Looking very far away in the universe is looking backwards through shells of time, and since we are observing from Earth, those shells are by definition centered on the Earth - the objects that we see as five billion years old are being viewed at that age because it took light that long to get here. The speed of light is the same in every direction, so you’ll see the same age in every direction at that distance, from the perspective of the Earth. This would be true of anyone observing from anywhere in the universe, but they might see a slightly different set of galaxies.

Because we only have coordinate systems that are centered on the earth or the sun, if you were elsewhere in the galaxy, or elsewhere in the universe, you’d have to constantly convert your location into where you would appear to be (from the perspective of the earth or the sun) if you wanted to use one of these systems. I suspect that whenever we do start exploring outside our solar system, we will come up with another coordinate system that’s convenient for keeping track of our spacecraft, but we’ll keep all the old ones we’ve come up with “for historical reasons”.

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