Do you remember learning about how to measure latitude and longitude? On the Earth, latitude measures how far north or south a place is from the Equator. For example, France is at about 45 degrees ( o) north. It is halfway between the Equator and the North Pole. The Equator is at 0o (neither north nor south), and the North Pole is at 90o north. At what latitude is your state or country?
Look at the Degrees Latitude diagram. This diagram illustrates how degrees of latitude are measured in the galactic coordinate system. The galactic plane is like the Equator. It is at 0o latitude. The Earth is on the galactic plane. It is also at 0o latitude.
Look at the diagram and find the celestial objects. These may be stars, faraway galaxies, supernova remnants, or any other kind of object in the universe. Look at objects 1 and 2. Notice that object 1 is at -10o latitude and object 2 is at +10o latitude. In galactic coordinates, we say plus and minus instead of north and south.
Latitude & Distance
On Earth, a place that is 10o north (example: the island of Tobago in the Caribbean Sea) is the same distance from the Equator as a place that is 10o south (example: Cape York, Australia). Each place is about 1110 km (or about 690 miles) from the Equator--the same exact distance. This is because these places are on the surface of the Earth. They are not hovering up in the sky or buried deep in the ground.
Look at the Degrees Latitude diagram again. See the large pink circle. If all objects in outer space were exactly on the circle*, then an object that was at +10o would always be the same distance from the galactic plane as would an object that was at -10o. However, this is not the case. None of the objects in the diagram are exactly on the circle. Some are nearer, and some are farther.
(*Actually, the yellow circle is just imaginary. It could be much bigger or much smaller. The circle is there to help the diagram show the degrees of latitude in galactic coordinates.)
The objects at +10o and -10o are at different distances from the galactic plane; object 2 is closer to the galactic plane than object 1 is because it is at the same latitude and is closer to the Earth. Try to figure out where objects 1, 2, 3 and 4 would be on the black and white map.