Unless you are completely disconnected from society (in which case you wouldn't be reading this), you have received mail of some type.
Have you ever thought about how it came to your mailbox? It is really a simple idea: if you have an address, you can receive mail. If you are in the United States, you probably live in a building on a street in a village or city which belongs to a township within a county that is part of a state in the U.S.
However, if we were to receive mail from "E.T." living on another planet somewhere else in the universe, what address would they put on the envelope?
Now, even if there is an extraterrestrial intelligence with the capability of sending us mail, their view of the universe will probably be different from ours, so with that in mind, we will use our current perspective to establish our address in the universe.
Other than the fact it has copious amounts of liquid water and life, the Earth is really a tiny place relative to everything else, but it is where we live ... our home. This tiny house of ours (Earth) orbits the sun once every 365 and one-fourth days as one of eight planets (I really miss Pluto).
It is the third planet from the sun which is our celestial street address. The sun, along with Earth and the rest of our solar system, is just one of several billion stars that make up our Milky Way galaxy. The Milky Way is shaped like a giant pinwheel with streams of stars spiraling out from the center.
Our sun belongs to a local group of stars that are just over halfway between the center and edge of the galaxy in what is known as the Orion Spur near the Sagittarius Arm of the Milky Way galaxy. As shown in Figure 1, the Milky Way is approximately one hundred light years across so that puts us just under 30 light years from the center of our galaxy. We orbit the center of the galaxy about once every 250 million years.
That means that our solar system has made approximately 18 orbits of the Milky Way galaxy since it began forming 4.6 billion years ago.
We now have our street (the solar system), village (the interstellar neighborhood), and township (Milky Way) but there is more. Our Milky Way galaxy belongs to a "Local Group" of more than 30 galaxies and includes our largest neighbor, the Andromeda Galaxy, which happens to be the farthest object we can see with the unaided eye at about 2.5 million light years. This Local Group is part of an even larger group of galaxies known as the Virgo supercluster which is comprised of about 20 of these galactic clusters. Is there more? Well, let's see...we have our house number (Earth) on our street (solar system) in our village (interstellar neighborhood) within our township (Milky Way) that is part of our county (local group of Galaxies) which is one of about 20 that make up the state (Virgo supercluster). Beyond the Virgo supercluster is what is known as the local super cluster group (our country) which resides as one of many such groups in the known universe (our world). So, what exactly is our celestial address? They say a picture is worth a thousand words so let's take a look at these.
If you look closely at Figure 2, below each image is part of the address of the Adirondack Public Observatory's roll-off roof facility. (178 Big Wolf Road, Tupper Lake, NY, USA ... with the township and county added). This is where we live, on a tiny planet orbiting a relatively small star. We may never get to travel very far from Earth but we have been receiving information from beyond Earth, since it formed. Through the science of astronomy, we have come to know the location and characteristics of other galaxies, stars and most recently, planets in other star systems not to mention what we have learned about our own system of planets. The universe is full of places to wonder about and even though our closest neighbors are very far away we have a responsibility, if for no other reason than to satisfy our human curiosity, to continue to explore the wilderness above.
With our roll-off roof facility up and running, astronomers of the Adirondack Public Observatory are eager to dazzle you with telescopic views of the moon and cosmos every other Friday night (next on Feb. 14). Go to the APO website at apobservatory.org, and click on "events" for more information and directions to our site above Little Wolf Pond in Tupper Lake.