THe silver is your ground wire
It looks like your house wire may be aluminum, so be extra careful when stripping any wires, as any nick would result in the wire breaking.
You should also use connectors that are approved for copper to aluminum connections

Thank you. I have another question. Since the ground wire is so thick it does not fit around the ground screw on the support bracket. Does it have to be wrapped around that screw? The lighting fixture ground copper wire fits fine but I can't seem to wrap both ground wire around the screw.

The ground wire must be attached to the outlet box,but it's not necessary to attach it to the hanger bar

I wrapped the light fixture's ground copper wire around the green ground screw. I took the aluminum ground wire and loosely wrapped it around the fixture's copper wire and green screw. Will this work? Since the aluminum wire was too thick to go under the screw I wasn't sure what else to do.

The light is working but I want to make sure I install it correctly.

thanks so much for your help!
Melissa

Connect the ground wire with the fixture ground wire, using a connector, and that'll do the trick

Since I am connecting aluminum to copper. What kind of connector am I looking for? Anything special or can i purchase standard box of assorted connectors? I'll head to HD tomorrow.

You should use ones that are approved for CU/AL. , or a compound that works with regular connectors
Copper and aluminum expand at dfferent rates, so if you don't use anything special ,the connection MAY eventually come loose.

I like to use alumiconn connectors. But you have to get them on the internet and follow the instructions carefully. Lowes stopped carrying them. None of these CU/AL connectors are cheap, even the purple Ideal connectors. I used an electrican last week. He said the connectors were not necessary because he would use a special No-lox. I said use the purple Ideal connectors (which I bought the day before from HD and Lowes fearing he would not have them and I was right). I wanted it to be clear and visible that he used the right thing in case the house burned down. He did say he uses the Ideal purple at the Marinas. (Then use them at my house!)
When I do my own electrical stuff, I use alumiconn connectors because I hate twisting these thick alumimum wires. The alumiconn connectors are like push-in connectors but they have a screw for tightening each wire; it's pretty easy; just make sure the wire is all the way in the holes (any pushin connector can fool you); then turn the screw PER INSTRUCTIONS. You have to read about it on the internet to understand what I am saying. I did not trust the electrican to get the alumiconn connectors right since they work so fast. (Also pushin connectors are for solid wire!!!)
Even easier, pay a electrican 1 hour of labor to do it. At least if someone gets electorcuted (sp) it will not be you. Seriously.
Bob

Sorry, I don't want to confuse things, which I appeared to have done. To be clear: DO NOT use pushin connectors with aluminum. Only CU/AL connectors!!!
I said alumiconn connectors are easy like pushin conectors; but they are NOT pushin connectors. DO NOT use pushin connectors with aluminum.
Use an electrican when in doubt. It's the best $100 you will spend.

Bob

Always use connectors that are rated for al/cu connections when doing so. If you do not, corrosion can take place and the connection will heat up. When at all possible, run new circuits with copper wire if you are adding outlets or lights. Adding on to existing aluminum wired circuits is not recommended. It is best to let a sleeping dog lie.