Vote Here or At Home
You may choose to vote either in your home town or in Gettysburg PA - but not both. Before choosing Gettysburg, consider if you might ever need to prove consistent residency "intent." Intent is best demonstrated by keeping all your legal addresses, including those for voting, driver's license, etc., together as one for several years. Reasons to prove intent include eligibility for in-state graduate school tuition in your home state, or for taxation reasons if you own stocks and bonds or receive income from a trust, or from other investments. Otherwise, you can choose to have different legal addresses for different purposes, and most states, including Pennsylvania, do not prohibit you from having different legal addresses for driver's license and for voting, so long as you have only one for each.
Other Voter Registration Information
To vote back home or by Absentee Ballot, follow the local voting rules for your home town or county. Ask for help from your city hall, or from your county court house. Much absentee ballot information is online, do a web search on your state and "absentee ballot". Find and read the information your state publishes on the subject. Here is a website with general information on obtaining absentee ballots: https://www.usvotefoundation.org/vote/home.htm
Absentee Ballot Request deadlines vary from state to state and sometimes county by county. Check with your municipality.
Pennsylvania Voter Registration deadline is October 9, 2012: By law, the deadline for Pennsylvania voter registration is 30 days prior to the next election
It is illegal to vote in two or more districts. If you wish to vote in Gettysburg but have already registered in another municipality, register here and then write the other election bureau to inform them of your change.