go to
http://en.aegeanair.com
Sign up for a Miles & Bonus account.
Add this number when you make the booking.
When you fly, make sure to ask the agent whether the number is in the booking. If it is not, ask them to add it again.
A couple days after arriving in PHL, your account will display Star Alliance Silver status. When you return to DEL, make sure that LH has the fact that you are Star Alliance Silver in the system (it should print on the boarding pass).
When you return to India, you should get a official Star Alliance Silver Card from Aegean within 2-3 months.
If you fly to the US one more time, or even if you flew to BKK or ICN or NRT, then you will get Star Alliance Gold, which gives you lounge access, extra baggage, etc.
Star Alliance silver by itself gives you some perks like IRROPS advantages, priority standby, free bags on some airlines, etc.