If the skies are clear, you should be able to see Mars in the night sky this week and next.
The Mars opposition -- when Mars, the Earth and the sun line up perfectly in the sky -- started on Sunday morning. The opposition occurs once every two years, when Mars and the sun move into positions on opposite sides of the earth.
Right now, Mars is about 48 million miles from Earth, and moving closer. On May 30, the red planet will pass within 47 million miles, marking Mars' closest approach in more than a decade.
In 2018, Mars will get even closer during its opposition, passing the Earth within 36 million miles.
You can figure out the times that Mars should be visible using the U.S. Naval Observatory's calculator here.
According to the Naval Observatory, the red planet should be visible in Philadelphia -- if weather conditions permit -- during these time spans:
Sunday, May 22: 10:08 p.m. to 5:52 a.m.
Monday, May 23: 10:02 p.m. to 5:37 a.m.
Tuesday, May 24: 7:57 p.m. to 5:31 a.m.
Wednesday, May 25: 7:51 p.m. to 5:26 a.m.
Thursday, May 26: 7:46 p.m. to 5:21 a.m.
Friday, May 27: 7:40 p.m. to 5:15 a.m.
Saturday, May 28: 7:35 p.m. to 5:10 a.m.
Sunday, May 29: 7:29 p.m. to 5:05 a.m.
Monday, May 30: 7:24 p.m. to 4:59 a.m.
Tuesday, May 31: 7:18 p.m. to 4:54 a.m.