New Horizons approximate distance from Earth: 3 billion miles; 4.8 billion kilometers (32.28 astronomical units)
New Horizons approximate distance from Pluto: 93 million miles; 149 million kilometers (1 AU)
Time for signal to reach Earth: 4 hours, 28 minutes, 31 seconds
Primary communications: NASA Deep Space Network Canberra Station, Australia (70-meter antenna)
Simple calculations show that at the enormous distance of 4.8 billion kms where Pluto is, one arcsecond equals some 24,000 kms.
Hence, when they point that "big seven-foot, high-gain dish antenna" of the New Horizons spacecraft towards Earth, they've to be pretty precisely so that the signal is received in Canberra. If you are about 15 arcseconds off, instead of the Earth, you might be pointing to the Moon.