Tomorrow evening Triton is predicted to occult a star at about 8:00 PM EDT, visible from much of the east coast. In trying to plan for observing this event, I've used Starry Night (versions 6 & 7) and SkySafari 5. Only SkySafari seems to plot this correctly at that time. The Starry Nights plot Triton and the star close about 3 hours later.
This appears to be mostly a display problem. When I measure the locations of Neptune, Triton, and the star all three give very similar coordinates (within a couple of arc seconds) except for Triton in SkySafari, which is about 5" from where the StarryNights place it. When I overlaid the DSS image (SNPP6) for the field it placed the Starry Night star almost perfectly on it.
Here are the values I measure:
Date: Oct. 05, 2017 08:00:00 PM EDT
Neptune
22h 55m 13.9s -07° 54' 32.7" 2017.8 SS5
22h 55m 13.9s -07° 54' 32" JNow SNP+6
22h 55m 14.1s -07° 54' 31" JNow SNP+7
Triton
22h 55m 13.6s -07° 54' 29.3" 2017.8 SS5 11.4" 287.3° from Neptune
22h 55m 13.6s -07° 54' 25" JNow SNP+6 8.1" 322.8° from Neptune
22h 55m 13.8s -07° 54' 24" JNow SNP+7 8.1" 322.8° from Neptune
Star
22h 55m 13.6s -07° 54' 29.4" 2017.8 SS5 GSC 5813-0456 11.4" 287.3° from Neptune 0.1" 195.3° from Triton
22h 55m 13.0s -07° 54' 28" JNow SNP+6 USNO J2254183-080007 13" 384.1° from Neptune 9.1" 250.5° from Triton
22h 55m 13.0s -07° 54' 28" JNow SNP+7 USNO J2254183-080007 15" 279.0° from Neptune 11.1" 249.9° from Triton
Here are the displays from the individual applications (I've tried to get them all to the same scale—Neptunes aligned and Tritons' orbits to the same size).
SkySafari 5 Pro
Starry Night Pro Plus 6
Starry Night Pro Plus 7
Why are these so different?