Delta to Frankfurt or Dubai or somewhere

This was last night at sunset. Every clear evening we can see aeroplanes headed across the Atlantic and I sometimes amuse myself by looking them up on a flight-tracking website to see whence they come and whither they go. This was listed as a Delta from, I think, Boston, going to, I think, Frankfurt. Or somewhere else; I'm not sure anymore. But I can say it's Delta Airlines since that is readable on the fuselage.