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and then - six months later - from the opposite side. Measuring stellar distances directly by parallax (trigonometry) only works for the nearer stars, however. For more, read Wikipedia's parallax page.
• Delta Cephei, prototype of Cepheid variable stars
• Indirect means - which may be subject to errors - must be employed to estimate the distances to the more distant stars, like Deneb. Deneb's given distance represents an educational guess, not a certainty. But there is little doubt that Deneb is one of the most distant stars that you can easily see with the unaided eye.
• Deneb is one the three brilliant stars in the famous Summer Triangle asterism, which you'll see over the east-northeast horizon by mid to late evening tonight. An asterism is a recognizable group of stars that isn't a constellation. At our mid-northern latitudes, Deneb will light up the evening sky from now till the end of the year.