Disappearing Triangle

Summer is long gone, and winter’s just a couple of weeks away. Yet one of the signature star patterns of summer remains in good view in the evening sky.
The Summer Triangle is well up in the west at nightfall. Its brightest point is the star Vega, about a third of the way up the sky. Deneb stands directly above it, with Altair well to the left of Vega.
Deneb represents the tail of Cygnus, the swan. At this time of year, though, the swan is nose-diving toward the horizon. In this position, the star pattern looks more like a crucifix, so it’s also known as the Northern Cross. It stands directly atop the horizon around 10 o’clock.
Every star and constellation has its own season. That’s because there’s a difference in the time it takes the Sun and the other stars to return to the same position in the sky.
The background stars — those we see at night — return to the same position every 23 hours and 56 minutes. But in that span, Earth moves a good distance in its orbit around the Sun. As a r