The faintest of the summer triangle, Deneb shines brightly in Cygnus
Straight overhead, Cygnus includes Deneb and the double star Albireo.
Among the constellations seen from Earth throughout the year, there are heroes, hunters, musical instruments, royalty, and all kinds of critters, including eight birds. The biggest and brightest bird constellation seen in the northern hemisphere is Cygnus the Swan, flying high overhead these autumn evenings.
The bright star at the tail of the high-flying swan is Deneb, nearly overhead in the early evening this time of year. Deneb is also one of the stars of the Summer Triangle. The other stars are Vega and Altair, the brightest in their respective constellations, Lyra and Aquila. Just look for the three brightest stars you can see straight overhead and that’s it.
Deneb is the dimmest star of the Summer Triangle, but it is by no means a small star. Quite the contrary; it’s an incredibly huge star at least 1500 light-years away, and some astronomers argue that it may be even more distant. Light years measure time as well as distance. Even if Deneb is just 1500 light-years away, the light we see from it tonight left that star around 500 AD. It’s not likely, but if Deneb were to experience a very violent supernova explosion tonight, our descendants wouldn’t see the blast until the year 3500.
According to the latest data, Deneb has a diameter of at least 175 million miles. Our own sun comes nowhere near that, less than a million miles across. Deneb is also estimated to kick out at least 60,000 times more light and other radiation than our sun.
Cygnus the Swan contains within it a pattern of stars called the Northern Cross. Deneb marks the head of the cross, and at the foot of the cross is the not-so-impressive star Albireo, at least to the naked eye. It’s actually much easier to first see the Northern Cross before taking on the entire swan. If you’re facing south, the cross will be nearly overhead, leaning to the left. By the way, Albireo, as benign as it appears to the naked eye, is a great telescope target. Even a small telescope reveals that Albireo is not just one star but a beautiful pair of stars, one gold and the other blue. It’s one of the best double stars in the sky.
To expand on the Northern Cross and find the rest of Cygnus is easy; extend both ends of the crosspiece. There are faint stars off both sides that convert the crosspiece into the swan’s wingspan. Deneb marks the tail of the swan and Albireo serves as the swan’s head.
Celestial happening this week: The very bright planet Jupiter is on the rise in the eastern evening sky, rising at sunset, you can’t miss it. Jupiter is by far the bright starlight object in the evening sky. This week Jupiter is the closest it’s been to Earth since 1951. Even with a good pair of binocular you may see up to four of Jupiter’s largest moons that appear as little points of light essentially forming a line with Jupiter on either side of the planet. You may even see some of Jupiter’s cloud bands.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul and is author of the book, “Stars, a Month by Month Tour of the Constellations” published by Adventure Publications. Send questions to email@example.com .
The Rochester Astronomy Club welcomes new members and puts on public star parties. Their website is rochesterskies.org .