Two At The Foot of the Cross

Tammy Plotner writes at Universe Today today:

Summertime conjures up great images of enjoying a double dip ice cream cone, and what more wonderful way to enjoy than with two flavors? Would you like to have some fun while the Moon waxes this coming week? Then invite someone along for the ride and let’s take a look at how differently people perceive stellar color!

Double stars are a fun observing experience. And for the examples Tammy gives, a small telescope or even good pair of binoculars are adequate for the double-dipping.

Above is the prime double star for amateur viewing, Albireo (actually a misrepresentation of ab-ireo that passed into astronomical tradition). Curious thing about Albireo and its constellation, Cygnus (the Swan) …

Here’s the star chart of the constellation Cygnus from Wikipedia. The star marked β at the end of the green line is Albireo. If you picture those stars as the swan, you’ll see Albireo is the beak of the bird.

In astronomy, we have popular “asterisms” in addition to the official constellations. An example of the former would be the “Big Dipper,” which is only the brightest part of the constellation Ursa Major. You can also see the official constellations have designated boundaries, making it easier to navigate and catalogue faint objects.

The central six stars of Cygnus are also an asterism. We know it as the northern cross. I find it interesting that the star at the foot of the cross is a double. Mary and John, perhaps?

Imagine if astronomical convention was based not on Arabic names and Greek mythology but on Christian (or other religious) sensibilities.