SKY REPORTER: Goldilocks and the Swan

Adding to pleasant times recently spent at the remote island hamlet where my father was born, many hundreds of stars were enjoyed under skies far darker than those over New York City. As dusk faded, Jupiter and Mars were joined by constellation patterns matching those seen on star charts—figures altogether lost in urban settings. Saturn later joined the array followed by other celestial jewels including brilliant Vega and Deneb, brightest star of Cygnus, the constellation of the Swan.

Habitability zone of Earth-sized-planet Kepler186f compared with that of Earth.
Credit: NASA Ames/SETI Institute/JPL-Caltech

That week the journal Science announced discovery of an Earth sized planet designated Kepler186f. Located 490 light-years from the Solar System it orbits in a so-called Goldilocks zone around its local star where liquid water might exist on a planet’s surface. This was the first extrasolar world found with such a promising combination of size and temperature. Although the planet’s mass has not yet been determined odds favor Kepler186f being a rocky world possibly having an atmosphere. The Kepler website provides more details about this remarkable discovery and how the prolific Kepler space observatory mission searched for planets in the area of Cygnus and adjacent constellation Lyra.

The newly announced planet’s local star, known as Kepler186, anchors a system of five earth sized worlds, including four closer to that star than sibling “f” which orbits in the comfort zone of habitability—not too hot and not too cold. The system is about a quarter of the way from star Delta Cygni in the sky, traditionally marking the Swan’s northwest wing tip, along a line toward Gamma Cygni, middle star of the asterism, where Cygnus’ wings and body are imagined to cross.

Kepler186f has an orbital radius equivalent to that of Mercury. However Kepler186 is a red dwarf star with half the Sun’s mass and just 40% of the Sun’s luminosity, so its Goldilocks zone is commensurately closer to that star than the region where Earth comfortably orbits our Sun.

Kepler186 is a faint 15^th magnitude star when viewed from Earth. A very dark sky and telescopic optics at least ten inches in diameter are required for it to be glimpsed. Planet Kepler186f itself has not been imaged even in our largest telescopes. Its presence was inferred by measuring aspects of the small fraction of one percent dip it periodically causes in the apparent brightness of its star during the planet’s five hour 24 minute passage between that star and us.

The Cygnus-Lyra sky region was chosen for Kepler observatory’s search because it’s near the Milky Way’s equator, where many planets were expected to be found. Cygnus is also the locale for other historic discoveries including Cygnus X-1 the first x-ray source confirmed as site of a black hole, 61 Cygni, the first star other than the Sun to have its distance measured, and NML Cygni, a red hypergiant with one of the largest known stellar diameters.

Astronomy may be experienced, practiced, and enjoyed from many standpoints. So it was with a melding of this historic planetary discovery in Cygnus with esthetic and personal perspectives we so recently savored looking at that field of cosmic view with unaided eyes, a small telescope, and imagination.

Even under urban skies, by finding one or more expanses of relatively unobstructed horizon over a park or perhaps over a body of water, we can this month (at about 10:30 pm mid-May and 9:30 by month’s end) trace a celestial chain I enjoyed from my island retreat. Those features extend from brilliant star Capella and Jupiter low in the northwest, eastward along the zodiac to Regulus the brightest star in Leo, on to Mars and Spica brightest star in Virgo, then to yellowish Saturn in Libra. Continuing left above the eastern horizon, we may witness the brilliance of Vega, and conclude our progression with Deneb at the Swan’s tail, heralding the new Goldilocks planet’s neighborhood.     

The Moon

Planets

May 10^th and 11^th, the gibbous moon is near Mars which now shines with magnitude minus one, brighter than any star in the night sky except Sirius. Saturn is at opposition on May 10^th, rising at sunset and setting at sunrise. Its apparent lunar rendezvous are on nights of May 13 and 14, when the moon passes just to the south of that great ringed planet.

Thursday May 15^th in the early morning sky, brilliant Venus is about one degree of arc from sixth magnitude Uranus. If you’ve never seen the seventh planet from the Sun, it’s a good time to aim your telescope at Venus then direct it two moon diameters north to see that much fainter world.

Anticipation is building about the possibility we may see a rich new meteor shower Memorial Day Weekend during the night of Friday into Saturday May 23-24. With its meteors radiating from the northern part of the sky, peak is predicted for several early morning hours of the 24^th following midnight eastern time.

The waning crescent moon and Venus are near each other in the pre-dawn sky on the morning of Sunday May 25.

Mercury is low in the western sky during most of the month. A thin three day old crescent moon passes 17 degrees of arc to the upper left of Mercury and six degrees beneath Jupiter during twilight the last evening of May.