What’s Up in the Night Sky? September 2016

Fred Barrett | Sep 07, 2016

One of the biggest announcements in astronomy recently was the discovery of a planet orbiting the star Proxima Centauri, the closest star to the Sun.

First, let’s look at a bit of introductory information. Proxima Centauri is part of a trinary star system called Alpha Centauri, which is about 4.4 light years from our Sun. The system is made up of a pair of stars called Alpha Centauri A and B. One star is a little smaller than the Sun and the other a bit bigger.

The 3rd member is Proxima Centauri and it is a small red dwarf star. Although scientists are not absolutely positive, it is more than likely that Proxima is gravitationally bound to the AB pair at a distance of about 0.24 light years. So what is the big deal about Proxima besides it being our closest star? Well, it has a special exoplanet (technically a planet that orbits a star other than our Sun). The special part of that exoplanet, called Proxima b, is that it is a rocky planet like Earth and orbits within the “goldilocks” zone of its star. The “goldilocks” orbital area is where conditions are similar to those on Earth and water can flow freely – life could be possible!

The Proxima system is close enough to perhaps visit and certainly close enough to study in more detail. One method of discovering exoplanets is to measure the Doppler shift of the parent star as it moves back and forth in response to the mass of the planet orbiting about it. In the case of Proxima b, that movement amounts to a velocity change of 3 kilometers per hour! That’s an incredible measurement. The mass of the goldilocks planet is about 1 ½ to 3 times the mass of the Earth. Since Proxima Centauri is a small red dwarf, its goldilocks zone is quite close to it. The planet is about 5% of the distance of the Earth to our Sun and a “year” is roughly 11.2 days.

Red dwarfs are prone to bursts of radiation, which complicates its habitability. Further complications include finding out what type of atmosphere it has. Since it is so close to its star, it is likely tidally locked to Proxima. Our Moon is tidally locked to the Earth and only shows one face to us. One side of Proxima b would be hot and the other cold. If the atmosphere were thick, thermodynamic heat flow would allow the temperatures to even out. It is probable that if there were life, it would be at the microbial level.

Proxima is near enough that we could possibly send probes there in a travel time measured in decades – 20 plus years or so. A very rich Russian, Yuri Milner, in partnership with prominent scientists, including Steven Hawking, are proposing to send thousands of small probes to Proxima. They would have large light sails attached to them. A laser would be aimed at the sails from Earth and they would be accelerated to 20% of the speed of light. Needless to say, it would take great technical advances to make it happen. I expect further investigations will bring us more exciting information about Proxima b and the efforts to send probes there.

There are some nice views through binoculars this month. Mars and Saturn are prominent in the southwest. To the east of Mars lie two nebulas, M8 and M20. The globular cluster M22 is just to the east of them.

The Summer Triangle is high above and easy to explore after 9pm. Let’s review finding it. Face south and look up. Almost overhead is a bright star called Vega. It’s in the constellation Lyra. Let your eyes slide about 25 degrees (a clenched fist at arm’s length is 10 degrees; your little finger is 1 degree) to the east. You are now in the constellation Cygnus, the Swan, and the star that is almost as bright as Vega is called Deneb. Move about 30 degrees southeast from Vega to find the final star in the triangle. You have arrived at Aquila, the Eagle, and the star that is as bright as Vega is called Altair.

For other sights, move your eyes west from Vega about 20 degrees. Now you are in the middle of Hercules. It is shaped like a box with stars branching off from its 4 corners. The globular cluster, Messier 13, is about a third of the way down the west side of the box. Messier 92, also a globular, can be found about 8 degrees above the middle of the top (north) side of Hercules.

Both of these DSOs (Deep Sky Objects) are easy binocular objects. Don’t forget to have a look at the constellation Corona Borealis. There aren’t any fancy deep space objects to be found there but it’s a lovely bright constellation. It’s just to the west of Hercules.

A challenge: During September, Neptune is prominent. It reaches opposition in early September. Pull out your star charts and hunt to the east of Aquarius. A small telescope provides a nice view. Let me know how you do.

Sept. 6: The Moon is at apogee.

Sept. 16: The Moon is full. This Moon is sometimes the Full Harvest Moon or the Full Corn Moon. The Harvest Moon is usually the closest Moon the Autumnal equinox. Every 3rd year or so, the harvest Moon comes in October. The light of the harvest Moon lets farmers work late into the night – as if they don’t work hard enough the rest of the year!

Sept. 18: The Moon is at perigee. This is a good time to explore the surface of the Moon. It is at its closest.

Sept. 22: Autumnal Equinox

Sept. 28: Best showing of Mercury just before dawn in the East. A sliver of a Moon will be above it.

Sept. 29: The Moon passes just a degree south of Mercury at dawn.

Sept. 30: New Moon.

Duncan Meikle from Maberly wrote me in early August about a bright object he saw flash across the southeast sky. It lasted about 10 to 15 seconds and made a turn to the northeast near the end as it faded. It was a Perseid meteor and I talked to Duncan about the turn it made. Likely it was a result of his viewing angle.

Have a good month and if you have any questions or special topics that you would like to see in this column, please email me. Let me know how your observing has gone this month, especially anything unusual. I enjoy the feedback.  

You may contact Fred Garrett through this paper or email to This email address is being protected from spambots. You need JavaScript enabled to view it.

The Beginner’s Observer’s Guide by Leo Enright is available at the Sharbot Lake Pharmacy or by contacting the Royal Astronomical Society of Canada www.rasc.ca/publications, subscriptions for our very own excellent Canadian astronomy magazine, Sky News, are also available from RASC..