Today’s Astronomical Events – July 17th, 2015

Sagitta the Arrow, a frequently overlooked constellation, reaches its best visibility of the year tonight. Although small and relatively devoid of deep sky objects, it has the virtue of being easily found and containing two accessible sights for small telescopes.

To find the constellation, first look for the constellations of Cygnus the Swan and Aquila the Eagle. For observers in the northern hemisphere, these stars will appear almost overhead from about 11pm to around 1am. Once you’ve found those, look for Albireo, the southernmost star in Cygnus (see also July 13th), and Altair, the brightest star in Aquila. Sagitta is relatively easy to find, midway between the two.

The first sight for small telescopes, the globular cluster M71 (see photo above) lies halfway between the constellations’ two brightest stars and should be visible at about 35x. It appears small and faint to me, uniformly grey with no bright core. In fact, it looked more like a nebula than a traditional globular cluster.

The second sight is Zeta Sagittae, on the other side of the invisible line from M71. I needed a magnification of 91x to split this double but once you do, you’ll see a bright white star with a faint blue companion close beside it. Try lowering the magnification to find the minimum required to split the pair. For me, the companion vanished at about 50x. How low can you go?

(Click on the image to enlarge. Adapted from 2015: An Astronomical Year, available in Kindle and paperback formats from Amazon in the US, Canada and the United Kingdom.)

Map courtesy of Mobile Observatory. Photograph taken by the author using Slooh.



The Perseid meteor shower begins. A maximum zenith hourly rate: 100. (Naked eye, Perseus, all night but best in the pre-dawn sky.)

The constellation Sagitta (the Arrow) culminates at midnight tonight. (Naked eye, all night. See images above.)



Events in bold involve objects and/or events that are visible with the naked eye.

All times are in Universal Time (UTC). To convert the time to your timezone, click here.

2015 An Astronomical Year (Kindle Edition) 2016 An Astronomical Year Paperback Cover 2016 The Night Sky Sights The Astronomical Almanac 2015-2019

2015: An Astronomical Year

2016: An Astronomical Year 2016: The Night Sky Sights The Astronomical Almanac (2015-2019) The Amateur Astronomer’s Notebook (Pocket Edition)

(Kindle & Paperback)

(Kindle & Paperback) (Kindle & Paperback) (Kindle & Paperback)


Amazon – US

Amazon – US Amazon – US Amazon – US Amazon – US
Amazon – UK Amazon – UK Amazon – UK

Amazon – UK

Details of all available books across the world can be found here or by visiting the author’s page on Amazon. If you have any comments or questions, please feel free to contact me at astronomywriter “at”


2 thoughts on “Today’s Astronomical Events – July 17th, 2015

  1. Pingback: Today’s Astronomical Events – July 19th, 2015 | The Astronomical Year

  2. Pingback: Today’s Astronomical Events – July 20th, 2015 | The Astronomical Year

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