Today’s Astronomical Events – July 31st, 2015

There are two full moons this month; the first was on the 2nd with the other occurring tonight, on the 31st. Now popularly known as a “blue moon” this won’t happen again until January 2018 when the full moons occur once again on the 2nd and 31st – and then again, a few months later in March.

A “blue moon” is a misnomer, as the Moon will not be changing color. The term traditionally applied to the third moon in a season with four moons, however, due to an erroneous article in the March 1946 edition of Sky & Telescope magazine, it now commonly refers to the second of two full moons that occur in any calendar month.

This year the Moon shines in the autumnal constellation of Capricornus but with the moonlight brightening the sky, you may not be able to see many of the stars at all. 

(Click on an 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.)

Images courtesy of Mobile Observatory.



03:50 UT – Mars appears 5.8° south of Pollux. (Mars: 100% illuminated, magnitude 1.7, diameter 3.6”. Gemini, not visible.)

06:18 UT – The almost full Moon passes dwarf planet Ceres. (Ceres: magnitude 7.3. Sagittarius, all night.)

10:43 UT – Full Moon. The second of two July Full Moons (mistakenly called a “blue Moon”). The first occurred on the 2nd. (Naked eye, Capricornus, visible all night.)

The bright star Deneb, culminates at midnight tonight. (Magnitude 1.2. Naked eye, Cygnus, all night. See July 13th for a map.)



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”


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