Star Calendar – July, 2015

Star Calendar

July 2015

Star Calendar Planets:

Moon is Full at both ends of this month; but most comely when a companion young crescent around the 18th.

Mercury slips behind the Sun on the 23rd. Our next chance to see Mercury may come August 16th, beside a crescent Moon.

Venus now approaches us in earnest and her disk is greatly increasing in size. At the same time she is showing us less of her disk as she wanes in phase. The visible (lighted) part of Venus covers the greatest angular area of our sky as she sets on the 9th, but she continues to brighten to a maximum on the 12th. Venus and Jupiter make the closest of three encounters on the 1st, separated by only 4/10 degree as the evening darkens. Their second (RA)* conjunction is less sensational at 6 degrees on the 31st, and the third will come on October 26th – that being a morning apparition.

Sun has appeared for half the number of days for our calendar year at noon on the 1st, but does not progress halfway round the ecliptic until the next day. The discrepancy may seem odd at first but makes sense when we consider that its progress is most rapid when nearer than average (Fall to Spring) and tardier when farther away (Spring to Fall). If the calendar year were to begin at spring equinox instead, we would be halfway through the calendar on Sept 19th, but the Sun would take another 5 days to reach halfway along the ecliptic. Put another way, the time between equinoxes are 186 ½ and 178 ¾ days respectively; between solstices 181 ¾ and 183 ½. The Sun does NOT run like clockwork!

Mars is on summer vacation.

Jupiter, encouraged by a kiss from Venus, continues his quest for Regulus. The evenings of the 17th, 18th and 19th offer especially picturesque arrangements of Crescent Moon, Crescent Venus, Jupiter and Regulus; don’t miss them.

Saturn culminates (is highest, in the south, at about 9:PM) just as it gets dark this month and shines now at the same brilliance as the brightest of our summer stars, Vega. Vega is to be seen then in the east, to the left of Saturn.

*RA, R.A. or Right Ascension refers to a sky coordinate system based on the celestial equator divided into 24 sections. It is the component of distance along the equator to the left of the vernal equinoctal point and is given in units of hours, minutes and seconds where 0h is vernal equinox point. The other component is degrees Declination, which is the distance above or below the equator (+/- 90). For example, the summer solstice point is at 6h, +23.5 degrees. Conjunctions are usually (but not always) considered to be when the RA of two objects are the same.

 Star Calendar Days:

1      Sunrise/sunset in Spring Valley at 5:27/20:33 EDT (15h6m daylight)

          Halfway through AD 2015 at lunchtime

          Venus and Jupiter in nearest of triple conjunction, .4 degrees apart

          Full Thunder Moon 10:20PM

2      Sun opposite its Jan.1st position on the ecliptic

6      Sun most distant for the year, 3% farther than in January; moves most slowly

9      Venus illuminates largest area of sky

12      Moon near Aldebaran predawn in east

          Venus brightest for this appearance, -4.7 mag.

16      Moon, Venus and Regulus within smallest circle, West at 9:PM

17-19 Moon, Venus, Jupiter and Regulus gather each evening in West

22-23 Moon passes Spica, SW after 9: each evening

23      Venus stationary to stars, begins retrograde motion

          Mercury at superior conjunction, crosses behind Sun

25      Moon approaches Saturn (from the right) SSW after 9:PM

26      Moon above Antares, Saturn to right, S – SSW after 9:PM

31      Sunrise/sunset in Spring Valley at 5:51/20:14 EDT (14h23m daylight)

          Full Hay Moon 6:43AM

          Venus and Jupiter are conjunct (same R.A.) again, 6 degrees apart

About pbdavis

Paul Davis is a former resident of the Threefold Community. He has been a teacher of Celestial Navigation, a Planetarium lecturer, and offered evening Astronomy classes at Sunbridge some years ago. He is now living in New Hampshire.
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