The Night Sky This Month: July 2015

Delta Aquarids

July offers warm nights, five glorious constellations, five naked-eye planets, a blue moon, a close up view of Pluto, albeit via a space craft, and lots to observe, so for as long as the summer atmosphere offers good seeing, make the most of the pleasant conditions to observe some of the spectacular deep sky objects in the skies this summer.

The Planets

Mercury

Mercury was at inferior conjunction on June 19th, so it will now be visible for most of July just before dawn toward the lower left of Venus; however, it will be very difficult to spot until around July 12th, when it reaches maximum western elongation. At this point, Mercury will have a magnitude of +0.4, since it will have less than 50% illumination; but towards the end of July, the little planet will increase in brightness to -1.4 as it descends toward the horizon.

Venus

Rising in the east-northeast at twilight, Venus remains only around 20 degrees above the horizon. Now in a gibbous phase and moving beyond the Sun, its angular diameter shrinks from 12- to 11 arc seconds; however, the area of its disc illuminated by the Sun increases by seven percent- from 85% to 92%, which means there will only be a very small decrease in magnitude, from -3.9 to -3.8.. During the beginning of the month, look for Venus in Taurus, close to Aldebaran.

Mars

Now in Virgo, Mars is located near Spica and will pass the star at a mere 1.3 deg, and slightly to the upper left of it on July 13th. During July, Mars will also shrink in angular diameter from 9.5 to 7.9 arc seconds, while simultaneously diminishing in brightness from magnitude 0.0 to +0.4. Although best viewed as twilight falls, it is likely that only Syrtis Major will be visible.

Saturn

Now seen in Libra close to the binary star Alpha Librae, Saturn is decreasing in brightness from +0.4 to +0.5. On July 21st, Saturn’s retrograde motion will cease, to continue on its eastward journey, but for observers in the northern hemisphere, Saturn is now approaching the lowest point of the ecliptic, and will therefore be somewhat obscured by the atmosphere even when it lies due south. July also sees the ring system at an inclination only 21 deg., which is its minimum inclination for 2015.

Jupiter

Jupiter is passing behind the Sun during July, so it will therefore only be in view for the first few days of the month. As July starts, Jupiter will set around an hour after sunset, which places it very low on the horizon, and thus hardly worth the trouble of finding during the month from the northern hemisphere.

The Moon

New Moon: July 26th
First Quarter: July 5th
Full Moon: July 12th
Last Quarter: July 19th

Deep Sky Objects in Ursa Major

M81/M82

The Great Bear is home to a great many spectacular deep sky objects, but it also contains some lesser known objects, such as a pair of interacting galaxies- M81 and M82, in the upper right hand corner of the constellation. Known as a starburst galaxy, M82 contains a major star forming region, and both galaxies are visible together with small telescopes at low magnifications.

M101

Discovered in 1782, M101 is one of the largest known spiral galaxies, and closely resembles a spinning firework, hence the name, “Pinwheel Galaxy.” Seen face-on, this 170 000 light year-diameter Sc-class galaxy presents a magnificent sight even from 24 million light years away, and its small nucleus and wide open spiral arms is well worth the trouble of finding. By way of contrast, the Milky Way galaxy is a “mere” 130 000 light years in diameter.

M51

Even though it falls just outside the boundary of Ursa Major close to Alkaid, which is the leftmost star of the Plough, M51 is another spectacular spiral galaxy about 37 million light years away. Part of the allure of M51 is the fact that is in the act of capturing a smaller galaxy, and the distortions caused by the gravitational interaction is clearly visible. Although the Whirlpool Galaxy, as it is also known, was discovered by Messier in 1773, it was Lord Rosse who first described the galaxy’s spiral structure in 1845, after viewing it through his mammoth 72” reflector from Ireland.

M97

Named the Owl Nebula by Lord Rosse in 1848 due to its close resemblance to the face of an owl, this planetary nebula close to the star Merak is well worth viewing.

Deep Sky Objects in Hercules

M13

Being the most luminous globular cluster visible from the northern hemisphere, M13 is a fuzzy naked eye object from dark sites about one third the angular diameter of the full moon, but its 300 000 stars packed into an area barely 100 light years across presents a glorious sight in any telescope. Look for this cluster along one side of the keystone in Hercules and take particular note of the brightness that increases toward the centre, where the stars are only a few billion miles apart.

Virgo ClusterDeep Sky Objects in Virgo

Virgo Cluster

Although Virgo contains just one luminous star, Spica, which is a short period binary, the constellation is home to the 13 members of the Virgo Cluster of galaxies, all of which can be observed with even modest telescopes in the upper right hand corner of the constellation. Look for M87, the most luminous member of the this group, a gigantic elliptical galaxy also known as Virgo A.

M104

Look for the 8th magnitude Sombrero Galaxy, an edge on spiral galaxy 30 million light years away to the right of Spica that appears to be an elliptical due to its orientation to our line of sight.

Deep Sky Objects in Lyra

Epsilon Lyrae

Known as the “Double-double”, this pair of orbiting binaries is best viewed with binoculars or small telescopes in good seeing conditions to resolve the two pairs of binaries orbiting each other.

Ring Nebula (M57)

One of very few objects that exhibit discernable color in a telescope the Ring Nebula, located between Gamma and Beta Lyra, resembles a greenish ring of diaphanous smoke, and although the stellar remnant in the centre may not be visible, M57 is a sight well worth seeing!

M56

Look for this pretty 8th magnitude globular cluster mid-way between Albireo and Gamma Lyrae. Located relatively close-by at 33 000 light years, and about 60 light years in diameter, M56 is an easy binocular target in good seeing conditions.

Deep Sky Objects in Cygnus

Albireo

There is little doubt that Albireo is the most beautiful double star visible from earth. The color contrast between its blue-green and amber component stars offers a sight that is unsurpassed by any other double star in the entire night sky- in both hemispheres!

North America Nebula

Best viewed in binoculars in dark site during good conditions, this area of nebulosity toward the upper left of Deneb resembles the outline of North America, hence the name. Also look for the Pelican Nebula directly to its right, although it might take a while to recognize the figure of a pelican, but look long enough, and it will fly out at you!

Meteor showers

Only the Delta Aquarids Meteor Shower occurs during this period, from July 12th to August 23rd but the full moon that occurs on the 31st , will obscure all but the most luminous meteors during the expected peak on the 28th and 29th of July.

Other highlights during July

1/07: Venus passes only 0.4 deg. from Jupiter at 9:00 Universal Time, making it the closest conjunction of any two naked eye planets for the entire 2015.
2/07: With some luck, Comet C/2013 US10 Catalina may become visible with binoculars.
6/07: Earth reaches aphelion at 13:00 Universal Time.
6/07: At 15:00 Universal Time Pluto reaches opposition, only a week before New Horizons’ historic flyby of the erstwhile planet.
12/07: The Moon will occult Aldebaran at about 18:17 Universal Time. This occultation will however only be visible from northeastern Asia.
19/07: Visible from the South pacific, the Moon will occult Venus at about 1:07 Universal Time.
25/07: At about 10:55 Universal Time , the asteroid 49 Pales will occult a star of +6.6 magnitude in an event that will be visible for observers in Mexico.
28/07: The Delta Aquarids are expected to peak.
31/07: A “Blue Moon” will occur, which is when two full moons appear in a single month.