JULY 2012 SKY CALENDAR
SUNDAY, JULY 1
VENUS 4.8 DEGREES SE OF JUPITER
An eye feast to start July. The two brightest planets together in the early morning. Lest we forget, Venus made quite a spectacle of itself last month with that transit trick. Now, it is lurking in the pre-dawn east, still as bright and beautiful as ever. Its giant companion world, Jupiter, outshines all the stars, but it still 12 times dimmer than Venus. Incidentally, that bright star amongst them is Aldebaran, Taurus the Bull's eye star. Though we often associate Aldebaran and its host constellation with winter, they are now observable by early risers
MONDAY, JULY 2
MERCURY 1.6 DEGREES SSW OF BEEHIVE STAR CLUSTER
We always hesitate to include Mercury, as it is close to the Sun and difficult to observe. However, this event is quite interesting. Both Mercury and the Beehive Star Cluster are low in the early evening sky. (The Beehive Star Cluster is Cancer the Crab's only prominent object.) What's interesting is that this close approach will be the first of three passages, properly called a "triple encounter."
We'll see Mercury close to the Beehive Star Cluster again on July 26th and August 18th. Such triple encounters happen because Mercury will travel through a retrograde loop and then resume prograde motion. Consequently, Mercury will pass the Beehive three times.
TUESDAY, JULY 3
A blue moon in July!
How delightful. A blue moon is the second full moon in one month. Though the phrase "once in a blue moon," signifies a rare occurrence, such double moons aren't that uncommon. The time period between successive full moons, called a "synodic month," is approximately 29.5 days. (This period ranges from about 29 days, 4 hours to 29 days, 22hours.) This duration is less than eleven months and therefore within these eleven months, it is possible to have two full moons.
July 2012 has two full moons. The second of these is the actual blue moon. Interesting is that this blue moon arrives just in time: the second full moon happens on July 31 at 11:26 p.m.
WEDNESDAY, JULY 4
EARTH AT APHELION
Nothing to see here, unless you measure the Sun's semi-diameter (apparent radius.) Earth's distance from the Sun changes constantly because our planet's path is elliptical, not circular. An ellipse is like an oval, though in Earth's case this oval circuit is close to, but not precisely, circular. If its path were a circle, its distance from the Sun would remain constant. Earth's distance varies from aphelion, its greatest distance to perihelion, its least distance.
Today, Earth is as far from the Sun as it will stray during this orbit. This maximum distance will be 94.4 million miles. For comparison, at the last perihelion (January 4th) our planet's distance was about 91.3 million miles.
Earth is moving slightly more slowly around this time than it does during the rest of the year. While we won't actually feel any different, this difference does explain why summer is our longest season and winter the shortest.
TUESDAY, JULY 10
VENUS AT MAXIMUM BRIGHTNESS
Venus is always brilliant, even in its dull moments. As is true with all planets, Venus' brightness is variable. Four factors influence a planet's brightess. Two of these factors, its size and the amount of sunlight it reflects, are rather constant. The other two, the planet's distance from the Sun and its distance from Earth, change constantly.
Consequently, a planet's apparent brightness changes. If it is close to Earth and also to the Sun, it will appear quite bright because the Sunlight it receives will be more intense and we'll see more of this reflected light than we would if we were farther away. Venus is at its brightest of the year right now.
TUESDAY, JULY 10
LAST QUARTER MOON
WEDNESDAY, JULY 11
VENUS AT APHELION
Well, that's interesting. Venus is at its maximum distance from the Sun during this orbit (67.34 million miles). Recall the previous paragraph mentioning that Venus' brightness is related to its distance from the Sun. Well, it is also related to its distance from Earth.
Today, Venus is also approximately 38 million miles from Earth: comparatively close, hence the maximum brightness.
THURSDAY, JULY 12
MERCURY AT APHELION
Every planet within the solar system travels along an elliptical orbit. So each planetary orbit has a minimum distance point (perihelion) and a maximum distance point (aphelion). Mercury reaches its aphelion position today and will be about 43 million miles from the Sun.
SATURDAY, JULY 14
MOON 0.81 DEGREES WNW OF JUPITER (PICK EVENT!)
We'll see the crescent moon and giant planet in the early morning eastern sky. While the sight of planet and Moon is always a spectacle, we chose this appulse as the month's pick event because in other areas (not here, darn it) this event will be an occultation! Jupiter will pass behind the Moon. Such occultations require precise alignments, so they're not visible everywhere. Observers in most of Europe; North Africa; Middle East; and north Asia will see this occultation.
SUNDAY, JULY 15
MOON 3.9 DEGREES N OF VENUS
Venus and the Moon is one of those monthly delicacies that is always worth a look. See the crescent and love goddess sphere in the pre-dawn eastern sky.
THURSDAY, JULY 19
Beginning of lunation cycle 1108.
FRIDAY, JULY 20
SUN ENTERS CANCER THE CRAB
Throughout the year, the Sun appears to travel through thirteen constellations: Pisces the Fish; Aries the Ram; Taurus the Bull; Gemini the Twins; Cancer the Crab; Leo the Lion; Virgo the Maiden; Libra the Scales; Scorpius the Scorpion; Ophiuchus the Serpent Charmer; Sagittarius the Archer; Capricornus the Seagoat; Aquarius the Water Bearer.
Today, the Sun enters the region defined as Cancer the Crab. This entrance is an illusion, for as Earth moves around the Sun, the Sun's position relative to the background stars changes.
TUESDAY, JULY 24
MOON 2.4 DEGREES OF MARS
We haven't paid much attention to Mars thus far. Today, we give it a nod as the red world will appear close to the waxing crescent Moon. See Mars and the Moon in the western early evening sky.
WEDNESDAY, JULY 25
MOON 5.7 DEGREES S OF SATURN
Saturn another neglected world. It, too, is in the western evening sky and will be close to our orbiting orb tonight. Interesting note: Saturn and Mars are nearly of equal brightness (Saturn is slightly brighter). Having the Moon near Mars on Tuesday and Saturn on Wednesday will help you distinguish between them. Also, Mars has that distinct reddish tint.
THURSDAY, JULY 26
FIRST QUARTER MOON
THURSDAY, JULY 26
MERCURY 6.2 DEGREES SOUTH OF THE BEEHIVE CLUSTER
Too close to the Sun, though. Nothing to see here.
(Refer to July 2 for more information about the Mercury-Beehive Cluster triple encounter.)
SATURDAY, JULY 28
MERCURY IN INFERIOR CONJUNCTION
Again, nothing to see. However, for completeness, we mention that Mercury passes between Earth and the Sun today. Venus passed into inferior conjunction early last month and because it was properly aligned with the Earth-Sun plane (the ecliptic) it passed directly in front of the Sun. Mercury won’t be so aligned, and therefore we won't have a transit of Mercury this time. (The next Mercury transit happens in May 2016.)
MERCURY: A fine, albeit low evening sky sight at month's beginning. Its brightness decreases throughout the month and will vanish by the middle of July. VERDICT: Best to find at month's beginning in the western evening sky.
VENUS: (PICK PLANET) Yes, we made Venus the pick planet last month, too, because of that transit nonsense. This month we give Venus the crown because it is at maximum brightness for the year. We suspect that Venus will lose the title for the rest of the summer. VERDICT: A bright sight to see before sunrise! Always a treat for the eye.
MARS: A lovely western evening sky planet. Almost as bright as Saturn, but closer to the horizon. Mars dims throughout the remainder of 2012, even though it remains visible in the western evening sky. VERDICT: Easy to find if you're out in the early evening.
JUPITER: Jupiter is preparing for a spectacular show later this year. Presently, it is growing brighter as it rises higher in the eastern pre-dawn sky. VERDICT: If you're out looking for Venus, why not search for the night sky's second brightest planet, as well?
SATURN: The most distant naked eye planet remains in the early evening sky until early Autumn. Watch for it tonight in the early evening western sky. VERDICT: Slightly brighter than Mars, Saturn is a cinch to find. Though not as bright as it was in early spring, Saturn remains conspicuous in the west.