July 2013 Night Sky Calendar
Wednesday, July 3
VENUS 0.34 DEGREES NNE OF BEEHIVE STAR CLUSTER (BRONZE EVENT)
How pleasing to begin the calendar with a medal winner. Tonight, we will see the second world within a finger's width of the Praesepe Star Cluster, Cancer the Crab's only prominent feature. Properly, we should write that Venus will be within 0.34 degrees of the cluster's center. Suffice it to say that the brilliant Venus and diffuse star cloud will appear nearly conjoined on Wednesday evening. Find them both well over in the western evening sky. (Note, the Beehive Star Cluster marks the Sun's August 1st position, so we'll lose it to twilight within the next couple weeks.)
Thursday, July 4
MOON 5.4 DEGREES S OF PLEIADES
On Wednesday, we saw a western evening sky planet close to a star cluster. On Thursday, one can see the waning crescent moon close to the Pleiades Star Cluster in Taurus the Bull. Of course, we know this means that on Wednesday evening, one can observe Venus and Praesepe and then toward night's end, which is Thursday morning, one can see the Moon and the Pleaides. Two solar system object-star cluster appulses in one night. Find the crescent Moon and the Pleiades -or Seven Sisters- star cluster in the eastern early morning sky. One issue: as the crescent moon is still luminous, one will notice slight lunar light obscuration: the Pleiades won't appear as bright as usual due to the moon's close apparent proximity to it.
Friday, July 5
EARTH AT APHELION (SILVER EVENT!)
Why confer the coveted silver medallion onto an "invisible event?" Simple: our Earth veers as far from the Sun as possible. You see, all of Sol's planets move along elliptical orbits. Consequently, a planet's heliocentric (Sun-based) distance varies continuously. During each orbit, a planet attains its least distance, Perihelion; and also its greatest distance, Aphelion. Earth reaches aphelion today: its distance from the Sun will be 152,096,000 kilometers, which is about 3.5% greater than its perihelion distance. (Earth reaches perihelion in early January.) The aphelion event earns the silver because it is responsible for our prolonged summer. We remember that a planet's velocity relates to its distance; the closer it is to the Sun, the faster it moves. Presently, Earth's orbital speed is at a minimum, though it still rockets along at more than 65,000 miles an hour. (We're blending the metric and English systems together today to make everyone mad.) Consequently, since we're moving slowest during summer, the summer season is the longest of the four: by about 2 -3 days. (Yes, it is winter in the southern hemisphere, so for the hobbits, winter is the longest season.)
Monday, July 8
Beginning of lunation cycle 1120.
Tuesday, July 9
Yes, avid readers, we have to go through the "don't worry, the planets are still moving," thing. Hello! Now, no need to fret, Saturn is still moving in the same direction as the other planets. However, from our perspective, Saturn will appear to halt its retrograde motion and then resume its prograde motion. In February, Saturn appeared to stop in its prograde (west to east) path before starting its retrograde (east to west) motion. Now, it reverses course again. Such reversals occur when Earth passes between the Sun and Saturn: an alignment called "opposition." Saturn reached opposition in late April, so its retrograde loop started about 2.5 months before and its prograde motion resumes about 2.5 months later. (The retrograde duration varies considerably between planets.)
MERCURY AT INFERIOR CONJUNCTION
Only Mercury and Venus can be at inferior conjunction: (i.e. between the Sun and Earth). Today, Mercury passes between us and the Sun. Actually, the first world moves just "below" the Sun. Were it to pass directly across the Sun's face, we'd see a "transit." (Remember, we saw the transit of Venus in June 2012.) This Mercurian inferior conjunction won't be a transit. We'll have to wait until 2016 for the next Mercurian transit. Note: "superior conjunction" occurs when the planet moves on the Sun's far side relative to Earth.
WEDNESDAY, JULY 10
MOON 6.7 DEGREES SSW OF VENUS
Beautiful sight, as always: the crescent moon and the brightest planet. See them both in the western evening sky tonight. We didn't designate this event as a medal winner because it ALWAYS gets medals. This time, we'll just mention it: see the two worlds together in the west this evening.
MONDAY, JULY 15
FIRST QUARTER MOON
MOON 0.95 DEGREES OF SPICA
A beautiful close approach of the first quarter moon and Virgo the Maiden's brightest star, Spica. This separation is too large to be an occultation for us, but you will see the star and quarter moon together. See them traverse the western sky through the evening.
TUESDAY, JULY 16
MOON 3.2 DEGREES SSW OF SATURN
On Monday, see the quarter moon by a star; on Tuesday, find a gibbous moon near Saturn. Observing both events is a splendid way to track the moon's motion over a 24-hour period. Generally, the Moon moves about twelve degrees an hour.
SATURDAY, JULY 20
SUN ENTERS CANCER THE CRAB
Throughout the year, the Sun appears to move through thirteen different constellations - the patterns comprising the "Zodiac." Today, we see the Sun cross into the Cancer the Crab region: an entirely illusory event resulting from our planet's orbital motion. The thirteen "zodiac" constellations are 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; and Aquarius the Water Bearer.
No, Mercury doesn't stop. Yet, like the other planets, its apparent direction changes because we're watching these moving worlds from our own mobile platform. It has been in retrograde motion since June 25 (we told you the retrograde periods varied from planet to planet). Now, it resumes prograde motion.
MONDAY, JULY 22
MARS 0.79 DEGREES N OF JUPITER (GOLD EVENT!)
One might take issue with us for giving the gold to this event. Both Mars and Jupiter are quite low in the eastern pre-dawn sky and therefore difficult to see. However, as far as we're concerned, this planetary appulse gets the nod for the must see July celestial event. These worlds will be about 25 degrees from the Sun, so they'll be visible for about an hour before the twilight obscures them. (As Mars is 25 times dimmer than Jupiter, it will vanish first.) See the two superior planets together early this morning: not the easiest sight, of course, but one worth observing even if one has to lose sleep to see it.
The Grain moon!
or the Hay Moon.
All names associated with this deep summer full moon.
We don't have the Harvest Moon..not just yet
TUESDAY, JULY 23
MERCURY 8.3 DEGREES ESE OF JUPITER
If you beat your head against a wall trying to find Mars and Jupiter, do your wounded cranium a favor and give this one a miss. One might find Jupiter and Mercury far apart in the eastern pre-dawn sky. Mercury is slightly brighter than Mars, but lacks Mars' distinctive reddish color.
SUNDAY, JULY 28
MERCURY 6.9 DEGREES E.S.E OF MARS
Slightly easier than the July 23rd event, as Mercury has had some time to ascend higher in the eastern pre-dawn sky. Mercury has also brightened a bit during the week, making it all the easier to find. The eastern early morning sky is quite active: a good time to find planets. (See Planet Watch for more information.)
MONDAY, JULY 29
LAST QUARTER MOON
TUESDAY, JULY 30
MERCURY AT GREATEST WESTERN ELONGATION (19.6 degrees from the Sun.)
It seems counter-intuitive, but remember that when an inferior planet is at western elongation, it is in the eastern morning sky; when it is at eastern elongation, one will find it in the western evening sky.
WEDNESDAY, JULY 31
MOON 5.6 DEGREES ESE OF THE PLEIADES
Well, we've seen this before! Find the waning crescent moon close to the Pleiades...again. This time, the two objects are up earlier than before as almost a month has elapsed since the last event: plenty of time for the Pleaides to move away from the Sun. (On July 4th, the Pleaides was 42 degrees from the Sun; today, it will be 68 degrees from the Sun.)
MERCURY: Nothing but trouble. That's what we secretly think of Mercury. It is close to the Sun and therefore moves far too quickly. It remains elusive, even at greatest elongation. Mercury is not in the sky before mid month. Then, one will find it in the pre-dawn eastern sky. VERDICT: Don't bother with Mercury until late month. Try to find it during the last week!
VENUS: A western evening sky planet! Venus recently returned from a long hiatus and will remain in the evening sky for the rest of the year. Tonight, one will see it for a few hours after sunset. And, of course, it is the brightest planet. VERDICT: Easy on the eyes! and, a lovely planet for the lazy ones who don't want to have to strain themselves to observe another world.
MARS: Like Mercury and Jupiter, Mars lurks low in the eastern pre-dawn sky. It is the dimmest of the three early morning worlds, but its distinct ruddy hue makes it stand out against the stellar backdrop. VERDICT: Mars is not an easy sight this month, but will climb higher in the sky throughout the rest of 2013. If you can't find it this month, don't worry. You'll have ample opportunity to see it throughout the rest of the year.
JUPITER: The giant world was absent in June, but now reappears in the early morning eastern sky. As soon as it shows up, Jupiter will already be brighter than Mercury and Mars, its two pre-dawn cohorts. And, like Mars, Jupiter will not have another vacation this year. VERDICT: Everybody loves Jupiter, but not everyone will want to take the time to find it. Jupiter is bright, but low. You can bid your time with Jupiter, as it rises earlier each day and will become gradually brighter throughout the year.
SATURN: PICK PLANET! Saturn gets the crown again, but it will soon lose it. Saturn is so designated because it is in the evening sky after sunset and remains in the sky until just after midnight (early month) and just before midnight (late month.) Though not as brilliant as its evening sky cohort, Venus, Saturn has the position advantage: you have more time to locate it. VERDICT: Saturn gradually grows dimmer until its October hiatus, but it is nevertheless moderately bright. Also, it still forms a lovely triangle with Arcturus and Spica. Catch it if you can.
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