Skywatchers’ Guide for July 2010

This sky chart shows Venus, Saturn, Mars and the star Regulus in the western evening sky on July 5, one hour and 15 minutes after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows the Moon, Mercury Venus, Saturn, Mars and the star Regulus in the western evening sky on July 14, one hour after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows Mercury, Venus, Saturn, Mars and the star Regulus in the western evening sky on July 31, one hour after sunset from the Desert Southwest. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico. This sky chart shows Jupiter, the Moon, and the southeastern sky on July 31 at around 1 a.m. MST from southern Arizona. This sky chart is most useful for the continental United States, Hawaii, southern Canada and northern Mexico.

HIGHLIGHTS: July 2010 features the trio of Venus, Mars, and Saturn lined-up in the western evening twilight for the entire month, and close groupings or ‘conjunctions’ of planets and stars. Mercury joins the planetary ‘line-up’ by mid-month but is much lower in the west. Brilliant Venus is our ‘evening star’ in the west and though high this month, it is not quite as high in our sky as in June. Venus groups with the star Regulus (July 9-10), while Mercury pairs with Regulus on July 27, and Saturn with Mars at the end of month. Venus, Mars, and Saturn group more tightly later in a triangle around August 9, just before the Perseid Meteor Shower. In the morning sky Jupiter shines brightly, and is highest overhead in morning twilight but also is easily visible by midnight by mid-month, and rising by 10 p.m. by month’s end. Also in the morning sky is a trio of planets for those viewing with telescopes: Faint Neptune lies far away from brighter Uranus, which is paired 2-3 degrees from bright Jupiter.

PLANETS

July 2010 should be the last month for sharp views of Saturn and its ring system in a telescope as Saturn is losing altitude in the western evening twilight. Saturn is currently the dimmest it will be this year at magnitude 1.1, but because it’s so far away from Earth this is not much dimmer than it was at opposition (when it is brightest and closest to Earth). Also, although the ringed planet is somewhat dimmer this year (compared to previous years) because its rings are more edge-on, it’s still easy to see during the evening hours, since it is fairly well placed during the first half of the month for telescopic viewing. Look for Saturn early in the month about 40 degrees above the western evening twilight, one hour after sunset. Saturn is found in the constellation Virgo the Virgin (though well east of Spica, Virgo’s brightest star).

Saturn’s rings still appear nearly as ‘narrow’ as they did earlier this year, due to our vantage point on Earth. The ringed world is drifting eastward with ‘direct’ motion in July, but not fast enough to elude speedy Mars: the two group at the end of the July less than two degrees apart in our sky. Look for Saturn and Mars about 1¾ degrees apart on July 30-31 (a spectacular view in a wide field telescope). The waxing crescent Moon slides less than 11 degrees below (south) of Saturn on the evenings of July 15-16.

Viewing of Saturn will be best when it is highest in the sky, probably in bright twilight early this month, but viewing is dependent on atmospheric stability and conditions, and of course, the quality and size of the telescope used. Large, high quality amateur telescopes in good “seeing” (stable atmospheric conditions) will best reveal any features on a planet’s disk.

The brilliant planet Venus loses altitude this month, and is moving rapidly against the background stars, passing out of Leo, the Lion and into Virgo the Virgin by early August. Venus has a close grouping with the star Regulus on July 9-10, with the two objects only 2 degrees apart in our sky. Also look for the thin, nearly 4 day old waxing crescent Moon to pass some 7 degrees from Venus on the evening of Wednesday, July 14.

Mars continues to fade this month and is in the western half of the sky after the end of evening twilight, in Leo the Lion. As noted previously, orange-reddish Mars groups very closely with the brighter planet Saturn by the end of the month. The two objects appear about 1¾ degrees apart on July 30-31 (a spectacular view in a wide field telescope). Orange-reddish Mars fades in July to minimum size and brightness for the year (1.5 magnitude in brightness, 4.7 arc seconds in apparent diameter). Mars is a long way off from Earth (hence its faintness compared to Venus) and so is currently an unremarkable object in a telescope. Mars, like Venus, is moving rapidly against the background stars as Earth continues to recede from it in our solar system. On the evening of July 15 look for the nearly 5-day old waxing crescent Moon to pass about 6 degrees ‘below’ (southeast of) Mars. The following evening, on July 17, look for the 6 day old Moon to lie about 9 degrees ‘below’ (southwest of) Saturn.

Bright Jupiter continues to gain altitude and rise earlier each night in the east-southeastern sky, rising by 11 p.m. mid-month, and by 10 p.m. at the end of July. As it becomes more prominent in our sky it comes closer to Earth, and also swells in size to 45 arc seconds in diameter. Jupiter is slowly nearing its opposition date on September 21, when it will be opposite from the Sun in the sky and nearly the brightest and largest it will be in a telescope this year. The thick gibbous Moon rises at around 11:10 p.m. well above Jupiter (about 7.5 degrees northeast) on the morning of July 3. The giant gas planet rises about 38 minutes later that evening from southern Arizona.

Mercury was largely lost in the glare of the Sun last month, but now has a favorable evening apparition, when it joins the line-up of planets in the western evening twilight. Mercury might first be visible 35 minutes after sunset this month (use binoculars) only 3-4 degrees above a crystal clear western horizon on July 12, when the razor thin 1.5 day Moon is 3 degrees ‘left’ or west of the elusive planet. The Moon that evening is even lower than Mercury in the sky, and is nearly at the horizon, 45 minutes after sunset (making it extremely difficult to view the Moon that night). On July 12 Mercury is fairly bright at -0.66 magnitude, but slowly dims each evening as it gains altitude in our evening twilight sky. A better time to view Mercury would be from July 16-July 27, when Mercury is higher in the sky but still fairly bright. On July 27 Mercury is grouped tightly (0.5 degree separation) with the bright star Regulus in Leo, the Lion (use binoculars).

Visitors to Flandrau’s 16-inch telescope should note of the planets Saturn is best visible in the telescope during public hours (Mars and Venus might also be visible), and other celestial objects will be shown in the telescope, weather permitting. Flandrau’s telescope remains open for viewing during public hours from 7-10 p.m., weather permitting, Wednesday through Saturday nights (excluding select holidays).

Finally, remember that in spotting planets there is a general rule: ’stars twinkle, planets don’t’. This is because stars are point sources of light; therefore starlight is easily disturbed and shifted by air currents in the Earth’s atmosphere. However when looking at Mars this month, note that it may appear to twinkle somewhat when near the horizon; however, this twinkling is of a slower nature than that of the bright stars.

JULY EVENING STARS

The “pointer stars” of the Big Dipper, Dubhe and Merak, point down to the ‘North Star’, Polaris. This sky chart shows much of the western half of the sky at 10:30 p.m. in early July, at 9:30 p.m. in middle July and at 8:30 p.m. in late July. The bright stars Antares and Vega provide a color contrast in the bright summer Milky Way. This sky chart shows the sky in early July at 9:45 p.m. and in middle July at 8:45 p.m.

The Big Dipper is easy to find in July, high in the northern half of the evening sky. Look for the Big Dipper high in the north 1 hour after sunset. Take the two end stars off of the bowl (the ‘pointer stars’) and point down to Polaris, the North Star. Polaris is a star of ordinary brightness, and marks the end of the handle of the Little Dipper. Polaris can also be found about 30 degrees (or 3 fists) above the northern horizon. Polaris stays put in the sky; to the eye it doesn’t appear to move. This is because Earth’s axis is pointed toward Polaris in space.

Bright stars of the July evening sky (1 hour after sunset) include ruddy Antares in the south, the bright yellow star Arcturus high overhead, and the blue star Spica, high in the southwest. Locate the bright yellow star Arcturus and the blue star Spica by recalling, “Follow the arc (of Big Dipper’s handle) to Arcturus and drive a spike to Spica”, or simply “Arc to Arcturus and spike to Spica”. Although Spica is said to mark the spike or ear of wheat in the hand of Virgo, it really looks like the bottom of a group of stars in Virgo that make up a diamond or kite shape.

High above the northeastern horizon in early July one hour after sunset is bright Vega, the brightest star of the summer sky. Blue-white Vega high in the northeastern sky contrasts sharply with Antares, the baleful red super-giant star of summer, now above the southern horizon in early July evenings. Throughout July the orange-red twinkling of Antares enlivens the southern sky, giving reason to its name “the rival of Mars”. From the southern United States Antares does not get very high, only about 30 degrees (or three fists held at arm’s length) above the southern horizon (due to its location in the southern sky). From Australia, though, Antares can be seen overhead in July and July. Antares is the brightest part of a most impressive scroll of stars, sort of like a long letter “S” fallen halfway forward. In this case the “S” stands for the constellation it is part of: Scorpius.

The Milky Way Prominent in the Late Night Hours!

The Milky Way is brightest in the south during July and August evenings. This sky chart shows the southern sky as seen looking toward the south in early July at 11:30 p.m., in middle July at 10:30 p.m. and in late July at 9:30 p.m.

Look for the Milky Way to rise late on moonless July evenings. It will be brightest around the constellation Scorpius, the Scorpion in the south. The Milky Way, the galaxy of stars, gas and dust our solar system resides in, is prominent all summer long, and is brightest after 10 p.m. in early July, but by late July can be seen well at the end of evening twilight. To see it, you’ll need to get away from city lights to a dark location, and look on a night when there’s not much interference from the moon. The Milky Way will appear as a “cloudy” band stretching clear across the sky. High power binoculars and telescopes reveal the Milky Way to be clouds of stars, millions of them, with attendant star clusters and gas clouds making up some of the “fuzzier” spots you’ll see.

MOON PHASES
The July last quarter Moon occurs on Sunday morning July 4. New Moon is on July 11 when a total solar eclipse will occur across a narrow path around 130-150 miles wide for parts of the Pacific Ocean, including Easter Island. The July 2010 first quarter Moon will occur on Sunday evening, July 18. The July Full (Buck/Thunder) Moon will rise on the evening of Sunday, July 25 and set on the morning of Monday, July 26. This full moon is the second lowest in the sky this year, and should appear deceptively large to many people. These dates and times are for southern Arizona, and are not necessarily Greenwich Mean Time dates, the moon phase dates used for calendars.

Note: Additional information can be accessed by phone at Flandrau Science Center’s Astronomy Newsline at (520) 621-4310 or as a menu option at 621-S-T-A-R.

Graphics done using Starry Night Pro, Starry Night Enthusiast and Adobe Photoshop. To purchase Starry Night Pro or Enthusiast, go to http://StarryNight.com