SkyEye

The Calendar

Favourable skies await the annual return of the Southern δ Aquariid meteor shower at the end of the month. Venus's tenure as the evening star is drawing to a close as it heads toward the western horizon.

The Solar System

The word planet is derived from the Greek word for 'wanderer'. Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies, including comets, are not so constrained, often moving far above or below the ecliptic.

Sun Gemini → Cancer

Mercury Gemini → Cancer → Leo

Mercury began the month of May at inferior conjunction; it begins this month at superior conjunction, opening the best evening apparition of the year for tropical and southern hemisphere observers. As always, the tiny planet is brightest near superior conjunction so Mercury will dim even as it climbs higher above the western horizon. The nearest planet to the Sun passes 0.2° north of the open cluster M44, also known as the Beehive Cluster, on 14 July. Near the end of the month, Mercury and Venus have distant encounter on 27 July and on the following day, the still-bright planet is only 0.1° south of the first-magnitude star Regulus.

Venus Leo

The evening star is getting very low in the west for observers in northern temperate latitudes, and disappears from view before the end of the month. However, planet watchers in tropical and southern latitudes continue to enjoy the sight of the magnitude −4.5 planet after sunset although it is sinking toward the horizon with every passing day. Venus passes close to Regulus on 16 July, with the two bright objects less than 2° apart. Venus enters into retrograde motion a few days later, with a distant conjunction with Mercury taking place on 27 July.

Earth and Moon

Earth reaches aphelion on 6 July, its closest approach to the Sun this year. The Moon continues to make increasingly close passes to a number of bright stars: 1.5° north of Antares on the first day of the month, 1.7° south of the Pleiades open star cluster on 13 July, just under 3° north of Spica on 25 July, and an even closer pass — 1.3° — by Antares three days later. The Moon is too close to the Sun for its flyby of Pollux to be visible in July.

Mars Leo

Mars finds itself 0.6° north of Regulus, the brightest star in the constellation of the Lion. Regulus is slightly brighter than the red planet and, as a blue subgiant star, should provide an interesting colour contrast. The following day, Mars is 2.5° north of the much fainter fourth-magnitude star 31 Leonis. On 12 July, Mars reaches solstice, with summer returning to the northern hemisphere and winter beginning in the south. The second-magnitude planet is just over 3° south of the waxing crescent Moon and 0.9° north of fourth-magnitude ρ Leonis, a blue supergiant star which is nevertheless much fainter in apparent brightness than Mars. Our rocky neighbour continues to linger in the evening skies but is getting difficult to spot low in summer twilight when viewed from the northern hemisphere.

Jupiter Aries

Jupiter shines at magnitude −2.3 this month and rises around midnight. The gas giant is found 2.2° south of the passing waning crescent Moon in morning skies on 11 July.

Saturn Aquarius

The ringed planet continues to put on its best show for astronomers in the southern hemisphere where it rises mid-evening. The ecliptic is fairly low to the horizon for observers in northern temperate latitudes, with Saturn not making an appearance until late in the evening. The waning gibbous Moon is found 2.7° south of the first-magnitude object on 7 July.

Uranus Aries

Uranus is visible in the morning skies ahead of sunrise. It rises just before midnight by the end of the month. The waning crescent Moon passes 2.3° north of the green ice giant on 12 July but it is better to choose a moonless night for observing this faint planet.

Neptune Pisces

Having reached a stationary point in ecliptic longitude on the last day of June, Neptune arrives as its stationary point in right ascension on the first day of July, and enters into retrograde motion. The faint planet is only 1.7° north of waning gibbous Moon on 8 July but the best time to view Neptune is later in the month when the Moon is not nearby. A small telescope is necessary to view the most distant planet in the solar system which is rising in mid- to late evening.