Night sky guide for July 2017

The Earth's annual orbit around the Sun will carry us to our furthest point from the Sun – aphelion – at a distance of 1.02 AU on July 3. Technically speaking, this marks the moment when the Sun appears smaller in the sky than at any other time of year, and when the Earth receives the least radiation from it. In practice, however, a 3% difference in the Earth's distance from the Sun is barely noticeable.

The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated – Full Moon – on July 9. This full moon was known by early Native American tribes as the Full Buck Moon because the male buck deer would begin to grow their new antlers at this time of year. This moon has also been known as the Full Thunder Moon and the Full Hay Moon.

The Moon will be located on the same side of the Earth as the Sun – New Moon – and will not be visible in the night sky on July 23. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

A minor meteor shower Alpha Capricornids will peak on July 28. The maximum amount of meteors seen during this meteor shower is 5 (ZHR). However, Alpha Capricornids are known for its fireballs, so keep an eye for those.

A major (Class I) meteor shower Southern Delta Aquariids will peak this year on July 30. The maximum rate of meteors expected to be visible is around 16 per hour (ZHR).The crescent moon will set by midnight, leaving dark skies for what should be a good early morning show. Best viewing will be from a dark location after midnight.

• July 1 – IC4756 well placed for observation. The open star cluster IC 4756 in Serpens will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of +05°27', it is visible across much of the world. It can be seen at latitudes between 75°N and 64°S. At magnitude 5.0, IC4756 is too faint to be seen with the naked eye from any but the very darkest sites, but is visible through a pair of binoculars or a small telescope.

• July 1 – Comet 71P/Clark at perihelion. Comet 71P/Clark will make its closest approach to the Sun, at a distance of 1.59 AU.

• July 1 – Moon at First Quarter – 00:52 UTC. The Moon will be prominent in the evening sky, setting around midnight. At this time in its monthly cycle of phases, it appears almost exactly half illuminated.Over coming days, the Moon will set later each day, becoming visible for more of the night. Within a few days, it will not make it very far above the eastern horizon before nightfall. By the time it reaches full phase, it will be visible for much of the night, rising at around dusk and setting at around dawn.

• July 1 – Conjunction of the Moon and Makemake – 08:24 UTC. The Moon and 136472 Makemake will share the same right ascension, with the Moon passing 26°43' to the south of Makemake. The Moon will be at mag -11.9 in the constellation Virgo, and Makemake at mag 17.1 in the neighboring constellation of Coma Berenices. The Moon will be 7 days old.

• July 1 – Close approach of the Moon and Jupiter – 09:15 UTC. The Moon and Jupiter will make a close approach, passing within 2°33' of each other. The Moon will be at mag -11.9, and Jupiter at mag -2.1, both in the constellation Virgo.The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars.

• July 2 – Conjunction of the Moon and Haumea – 21:02 UTC. The Moon and 136108 Haumea will share the same right ascension, with the Moon passing 24°58' to the south of Haumea. The Moon will be at mag -12.1 in the constellation Virgo, and Haumea at mag 17.4 in the neighboring constellation of Bootes.

• July 3 – Earth at aphelion – 20:12 UTC. The Earth's annual orbit around the Sun will carry it to its furthest point from the Sun – its aphelion – at a distance of 1.02 AU. The Earth's distance from the Sun varies by around 3% over the course of the year because its orbit is slightly oval-shaped, following a path called an ellipse. In practice, this variation is rather slight, however, because the Earth's orbit is very nearly circular. The Earth completes one revolution around this oval-shaped orbit each year, and so it recedes to its greatest distance from the Sun on roughly the same day every year. Technically speaking, this marks the moment when the Sun appears smaller in the sky than at any other time of year, and when the Earth receives the least radiation from it. In practice, however, a 3% difference in the Earth's distance from the Sun is barely noticeable. Annual changes in our weather, for example between the summer and winter, are caused entirely by the tilt of the Earth's axis of rotation, rather than by any change in its distance from the Sun.

• July 7 – Close approach of the Moon and Saturn – 03:50 UTC. The Moon and Saturn will make a close approach, passing within 3°13' of each other. The Moon will be at mag -12.5, and Saturn at mag 0.0, both in the constellation Ophiuchus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. The Moon will be 13 days old.

• July 8 – Conjunction of Jupiter and Makemake – 06:58 UTC. Jupiter and 136472 Makemake will share the same right ascension, with Jupiter passing 29°26' to the south of Makemake.& Jupiter will be at mag -2.0 in the constellation Virgo, and Makemake at mag 17.1 in the neighboring constellation of Coma Berenices.

• July 9 – NGC 6752 well placed for observation. Across much of the world, the bright globular cluster NGC 6752 in Pavo will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -59°58', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 10°N. At magnitude 5.4, NGC6752 is too faint to be seen with the naked eye from any but the very darkest sites, but is visible through a pair of binoculars or small telescope.

• July 9 – Full Moon – 04:08 UTC. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This full moon was known by early Native American tribes as the Full Buck Moon because the male buck deer would begin to grow their new antlers at this time of year. This moon has also been known as the Full Thunder Moon and the Full Hay Moon. Over the nights following July 9, the Moon will rise around an hour later each day, becoming prominent later in the night. Within a few days, it will only be visible in the pre-dawn and early-morning sky. By the time it reaches last quarter, a week after full moon, it will rise at around midnight and set at around noon. At the exact moment when the Moon reaches full phase, it will lie at a declination of -19°14' in the constellation Sagittarius, and so will appear highest in the southern hemisphere. It will be visible from all latitudes north of 60°N. Its distance from the Earth will be 402 000 km (250 000 miles).

• July 9 – Conjunction of the Moon and Pluto – 06:41 UTC. The Moon and 134340 Pluto will share the same right ascension, with the Moon passing 2°18' to the north of Pluto. The Moon will be at mag -12.5, and Pluto at mag 14.8, both in the constellation Sagittarius. The pair will be too widely separated to fit within the field of view of a telescope but will be visible through a pair of binoculars. The Moon will be 15 days old.

• July 10 – Pluto at opposition – 04:10 UTC. Across much of the world, Pluto will be well placed for observation, in the constellation Sagittarius. It will be visible for much of the night, reaching its highest point in the sky at around midnight local time. This optimal positioning occurs when Pluto is almost directly opposite the Sun in the sky. Since the Sun reaches its greatest distance below the horizon at midnight, the point opposite to it is highest in the sky at the same time. At around the same time that Pluto passes opposition, it also makes its closest approach to the Earth – termed its perigee – making it appear at its brightest and largest. This happens because when Pluto lies opposite the Sun in the sky, the solar system is lined up so that Pluto, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Pluto. In practice, however, Pluto orbits much further out in the solar system than the Earth – at an average distance from the Sun of 39.69 times that of the Earth, and so its angular size does not vary much as it cycles between opposition and solar conjunction. On this occasion, Pluto will lie at a distance of 32.35 AU, and reach a peak brightness of magnitude 14.8. Even at its closest approach to the Earth, however, Pluto is so distant from the Earth that it is not possible to distinguish it as more than a star-like point of light.

• July 13 – Close approach of the Moon and Neptune – 18:19 UTC. The Moon and Neptune will make a close approach, passing within 0°49' of each other. The Moon will be 19 days old. The Moon will be at mag -12.4, and Neptune at mag 7.8, both in the constellation Aquarius. The pair will be a little too widely separated to fit comfortably within the field of view of a telescope but will be visible through a pair of binoculars.

• July 15 – Conjunction of Uranus and Eris – 14:41 UTC. Uranus and 136199 Eris will share the same right ascension, with Uranus passing 12°28' to the north of Eris. Uranus will be at mag 5.8 in the constellation Pisces, and Eris at mag 18.8 in the neighboring constellation of Cetus.

• July 16 – M55 well placed for observation. Across much of the world, the globular cluster M55 (NGC 6809) in Sagittarius will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -30°58', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 39°N. At magnitude 7.0, M55 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or small telescope.

• July 16 – Moon at Last Quarter – 19:27 UTC. The Moon will be prominent in the dawn sky, rising at around midnight. Over coming days, the Moon will rise later each day, so that it is visible for less time before sunrise and it less far above the eastern horizon before dawn. By the time it reaches new moon, it will rise at around dawn and set at around dusk, making it visible only during the daytime. Over the next few days, the distance between the Moon and the Sun will decrease and it will rise later each day. By the time it disappears into the Sun's glare as it approaches new moon, it will only be visible very shortly before sunrise.

• July 17 – Conjunction of the Moon and Eris – 23:37 UTC. The Moon and 136199 Eris will share the same right ascension, with the Moon passing 8°08' to the north of Eris.The Moon will be at mag -11.9 in the constellation Pisces, and 136199 Eris at mag 18.8 in the neighboring constellation of Cetus. The Moon will be 22 days old.

• July 17 – Comet 217P/LINEAR at perihelion. Comet 217P/LINEAR will make its closest approach to the Sun, at a distance of 1.23 AU.

• July 17 – Comet 217P/LINEAR reaches its brightest. Comet 217P/LINEAR is forecast to reach its brightest, at around mag 12.2. It will lie at a distance of 1.23 AU from the Sun, and at a distance of 1.42 AU from the Earth.

• July 20 – Conjunction of the Moon and Venus – 11:50 UTC. The Moon and Venus will make a close approach, passing within 2°42' of each other. The Moon will be at mag -10.5, and Venus at mag -4.0, both in the constellation Taurus. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. The Moon will be 26 days old.

• July 21 – Conjunction of the Moon and Ceres – 16:01 UTC. The Moon and 1 Ceres will share the same right ascension, with the Moon passing 4°41' to the south of Ceres. The Moon will be at mag -9.4 in the constellation Orion, and Ceres at mag 8.9 in the neighboring constellation of Gemini. The pair will be too widely separated to fit within the field of view of a telescope, but will be visible through a pair of binoculars. The Moon will be 27 days old.

• July 23 – New Moon – 09:47 UTC. The Moon will be located on the same side of the Earth as the Sun and will not be visible in the night sky. This is the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

• July 25 – Conjunction of the Moon and Mercury – 08:50 UTC. The Moon and Mercury will share the same right ascension, with the Moon passing 0°51' to the north of Mercury. The Moon will be at mag -9.5, and Mercury at mag 0.2, both in the constellation Leo. The pair will be a little too widely separated to fit comfortably within the field of view of a telescope, but will be visible to the naked eye or through a pair of binoculars. The Moon will be 2 days old.

• July 27 – Mars at solar conjunction – 01:17 UTC. Mars will pass very close to the Sun in the sky as its orbit carries it around the far side of the solar system from the Earth. At closest approach, Mars will appear at a separation of only 1°06' from the Sun, making it totally unobservable for several weeks while it is lost in the Sun's glare. At around the same time, Mars will also be at its most distant from the Earth – receding to a distance of 2.66 AU – since the two planets will lie on opposite sides of the solar system. If Mars could be observed at this time, it would appear at its smallest and faintest on account of its large distance. It would measure 3.5 arcsec in diameter. Over following weeks and months, Mars will re-emerge to the west of the Sun, gradually becoming visible for ever-longer periods in the pre-dawn sky. After around a year, it will reach opposition, when it will be visible for virtually the whole night.

• July 28 – Mercury at dichotomy – 23:18 UTC. In the southern hemisphere, Mercury will be well placed for observation in the evening sky, shining brightly at mag 0.2. Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few days each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. Mercury's phase varies depending on its position relative to the Earth. When it passes between the Earth and Sun, for example, the side that is turned towards the Earth is entirely unilluminated, like a new moon. Conversely, when it lies opposite to the Earth in its orbit, passing almost behind the Sun, it appears fully illuminated, like a full moon. However, at this time it is also at its most distant from the Earth, so it is actually fainter than at other times. Mercury shows an intermediate half phase – called dichotomy – at roughly the same moment that it appears furthest from the Sun, at greatest elongation. The exact times of the two events may differ by a few hours, only because Mercury's orbit is not quite perfectly aligned with the ecliptic. Over coming weeks, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare.

• July 28 – Conjunction of the Moon and Makemake – 16:33 UTC. The Moon and 136472 Makemake will share the same right ascension, with the Moon passing 26°19' to the south of Makemake. The Moon will be at mag -11.3 in the constellation Virgo, and Makemake at mag 17.1 in the neighboring constellation of Coma Berenices. The Moon will be 5 days old.

• July 28 – Alpha Capricornids meteor shower. This is a minor meteor shower and the maximum amount of meteors seen is few (ZHR 5). However, this meteor shower is known for its fireballs, so keep an eye for those. The shower runs annually from July 8 to August 10. The Moon will be 4 days old and will present minimum interference.

• July 29 – Close approach of the Moon and Jupiter – 22:16 UTC. The Moon and Jupiter will make a close approach, passing within 2°57' of each other. The Moon will be at mag -11.4, and Jupiter at mag -1.9, both in the constellation Virgo. The pair will be too widely separated to fit within the field of view of a telescope but will be visible to the naked eye or through a pair of binoculars. The Moon will be 5 days old.

• July 30 – Southern Delta Aquariids meteor shower. This is a major (Class I) meteor shower. It runs annually from mid-July to mid-August and peaks this year on July 30. The maximum rate of meteors expected to be visible is around 16 per hour (ZHR). However, this assumes a perfectly dark sky and that the radiant of the meteor shower is directly overhead. In practice, the number of meteors you are likely to see is lower than this. The crescent moon will set by midnight, leaving dark skies for what should be a good early morning show. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius but can appear anywhere in the sky.

• July 30 – Mercury at greatest elongation east – 00:24 UTC. In the southern hemisphere Mercury will be well placed for observation in the evening sky, shining brightly at mag 0.3. Mercury's orbit lies closer to the Sun than the Earth's, meaning that it always appears close to the Sun and is very difficult to observe most of the time. It is observable only for a few days each time it reaches greatest separation from the Sun – moments referred to as greatest elongation. These apparitions take place alternately in the morning and evening skies, depending whether Mercury lies to the east of the Sun or to the west. When it lies to the east, it rises and sets a short time after the Sun and is visible in early evening twilight. When it lies to the west of the Sun, it rises and sets a short time before the Sun and is visible shortly before sunrise. On this occasion, it lies 27° to the Sun's east. After greatest elongation, the distance between Mercury and the Sun will decrease each night as it sinks back into the Sun's glare.

• July 30 – Conjunction of the Moon and Haumea – 04:15 UTC. The Moon and Haumea will share the same right ascension, with the Moon passing 24°34' to the south of Haumea. The Moon will be at mag -11.7 in the constellation Virgo, and Haumea at mag 17.4 in the neighboring constellation of Bootes. The Moon will be 7 days old.

• July 30 – Moon at First Quarter – 15:25 UTC. The Moon will be prominent in the evening sky, setting around midnight. At this time in its monthly cycle of phases, it appears almost exactly half illuminated. Over coming days, the Moon will set later each day, becoming visible for more of the night. Within a few days, it will not make it very far above the eastern horizon before nightfall. By the time it reaches full phase, it will be visible for much of the night, rising at around dusk and setting at around dawn.

Video courtesy Hubble Space Telescope

Sources: In The Sky (Dominic Ford), NASA, AMS

Featured image credit: Solar System Scope. Edit: The Watchers