Night Sky Guide for July 2018 – longest lunar eclipse of 21st century, partial solar eclipse

The Earth's annual orbit around the Sun will carry it to its furthest point from the Sun – its aphelion – on July 6 at a distance of 1.02 AU.

This month's New Moon is on July 13, making it the best time of the month to observe faint objects such as galaxies and star clusters because there is no moonlight to interfere.

A partial solar eclipse will take place on the same day. However, the alignment will not be very exact and total eclipse will not be seen from any point on Earth. This partial eclipse will only be visible in extreme southern Australia and Antarctica.

A total lunar eclipse will be observed throughout most of Europe, Africa, western and central Asia, the Indian Ocean, and Western Australia on July 27. This will be the longest total lunar eclipse of the 21^st century, lasting 1 hour and 43 minutes. From start to finish, the eclipse will last nearly 4 hours.

Southern Delta Aquariid meteor shower will be seen from the southern tropics on July 28 and 29.

• July 1 – Close approach of the Moon and Mars. The Moon, 18 days old, and Mars will make a close approach, passing within 4°41' of each other. The Moon will be at mag -12.4, and Mars at mag -2.2, both in the constellation Capricornus. 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 1 – Conjunction of the Moon and Mars. The Moon and Mars will share the same right ascension, with the Moon passing 4°46' to the north of Mars. At around the same time, the two objects will also make a close approach, technically called an appulse.

• July 1 – M22 well placed for observation. Across much of the world, the globular cluster M22 in Sagittarius, near the Galactic center, will be well placed for observation. It will reach its highest point in the sky at around midnight local time. At a declination of -23°54', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 46°N. At magnitude 6.2, M22 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• 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 4.6, 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 4 – Close approach of Mercury and M44 – 13:22 UTC. Mercury and M44 will make a close approach, passing within 0°22' of each other. Mercury will be at mag 0.0, and M44 at mag 3.1, both in the constellation Cancer. The pair will be close enough to fit within the field of view of a telescope, but will also be visible to the naked eye or through a pair of binoculars.

• July 6 – 37P/Forbes reaches its brightest. Comet 37P/Forbes is forecast to reach its brightest, at around mag 11.0. It will lie at a distance of 1.73 AU from the Sun, and at a distance of 1.09 AU from the Earth.

• July 6 – Moon at Last Quarter – 07:52 UTC. The Moon will be prominent in the dawn sky, rising at around midnight.

• July 6 – The Earth at aphelion – 16:48 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 – Mercury at dichotomy. 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 the greatest separation from the Sun – moments referred to as greatest elongation.

• 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 6.3, NGC6752 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• July 9 – P/2013 CU129 (PANSTARRS) reaches brightest. Comet P/2013 CU129 (PANSTARRS) is forecast to reach its brightest, at around mag 11.4. It will lie at a distance of 0.84 AU from the Sun, and at a distance of 0.24 AU from the Earth.

• July 12 – Mercury at greatest elongation east – 04:00 UTC. In the southern hemisphere, Mercury will be well placed for observation in the evening sky, shining brightly at mag 0.4. 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 the 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 26° 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 12 – Pluto at opposition – 09:41 UTC. Across much of the world 134340 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 134340 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 134340 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 134340 Pluto lies opposite the Sun in the sky, the solar system is lined up so that 134340 Pluto, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as 134340 Pluto. In practice, however, 134340 Pluto orbits much further out in the solar system than the Earth – at an average distance from the Sun of 39.71 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, 134340 Pluto will lie at a distance of 32.59 AU, and reach a peak brightness of magnitude 14.4. Even at its closest approach to the Earth, however, 134340 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 – New Moon – 02:49 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 13 – Partial solar eclipse – 00:00 – 05:58 UTC. A partial solar eclipse occurs when the Moon covers only a part of the Sun, sometimes resembling a bite taken out of a cookie. A partial solar eclipse can only be safely observed with a special solar filter or by looking at the Sun's reflection. This partial eclipse will only be visible in extreme southern Australia and Antarctica.

• July 15 – Conjunction of the Moon and Mercury – 22:04 UTC. The Moon and Mercury will share the same right ascension, with the Moon passing 2°11' to the north of Mercury. The Moon will be at mag -9.5, and Mercury at mag 0.5, both in the constellation Leo. 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 16 – Conjunction of the Moon and Venus – 03:32 UTC. The Moon and Venus will share the same right ascension, with the Moon passing 1°37' to the north of Venus. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -10.5, and Venus at mag -4.1, both in the constellation Leo.

• July 16 – Close approach of the Moon and Venus – 04:22 UTC. The Moon and Venus will make a close approach, passing within 1°33' of each other. The Moon will be at mag -10.6, and Venus at mag -4.1, both in the constellation Leo. 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. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• July 17 – 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°57', it is easiest to see from the southern hemisphere but cannot be seen from latitudes much north of 39°N. At magnitude 6.5, M55 is quite faint, and certainly not visible to the naked eye, but can be viewed through a pair of binoculars or a small telescope.

• July 19 – C/2016 N6 (PANSTARRS) at perihelion. Comet C/2016 N6 (PANSTARRS) will make its closest approach to the Sun, at a distance of 2.66 AU.

• July 19 – Moon at First Quarter – 19:54 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 20 – Asteroid 88 Thisbe at opposition – 04:48 UTC. Asteroid 88 Thisbe will be well placed for observation, lying in the constellation Sagittarius, well above the horizon for much of the night. Regardless of your location on the Earth, 88 Thisbe will reach its highest point in the sky at around midnight local time.

• July 21 – Conjunction of the Moon and Jupiter – 23:57 UTC. The Moon, 7 days old, and Jupiter will share the same right ascension, with the Moon passing 4°26' to the north of Jupiter. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -12.1, and Jupiter at mag -2.2, both in the constellation Libra. 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 1 – Close approach of the Moon and Jupiter – 02:35 UTC. The Moon and Jupiter will make a close approach, passing within 4°13' of each other. The Moon will be at mag -12.1, and Jupiter at mag -2.2, both in the constellation Libra. 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. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• July 21 – Conjunction of Venus and Ceres – 18:26 UTC. Venus and 1 Ceres will share the same right ascension, with Venus passing 8°10' to the south of 1 Ceres. Venus will be at mag -4.1, and 1 Ceres at mag 8.8, both in the constellation Leo.

• July 25 – Conjunction of the Moon and Saturn – 05:35 UTC. The Moon and Saturn will share the same right ascension, with the Moon passing 1°59' to the north of Saturn. The Moon will be 12 days old. At around the same time, the two objects will also make a close approach, technically called an appulse. The Moon will be at mag -12.4, and Saturn at mag 0.0, 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 to the naked eye or through a pair of binoculars.

• July 25 – Close approach of the Moon and Saturn – 06:05 UTC. The Moon and Saturn will make a close approach, passing within 1°59' of each other. The Moon will be at mag -12.4, and Saturn at mag 0.0, 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 to the naked eye or through a pair of binoculars. At around the same time, the two objects will also share the same right ascension – called a conjunction.

• July 27 – Mars at opposition – 05:07 UTC. Mars will be well placed for observation, in the constellation Capricornus. 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 Mars 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 Mars 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 Mars lies opposite the Sun in the sky, the solar system is lined up so that Mars, the Earth and the Sun form a straight line with the Earth in the middle, on the same side of the Sun as Mars. The time of Mars's perigee is an especially good time to observe it, since it neighbors the Earth in the solar system and has the greatest variation of all of the planets in its distance from the Earth. This, in turn, leads to a large variation in its apparent size and brightness. Mars's distance from the Earth can vary between 0.36 AU and 2.68 AU, meaning that its disk varies in diameter between 25.68" and 3.49". When it passes opposition, Mars glides past the Earth rather quickly, and so only appears large and bright in the sky for a few weeks. A graph of the angular size of Mars at this opposition is available here, and a graph of its brightness is available here. On this occasion, Mars will lie at a distance of 0.39 AU, and its disk will measure 24.3 arcsec in diameter, shining at magnitude -2.8. Even at its closest approach to the Earth, however, it is not possible to distinguish it as more than a star-like point of light without the aid of a telescope.

• July 27 – Full Moon – 20:22 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.

• July 27 – Total lunar eclipse – 18:25 – 22:19 UTC. A total lunar eclipse occurs when the Moon passes completely through the Earth's dark shadow, or umbra. During this type of eclipse, the Moon will gradually get darker and then take on a rusty or blood red color. The eclipse will be visible throughout most of Europe, Africa, western and central Asia, the Indian Ocean, and Western Australia. This will be the longest total lunar eclipse of the 21^st century, lasting 1 hour and 43 minutes. From start to finish, the eclipse will last nearly 4 hours.

• July 28 – Conjunction of the Moon and Mars – 22:04 UTC. The Moon, 14 days old, and Mars will share the same right ascension, with the Moon passing 6°43' to the north of Mars. The Moon will be at mag -12.5, and Mars at mag -2.8, both in the constellation Capricornus. The pair will be too widely separated to fit within the field of view of a telescope or pair of binoculars but will be visible to the naked eye.

• July 28, 29 – Southern Delta Aquariids. The Delta Aquariids are another strong shower best seen from the southern tropics. North of the equator the radiant is located lower in the southern sky and therefore rates are less than seen from further south. These meteors produce good rates for a week centered on the night of maximum. These are usually faint meteors that lack both persistent trains and fireballs. The Moon will be 16 days old at the time of peak activity, and being so close to Full Moon will severely limit the observations that will be possible. But if you are patient, you should still be able to catch a few good ones. Best viewing will be from a dark location after midnight. Meteors will radiate from the constellation Aquarius but can appear anywhere in the sky.

Video courtesy Hubble Space Telescope

Sources: In The Sky by Dominic Ford, NASA, The Watchers

Featured image credit: jsOrrery. Edit: TW