The night sky in July 2019

posted 30 Jun 2019, 13:30 by Pete Collins   [ updated 1 Jul 2019, 05:31 ]
by Anne Holt

Sunrise      1st:   04.44          31st:   05.22
Sunset       1st:   21.40          31st:   21.07

Astronomical darkness:  none until 31st, then  00.54  to 01.36 
Astronomical twilight   1st:  00.05 to 02.20 increasing by a few minutes each day to 3.5 hours on 30th.

New Moon:    2nd July at  20.16
Full Moon:    16th July at  22.38

The July full Moon is known as the Buck Moon, because this is the time when new antlers start to grow on the head of the deer.  Other names are the Thunder Moon and the Anglo Saxon Hay Moon or Wort Moon. 

Lunar Perigee:     5th  at  04.56    (363727 km)
Lunar Apogee:   21st  at  00.02    (405478 km)

Earth is at aphelion on 4th at 03.11, when it will be 152 million km (1.02 AU) from the Sun.

Highlights

We have a partial Lunar eclipse on 16th.  However, like nearly everything else at the moment, it will be very low in the sky. When the Moon rises at 21.25 it will already be partly in shadow. The maximum of 65% is at 22.30, when the Moon will still be only 5.9 degrees above the horizon.  The umbra leaves the face of the Moon at 23.59, when it is at an altitude of 12 degrees.  As if that wasn't bad enough, statistically this evening has an 82% chance of being cloudy.

There's a total Solar eclipse on 2nd.  This one starts over British territory,  unfortunately it's not somewhere close to here - it's Oeno Island in the South Pacific. The path of totality then moves over the ocean to La Serena in Chile, over the Andes and into Argentina, ending to the south of Buenos Aires.  
Closer to home, Jupiter is still shining brightly, unmissable despite being so low in the sky,  Saturn reaches opposition so the rings will appear extra bright for a few days, but again very low.  For binocular and telescopic observing the positions of Uranus and Neptune are both improving.  They are much higher than the naked eye planets.

We are still in the noctilucent cloud season.  These normally occur a couple of hours before sunrise in the NE and after sunset in the NW, but recent displays have been more widespread.

And, of course, we have the 50th anniversary of the Apollo 11 mission  - the Giant Leap for Mankind.  The Eagle landed at 21.18 BST on July 20th 1969.   The Moon doesn't rise until 23.17 on this day, so we can't look up at it at the exact moment.  Neil Armstrong first stepped on to the Moon's surface on 21st at 03.56, followed at 04.15 by Buzz Aldrin.  The waning gibbous Moon sets at 09.44 on this morning, so will be above the horizon at the exact time of the anniversary. 

Constellations

The Summer Triangle (made up of Vega in Lyra, Deneb in Cygnus and Altair in Aquila) is now quite high in the southern half of the sky. Cygnus, with its Northern Cross asterism, and Lyra are particularly prominent.

At the start of the month Pegasus, followed by Andromeda, is rising in the early hours.

As always during the summer months, it isn't the best time to see the zodiac constellations or planets as the ecliptic never gets very high in the sky.  However, if you do happen to visit a dark sky site over the next few months you should be rewarded with good views of the Milky Way high overhead running through Cygnus and down to Sagittarius just above the southern horizon.



Planets

Mercury:  in Cancer,  mag 1.0
Not easy to see this month. On 1st it sets at 22.43, about an hour after the Sun, but is just below the horizon by the time the sky begins to darken.  On 3rd it is only 3.8 degrees from Mars with the thin crescent Moon also close.  The Moon sets 45 minutes after the Sun, with the planets following soon after. On 7th it is at aphelion, the furthest point in its orbit from the Sun, at a distance of 0.47AU (about 70 million km). On 21st it reaches inferior conjunction, passing between the Earth and the Sun, but because of the inclination of its orbit to the ecliptic this rarely results in a transit.  This time the planet passes about 5 degrees south of the Sun.  Mercury moves into Gemini on 23rd but is still too near the Sun to be visible.   On 31st it rises at 04.29 nearly an hour before the Sun but is separated from it by only 14 degrees.  On this day the 1% Moon passes 4 degrees to the north but they are only 2 degrees above the horizon when the sky brightens.

Venus:  in Taurus, mag -3.9
On 1st it rises at 03.49 but only reaches 1 degree above the horizon by dawn. It moves into Gemini on 4th and into Cancer on 27th.  By 31st it rises 30 minutes before the Sun and appears separated from it by only 4 degrees.

Mars:  in Cancer, mag 1.8
Still an evening object but now very difficult to see as it sets before the sky gets really dark.  On 1st it sets at 22.52, about 70 minutes after sunset and has sunk below the horizon by dusk.  It moves into Leo on 31st, when it sets only a few minutes after the Sun and appears only 10 degrees from it.

Jupiter:  in Ophiuchus, mag -2.6
Still very bright in the southern sky. On 1st it culminates at 23.33, at 14 degrees above the southern horizon.  On 13th the 90% lit Moon passes less than 3 degrees north of the planet.  The pair should be visible, 13 degrees above the horizon, at around 22.00.  On 31st it culminates at 21.25, as the sky darkens, setting at 01.20 and will have faded slightly to mag -2.4.

Saturn:  in Sagittarius, mag 0.1
Now at its best for the year but still very low and, unlike Jupiter,  not bright enough to really stand out at that altitude.  On 1st it culminates at 01.50, only 14 degrees above the southern horizon, setting at 05.42.  It's at opposition on 9th, when it reaches its highest point, still only 14 degrees, at 01.16.  For a few days around this time the rings appear much brighter than usual because of the sunlight falling directly on them at this time.  Firstly, the shadows of the particles comprising the rings  fall directly behind and can't be seen, rather than being visible to the side and having a dimming effect.  Also sunlight is reflected directly back, which again makes the rings appear brighter.   The full Moon passes only 13 arcminutes from the planet on 16th at 08.16, in daylight.  It will appear to the west of the planet on the night of 15/16th and to the east on 16/17th.  On 31st Saturn culminates at 23.38, now marginally fainter at mag 0.2, setting at 03.32.

Uranus:  in Aries, mag 5.8
Not easy to see in early July.  On 1st it rises at 01.30 but is barely above the horizon by the time the sky starts to brighten.  Its position improves during the month and in the second half it should be high enough in the still dark sky to be a reasonable binocular target, maybe even a naked eye object from a dark sky site.  On 15th it reaches 15 degrees in the east while the sky is still reasonably dark and on 22nd will be at 22 degrees by dawn. On 25th the third quarter Moon passes about 6 degrees south of the planet.  By 31st it rises at 23.29 and is at 31 degrees in the SE when the sky begins to brighten.

Neptune:  in Aquarius, 7.8
Another morning object, quite low in the first half of July but then should be high enough in the early hours to be seen in amateur scopes. On 1st it rises at 00.18 and reaches 10 degrees by dawn.  Like Uranus its position improves during the month, by 15th it is at 22 degrees in the SE when the sky begins to brighten.  On 21st the waning gibbous Moon passes about 6 degrees south of the planet at 2am.  On 31st it rises at 22.16 and gets to 30 degrees in the south in darkness.

Dwarf Planets
Of the 5 officially designated dwarf planets only Ceres, orbiting in the Asteroid Belt, is close enough and bright enough to be within range of amateur scopes - and even that is so small that, despite having a magnitude similar to Neptune, it will never appear as anything other than a point of light. The others, orbiting way out in the Kuiper Belt are very faint but can sometimes be possible targets for experienced astrophotographers using the comparison method, similar to the way Pluto was found by Clyde Tombaugh in 1930.

Ceres: in Libra, mag 7.8
On 1st it culminates at 22.28 at 17 degrees in the south, setting at 02.07. By month end it will have faded to mag 8.4,  culminating before the sky gets dark and setting at 00.36.

Pluto: in Sagittarius, mag 14.6
Still too low to be successfully imaged this month despite reaching opposition on 14th, when it will be 14 degrees above the southern horizon at 01.16.

Haumea in Bootes, mag 17.4, and Makemake in Coma Berenices, mag 17.2 are both reasonably high in the sky in early July but losing altitude during the month.  Haumea reaches 31 degrees in the west by dawn on 1st and 28 degrees on 31st.  Haumea is slightly lower at 26 degrees and 23 degrees.

Eris:  in Cetus, mag 18.8
The most distant of the dwarf planets has a very eccentric orbit, almost twice as far from the Sun as Pluto at aphelion, taking 558 years to complete one orbit.  It is very low in the sky for most of July but by month end it might be a reasonable photographic target at around 03.15, when it will reach 22 degrees before the sky begins to brighten.

Comets

46P/Wirtanen amd 38P/Stephan-Oterma are now too faint and too low to be seen.

However, there are 4 which are quite promising, all still below the horizon at dawn in early July but improving position and brightening as the month progresses.

C/2017T2 (PANSTARRS) in Taurus, mag 10.8
Should be high enough to be seen in a decent scope by the end of the month.  On 31st it should be at mag 10.1, rising at 01.32 and reaching 13 degrees before the sky brightens.

C/2018N2 (ASSASSN) in Cetus, mag 11.8
Moves into Aries on 12th, when it is still only 6 degrees above the eastern horizon by dawn.  By 31st it should have brightened to mag 11.4 and will reach 29 degrees before the sky gets too light for it to be seen.

168P1/Hergenrother in Pisces,  mag 12.2
Briefly visits Cetus on 9th, then moves into Aries on 10th, when it will be only 8 degrees in the east by dawn.  By 31st it should have brightened to mag 11.8 and be at 31 degrees in the east in reasonable darkness.

260P/McNaught in Cetus, mag 13.2
Should reach 12 degrees by daybreak on 12th, when it is predicted to be at mag 12.8.  By 31st it should have brightened to mag 12.1 and get to 29 degrees in the SE before the sky begins to brighten at around 03.15.

For more information and exact positions of all Solar System objects see;

and for currently visible comets

Meteor Showers

We have a few minor showers, especially towards the end of the month

Alpha Capricornids:  active July 3rd to August 15th have a plateau-like peak centred on 30th,  ZHR 5 but with a strong possibility of several bright fireballs.  Parent comet 169P/NEAT.

Southern Delta Aquarids:  July 12th to August 23rd, peak 29/30th, ZHR 16 - from the southern hemisphere, far fewer here.  These medium paced meteors are debris from comet 96P/Machholz.

Piscids Austrinids: July 15th to August 10th peak 28th,  ZHR 5.  Again the radiant is very low from our latitude, the shower is much better seen from further south.

The antihelion source, meteors not belonging to any particular shower, having a radiant on the ecliptic opposite the position of the Sun, is active in July, ZHR 2 to 3. Meteors from this should be distinguishable from the named showers above, despite the radiants being quite close together, as those from the ANT are much faster moving.

And, of course, towards the end of July we might see some early Perseids.
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