Stargazing in July 2015
The July Night Sky
The General Weather patterns
July is usually the warmest month of the summer, but it is also often the wettest. Temperatures are usually above 10 ºC at night, and when moist hot air arrives from the south humid, hazy nights result. Sultry afternoon weather may well result in thunderstorms.
Although the nights are getting longer, astronomical darkness is short at best here in South Wales, and it will be a while before we notice a difference. Aphelion occurs on the 6th July.
Mid-month the Sun is in Gemini. Nautical twilight exists when the Sun is between the horizon and 12º below the horizon. Astronomical twilight ends or begins when the centre of the Sun reaches 18º below the horizon. Most of June and until mid-July, the Sun doesn’t reach that far and officially, astronomical twilight lasts all night. Ask experienced members for help if you want to observe the Sun.
In the second half of June aurorae were observed in the UK, so inform other members if you hear of any in July.
The Full Moon is on 2nd at about 02:20 in the constellation of Sagittarius.
The Last Quarter is on 8th at about 20:25 in the constellation of Pisces.
The New Moon is on 16th at about 01:25 in the constellation of Gemini.
The First Quarter is on 24th at about 04:05 in the constellation of Virgo.
The second Full Moon is on 31st at about 10:45 in the constellation of Capricornus.
The Moon is at perigee (nearest Earth) on the 5th and at apogee (most distant from Earth) on the 21st.
There are two full Moons this month.
Mercury -- is moving towards superior conjunction on the 23rd, consequently, the early part of the month is best to see it. Even at this time the planet is below the shallow ecliptic and consequently is only about 5° above the horizon when it disappears into the morning twilight. It is not an easy object to observe this month.
Venus -- can be seen in the evening sky for about two hours after the Sun sets and is best observed early in the month when its crescent shape may be seen. As the month progresses Venus moves closer to the sun from our vantage point as its orbit takes it towards inferior conjunction in August. On the 1st Venus can found ahead of Leo with Jupiter just visible, having just past conjunction. They separate more until on the evening of the 19th in the early twilight Venus and Jupiter will be accompanied by the thin crescent Moon.
Mars -- progresses westward from the Sun after the conjunction in June and is best observed at the end of the month in the morning twilight. It is not a significant object this month.
Jupiter -- slowly migrates through Leo as Venus moves away from it, and by the 19th, in the early twilight, Venus and Jupiter will be accompanied by the thin crescent Moon. As the month progresses Jupiter also moves closer to the sun from our vantage point as its orbit takes it towards conjunction in August. Jupiter is far less bright than Venus; it is on the other side of the Sun.
Saturn -- is in the constellation of Libra this month. It is situated just above the ecliptic but in a position which is low as seen from the UK and it therefore culminates at less than 20° above the southern horizon, and in daylight. Saturn is still progressing westward, in retrograde motion, against the background of ‘fixed stars’. For casual observers, Saturn will be most conveniently placed at the beginning of the month. Dedicated observers will be pleased with the open ring system, and a waxing gibbous Moon in the evening of the 25th and 26th will provide two photo-opportunities.
Uranus -- rises around midnight at the end of the month and is becoming better placed to observe. It can be found in the constellation of Pisces at RA 1h 16m 43s, Declination 7º 24' 01"; in the south-east, at a magnitude of 5.79.
Neptune -- an hour or so before Uranus and is slightly better placed for dedicated observers. At the end of the month at around 01:00, it can be found in the constellation of Aquarius at RA 22h 44m 33s, Declination -8º 50' 51"; in the south-east. It has a magnitude of 7.83.
Solar System Explorations
The probe ‘New Horizons’ is due to make its flyby of the dwarf planet Pluto on the 14th July.
The Delta Aquarids can be seen from about 15th July to 15th August, but are not noted for their brightness. There are two radiants to this shower. The southern stream, radiating from near the star Skat in Aquarius, has a maximum around about 29th July. The ZHR is about 20 with a medium atmospheric entry velocity.
Next month the Perseids can best be seen between 9th and 14th August, with a ZHR of about 75, the radiant is in the north of Persius. The Perseids are associated with Comet P/Swift-Tuttle.
With the Bull and the Lion, is a zodiacal constellation first characterized in the Euphrates Valley, in ancient Mesopotamia, back about 4000 BC, over 6000 years ago. Here in the southern UK, Scorpius is only two-thirds above the horizon and most of that is lost in the murk of our atmosphere. Early in the mornings of June, Antares (α Scorpii), the constellation’s brightest star, only reaches around 12º above the horizon at best. However at the latitude of the Mediterranean, Scorpius can be seen in its entirety in a magnificent part of the sky, against the backdrop of the Milky Way.
Antares is said to mean either ‘the heart of the scorpion’ or ‘the rival of Mars’ in ancient Greek. The latter because it is an M1 type star, a red supergiant, and shines in the sky with rose-coloured hew much like Mars. It has a variable magnitude of between 0.9 and 1.8 even though it is about 500 light-years away. Antares is so large that if we replaced the Sun with it, it would reach out to the asteroid belt.
With a reasonable telescope, Graffias/Acrab, in the left claw of the modern scorpion, can be resolved into a double.
There are globular clusters to be found in this region of the sky. M4 is a little to the west of Antares in the same field of view as each other.
There are a number of stars in Scorpius which have Arabic names making reference to its origins. Starting in the tail we find Shaula (Al-Saulah) which means the tail of the scorpion, and then we come to Lesath (Al–Las’ah) meaning the sting. At the other end we find Dschubba (Al–Jabhah), ‘the forehead’ of the scorpion and Graffias which is also called Acrab (Al–Aqrab) meaning the scorpion.
To the Babylonians the scorpion represented ‘The Scorpion Man’ created by Tiamat a female deity, and was one of ‘Eleven Mighty Helpers’.
The Hebrews regarded the scorpion as symbol of evil.
David J Thomas