June is significant for Astronomers in may ways. For those of us who find ourselves in the Northern Hemisphere, June is the lightest part of the year. This owes itself to the Summer Solstice falling on the 21st June for the Northern Hemisphere. At this point, the Sun reaches the most northerly point in the Ecliptic and its highest separation from the horizon at Midday. Of course, for every action, there's an equal and opposite reaction - while we Northerners bask in the glory of Midsummer, those in the Southern Hemisphere are in the grip of Midwinter. The cause of these extremes - and all our seasonal weather on Earth - is our planets' rotational tilt (around 23.5 degrees from vertical) in comparison to the plane of our orbital path around the Sun. During the Summer time, the leading hemisphere is pointed towards the Sun, thus receiving more light to warm up the land and sea. Days are subsequently longer and nights are shorter, the further towards the pole you find yourself. In Midsummer, those above the Arctic Circle experience 24 hour daylight. Of course, the opposite is true for all of this if you find yourself in the trailing hemisphere.
This has noticeable effects on the quality of darkness for those in temperate Northern latitudes, as during this point of the year, the Sun, even at the deepest point of the night is not so far below the horizon. For those in the Northern Europe and the Northern parts of the USA and Canada and Asia, this can mean permanent Astronomical Twilight for a while around the Summer Solstice.
From the 27th of May to 15th July 2021, there is a state of permanent Astronomical Twilight for those in Southern UK latitudes (around 50.5 degrees N), which means that the Sun is less than 18 degrees below the horizon all night long. This means that the skies are never truly dark and that objects around or below the 6th magnitude are unable to be distinguished with the naked eye (technically, +6.5 mag is generally seen as the limit of human eyesight, though this does vary from individual to individual). This obviously has knock-on effects for deep sky observation and astrophotography. The further north one observes from, the longer this period of permanent Astronomical Twilight persists: in Manchester UK (latitude 53.5 degrees N) this extends from mid-May to the end of July; in Edinburgh (just shy of 56 degrees N) the period is yet longer, from early May to the end of the first week of August. Do bear in mind, if you find yourself in latitudes similar to Reykjavik, Iceland (64 degrees N) Astronomical Twilight persists from early April to the beginning of September . North of the Arctic Circle, the Sun will not set at all around the Solstice, whereas south of the Antarctic Circle, the Sun won’t rise at all during this period.
The Solar System
It's rare that we cover the Sun in the monthly sky guide, which doesn't mean that it is without interest! However, this month brings a significant event that is well worth commenting on. On 10th June the track of an Annular Solar Eclipse will cut a swathe through the Northern Canada, Greenland, the extreme East of Russia and the Arctic Ocean. Although only those on the central track will witness the eclipse's Annular Totality (which in itself isn’t fully Total, an Annular Eclipse showing a “Ring of Fire” of the extreme edges of the Sun during its most “total” part), it will be visible as a partial eclipse over a huge area, which will take in the large parts of the Eastern USA, Canada, much of Greenland and of the North Atlantic Ocean, including Iceland and most of Europe and Russia. Large parts of Central Asia will see it too. China, Mongolia and Tibet will witness a the eclipse later in the day (owing to difference in relative time zones) and the event will even glance the tip of Morocco in Africa (but will be invisible to the vast majority of Africa and the Middle East). As such, assuming reasonable weather, this eclipse stands a good chance of being very widely-observed.
For those in Europe, the eclipse reaches its maximum point in the late morning or around midday. For those in the UK, the Eclipse starts at around 10am with first contact, reaches its maximum at just after 11am and ends a little after 12pm. It is always worth re-emphasising the old adage: do not attempt to observe the Sun without proper filtration. Sunglasses, smoked glass, welders glasses are not enough - you will need to use properly certified solar film, solar polymer filers or glass solar filters. Of course, H-Alpha and Calcium-K or Herschel Wedge equipped telescopes are perfectly safe to use, though do check the internal makeup particular instrument you're using before installing a Calcium-K or Herschel Wedge - these two should only really be installed in refracting telescopes of under 4-or-so inches of aperture. If you've got a reflector, then a full aperture white light filter or film is recommended. A dedicated solar scope such as those available from Lunt Solar Systems are the safest bet for long term solar observations - as these will also show spectacular solar prominences and other atmospherics. Solar Eclipse glasses are also available, though if you're trying to observe the extreme beginning and end of the partial eclipse from Europe, white light solar binoculars will be needed at the very least to provide the magnification required to observe these parts of the event.
The Moon and Sun in mid-Partial Eclipse, June 10th 2021. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
Unlike some recent partial eclipses, this shouldn’t be a challenging event (clouds aside) to witness from European locations, given the time of day it occurs. The Sun and Moon will be at a decent observing elevation and we at Telescope House will be on the lookout. If you decide to as well, we wish you good fortune in the attempt, but urge you to remember our solar safety warnings. No matter where you find yourself, if you have any pictures you'd like to share, please send them to us, we'd love to feature them in next month's Sky Guide.
The Moon starts June on the Capricornus-Aquarius borders, at a 63% Waning phase. Rising at a little after 2am (BST) from the UK, the Moon will be found just over 6 degrees below Jupiter, with the two bodies transiting in the south a little before 7am during the early part of the month (this occurs after the Sun has risen)
The Moon will reach New in Taurus on the 10th and as previously covered this New Moon will also cause an Annular Eclipse of the Sun. It’s worth stating for less experienced readers that Solar Eclipses can only occur when the Moon is New and subsequently found on the “Sunward” side of its orbit around the Earth.
From this point, the Moon becomes an evening object and may just be found a few days later Venus in Gemini, though you will need clear horizons and decent observing conditions to see the tiny sliver of the Moon alongside the planet in the early evening of the 12th.
The Moon alongside Venus, sunset, 12th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
Although we are now past the point of the High Spring Crescent phase of early evening observations of the Moon, June still gives us plenty of opportunity to see the Moon at reasonable altitude in the sky,(from a northern hemisphere perspective), being found in the more northerly parts of the ecliptic in the evenings at this point in time. The Crescent Moon moves through Gemini and Cancer and on into Leo, during the next few days. It is in Virgo, on the 18th, where we find the Moon back at First Quarter, transiting at a little under an hour and half before sunset.
The Waxing Gibbous Moon imaged by Malcolm Porter, using an Explore Scientific David H Levy Comet Hunter 152mm f/4.8 Maksutov-Newtonian and a Canon Ra (ISO 800, 1/2000th second). Image used with kind permission.
The Moon will reach Full on the 24th, when it will be found in the constellation of non-zodiacal constellation of Ophiuchus. This is another of the popularly-called “Supermoons” - more properly described as a Perigee-Syzygy Moon. This occurs a few times a year when the Moon reaches Full Phase at its closest point to Earth. While there’s no great scientific importance to this, the Moon can look a little larger than usual, though this perception is often enhanced further by atmospheric lensing effect when he Moon is viewed when rising, when it’s lower in the sky. Sadly, as potentially exciting to beginners a “Supermoon” may sound, the Moon at Full phase is actually the worst time to observe it, as surface relief is bleached out by the Sun sitting directly behind us as we observe it from the surface of the Earth. Those using a telescope will often need a Moon filter to deaden down the glare and reveal a little more surface detail when the Moon is Full. While Full Moon is not the greatest time to observe the majority of its surface, use this time to check out extreme edges of the Moon and see what discoveries you can make.
Naturally, around the end of June isn’t the greatest part of the month for visual deep sky observations, or imaging without narrowband filtration - though the lack of true darkness at this time of year is also a major challenge in this department. After becoming Full, the Moon will continue its sedate path through the descending southern section of the Ecliptic, into Sagittarius, until it begins to climb back northwards, through Capricornus - rising in the early morning of the 28th, when early-rising observers will find it lined up in a row alongside Jupiter and Saturn in eastern dawn sky.
We leave the Moon on the 30th back in Aquarius, just a day shy of Last Quarter.
The beginning of the month is a poor time for potentially observing Mercury. It is currently arcing its waySunward and the 1st finds it at a very acute phase of just 6.5% illumination and at the equivalent of magnitude +3.3 will be unobservable.
The planet reaches Inferior Conjunction - between the Earth and the Sun - on the day of the eclipse, 10th June, after which it will re-emerge in the morning sky.
As we well know, nothing stays the same as far as Mercury is concerned. A planet with an 88 day year won’t stay in the same place for long. By the end of June, Mercury will be at a respectable +1.1 magnitude, showing a 25% phase. It will be found just under 8 degrees high in the east at sunrise on the 30th. Over the first couple of weeks of July, it will brighten yet further and while not quite as well-placed for observations as recent evening apparitions, will be seen respectably from the northern hemisphere.
Mercury, sunrise, 30th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
Venus is an evening object and can be found in Taurus at the beginning of June shining at a distinctive -3.9 magnitude. At 10.3 arc seconds diameter and showing a 95% illuminated disk, the planet will certainly be distinctive for those with clear westerly horizons, though sitting at just over 11 degrees altitude (from 51 degrees N) at sunset on the 1st won’t be in the best place to be observed by those of us in higher northern latitudes.
By mid-June not much has changed as far as Venus is concerned. It is still -3.9 mag and showing a fractionally larger disk than that presented at the month’s beginning. Although increasing angular distance from the Sun, Venus is approaching the highest northerly point in the Ecliptic and it will soon start dipping towards the horizon again, as seen from more northerly climes, making observations even more challenging.
By the end of the month, Venus will be in Cancer and keeping the much fainter Mars company. Still at -3.9 mag, it is now 11.2 arc seconds in diameter and sits at just over 12 degrees high (from 51 degrees N) in the west at Sunset.
Venus and Mars, sunset, 30th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
The Red Planet is a rather pitiful sight in Gemini at the month’s beginning. At +1.7 mag and just 4.1 arc seconds diameter, it sits just over 24.5 degrees high (from 51 degrees N) in the west at sunset. At this point in the Martian cycle, disappointment reigns if you try and find it in a telescope.
By the end of June, as previously reported, it can be found in Cancer alongside the much brighter Venus. Indeed, if you didn’t know it was Mars you were looking at, you could easily mistake it for a medium brightness naked eye star. As Cancer contains no really bright stars, Mars will be noticeable if you know where to look, but Venus outshines it by such a vast amount, it will be easy to miss.
The ever-reliable Jupiter is a great target in the mornings and is now found at 23 degrees elevation in the SE as the day begins. At -2.4 magnitude and 41.2 arc seconds across it will be a great sight in telescopes and will continue to improve in the run up to August’s Opposition.
As we reported with Saturn last month, Jupiter will start to go retrograde in the latter part of the month, a sure precursor of Opposition. This occurs beyond the 21st June this year, after which point the planet will appear to move backwards against its usual “proper” motion through the sky. This is caused by our “catching up” with the outer body on our faster interior orbit, causing the angle at which we observe the outer body in relation to the background stars to change. The analogy of catching up and undertaking a car and noting its apparent motion, relative to the car you are travelling in, is a simple version of what’s happening here. Of course, the outer planet never actually changes its orbital course, but apparent retrograde motion is a clear demonstration of the visual effects of orbital dynamics at work and as such a clear demonstration of the way our Solar System works and our place within it. While we’re still some time away from Jovian Opposition, which occurs on the 20th August this year, the retrograde motion of any of the outer planets is always a sign that this is upcoming.
We end June with Jupiter showing a 45.1 arc second diameter disk, having increased brightness a little to -2.6 magnitude. The King of the Planets now sits just under 28 degrees high in the south (from 51 degrees N) as the Sun rises, having transited just a few minutes before this.
Jupiter at the beginning of a multiple Great Red Spot, Io and Io Shadow Transit, 1am (BST), 28th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
18 degrees to the east of Jupiter on the 1st, Saturn, like its neighbour is a morning target. Found in Capricornus, as ever, Saturn presents itself as a much less immediately noticeable object than Jupiter, though is by far the brightest “star” in the constellation. Once found, Saturn’s creamy-yellow colour is unmistakable and magnifications of just over 40x will start to reveal the rings for which it is so famous.
On the 1st, Saturn presents a 17.6 arc second diameter disk, shining it a steady +0.6 mag. A little optical aid will easily reveal Titan, Saturn’s largest Moon and a little more aperture will reveal other members of Saturn’s retinue of moons - though observations of these will have to wait until a little later in the year when Saturn can be seen with a darker background sky.
Those looking at Saturn through a telescope will note that the ring system, which had appeared wide open over the past few years, as Saturn moved through the extreme south of the Ecliptic, from our perspective here on Earth, are now closing and while unmistakable are not as wide as they have appeared in recent years. The angle of the rings does affect Saturn’s maximum brightness around Opposition, so this year’s maximum brightness will not be quite as high as though of recent years. Other things - most noticeably sheer distance between Earth and Saturn and its subsequent angular size can also affect maximum brightness. But it is interesting to note that the angle of the ring system, while being invisible to the naked eye, can still affect the perceived naked eye brightness of Saturn when observed from Earth.
Saturn ends June having brightened a little to +0.4 mag and now displays a 18.3 arc seconds diameter disk. It will stand just over 19 degrees high in the SSW at sunrise (from 51 degrees N).
Saturn and Inner Moons, just before sunrise, 15th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.
Uranus and Neptune
Both morning objects, Uranus and Neptune are not particularly easy targets during June. Neptune, at +7.9 magnitude, being that much further east in the Ecliptic in Aquarius, will rise earlier and attain a decent height from the horizon before daybreak. Uranus, on the other hand, while brighter at +5.9 mag, is still slowly emerging from Superior Conjunction, so will be much less favourably placed for moving observation, attaining just over 27 degrees height at sunrise on the 30th (from 51 degrees N). The lighter night skies in the higher northern latitudes at this time of year makes finding both planets a little more challenging than they would be at other times.
Relative positions of Uranus and Neptune, sunrise, 15th June. Image created with SkySafari 5 for Mac OS X, ©2010-2016 Simulation Curriculum Corp., skysafariastronomy.com.