Well, what can I say. Very little is the answer! From York for the whole of June, the sky is so bright at night that we don’t have darker skies than nautical twilight apart from a few nights around 1 a.m. at the beginning of the month. However, June is a great month for just lying outside on loungers late at night with friends without freezing to death! See below.
15th June 2019 midnight sky from Stellarium
The Great Bear isn’t far from overhead and the summer
triangle (Altair, Vega and Deneb) is
coming up in the east. The milky way stretches from Scorpio down in the south
through the beautiful star fields in Cygnus up to the “W” of
Cassiopeia. You’ll also see Jupiter and Saturn lurking low in the south.
The Moon
Best seen as a waxing crescent through first quarter to
gibbous from Thurs 6th to Thurs 13th when it will be about 30° above the SW
horizon at 2230 hrs. After the 14th, it dives into the southern hemisphere so
is rather low in the sky.
Planets
Mercury:
A brief and lacklustre appearance very low after sunset
between the 7th and the 21st. The best time to see it is from civil twilight,
which is at 10:30 pm when Mercury will be 5 degrees above the NW horizon, about
10 degrees to the left of where the sun set. A low horizon and crystal clear
skies will be needed, as Mercury is a difficult enough planet to spot at the
best of times.
Jupiter:
Jupiter reaches opposition on the 10th and will be due south
at 0100 hrs on the 11th. Unfortunately, the planet only climbs to about 14°
above the horizon so views will suffer from low altitude seeing issues. Jupiter
is visible in the evening sky right through June and July so you might want to
leave it until the end of the month, when it’s due south at 2330 hrs.
Forget the other planets until July or later.
Non-Solar System Objects
Passes of the International Space Station (ISS)
This is visible just once in June, and for two minutes only
on the 1st. It appears at 10° altitude in the WSW at 2251, rises slightly to
11° in the SW, and disappears at 10° altitude in the SSW at 2253.
No 2. in a series created and compiled by Dave Armeson
The NEXT step – going further than naked eye observing…
If you’ve had a few nights out under the stars and learnt a few constellations, then you might wonder what is there to see just below naked-eye limit. Well, rather than plunging in the “deep end” and buying a telescope that might/might not be suitable for you, a prudent step is binoculars. Binoculars bring into view star clusters, glorious Milky Way star fields, Jupiter’s four largest, Galilean moons and of course some craters on the Moon and some of the brighter “Deep Sky” objects like the Andromeda Galaxy.
May, June and July are of course the months when the sky doesn’t get dark until 10pm or later, and for two or three weeks either side of the summer solstice (June 21st) observations of low surface brightness objects such as galaxies and nebulae are virtually impossible. So this is the time of year to concentrate on the Moon, the planets, double stars, and open and globular clusters. Further, the International Space Station (ISS) will be well seen in May. Oh yes, there’s also a meteor shower.
Finally, I would normally include a reminder that this is a good time of year to observe sunspots, but we are currently deep in the minimum of the Sun’s 11 year cycle and you’ll be lucky to see any sunspots at all.
The Moon
Best seen as a waxing crescent through first quarter to gibbous from Wed 8th to Wed 15th. It’s really well placed around the 12th. If you’d like something specific to spot, there’s a wonderful feature called Schroter’s Valley. It’s near the crater Aristarchus and is best seen when the moon is about 11 days old. That’s on the 15th this month. The moon is in Virgo and reasonably high in the south at about 10pm, shortly after the end of civil twilight.
You will find bright Aristarchus, its nearby much darker crater Herodotus and Schroter’s Valley in the north-west section of the moon in position 73/32 on the map below.
Aristarchus itself is an amazing crater worth your attention with a high power eyepiece, and when the sun is at the right angle, Schroter’s valley jumps out at you. It looks like a sinuous river valley and in a way it is, but the liquid was lava not water. It’s an old collapsed lava tube. Aristarchus, Herodotus and Schroter’s valley are well seen in this NASA image of the area.
The crater Aristarchus (courtesy NASA)
Planets
Having said above that this is the time of year to observe the planets, unfortunately in May 2019 the planets are a dead loss. Why?
Mercury: Unobservable.
Venus: Very low before sunrise and not really worth looking for.
Mars: 4° above the thin crescent moon low in the WNW on the 7th, but faint and unimpressive.
Jupiter: Only visible after midnight, and very low in the S to SE. Forget it until June.
Saturn: Only visible after 2 or 3 a.m. and very low. Forget it until July.
Uranus: Unobservable.
Neptune: Unobservable.
There, I told you!
Non-Solar System Objects
Mizar and Alcor
This famous naked eye double star one away from the tail end of the Great Bear is directly overhead in May and offers a quick opportunity to check your eyesight. The separation is about 12 arc minutes. Mizar itself is a double with a separation of 14 arc seconds and is easily seen with even a small telescope. This Sky and Telescope article describes them in more detail.
Three Globular Clusters: M3, M5 and M13
The star map below shows the locations of these three objects. Compass direction is shown along the horizon. For the best views, wait until way past 10 pm if possible.
For an insight into these mysterious objects, read the Wikipedia entry.
Globulars star chart
M3 is a truly fine globular about 18 arc minutes in diameter and of magnitude 6.2. It lies north of Arcturus and about half way between it and the 3rd magnitude star Cor Caroli. As with all globulars, whack up the magnification for a chance to see individual stars (of which there are 500,000!).
M5 is another stunning globular, magnitude 6.0 and 23 arc minutes in diameter. Find it by following the line of 4th magnitude stars running along the top edge of Virgo.
M13 is the daddy of all globulars and deserves the name “The Great Globular Cluster”. Its magnitude is 5.8, 2/3rds the apparent diameter of the moon and easy to find on the edge of the central “square” of Hercules. A small telescope will see it as a fuzzy patch but 6-inch telescope is needed to resolve its stars. Do give it a go.
The Eta Aquarids Meteor Shower and the ZHR Value
Unlike some astronomy web sites (such as one claiming you’ll be able to see “up to 55 meteors an hour” ), you’ll only get hype-free facts here. I’d rather this be the case than woo you with exaggerated claims about what you can see, only for you to be disappointed when you observe.
The Eta Aquarids meteor shower peaks on the 7th May with a ZHR of 55, but don’t get excited. Read on. ZHR stands for Zenithal Hourly Rate and is defined as:
ZHR is the number of meteors a single observer with an unobstructed view of the sky is likely to see on the date the radiant peaks and if the radiant is directly overhead and the sky is crystal clear and dark enough to see stars down to magnitude 6.5.
Now the Eta Aquarids’ radiant (the position in the sky from which the meteors appear to radiate) is – as the name suggests – centred close to the star Eta Aquarii. This star’s position on the celestial sphere is at RA 22h 20m and Dec. -1.0. In other words, it’s about on the celestial equator. So far so good. The problem is that on and around the peak date, the Sun’s position is at about 3h 0m and Dec. +17°. That means that the angular separation between the radiant and the Sun is about 70°. That in turn means that from nowhere on Earth and at no time of day for hundreds of years into the future, will the radiant be overhead when the Sun is below the horizon! The best place to see this shower from is actually latitude 10° S (Peru, Tanzania, Indonesia). From there, when the Sun is 18° below the horizon (the condition needed for total darkness and thus allowing us to see stars down to magnitude 6.5), the radiant is 52° above the horizon, not overhead.
So what if the radiant is not overhead? How does the altitude of the radiant affect the numbers of meteors one is likely to see? There’s a simple formula giving the number, N:
N = ZHR x sin(θ)
Where θ is the altitude of the radiant above the horizon in degrees. This formula is disputed in some quarters but it’s the only one that’s generally accepted.
Using this, from our favoured latitude of 10° S, we would expect to see 55 x sin(52) = 43. Not bad.
So, what about from York? Well, at the beginning of astronomical twilight, (0200 hrs), Aquarius is below the horizon so that’s no good. Let’s push it and consider looking out at nautical twilight (at 0336 hrs). By then, the radiant has risen and is 8.5° above the horizon. The formula is then:
N = 55 x sin(8.5°) = 8
Hmm! And if we waited until civil twilight (at 0434 hrs), the radiant has climbed to 16.6° and the formula gives us 16. But by then of course, the sky is getting pretty bright – and particularly so in that direction (east) – and it’s unlikely that we would spot many meteors.
So, this is a meteor shower whose ZHR is unachievable – world wide – and from York and most of the UK, the best we might expect is 8-10 meteors per hour. But if you’re an insomniac and fancy counting meteors not sheep (optimistically at an average rate of one every 6 minutes) any morning for two or three days either side of the 7th, and you have a window affording a good view down to near the eastern horizon, this is the meteor shower for you! There’s no moon to further lighten the background sky, and these meteors are some of the brightest of any shower, so, you never know.
Passes of the International Space Station (ISS)
This May – and particularly in the second half of the month – is a particularly good time to spot the ISS as it passes over the UK. It can be very bright as it catches the sunlight high above us when from the ground, the sun has already set. It is visible every night from the 4th to the 30th inclusive, and twice on some nights. The Heavens-Above web site has an excellent visibility table. Use it like this:
Note (in the top right) that I have set the link to provide the visibility from York.
Note the “Search period start” and “Search period end” indicators.
Move to a later or earlier date range by clicking the arrow buttons.
Ensure that the “visible only” radio button is selected.
If no table entries are shown for a particular date range, the ISS is not visible on those days.
The “Start”, “Highest Point” and “End” columns indicate when and in what direction the ISS can first be seen, reaches its highest point in the sky, and disappears respectively.
In the FAQ on the web site it states that all the times in the tables are “given in local time”.
Clearly, the extraordinary image of the black hole at the centre of the M87 galaxy has wowed the whole world. Here it is with annotations added by webcomic XKCD to give a sense of scale.
M87 black hole
I’d just like to ponder the facts we’ve been given about it:
Its diameter is roughly four times the diameter of the solar system (out to Pluto).
It has a mass 6.5 billion times the mass of the sun.
The concept of “diameter” when applied to a black hole is worth a thought. I mean, it’s not as if there’s a solid object there like a planet or a star. So what is it a diameter of? The answer is that it’s the diameter of the event horizon. That’s the point of no return. Anything – including light – that’s within the event horizon cannot escape, so of course, it’s black. (See Schwarzschild radius)
Now, let’s consider this figure of 6.5 billion times the mass of the sun. If we gathered together 6.5 billion suns, moulded them into cubes so there was no space between them, and started piling them round the sun, by the time we finished, the diameter of that sphere would be about the same as the diameter of Saturn’s orbit. So we have a sun-like sphere the size of Saturn’s orbit, then presumably empty space out to the event horizon ten times further away. But wait; if we did gather together 6.5 billion suns, there’s no way they’d just sit there; they would squash and squash through gravitational collapse until the size of the resultant “object” was, well, I just don’t know. Does anyone? So now, we have a relatively small object – sun-size perhaps – surrounded by space four times the diameter of the solar system, inhabited only by the tortured remains of light and matter falling in from beyond the event horizon. And how can we speculate that it’s sun-sized when in its vicinity, gravity distorts the very fabric of space-time so measurements become meaningless? What in pity’s sake is the nature of this central object? Is it just pure mass? Does it have a surface? Does it exist as a tangible object at all? As good old Patrick would say in his inimitable way, “Well, we just don’t know”.
You will obviously have heard of NASA, but have you heard of the National Space Council? Probably not. But you’ll be interested to know that this body has been the primary steer group for all the USA’s activities in space. Whilst it’s had its ups and downs, it has always been chaired by the President or Vice President, with members as powerful as The Secretary of State and the Secretary of Defense. In its latest incarnation, Vice President Mike Pence chairs, and the council also includes the Secretary of Homeland Security, the Director of National Intelligence, the Director of NASA and the chairman of the joint chiefs of staff. These guys are big, and what they decide happens, and clearly, the push has come down from President Trump that the USA is going back to the Moon – just in time for the end of his second term, by the way! Read this Wikipedia article for more info on this council. It’s fascinating.
And what about this, the “United States Space Force“. To become the sixth branch of the US armed forces. Serious stuff. Bet you didn’t know about this either.
So things are hotting up in space. We’ve got the $500M “Lunar Gateway” project and now, Mike Pence has left us in no doubt regarding America’s intentions with these words at the latest meeting of the National Space Council, “Today, we stand at the dawn of a new era of space exploration”. Fine words and a seemingly worthy cause, but don’t forget the hand of the military resting on the levers of power – see comments and the video of Mike Pence’s speech.
I think the space race is back on, but it’s not a race between nations; rather a battle between complacency and one man’s ego!
No 1. in a series created and compiled by Dave Armeson
First steps…
It’s not as difficult as you first think!
Starting out in astronomy at first seems a very daunting prospect. When I first got into stargazing nearly 40 years ago I thought this is going to be difficult – but I was pleasantly surprised. When you learn just a few constellations it is surprising how everything else tends to start to fall into place – and a few months of perseverance you will start to gain a very satisfying working knowledge of the night sky. You should be able to identify nearly all the northern sky star patterns within a year of dedicated looking.
Martin Dawson joined the York Astronomical Society in
1973 shortly after the society was formed and has been a member ever since. He
kept an occasional diary of events from that time. Some of the entries bear a
similarity to current happenings at the Society: meetings, talks and working
parties at the observatory, then at Acaster Airfield. An example entry:
7 Jan 1977 – ‘YAS Member Mrs. Gibson presented her talk on her trip to West Africa to see the 1976 October eclipse. 0.90p made in raffle (1.75) Planisphere as prize.’
York Astro member Martin Dawson, has sent us a copy of the Society’s newsletter from 1974, two years after the Society was formed. Although the newsletter was printed on old technology with hand drawn illustrations, the topics covered would be familiar to members now; reports on recent talks, what’s to be observed that month and progress with the observatory. Back then, meetings were held at the Railway Institute and planning permission for the observatory had been obtained, plus the Society has acquired a 12.5″ reflecting telescope – wonder what happened to that.
Inclement weather threatened us at the start of the day, but
it eventually turned sunny. There was a good turnout of volunteers and a number
of tasks completed. After setting the world to rights we started work. We were
refuelled at lunchtime by some great bacon and sausage baps from Angela.
Talk by David Cook at Priory Street, 1 March 2019.
There is more to sundials than things plonked in a garden on screwed to a church wall and you would be surprised how accurate they can be.
David presented an interesting talk for the Society at the Priory Street Centre on Friday 1 March. He started out by saying that sundials are ‘rubbish’ and then went on tho show that a lot of them aren’t, demonstrating a range of different sundials from his own collection. Continue reading →
A monthly look at astronomical events in the sky and on Earth
March 2019
The following article often refers to angles in the sky. The diagram above is a rough guide. Hold your hand at arm’s length. (Courtesy of timeanddate.com)
Fri/Sat/Sun 1st/2nd/3rd
A rare opportunity to catch a naked eye glimpse of elusive Mercury in the evening sky after sunset. Find a place where you’ve got a good view of the western horizon, note where the sun sets (at about 1740), wait until 1815 then look at a point 10° directly above where the sun set and there will be Mercury. Binoculars will help you to spot it initially but it’s easily visible without them. A small telescope will show it as a 36% illuminated orange coloured crescent. It’s visible until after 1845 as it slowly approaches the horizon.
BEWARE! Don’t try using binoculars to scan the sky for Mercury before the sun has completely set. You could blind yourself!
Sat 2nd
If you’ re awake by 0615, look low in the SE to see Venus and the crescent Moon together just 5° above the horizon. A nice sight.
Fri 8th
A wafer thin crescent Moon appears in the WSW after sunset (1754). It’s only 4% illuminated so will be a challenge to spot but it’s worth a try. By 1830 it should be easier to see, and Mercury may still be spotted at 5° altitude due west.
Mon 11th
The waxing crescent moon passes near to Mars. Spot the red planet 3° above and to the right of the Moon any time from 1900 to 2100 in the SW to W.
Thu 14th
Moon at first quarter. This is a great time to observe it, as the terminator is facing us and throwing lunar features into sharp relief.
Objects of the Month
There follows a shortlist of objects that are roughly in the south this month at 2030 hrs – a convenient time for family viewing.
Click on image to enlarge
The image above shows the sky at about this time, looking south (from Stellarium).
Castor and Pollux
The “heavenly twins” and the two brightest stars in the constellation of Gemini.
A 2 or 3-inch telescope will show Castor as a double star (separation 4 arc seconds) but in fact each of those stars is itself a double, discovered spectroscopically as they are too close to be separated optically. Each pair comprises a hot, bright A-class main sequence star orbited by a cool, faint M-type red dwarf. What’s more, this pair of doubles is orbited by another very faint double, making Castor an amazing 6-star system. Its combined magnitude is 1.58.
While your telescope is pointing at Gemini, take a moment to look at Pollux. Its orange colour is clearly very different from that of Castor. Pollux is a giant K-type star nine times the diameter of the Sun but only twice its mass. At 34 light years distant, it’s the nearest giant star to us. It does have a planet at least twice the size of Earth orbiting it called Thestias. Unfortunately, at only 1.6 astronomical units (a.u.) from the star when the habitable zone round Pollux is between 6 and 12 a.u., life on Thestias could be a tad challenging!
The Winter Triangle (Procyon, Sirius and Betelgeuse)
These three interesting stars form a near-equilateral triangle. See star map above.
Sirius
Hubble image (NASA)
SiriusThe brightest star in the sky. Is actually a binary. Sirius A is a main sequence A0 star; Sirius B is a white dwarf hundreds of times fainter than Sirius A. Although their angular separation is currently 10 arc seconds, the difference in brightness (magnitudes -1.44 and 8.5) makes spotting Sirius B a challenge for even large telescopes. The Hubble image on the left illustrates this.
Procyon
Another binary star. Procyon A is an F5 star and thus cooler and yellower than Sirius. Procyon B is another white dwarf. Their magnitude difference and closer separation (4.3″) makes spotting the fainter component even more difficult than for Sirius but Giuseppe Donatiello has done it with a home made 127mm f/9 ED refractor!
Betelgeuse
Image courtesy of NASA
Now Betelgeuse is something quite extraordinary. It’s an M1 red supergiant and one of only a handful of stars that are large and near enough for specialist telescopes to see their surface as a disc. This is a NASA image. Put it where the sun is and it would extend nearly to the orbit of Jupiter. It’s a semiregular variable whose magnitude changes by 1.3; its surface temperature is only 3600K but it’s luminosity is 90,000 to 150,000 times that of the sun.
And finally, two Open Clusters, M41 and M47
Click image to enlarge
These often neglected clusters are fine targets in modest telescopes and even binoculars. M41 is 5° below Sirius, and M47 is 12° east and 2° north of Sirius. They’re both at magnitude 4.5 and about the apparent diameter of the full moon. Note that M41 contains a mixture of red giants and white dwarfs but M47 comprises mainly young blue stars and only a few red giants.
M41
Image courtesy of NASA
M47
Image courtesy of NASA
Stop press – space news
As this item is being uploaded, we have news of the successful launch of Israel’s Beresheet lunar lander. This privately funded mission by Israel’s SpaceIL company lifted off using a SpaceX Falcon 9 rocket. The name Beresheet comes from the book of Genesis and means “In the beginning”. Clearly, Israel intends this to be the beginning of their efforts in space. For the latest news, see this Sky & Telescope article and this Beresheet fact sheet.
People in York (well, those prepared to be up through the night) were rewarded with a spectacular view of the lunar eclipse on Monday morning. I feel sorry for some I know who got up through the night and see clouds, only to go back to bed to miss the spectacle when they cleared. Continue reading →
