What’s Up! December 2019

A monthly look at astronomical events in the sky and on Earth

One really has to wonder whether we are “poco loco” to choose astronomy as our hobby. We’ve just had the cloudiest and wettest couple of months that I can remember for some time, and although we may have a few clear nights in the first week of December, the Met Office isn’t forecasting much in the way of clear and stable conditions for the rest of the month. Still, mustn’t grumble. Let’s at least take advantage of the odd observing night that happens to come our way and be grateful for small mercies. Important thing is to make sure that telescope is in tip-top condition and ready for action if the opportunity presents itself.

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What’s Up! November 2019

A monthly look at astronomical events in the sky and on Earth

Well, it’s arrived: the astronomy season for real. Suddenly, shockingly  for some, now the clocks have gone back it’s getting dark by just after 5 p.m. and that’ll be 4:30 p.m. at the end of the month. No longer do we have to wait until after bedtime to see anything. The whole evening is at our disposal. So what’s up there?

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What’s Up! September 2019

A monthly look at astronomical events in the sky and on Earth

See What’s Up! for August 2019

After the short and light nights of summer, September is the first month in which the sky goes completely dark every night (i.e. astronomical twilight ends, and the sun dips to more than 18° below the horizon). At the start of the month, total darkness runs from 2211 to 0355 BST, but by month end, it runs from 2043 to 0504 BST. So in addition to other delights of the night sky, we can observe faint and diffuse deep sky objects without having to stay up really late.

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What’s Up! August 2019

A monthly look at astronomical events in the sky and on Earth

See What’s Up! for July 2019

August the 8th is the first night since early May that the sky goes completely dark – for a short time centred on 1 a.m. This increase in the length of the night is noticeable in the late evenings in August and heralds the “shoulder season” for astronomical observations. By the 15th, astronomical twilight ends at 2316 BST, and by the end of the month it’s at 2214. Just taking the dog for its last walk or strolling home from the pub, August is the month when one begins to notice the stars again. And with it being predominantly warm, August is probably the month with the best combination of evening comfort and  darkness. So break out those 7 x 50s, dust off that ‘scope and get out there!

The Moon

Best seen as a thin waxing crescent low in the west after sunset on Mon 5th to late gibbous low in the south on Mon 12th. It doesn’t climb much above 13° altitude throughout this period due to the angle of the ecliptic at this time of year. Jupiter will be seen about 1.5° below it on the 9th.



Mercury may be spotted low (6 – 10°) in the ENE very early in the morning at around 0440 to 0500 between the 8th and 15th of the month.

Venus and Mars

Are both on the far side of the sun and completely unobservable this month.

Jupiter and Saturn

Both can be seen low in the south by about 2100 BST. Jupiter is in Scorpio and fairly near the star Antares; Saturn is 30° to its left in Sagittarius. The low altitude of these planets is not conducive to seeing them at their best. However, the YAS has organised a special observing event for Saturday the 31st August where we will be bringing an armoury of high power telescopes to bear on Saturn. This is probably your best chance this year to see this spectacular planet. See the Events page for more details and to book a place.

Uranus and Neptune

Visible only after midnight. Wait until later in the year for these two.

Perseid meteor shower 11th – 13th

Normally the northern hemisphere’s favourite meteor show, the Perseids this year will be a bit of a challenge. The problem is the moon. As the shower reaches its peak, not only date-wise but hour-wise, the waxing gibbous moon will reduce the number of meteors seen. Despite this, if you are prepared to stay up very late or even go to bed then get up very early, the Perseids are definitely worth observing.

The graph below shows the daily Perseid numbers observed in 2017, and this year’s peak will be on the same day – the 13th.  The numbers for 2017 were perfectly normal and typical of this shower.

Perseids 2017 ZHR graph
Perseids 2017 ZHR graph

Data from Hong Kong Space Museum

10th Aug23001711-15No
11th Aug300100222-21No
12th Aug400100296-21No
13th Aug7501005410-21No
14th Aug5001003613-21No
Table showing the zenithal and actual hourly rate for the Perseid meteor shower in 2019

The zenithal hourly rate (ZHR) is what a single observer would expect to see each hour if the sky was perfectly clear and completely dark and the radiant was overhead. You’ll see the ZHR rises, especially from the 9th, reaches a peak on the 13th then quickly reduces.

From the UK, the radiant – at the northern end of the Perseus constellation – rises in the NE while it’s still light, but by 3 a.m. has risen to a very respectable 60° altitude. After that, the sky begins to brighten as dawn approaches.  The number of meteors to be seen is roughly equal to the sine of the radiant altitude.

  • The ZHR column shows how the ZHR numbers change day by day.
  • The AHR (actual hourly rate) column shows the number of meteors actually expected to be seen by an observer in York.
  • The Moon Alt column gives the altitude of the Moon. Negative numbers mean it’s below the horizon.
  • The Sun Alt column shows how far below the horizon the sun is. Less than 18 means some sky glow.

So there are five one-hour slots centred on the times given when it’s worth giving it a try.

On the 11th, expect to see a meteor every 2½ minutes or so; on the 12th, one every 2 minutes; and on the 13th, if you wait until between 0230 and 0330, one every minute.

You don’t need to identify the constellation of Perseus to see these meteors. The best way is to set your chair or lounger to face north east (the opposite area of sky to where the moon is) and just relax. Good luck!

Non-Solar System Objects

Deep Sky

July was the month to focus on the many nebulae and clusters in Scorpio and Sagittarius. In August we should turn our attention to the summer triangle and surrounding area. In case you don’t know the summer triangle, it is formed by the stars Altair in Aquila, Vega in Lyra, and Deneb in Cygnus. During the first week of August – when the moon is not around – but particularly from the 22nd onwards, this area of sky through which the Milky Way passes on its route northwards is riding high in the south and is peppered with deep sky splendours.  The Astronomy Now chart below shows the best of these. Look high in the south at 2300BST. Each object is described in the table below.

summer triangle: Lyra, Aquila, Cygnus

The Summer Triangle area of sky  (Chart courtesy of Astronomy Now)

Albireo3β Cygni. A beautiful and bright 3rd magnitude double star with amber and sapphire components 35 arc seconds apart. Use a magnification of x30 to see them at their best.
ε Lyrae4.7The famous "double double" comprising two pairs of stars. The pairs are separated by about 3 arc minutes but the components of each pair are only about 2.4 arc seconds apart. This object is a good test for a 4-inch telescope; you'll need a magnification ox x200 or more.
M579The Ring Nebula. Another famous object. It's a planetary nebula that looks like a smoke ring. Although small and faint, it's easy to find, half way between the two stars shown on the chart and will stand a fair degree of magnification. In fact, it is about 4 arc minutes in diameter, nearly six times the apparent diameter of Jupiter.
M277.5The Dumbbell Nebula, another famous planetary nebula. This showpiece of the northern hemisphere never fails to impress, but do try to view it only when the sky is very dark. At 8 arc minutes in diameter, it's easily visible even in binoculars. Not to be missed,

Just lying on a lounger and with binoculars, sweeping the star fields in this area of the Milky Way, stretching right across the sky from SW to NE will reveal many beautiful star clusters. I find doing just that is amazingly relaxing. Do try it; it’s a tonic!

But if you would like the opportunity to see these objects with the array of society telescopes, we’ll be observing them at the event (previously mentioned) on Saturday 31st August. Go to the Event Page on our web site for more info.

Passes of the International Space Station (ISS)

The ISS is visible on only four nights in August: on the 1st and 3rd at around 10 p.m. and then on the 29th and 31st at around 5 a.m. See the Heavens-Above web site for more details.

Space News

For up-to-date news on space missions, rocket launches etc. scroll https://www.space.com/32286-space-calendar.html

Clear skies and good viewing.

John Rowland 25 July 2019

What’s Up! July 2019

A monthly look at astronomical events in the sky and on Earth

See What’s Up! for June 2019

The Moon

Best seen as a thin waxing crescent low in the west after sunset on Fri 5th to late gibbous low in the south on Sat 13th. It doesn’t climb much above 18° altitude throughout this period due to the angle of the ecliptic at this time of year. Jupiter will be seen about 1.5° below it on the 13th.

Partial Eclipse of the Moon on July 16th

On that date, the moon will rise in the SE at 2123 BST partially eclipsed. The eclipse will continue until midnight, with its maximum at 2230. The sky view below shows the situation at 2230; note the partially eclipsed moon near lower left together with Jupiter and Saturn.

Night sky for partial lunar eclipse
Night sky for partial lunar eclipse showing Saturn and Jupiter (Stellarium screenshot)

See the full details of the eclipse.

The Sun

If you happen to be visiting the South Pacific, Chile or Argentina, then there’s a total solar eclipse on the 2nd July. All right for some!


Mercury, Venus and Mars:

All too near the sun to be observable this month.


Jupiter reached opposition on the 10th of June and is observable in the late evenings throughout the month. Unfortunately, it rises to only a little less than 14° so will suffer from poor seeing and a lessening of brightness due to that low altitude. The optimum time to view it is when it transits (is due south) and this occurs at 2330 on the 1st, 2230 on the 15th, and 2130 on the 30th.

One thing that’s not affected by poor seeing is the visibility of the four Galilean moons as they perform their orbital dance. As the moons pass behind Jupiter they disappear, but what’s worth looking out for is when they reappear. Interestingly, once we’re a week or so beyond opposition, a moon emerging from behind Jupiter is still in its shadow and is there but we can’t see it because it’s eclipsed. And if you’re looking at the right time, the moon suddenly appears as if by magic, not from behind Jupiter but some distance from it, to its east. Here are three examples that can be seen  this month. Start looking two or three minutes before the time, to ensure you don’t miss the appearance. And make sure you know which way east is as seen in the eyepiece. If you’re not sure, it’s the direction away from which the planet is moving. If you have a driven telescope, stop the drive for a moment to see which way the planet drifts.

Date Time (BST) Satellite Notes
July 14th 2319 Io  
July 18th 2349 Europa  
July 30th 2138 Io Only 30 mins after sunset.
Screenshot of Jupiter showing the Galilean moons on 14 July
This is the view just after Io’s appearance on July 14. (From SkyViewCafe.com)


Saturn reaches opposition on the 9th of July. Unfortunately, like Jupiter, it only climbs to an altitude of 14° and is thus best seen within an hour either side of transit. You might care to wait until August to see it, but if you don’t want to wait, the transit times are 0146 on the 1st, 0047 on the 15th, and 2339 on the 30th. One good thing about this opposition is that Saturn’s rings are really wide open and well seen.

Non-Solar System Objects

Deep Sky

June and July are difficult months to observe deep sky objects because the sky never gets really dark, but they are also the months when some famous nebulae and clusters are visible. These are clustered in the direction of the galactic centre and therefore low in the sky. If you don’t have a go at them in July – the best time – then you’ll miss out until next year. Unfortunately, the Moon is a big problem between the 10th and the 23rd, so avoid that 14 day period. The other thing you need to accept is that these objects can only be seen well very late at night. e.g. around 0100 BST before the 10th and midnight after the 23rd. But if you’re keen enough, your efforts will be rewarded.

The sky view below shows these objects at 0100 on the 5th (or midnight after the 23rd).

Deep sky objects visible in July 2019
Deep sky objects visible in July 2019 (screenshot from SkyViewCafe.com)

Some of the objects listed in the table below can be seen with the naked eye and all are well seen in binoculars or a small telescope.

Messier No.MagnitudeDescription
M115.8The Wild Duck Cluster. One of the richest open clusters (2,900+ stars).
M166.0The Eagle Nebula, cluster and cloud of hot gas. Famous for the Pillars of Creation feature at its centre.
M176.0The Omega Nebula. A cluster of 35 stars within cloud of gas.
M215.9Open cluster of about 40 stars. Impressive in a small telescope.
M225.1Bright globular cluster of about 70,000 stars.
M235.5Loose galactic cluster of about 150 stars
M254.6Compact galactic cluster of about 86 stars of various colours.

Noctilucent Clouds

July is a great month for looking out for the eerie and beautiful noctilucent clouds. (From the Latin for night shining.) These are ice crystal clouds, and the highest on Earth, at about 50 miles up. They can only really be seen between midnight and 2 a.m. low above the northern horizon if the sky is otherwise clear.  The image below was taken on 19th June this year.

Noctilucent clouds
Noctilucent clouds shot by Nando Harmsen of Fstoppers

Passes of the International Space Station (ISS)

July is a particularly good month 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 on the 5th then every night from the 7th to the 31st inclusive. On many nights it is visible twice, and on some nights, three times. 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”.

Space News

For up-to-date news on space missions, rocket launches etc. scroll https://www.space.com/32286-space-calendar.html

Other News

The world famous Sky&Telescope magazine, founded in 1941, has been acquired by the professional organisation, the American Astronomical Society. The magazine has been published for some years by F+W Media, but they have just filed for bankruptcy. The AAS paid $1.23 million for the magazine and have assured staff and readers that the existing staff will remain in post and the magazine will carry on as normal. Full story here.

Clear skies and good viewing.

John Rowland 22/06/2019

What’s Up! May 2019

A monthly look at astronomical events in the sky and on Earth.

See April 2019 issue

What to See in May

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.

moon map


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)


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”.

Space News

M87’s Black Hole

See this S&T article for details.

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”.

Israel’s Beresheet Lunar Lander Crashes

Full story in this Sky & Telescope piece.

The USA is Going Back to the Moon by 2024

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!

Clear skies and good viewing.

John Rowland 22/04/2019

What’s Up! March 2019

A monthly look at astronomical events in the sky and on Earth

March 2019

angles in the sky

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.

Screenshot showing Gemini
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 double star
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 A-B

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!


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

M41, M47 clusters
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.


Image courtesy of NASA


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.

Clear skies and good viewing!

John Rowland