On Thursday 12th, comet 103P/Hartley, also known as just Hartley 2 reaches perihelion - the point when it is closest to the Sun in its orbit.

Now you normally associate comets as coming from the Kuiper Belt in the far reaches of our outer Solar System and their orbits around the Sun can take hundreds of years.

Hartley 2 is a bit different in that it actually originates from the Asteroid Belt between Mars and Jupiter.  Its orbit only takes six and a half years while it sweeps in close to the Sun and then heads back out to join its mates in the Asteroid Belt.  It is known as a "Jupiter-family" comet because of this.

The comet is peanut-shaped and only has a diameter of about one mile.  You will need binoculars at least to see it as the magnitude will be around +8.5

So how do you find it?  Venture outside after 1am on the morning of 12th and look towards the east.  You will see the obvious constellation of Orion.  To the left of Orion is the constellation of Gemini, the "Twins", who will appear to be lying on their side.

Locate the star "Wasat" which marks the waist of the lower twin.  Comet Hartley 2 will be situated just below Wasat with the comet's tail pointing towards the star.

I have provided an image of the comet, courtesy of NASA, but this was taken from only 435 miles away by their Epoxi mission in 2010.  You will see a fuzzy blob!  The good news is that the Moon will be below the horizon and so not creating any light pollution!

We're going to concentrate on Jupiter's moons as during the coming week, there are several transits where one of the moons passes in front of the planet, casting a shadow.

If you zoom into Jupiter with your telescope it will be possible to see all four of the Galilean moons, from left to right - Ganymede, Europa, Io and Callisto.  Look closely at Jupiter and you should see Europa's shadow on the surface of the planet.

If you prefer not to stay up so late, try around 10.30pm on Thursday 5th and you will be able to catch Ganymede's shadow near Jupiter's south pole.  At this time, Jupiter will be more towards the east.

Should you then decide to stay up really late and follow Jupiter, from 3am on the Friday morning, it is Io's turn to cast a shadow.

The shower is so named because its radiant point appears to be in the same part of the sky as the constellation of Draco.

Finally, I have just agreed to run another couple of my popular astronomy evenings at the Ham Hill Centre this autumn.  Booking information will be available soon, but in the meantime the dates for your diary are Friday 27th October and Friday 15th December.

The evening of Monday 25th is an ideal time to spot the impact crater on the lunar surface known as Vitello.  If you venture outside around 10pm, a Gibbous Moon will be located to the south, with Saturn a little above it and to the left.

Imagine the face of the Moon as a clock, Vitello will be located towards 7 o'clock, on the southern shore of Mare Humorum.

Vitello location map courtesy of IAU Working Group for Planetary System Nomenclature

The crater has a diameter of 41Km and is around 4 billion years old.  A telescope will reveal that it has a mountain complex in the centre and a very well-defined outer edge or rim.  The craters neighbouring it are not so clear because they filled with lava, but Vitello has an elevated position, so its rim and floor were left intact and not destroyed by the ancient lava flow.

Vitello image courtesy of Bruce Rohrlach

After all the excitement of that Blue Supermoon at the end of August, Friday 29th September sees the next Full Moon.  I mentioned the autumn equinox last week and this Full Moon is known as the 2023  "Harvest Moon" because it is the closest one to that September equinox.

There are several opportunities to spot the International Space Station in the early evening next week, the best chances being Monday 25th at 7.49pm and Wednesday 27th at 7.50pm.  In both cases, the ISS will appear towards the west and spend about six minutes passing almost directly overhead before disappearing to the east.

If you are up early, any morning next week and look towards the east, Venus will have risen above the horizon from about 4am.  It is currently shining very brightly at a magnitude of -4.5

By around 5.30am, Venus will have climbed higher in the sky and to the left of it, Mercury will be popping its head up above the horizon.  Towards the end of the coming week, Mercury reaches its greatest western elongation from the Sun (when it appears to be furthest from it).  Mercury won't be quite as bright as Venus as it currently has a magnitude of -0.3

Remember that the magnitude scale is back to front, so the more negative the number, then the brighter an object is.  To put that into context, our own Sun has a magnitude of around -26 so that is why you never attempt to look at it through binoculars or a telescope!  For this reason, I would not be tempted to use your telescope to get a better view of Venus and Mercury next week as the Sun will be rising in the same spot a little later and you don't want to accidentally catch a glimpse of it!

While we are on the subject, on the morning of Saturday 23rd, the centre of the Sun crosses the celestial equator as it moves from the northern celestial hemisphere to the southern celestial hemisphere.  What on Earth does that mean?  Well it marks the autumn equinox or the point on the autumn calendar when we have equal periods of night and day.  In other words, we are halfway towards the shortest day in December - hard to believe after all that hot weather last week!

The coming week will appeal more to the early risers amongst us rather than staying up into the late evening.

Go outside anytime from 4am on Monday 11th and a 12%-lit Waning Crescent Moon will have risen above the horizon towards the east.  Below and to the right of it will be Venus who will also appear as a crescent shape if viewed in a telescope.

Aim your telescope to a point just below the Moon, running in a line towards Venus and you should be able to find the Beehive open cluster of stars, also known as M44 in the Messier Catalogue.

The cluster has around 1000 stars and is one of the closest clusters to us, about 610 light years away.  It has a magnitude of -3.7 so from a dark location you should even be able to see it with the naked eye, although without a telescope it will resemble a fuzzy blob.

Much easier to spot is the bright star Procyon to the right of the Moon and Venus.  Procyon is the 8th brightest star in the night sky with a magnitude of +0.34 and it is actually a binary system, but you will only be able to see the main star.  Its companion faint white dwarf star will be invisible.

If you really fancy a challenge, a 1%-lit Crescent Moon rises above the eastern horizon about an hour before sunrise on the morning of Thursday 14th.  To the right of it will be a magnitude +1.8 Mercury.

Please remember not to risk using a telescope to obtain a better view as the Sun will be rising shortly afterwards in the same place!

If you venture outside around 11pm on Monday 4th, a 70%-lit Waning Gibbous Moon will have risen above the horizon towards the east with a magnitude -2.5 planet Jupiter just to the right of it.

When you look through your telescope's eyepiece, the four moons will be the opposite way around to have I have listed them - because of the way their optics are designed, astronomical instruments always produce an inverted or upside-down view!

If you use binoculars, which are designed for looking at things on the Earth, then the image will be the correct way round.  Binoculars incorporate an extra prism to correct the image, but the process loses a little bit of light.  This is done because if you're looking at a ship in the distance, it's nice to have the sea at the bottom and the sky at the top!  Astronomers don't care if their target is the other way up as it's far more important for them to collect as much light as possible!

There are a couple of great opportunities to spot the International Space Station at the beginning of next week.  On Monday 4th it appears over the horizon to the west at 5.23am and reaches an altitude of 77 degrees as it spends 6 minutes heading towards the east.  On Tuesday 5th, it will appear in the west at 4.37am and pass directly overhead.

Thursday 31st August sees the second Full Moon of the month.  When this occurs, the second one is commonly called a Blue Moon, but this is technically incorrect.  The mis-interpretation of the definition first appeared in print back in 1946 and it stuck because it is easier to understand.  Officially, a Blue Moon is the third full moon in a season of four.  Let's just stay with the first definition!

This Full Moon occurs at perigee again, when the Moon is closest to the Earth in its orbit around us and looks slightly brighter and larger than at other times, so it is therefore called a Super Blue Moon.

On 31st, just as it's getting dark, the Moon will have risen above the horizon towards the east, with Saturn shining to the right of it and a little higher in the sky.

If you stay up to around 11pm, then the Moon will appear more towards the south east and Jupiter will have risen to the left of it in the east.

Ironically, full moons at this time of year tend to be at a relatively low altitude so they appear more orange than blue!  The light being reflected from the Moon's surface passes through more of our atmosphere and this scatters the blue wavelengths.  If you catch the Moon rising above the horizon, it sometimes looks huge.  This is known as "Moon Illusion" and is simply a trick that your brain plays on you - although the effect has been known about for thousands of years, we still don't understand why!  It has nothing to do with the Moon being at perigee.

Moon Illusion image courtesy of NASA

On Sunday 27th, Saturn reaches opposition to the Sun, so it is well-placed for observing with a magnitude of around +0.3 and the planet reaches a maximum elevation of 25 degrees above the horizon.

If you venture outside any evening next week and look towards the south around midnight, Saturn will be approaching this maximum height in the sky. 

As light passes through our atmosphere, it becomes distorted which can spoil the view through a telescope with high magnification eyepieces and it is also why stars appear to twinkle.  Astronomers always prefer to observe objects when they are at high elevations and the light from them is passing through less atmosphere, so next week is an ideal opportunity to point your telescope towards Saturn and look at those amazing rings circling around it!

The rings are made from countless particles ranging in size from a few micro-meters to several meters in diameter.  They are mainly made from water ice and to this day, space scientists cannot agree how they were originally formed.

Mercury and Venus are "inferior planets".  Now that sounds like I'm being a bit nasty, but in astronomical terms it's nothing derogatory at all.  It simply means that those planets orbit around the Sun inside our own orbit or in other words, they are closer to the Sun than us and we are classed as the "superior planet".

To a Martian, Mars would be the superior planet and the Earth would be classed as another inferior planet!

At the beginning of next week, Venus will have just passed an "inferior conjunction" with the Sun.  An astronomical conjunction occurs when two objects appear close together, but of course this is only from the observer's perspective which is two dimensional as you have no depth perception when looking at something in the distance - in reality the objects will still be far away from each other when you think three dimensionally.

As they orbit around the Sun, inferior planets also show different phases, just like our own Moon.  If you were to try observing Venus at its inferior conjunction, you would see a thin phase of 0.1%, like a very, very thin crescent, but please don't be tempted to try it as you would be looking directly towards the Sun and this would cause instant and permanent blindness.  The experiment would need very specialised equipment and a camera rather than an eyepiece!

It's worth staying up to around 2am on the early morning of Wednesday 9th as there will be a nice treat for the naked eye - no telescope necessary.  Look towards the east and you will see three targets - running left to right - the Pleiades open cluster of stars, a waning Crescent Moon and Jupiter.

The Pleiades is at the top of the constellation of Taurus.  If you really feel the urge to dig out your telescope, aim it that direction and locate the bright star Aldebaran in Taurus.  To the right of Aldebaran will be the Hyades open cluster.

If you'd prefer an activity earlier in the evening, look high up towards the south east after dark anytime next week and find the constellation of Cygnus, the "Swan".  Below the tail of Cygnus will be two small constellations called Vulpecula and Sagitta.  When lines are drawn to show the shapes of constellations, Vulpecula looks like a straight line and Sagitta looks like an arrow.

My reason for sending you towards these two unremarkable constellations is that between them you will find an asterism or recognisable pattern of stars known as the "Coat Hanger".  It will take a bit of looking for and will actually appear to be upside down.

The asterism consists of ten main stars and is officially known as "Brocchi's Cluster".  This is a bit of a misnomer though, as the stars are not thought to be gravitationally tied to each other, so technically they are not a cluster!  With the naked eye, the asterism will only look like a faint patch of light - binoculars or a small telescope will be needed to resolve the detail.  Just need some clear sky to be able to do it!

On the evening of Tuesday 1st August, we have a Full Moon.  At 10pm, our celestial neighbour will have just risen above the horizon towards the south east.

Nothing out there in space is a perfect circle and the Moon's orbit around us every 27 days is slightly elliptical or "egg shaped".  The point where the Moon gets closest to us is known as "Perigee" and at that time it is about 225,000 miles away.  The opposite point, when the Moon is furthest from us is called "Apogee" and then the Moon is about 251,000 miles from us.

The Full Moon on 1st happens to occur very close to perigee which means that it will appear to be 14% larger and 25% brighter than a Full Moon at apogee.  This is referred to as being a "Supermoon".  August is also unusual in that there will be two full moons in the same month, with another on 31st August.

Now I was never that good at maths, but if the Moon takes 27 days to orbit around us, why is it a few days longer than that between the full moons?

If you venture outside around 2am any day next week and look towards the east, Jupiter will have risen above the horizon.  To the left of Jupiter you will find the familiar shape of the Pleiades open cluster of stars.

For those of you preferring not to stay up quite so late, try looking towards the south west around 11pm on Thursday 27th and you will see a slightly gibbous-shaped Moon.

With a magnitude of around +1.0 it is one of the brightest stars in the night sky and one of the largest stars that can be seen with the naked eye.  Its mass is about twelve times that of our Sun.  If we stuck Antares in the middle of our Solar System, it would stretch out as far as Jupiter and consume all the rocky planets of our Inner Solar System!

Antares is actually a binary star - you will only see the red supergiant, but there is also a smaller, magnitude +5.5 dwarf star beside it.

It's time to go hunting for a minor planet in the Asteroid Belt.

Last week I suggested looking towards the east to see Jupiter and the bright star Capella.  Look east again at around 3am on Tuesday 18th and you will have a similar view, with the Pleiades open cluster of stars sitting about half way between Jupiter and Capella.  Down from the Pleiades and quite close to the horizon will be the bright star Aldebaran.

(4) Vesta is the second-largest minor planet in the Asteroid Belt (second only to Ceres) with a mean diameter of 525Km.  It is also the brightest object in the belt.  The asteroid is rocky and made from the same materials that formed the planets of the inner Solar System billions of years ago, but how do we know this?

Vesta is covered in impact craters.  Around 1 - 2 billion years ago, numerous fragments were ejected after several collisions and some of this debris made its way to Earth, landing as meteorites for scientists to subsequently study.

Interest is this little rocky fella has been so great that the NASA Dawn spacecraft spent a year orbiting around it in 2011 before continuing its main mission towards Ceres.

If you look towards the east early in the morning on Wednesday 12th, say around 1.30am, a 29%-lit Crescent Moon will have just risen above the horizon, with planet Jupiter immediately to the right of it shining at a magnitude of -2.1

Taking in a wider view, Saturn will be located towards the south east and the bright star Capella will be towards the north east.

Capella is actually the sixth brightest star in the night sky and the alpha star in the constellation of Auriga.  Although it appears to be a single star to the naked eye, Capella is a quadruple star system comprising two bright yellow giant stars that are about two and a half times the size of our Sun and two much fainter red dwarf stars.  The stars are relatively close to us - around 43 light years away.

If you want to see the whole of Auriga, you will have to wait until around 3am when all its stars will have all risen above the horizon.  Immediately to the right of Auriga and very close to the horizon will be the constellation of Taurus, with the easily-identifiable Pleiades open cluster of stars just above Taurus.

There are a number of really good opportunities to spot the International Space Station next week.  Monday 10th at 1.21am, Tuesday 11th at 2.10am, Wednesday 12th at 1.22am, Thursday 13th at 12.34am and again on the Thursday at 2.11am.

In all these cases, the ISS will appear towards the west and spend around 7 minutes passing almost directly overhead before disappearing to the east.

Lately I've been encouraging everyone to look towards the west just as it's getting dark to see Venus and Mars.  Well how about giving our old friends, the gas giants Saturn and Jupiter, a chance?  Unfortunately this does mean either a late night or early morning though!

If you look towards the south east around 2am on Friday 7th, Saturn will be sat just above an 81%-lit waning Gibbous Moon.  If at the same time you look further east, Jupiter will have just risen above the horizon.

Remember that the whole month of July is also a good opportunity to observe Noctilucent clouds for up to a couple of hours after sunset.  These "night-shining" clouds are caused by sunlight reflecting off layers of ice crystals in the upper atmosphere and are notoriously difficult to predict.

There are three good opportunities to spot the International Space Station next week.  Monday 3rd at 3.45am, Wednesday 5th at 3.44am and Thursday 6th at 2.56am.  In all three cases, the ISS will appear towards the west and spend around 7 minutes passing almost directly overhead before disappearing to the east.

If you have never observed the ISS before, it appears to look like a star that is eerily moving quickly against the background sky.  The space station is actually travelling at an incredible 7.5km/s or approximately 17,500mph.  It has to travel that fast to remain in orbit and not fall back to Earth!

Screenshots courtesy of Stellarium

Copyright Adrian Dening and Radio Ninesprings 2023