Morning Conjunction: Venus and Jupiter, August 2014

On Monday morning, 18 August 2014, in the eastern sky before sunrise you’ll see a very close conjunction of the two brightest planets, Venus and Jupiter.

They’ve been shining brightly in the pre-dawn sky for a while now, but as they trace out their separate orbits around the Sun they appear to move relative to one another, Venus the faster of the two. And they’re getting closer every day, until on Monday 18 August they’ll be at their closest, only 12 arcminutes apart, about one third of the diameter of the Moon.

This is closest conjunction in 15 years, and will be a very striking sight in the morning sky, but you’ll need to be up and about early to see it, about an hour before sunrise, around 0450 BST (sunrise is around 0550BST for most of the UK – Orkney gets an earlier sunrise at 0535, while the southwest of England have to wait till around 0605).

If you’ve got a pair of binoculars and a tripod, or even better a telescope, it’s really worth looking at these two planets. Venus is the brighter of the two, shining about twice as brightly as Jupiter through the morning twilight, but if you can magnify them (and you’ll catch them in the same field of view in a pair of binoculars), then Jupiter will be around three times the diameter of Venus (30 arcseconds compared to 10), and you’ll see Jupiter’s four largest moons as tiny points of light near the giant planet.

Don’t worry if you’re clouded out, or if you sleep in, on Monday morning; they’ll be close together in the pre-dawn sky for a few days afterwards too.

Venus-Jupiter conjunction this morning, 0450BST 16 August 2014

Venus-Jupiter conjunction 0450BST 17 August 2014

Venus-Jupiter conjunction at its closest, 0450BST 18 August 2014

Venus-Jupiter conjunction in close up, 0450BST 18 August 2014

A Bright Nova Appears in Delphinus

Last night a bright nova was discovered in the constellation of Delphinus. It’s bright by nova standards: you normally need telescopes to see novae but this can can be seen with the naked eye – just! – and is easily spottable through binoculars. At the time of writing it has been observed at magnitude 6.3 by Koichi Itagaki, of Yamagata, Japan, and at magnitude 6.0 by Patrick Schmeer, of Bischmisheim, Germany. This means that under dark skies, free from light pollution, with good seeing conditions and good eyesight, it’s within the limit of human eyesight. If you’re in a city though, or if your eyesight isn’t perfect, you’ll need binoculars.

UPDATE 16/08/13 at 1525UT
The British Astronomical Association e-bulletin 00757 is reporting that observations have been submitted to the AAVSO database suggesting the Nova Delphini 2013 has brightened to magnitude +4.5, making it an easy naked-eye object from rural and many suburban sites.

UPDATE 17/08/13 at 0630UT
The AAVSO light curves suggest that Nova Delphini 2013 is dimming, and is currently at magnitude +4.9. This is still naked eye under dark skies and an easy binocular object from cities but get outside as soon as it’s dark and clear; it’s going to keep dimming and soon won’t be naked eye.

UPDATE 18/08/13 at 1430 UT
Although it has dimmed slightly from its maximum brightness of +4.4 magnitudes, it has stayed at +4.9 magnitudes for almost two days now, meaning it’s still naked eye.

UPDATE 22/08/13 at 1330 UT
Nova Delphinus 2013 has dropped below +5.5 magnitude, and will probably drop below human eye detectability in a few days time (it’s already a non-naked-eye object except in very dark sky sites).

Here are some finder charts for the nova, produced using the excellent (free!) Stellarium package.

Nova Delphini 2013 marked with a +

Your first task will be to locate the small constellation of Delphinus. Luckily, that’s really easy at the moment. It’s high in the south around midnight (SE in the evening), and right next to the prominent stars of the Summer Triangle. The brightest stars in Delphinus make up a tiny diamond shape in the sky. Got it? OK, here’s where it gets a little trickier.

Three steps to Nova Delphini 2013 marked with a +

Step 1: Find the diamond shape of Delphinus, shown in the lower left portion of this star chart, with the bright stars of the diamond α, β, γ, and δ labelled (along with ζ nearby).

Step 2: Draw a line from the lower left star of the diamond, δ, past the upper right star, α, but missing it slightly to the “left” of α. Continue for approx. five times the α-δ distance. Here you’ll find another four stars in a diamond of almost exactly the same shape and orientation as (albeit slightly smaller than) the bright diamond of Delphinus. These stars are all really faint. Their magnitudes are marked on the chart above, and they’re all at the very limit of naked eye visibility. Use binoculars if you can’t see them directly.

Step 3: Continue your line onwards, through the lower left star of this fainter diamond to the upper right star, and now take an approximately 45° turn to the “right”, past a very faint star (magnitude 7.85) to the new nova!

(The bright star in the top left of this star chart is 29 Vul, magnitude 4.8)

Nova means “new”, a term coined in 1572 by astronomer Tycho Brahe after he discovered a “new star” in the constellation of Cassiopeia. But these stars aren’t new at all. In fact their brightness is a result of a giant explosion on the surface of a dead white dwarf star.

White dwarf stars form when small stars die and collapse down into a much smaller volume. If there’s another star nearby then the gravity of the white dwarf star can draw some hydrogen gas from the surface of its neighbour onto its own surface. This gas builds up until there is a sufficient quantity of it that it undergoes runaway nuclear fusion, igniting, flaring off, and temporarily brightening the otherwise very faint white dwarf.

No one’s quite sure how this new nova will develop. It might brighten further, or it might begin to dim over the course of days or weeks. All the more reason to get out an find it as soon as you have clear skies. Happy nova hunting!

My Perseids Meteorwatch

On Monday night one of the year’s most spectacular meteor showers is set to peak.

You’ll get a great view of it if you’re somewhere dark with clear skies. But those of us stuck in the city can see plenty too.

I’ll be heading to the grounds of Glasgow Science Centre to view it, and you’re welcome to join me. A few things first:

If it’s cloudy or raining DON’T COME! I won’t be there.

I’ll be there from around 10pm, probably till around midnight.

If you want a great view then head somewhere dark, but if you’re in Glasgow and don’t want to head out of the city this is a decent site.

This ISN’T a formal event; I’ll be hanging out there and you’re welcome to come under your own steam. You’ll be responsible for your own safety and comfort; bring extra clothing, a torch, and a deck chair if you have one.

You can park in Glasgow Science Centre car park for £3. Public transport at that time of night is pretty sparse.

Glasgow Science Centre will NOT be open, so there’s no access to refreshments or toilets etc.

Thanks to Glasgow Science Centre for letting us use their outside space.

August Asteroids: 3 Juno and 7 Iris at Opposition

This month two of the brightest asteroids, 3 Juno and 7 Iris, will be at opposition in our skies, giving a great opportunity for asteroid hunters to track down these lumps of space rock.

Bear in mind though that you (almost certainly) won’t be able to see them with the naked eye, and that you’ll need binoculars on a tripod or a telescope to find them properly. And even then they’ll just look like very faint stars. But they’re not stars; they’re asteroids, lumps of rock in our solar system orbiting the Sun between Mars and Jupiter.

How big and bright are they?

3 Juno and 7 Iris are amongst the largest of the asteroids, a few hundred kilometres along any one axis. This might seem pretty big but they’re tiny compared to the planets, and so don’t reflect nearly as much light back to us, and are therefore much fainter.

Their magnitudes vary depending on how far away they are from us. They both vary between around seventh and eleventh mag; at their brightest 3 Juno is magnitude 7.4 and 7 Iris is magnitude 6.7. This only occurs under perfect conditions, and this year’s oppositions for both asteroids won’t have them presenting their very brightest aspect. The generally-accepted view is that the human eye can only see down to magnitude 6, but in exceptional circumstances – very dark skies free from light pollution, and very good atmospheric conditions – and with exceptional eyesight, you might just be able to see 7 Iris when it’s closest to us, and at its brightest.

When can I see them?

They’re visible all month but the best time to look at them is when they’re at opposition. That means they’re directly opposite the Sun in the sky, and therefore rise as the Sun sets and set as the Sun rises, getting to their highest due south around midnight.

3 Juno reaches opposition on Sunday 4 August 2013 and it’ll brighten up to magnitude 9. You’ll need a scope, a good star map, and patience to track it down.

7 Iris reaches opposition on Friday 16 August 2013, and it’ll be brighter than 3 Juno, but still not near its best, gaining magnitude 8 during this year’s opposition. Again, a good star chart and telescope is needed.

Where can I see them?

They are both visible in the lower part of the southern sky in the constellation of Aquarius, but you’ll need very detailed star maps to help you find them. 7 Iris is only a degree or so away from the brightest star in Aquarius, β Aquarii, on the night of opposition, making it a bit easier to find. The British Astronomical Association computing section has downloadable star-charts to help you find these asteroids, and others.

How will I know that I’m looking at an asteroid?

The short answer is: you won’t, at least not at first. Asteroids, even the brighter ones like 3 Juno and 7 Iris, will only ever appear as tiny specks of light when seen through a telescope, just like the millions of other tiny specks of light, the stars. However if you observe them over the course of a number of nights around opposition, and mark their position on a star map, then you’ll notice that their position changes relative to the “fixed” stars, as they circle the Sun and move through space.

Don’t be put off if you don’t manage to find them. While you’re out hunting for them don’t forget you can check out lots of other amazing sights through your telescope. Why not have a go at finding the Ring Nebula in Lyra, high overhead this month.

Good luck, and happy asteroid-hunting!

Constellation of the Month: Lyra

August’s evening skies are dominated by the Summer Triangle high in the south, made up of the three brightest stars in three different constellations, the stars Deneb in Cygnus, Altair in Aquila, and brilliant Vega in Lyra.

Vega is a magnitude 0 star, the fifth brightest star in the night sky, and the third brightest (after Sirius and Arcturus) visible to UK stargazers.

Look high in the south (almost directly overhead) in the late evenings in August and the very bright white star you’ll see is Vega. Look “down and left” of Vega and you’ll see the four other bright stars of Lyra in a rhombus shape.

Lyra represents the lyre of Orpheus, and it’s a great little constellation to observe through a telescope since, despite its diminutive size, is home to two Messier objects, M56 and M57.

Messier 56 (marked 2 above) is a loose globular cluster lying about 33000 light years away. It sits halfway along a line drawn between the “lowest” star of the lyre (the one furthest from Vega) and Albireo (beta Cygni). Through binoculars or a small telescope it looks just like a fuzzy star. You’ll need a pretty decent sized telescope (20cm+) to resolve individual stars.

Messier 57 (marked 1 above) is known as the Ring Nebula, and is one of the most-photographed of astronomical objects. It’s a planetary nebula, an expanding shell of gas that’s been puffed off by a giant red star in its death throes. Small scopes should show the elliptical shape but you’ll need a larger (20cm+) scope to see the hole in the middle and any features within the nebula. M57 is easy to find as it sits almost exactly half way between the two “lowest” stars of Lyra (the two furthest from Vega) beta and gamma Lyrae.

Perseids 2013: The What, How, Where, When, and Why

Here’s a simple guide for observing the Perseids 2013 meteor shower this year, covering five basic questions:
What is the Perseids meteor shower?

The Perseids meteor shower is the most reliable of the active regular meteor showers that happen throughout the year. A meteor shower is a display of meteors (or shooting stars) where you see lots of them in the space of just a few hours. The Perseids occurs around the same time each year, in mid-August, and during the peak of the shower meteor rates increase from just a few an hour (the background rate that you’ll see on any clear, dark night) up to maybe 100 or 200 meteors every hour for observers in the perfect location. Meteorwatchers in the UK will probably see dozens per hour from dark sites, dropping to a few an hour (still worth watching for) in towns and cities.

How can I observe the meteor shower?

You don’t need any special equipment to observe a meteor shower; just your eyes. Try and get as far from city lights as possible (out into the countryside if you can, or into a local park if not), and get comfortable. You might want to bring a reclining deck chair with you, as that makes meteorwatching much more civilised! Just lie back and take in as much of the sky as possible. If you’re lucky enough to see a good display of meteors, you might see as many as one a minute, maybe more!

Where should I look?

Meteors streak across the whole sky, so you don’t need to look in any specific direction, but of course if you’ve got a tall building or tree that’s blocking the view, or a streetlight nearby that’s a bit glare-y, then put these to your back. The Perseids meteors all appear to streak from a point in the sky (called the radiant) in the constellation of Perseus (hence the name) which rises in the east about 10pm local time, climbing to its highest in the sky towards dawn.

When is it happening?

The peak of the meteor shower will probably happen some time around 1815 and 2045 UT (1915 and 2145 BST) on Monday 12 August 2013, although there are uncertainties here. The peak could happen any time between 1415 BST 12 Aug and 0215BST 13 Aug. This means that observers in the UK might catch the peak of the shower, if it happens after the sky darkens on 12 August. Even on the nights on either side we’ll still see plenty. In fact the peak of the Perseids is several days wide, so you can start meteorwatching early, and carry on well after 12 August, so that even if this weekend is cloudy you’ll almost certainly have a chance to see some Perseids. Whatever night you’re out you’ll see more the later you’re up. Starting after dusk, the meteor rate will increase each night as Perseus climbs higher in the sky towards dawn.

Why do meteor showers happen?

Meteors are tiny bits of space dust streaking through our atmosphere. These motes of dust float about in space and as the Earth orbits the Sun it hoovers them up. Sometimes the Earth passes through a particularly dense clump of dust, and we get lots of meteors, in a meteor shower. These clumps of dust are left behind by comets as the orbit the Sun, their streaking tails leaving behind a trail of tiny rock particles. The comet that left behind the space-rocks that we’ll see in the Perseids meteor shower is called Swift-Tuttle, after the two astronomers that discovered it in 1862.

Perseids 2013: The What, How, Where, When, and Why

Here’s a simple guide for observing the Perseids 2012 meteor shower this year, covering five basic questions:
What is the Perseids meteor shower?

The Perseids meteor shower is the most reliable of the active regular meteor showers that happen throughout the year. A meteor shower is a display of meteors (or shooting stars) where you see lots of them in the space of just a few hours. The Perseids occurs around the same time each year, in mid-August, and during the peak of the shower meteor rates increase from just a few an hour (the background rate that you’ll see on any clear, dark night) up to maybe 100 or 200 meteors every hour for observers in the perfect location. Meteorwatchers in the UK will probably see dozens per hour from dark sites, dropping to a few an hour (still worth watching for) in towns and cities.

How can I observe the meteor shower?

You don’t need any special equipment to observe a meteor shower; just your eyes. Try and get as far from city lights as possible (out into the countryside if you can, or into a local park if not), and get comfortable. You might want to bring a reclining deck chair with you, as that makes meteorwatching much more civilised! Just lie back and take in as much of the sky as possible. If you’re lucky enough to see a good display of meteors, you might see as many as one a minute, maybe more!

Where should I look?

Meteors streak across the whole sky, so you don’t need to look in any specific direction, but of course if you’ve got a tall building or tree that’s blocking the view, or a streetlight nearby that’s a bit glare-y, then put these to your back. The Perseids meteors all appear to streak from a point in the sky (called the radiant) in the constellation of Perseus (hence the name) which rises in the east about 10pm local time, climbing to its highest in the sky towards dawn.

When is it happening?

The peak of the meteor shower will probably happen some time around 1815 and 2045 UT (1915 and 2145 BST) on Monday 12 August 2013, although there are uncertainties here. The peak could happen any time between 1415 BST 12 Aug and 0215BST 13 Aug. This means that observers in the UK might catch the peak of the shower, if it happens after the sky darkens on 12 August. Even on the nights on either side we’ll still see plenty. In fact the peak of the Perseids is several days wide, so you can start meteorwatching early, and carry on well after 12 August, so that even if this weekend is cloudy you’ll almost certainly have a chance to see some Perseids. Whatever night you’re out you’ll see more the later you’re up. Starting after dusk, the meteor rate will increase each night as Perseus climbs higher in the sky towards dawn.

Why do meteor showers happen?

Meteors are tiny bits of space dust streaking through our atmosphere. These motes of dust float about in space and as the Earth orbits the Sun it hoovers them up. Sometimes the Earth passes through a particularly dense clump of dust, and we get lots of meteors, in a meteor shower. These clumps of dust are left behind by comets as the orbit the Sun, their streaking tails leaving behind a trail of tiny rock particles. The comet that left behind the space-rocks that we’ll see in the Perseids meteor shower is called Swift-Tuttle, after the two astronomers that discovered it in 1862.

Perseids Meteor Shower 2012

UPDATE: Here’s my easy guide to the what, how, where, when and why of the Perseid Meteor Shower.

This month sees the most reliable meteor shower of the year; the Perseids. You can begin watching for Perseid meteors now, and the shower will last until late-August, but the peak of the shower occurs around mid-day on Sunday 12 August 2012, which means that the nights on either side of this will be good for meteorwatching.

Perseus at 0200 Monday 13 August 2012

The best time of night to watch the meteor shower is from around 2200 onwards on both 11 and 12 August 2012, once the radiant, the point from where the meteors appear to originate, rises above the horizon.

The number of meteors that you will observe every hour depends on a number of factors:

• the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
• the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
• the fraction of your sky that is obscured by cloud;
• the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.

The Perseid meteor shower has a zenith hourly rate (ZHR) of between 50 and 200. This is the number of meteors that you can expect to see if the radiant is directly overhead (the point in the sky called the zenith), and you are observing under a cloudless sky with no trace of light pollution.

However conditions are rarely that perfect. In the UK, for example, the radiant of the shower will not be at the zenith; it will be around 30° above the horizon at midnight, and 45° above the eastern horizon at 2am.

Assuming a clear night, the other factor is the limiting magnitude of the sky, a measure of the faintest object you can see. Man-made light pollution will be an issue for most people. From suburbia the limiting magnitude of the sky is ~4.5 (around 500 stars visible), so you will only be able to see meteors that are at least this bright; the fainter ones wouldn’t be visible through the orange glow. In a big city centre your limiting magnitude might be ~3 (only around 50 stars visible); in a very dark site like Galloway Forest Dark Sky Park the limiting magnitude is ~6.5 (many thousands of stars visible), limited only by the sensitivity of your eye. So in most cases it’s best to try and get somewhere nice and dark, away from man-made light pollution.

The calculation that you need to make in order to determine your actual hourly rate is:

Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Let’s plug the numbers in for the Persieds 2012.

ZHR = 100 at 1200 on Sunday 12 August 2012, but by 0001 on Monday 13 August, ZHR might be down to 50 say, maybe less.

h = 30° at 0001, 45° at 0200, 60° at 0400

k = 0 (let’s hope!)

m = 6.5 (assuming you can get somewhere dark).

So your actual hourly rate at 0200 under clear dark skies is

(50 x sin(30))/((1/(1-0) x 2^(6.5-6.5) = 25 meteors per hour at 0001 Monday 13 August
(50 x sin(45))/((1/(1-0) x 2^(6.5-6.5) = 35 meteors per hour at 0200 Monday 13 August
(50 x sin(60))/((1/(1-0) x 2^(6.5-6.5) = 45 meteors per hour at 0400 Monday 13 August

Remember though that these numbers might be lower if the ZHR drops off after the daytime peak.

It is of course worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

You can keep track of the increasing ZHR at the International Meteor Organisation website.

*UT = Universal Time = GMT, so for UK times (BST) add one hour to these

Curiosity

In the early morning hours (UK time) of Monday 6 August, NASA’s latest Mars rover, the Mars Science Laboratory, or Curiosity to its friends, will land on the red planet after an eight month journey from Earth.

The Mars Science Laboratory, Curiosity

Curiosity is the largest rover ever sent to Mars – it’s about the size of a Mini – and has a huge array if scientific instruments, which will enable it to complete its science missions: to determine if Mars could ever have supported life; to study Mars’ geology; to study Mars’ climate; to plan for a human mission to Mars.

Curiosity will touch down on Mars after a not-entirely-risk-free landing procedure, which uses a heat shield, parachute, engine, and sky crane, a system by which the lander separates from the sky crane, attached by a tether. The sky crane will use its engines to slow it down to almost a dead-stop, and lower the rover gently onto the surface of Mars.

If you want to watch the landing live, NASA and others are streaming it live. Landing is scheduled for 0631 BST, so you’ll have to tune in a bit before that to watch the whole process. You can also follow Curiosity on Twitter.

And if you want to see the red planet yourself, it’s visible low in the west just after sunset, forming a beautiful triangle with Saturn and Spica, the brightest star in the constellation of Virgo. Mars is the right-hand most of the three bright points of light. You’ll only just catch a glimpse of Mars after the sky darkens enough for it to appear, and before it sets around 2245 BST.

Perseids Meteor Shower 2011

This month sees the most reliable meteor shower of the year; the Perseids. You can begin watching for Perseid meteors now, and the shower will last until mid-August, but the peak of the shower occurs in the small hours of Saturday 13 August 2011.

Perseus under dark skies

Perseus under moonlit skies

Unfortunately this year’s shower will be obscured by the full Moon which occurs on the same day, and so it won’t present its usual excellent display.

The number of meteors that you will observe every hour depends on a number of factors:

• the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
• the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
• the fraction of your sky that is obscured by cloud;
• the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.

The Perseid meteor shower has a zenith hourly rate (ZHR) of between 50 and 200. This is the number of meteors that you can expect to see if the radiant is directly overhead (the point in the sky called the zenith), and you are observing under a cloudless sky with no trace of light pollution.

However conditions are rarely that perfect. In the UK, for example, the radiant of the shower will not be at the zenith. Observing from Glasgow, as I will be, the radiant will be around 60° above the eastern horizon at 2am. (In the far south of the UK it will be a few degrees lower, and in the far north a couple of degrees higher).

Assuming a clear night, the other factor is the limiting magnitude of the sky, a measure of the faintest object you can see. Even if the Moon were not in the sky, man-made light pollution would be an issue for most people. From my garden the limiting magnitude of the sky is ~4.5 (around 500 stars visible), so I will only be able to see meteors that are at least this bright; the fainter ones wouldn’t be visible through the orange glow.

In a big city centre your limiting magnitude might be ~3 (only around 50 stars visible); in a very dark site like Galloway Forest Dark Sky Park the limiting magnitude is ~6.5 (many thousands of stars visible), limited only by the sensitivity of your eye. So in most cases it’s best to try and get somewhere nice and dark, away from man-made light pollution.

However a full Moon introduces natural light pollution that can be as bad the man-made glare in a city centre, with a limiting magnitude of ~3 (it is hard to estimate what the limiting magnitude will be exactly, but this is a decent estimate).

The calculation that you need to make in order to determine your actual hourly rate is:

Actual Hourly Rate = (ZHR x sin(h))/((1/(1-k)) x 2^(6.5-m)) where

h = the height of the radiant above the horizon

k = fraction of the sky covered in cloud

m = limiting magnitude

Let’s plug the numbers in for the Persieds 2011.

ZHR = 100, say (might be as low as 50 or as high as 200, so our final answer might be out by a factor of two in either direction)

h = 60°

k = 0 (let’s hope!)

m = 3 (for the full Moon)

So your actual hourly rate under clear skies is

(100 x sin(60))/((1/(1-0) x 2^(6.5-3) = 7.7, or 8 meteors per hour. This might be out by a factor of two, so you might see as few as 4 per hour, or as many as 16 per hour.

If the full Moon wasn’t present we might expect somewhere around 80 meteors per hour.

So, this might be a poor show compared to moonless Perseids displays, but you will still still see plenty of shooting stars if you’re out for a few hours around the peak time (between 2200 UT* on 12 August and 0300 UT* on 13 August 2011).

It is of course worthwhile having a look on the days leading up to the peak, when the numbers of meteors will be gradually increasing towards this rate.

You can keep track of the increasing ZHR at the International Meteor Organisation website.

*UT = Universal Time = GMT, so for UK times (BST) add one hour to these