Archive for the ‘Planets’ Category

Here’s a brief run down of where the planets are going to be in July.  Check out my planetary elongation chart to see when conjunctions are going to happen in 2012.

The Moon

The principal phases of the moon this month are:

Full moon

Last quarter

New moon

First quarter

 July 5th  July 11th  July 19th  July 26th
The Planets

Mercury is an evening sky object and it reaches greatest elongation east of the Sun on July 1st at 26°E.  However, it sets shortly after sunset so is not likely to be seen by UK astronomers.

Venus is a brilliant object, at magnitude -4.5, in the morning sky among the stars of Taurus.  During the first week of July it lies not far from Jupiter and the Hyades star cluster.  Telescopes show Venus to be a waxing crescent and the angular diameter is decreasing as the planet recedes from Earth.

Looking northeast on July 7th at 3.10am. Aldebaran, Venus, Jupiter and the Pleiades make an almost perfect line in the sky.

Earth is at aphelion – the furthest distance from the Sun of the year – on July 5th.  The distance between our planet and the Sun will be just over 94½ million miles that day.

Mars is an evening sky object in the constellation Virgo.  The Red Planet is a fading first magnitude star and it is visible low in the western sky for a few hours after twilight has fallen.  Mars is now so distant that high magnifications on well collimated telescopes will be required to see the gibbous disk of the planet.

Jupiter is shining at magnitude -2.1 in the morning sky before dawn.  It will rise a little earlier each successive morning.  Look for Jupiter near the northeast horizon near the more brilliant Venus.  On the morning of July 15th the Moon will pass very close to Jupiter.  From the south of England the moon will graze [PDF] or completely cover the distant planet.  From Northumberland we’ll get the kind of view shown below.

Crescent moon and Jupiter at 3.10am on July 15th as seen from Northumberland.

Saturn is visible in the evening sky, in the west, for a few hours after dark.  Saturn is marginally brighter than Mars, also in the constellation Virgo.  Saturn is to be found 5 degrees north of Spica, the brightest star in Virgo and about the same magnitude as Saturn.

Uranus and Neptune are best seen in the morning sky.  Uranus shines like a star of magnitude +5.8 in the constellation Pisces.  From exceptionally dark skies Uranus is a naked eye object for keen sighted observers.  Binoculars will show it easily enough.  Neptune resides in the constellation Aquarius and telescopes are required to see this 8th magnitude planet.  The positions of both worlds are shown in the chart below:

Positions of Uranus and Neptune at 2am on July 15th 2012.


Summer astronomy

Posted: June 13, 2012 in Imaging, Planets, Sun

The summer solstice approaches and dark nights have all but vanished from Northumberland.  It seemed like I was just getting into deep sky imaging and now I’m waiting for the autumn to come so I can get back to it.  Realistically, I’ve got a couple of months before I’ll be doing that kind of imaging again.  With that in mind I’ve deferred getting an autoguider (and new finderscope) in order to get a solar telescope.  While I’m waiting for that to be delivered I took the chance to get some ‘white light’ images this afternoon.

Here is a composite of two images taken through the NexStar 102SLT (and 2x Barlow) filtered with Baader film.

Some very prominent groups of sunspots today.  I hope they’re still there when I get my PST in the next day or two!

After getting some solar images I had an attempt at finding Venus.  With the HEQ5 mount not accurately polar aligned it’s not that easy.  My method was to find the difference in altitude and azimuth from the Sun then slew the telescope to the approximate place.  Skymap Pro told me to move the telescope 9 degrees lower and 10 degrees right of the Sun.

Here’s a star chart showing the location of Venus this afternoon.  With an elongation nearly 12 degrees west of the Sun the planet was far enough to safely observe without taking steps to block out sunlight falling into the telescope tube.  Here’s a Stellarium rendition of the afternoon sky.

The real sky was much cloudier – lots of slow-moving patchy cloud.  After a gap appeared in the clouds Venus was easily visible in the camera field of view.  Venus is currently very narrow crescent – shimmering through what was obviously very unsteady air.  There followed a frustrating hour in which switching between eyepiece and camera was thwarted by the ever shifting clouds.  Eventually I had Venus in the field of view with the camera and 2x Barlow lens.  I began clicking away on the remote…

This is a stack of 33 images taken with the Nikon D80 through the NexStar 102SLT (and 2x Barlow) at ISO100 and 1/250s exposure.  Stacked in Registax 5 and post processed with GIMP.

Now that Venus is west of the Sun it will soon be a prominent morning sky object before sunrise.  As it recedes from Earth the angular size will grow smaller and the phase will increase.

It seems that you can do astronomy in the summer – you just have to change your targets, that’s all 🙂

As I mentioned in a previous post, transits of Venus across the Sun are very rare events.  Mercury can also transit the Sun too – about a dozen times a century on average.  I saw a transit of Mercury on May 7th 2003.  This was the view through my 10 inch telescope;

There’s a sunspot just above the centre of the disk.  Mercury is the tiny speck towards the top.  This picture was one of many taken using a basic digital camera held at the eyepiece of the telescope.  I found the images on an old CD-ROM the other day and had a go at reprocessing them.  The telescope was filtered with a Baader filter paper and the orange colour was added later – an aesthetic choice.

Here’s a zoomed in image showing Mercury a bit more clearly:

The first version I did of this picture actually got published in a journal of the Association of Lunar and Planetary Observers.  Mercury is a small rock about 3,000 miles across and 52 million miles away.  The Sun is about 865,000 miles across and about 42 million miles behind Mercury.  Being so small are far away means that Mercury is a tiny speck against the brilliant Sun – about 1/5th of the apparent size of Venus during a transit.

How do you take images like this?  Well this was my method.

I think I’m under there with a camera!  The next transit of Mercury will be visible from the UK.  It will happen on May 9th 2016.

Venus has been a fixture, or so it seems, in the evening sky since the start of the year.  This superb evening apparition has seen the planet in some beautiful alignments with Jupiter, the Moon and Pleiades.  Only a month ago it was shining brilliantly in the evening sky until well after midnight for UK astronomers.

In recent weeks Venus has been getting lower in the evening sky – setting earlier and earlier – and in a week or so it’ll be very tough to spot in the evening twilight.  This is how the inner planets of the solar system stood yesterday:

As seen from Earth, Venus is almost in the same direction as the Sun.  In the coming days Venus will continue to swing between the Earth and Sun.  I took this picture of Venus last night with my 8 inch Meade LX10 telescope:

Only a very narrow sliver of the planet is visible.  Not surprising, as Venus is now almost between the Earth and Sun so that it’s the far hemisphere of the planet getting illuminated.  You can see from the orbit diagram that Venus is almost at its closest possible distance from us; the picture above was taken when Venus was just over 30 million miles away.  Through a telescope eyepiece it’s now bigger than any other planet can be.  The crescent was fairly easily seen in my 7×50 binoculars!

Venus will continue to draw closer to the Sun and will pass between the Earth and Sun on June 5th/6th.  Astronomers call this type of alignment an inferior conjunction.  As you may already know, the inferior conjunction on that date will be very special: Venus will be seen by many around the world to be silhouetted against the Sun in an event called a transit.

More about that very soon….

Venus and Jupiter have been converging in the early evening sky for the last few months.  Venus has been climbing higher into the evening sky, whilst Jupiter has been drawing closer to the fading twilight in the western sky at dusk.  At present they shine close together in the evening sky at mid-latitudes for more than four hours after sunset.  Here’s a picture I took the other night from near Alnwick, Northumberland:

On March 13th the pair will be at their nearest to each other in the sky – a spectacular sight.  It’s hard to visualise the solar system in 3D when you see a scene like this.  Here’s a picture of the solar system as seen from above; it depicts the positions of the planets on March 13th 2012 when the planets are at their closest together in the sky.

Venus will be 121 million km from Earth and Jupiter is more than six times that distance further away at 842 million km.  Venus appears brighter not only because it is nearer to us, but also because it is enshrouded with a dense atmosphere with very reflective cloud tops.  Also, notice another alignment.  The planet Mars is almost directly on the other side of the Earth to the Sun.  I wrote about that earlier.

As seen from Earth, the planets Venus and Jupiter will be almost perfectly lined up and we observe them to be in the same direction in the night sky.  The alignment isn’t perfect and Venus will not pass directly in front of Jupiter.  At their closest there will still be a gap of sky with an angular size of three degrees.  You could fit three full moons into that gap on the sky!

On March 13th at around 7.30pm the western night sky will look like this:

Venus glides to the north of Jupiter (above).  The magenta lines show orbits that both planets follow around the Sun and they also show why the alignment isn’t perfect.  First, to explain the differing shapes of the orbits that you see above.  Jupiter’s orbit around the Sun is five times wider than the Earth’s orbit and so we are inside it looking out; it wraps completely around the sky so we’re just seeing a small section of it here.  Venus, on the other hand, has its orbit inside the Earth’s orbit.  We can see the entire orbit in the same direction as the Sun.  In the evening sky scene above, the Sun has just dipped below the western horizon and so we see that part of the orbit to the east of the Sun.

So why doesn’t the orbit of Venus look like a line in the sky?  I mean that’s what we might expect if we see a circular orbit from the side!  Although the solar system is approximately disk shaped when viewed from the side….the orbits are not perfectly aligned with each other.  In most cases the orbits are tilted very slightly to each other (just a degree or so) so that most of the time the planets appear to be strung out on a line across the sky called the ecliptic.  But when they get close together then the tiny little differences in the tilt of the orbits becomes more noticeable.  The tilt of the orbit of Venus is particularly obvious because it’s also the nearest planet to us at times.  So in the picture above we’re looking at the circular orbit of Venus – not from edgeways on – but from slightly underneath.

Date of the conjunction

When two planets are close together in the sky the event is often called a conjunction.  Depending on where you look you’ll find the date of the Jupiter-Venus conjunction listed as March 15th despite the planets being closest together in the sky on March 13th.  Why the difference?  Astronomers have different definitions of conjunction! Two planets are in conjunction when they have the same longitude on the celestial sphere.  Using equatorial coordinates, this means they must have the same Right Ascension.

Here’s a map of the sky (thanks to SkyMap Pro) showing the positions of the planets at closest approach at 10.25pm (GMT) on March 13th.

The vertical lines represent Right Ascension.  Although they are at their closest on the 13th the planets are at different Right Ascensions.  Here is the actual conjunction in Right Ascension:

This map shows the positions on March 15th at 10.37am; both planets are on the same Right Ascension line – the conjunction!  They are a little further apart by this time but the difference is tiny.

On a final note, just as the tilt of the moons orbit around the Earth doesn’t stop eclipses happening – just makes them rarer – then so the alignment of the planets can also occasionally be perfect.  On January 3rd 1818 Venus actually transited in front of the planet Jupiter.  Imagine the view through a telescope!

The next event like this will also involve Venus and Jupiter again but won’t happen until November 22nd 2065 and will much more difficult to observe (aside from the practicalities of being alive on that date!)

Saturday night planets

Posted: March 4, 2012 in Imaging, Planets

Mars was at opposition yesterday – it was directly opposite the Sun in the sky.  This event means that the the Sun, Earth and Mars are lined up and the distance to Mars is at a minimum.  Unfortunately the opposition of 2012 occurs when Mars is almost at its furthest possible distance from the Sun!  You can see this in the following diagram:

The oppositions from 2014 to 2025 will all have Mars closer to the Earth.  Yesterday, the distance to Mars was 101 million km (about 63 million miles).  Mars looks tiny through a telescope and it takes a lot of magnification and steady atmospheric seeing to see any surface detail.  Last night I could just about make out the north polar cap – looking like a little white spot – but not much else.  It’s a lot easier to bring out detail using a CCD camera.  Here is my attempt from last night:

The polar cap is visible with a dark feature just below it.  That linear feature in the southern hemisphere is Mare Cimmerium.  I noticed after the image was taken that the corrector plate on the telescope had dewed up – it was amazing I was able to get anything.  I’ll return to this for a better picture as soon as I can!

Earlier on I snapped Venus with the same setup.  Here’s the picture:

 The distance to Venus was 0.89 AU (133 million km) and the angular size was 19 arcseconds.  The phase was gibbous 63%.  No surface details, obviously, because the planet is permanently enshrouded with a dense atmosphere of opaque clouds.  Venus will continue to blaze in the evening sky over the next few months and it’ll grow larger in size as the distance between Earth and Venus closes up.  That almost-half Venus will grow into a magnificent crescent – large enough to be seen with binoculars.

Dancing Planets

Posted: February 28, 2012 in Alignments, Imaging, Planets

It’s been an interesting week for observing the moon and planets.  In the evening sky Venus and Jupiter have been on show for ages but the gap between them is rapidly closing up.  They were joined by the crescent moon late last week – it skipped past the planets over successive evenings.

On Friday Feb 24th after sunset I captured this picture from Barrowburn Camping Barn in the Coquet Valley among the Cheviot Hills.

It was a fantastic, clear night (mostly) and very dark compared to my usual observing site at Hauxley.  Saturday night was mostly cloudy but there were enough gaps in the cloud to get some more pictures.  The moon had climbed higher into the sky and was sat next to Venus.  The proximity of the two meant that it was relatively easy to spot Venus a couple of hours before sunset! 

Here’s a closer view of the crescent moon with Venus taken through a Skywatcher 80mm refractor with the camera at prime focus.

The moon’s distance was 403,300 km. Venus was 140 million km away (about 350 times further!)  On Sunday and Monday evening it was too cloudy to see the moon as it bypassed Jupiter in the sky but tonight it was clear enough to get some more pictures.  I drove west of Morpeth – just past a little village called Mitford – and set the camera up just some patchy clouds were drifting over.  This is what I saw:

The moon will move away from this scene  but the show will go on without it.  Mercury will join these planets in the sky after sunset and the gap between Jupiter and Venus will continue to close up, reaching a minimum on March 12th/13th.

On the other side of the sky, the planet Mars is nearly at its closest to Earth.  A couple of hours after Mars clears the horizon, it is followed by the planet Saturn. It’s not often we have an evening sky filled with so many of the brightest planets so make the most of it!