Archive for the ‘Observing’ Category

Near and far

Posted: February 23, 2013 in Deepsky, Imaging, Minor Planets, Observing

I’m a little late posting this but I did manage to get a picture of asteroid 2012 DA14 during last weeks close approach.

The evening started clear but clouded over just as me and few other friends from NASTRO were arriving at Hauxley Nature Reserve.  I got polar aligned with the 80mm refractor through occasional gaps in the cloud so that when the sky did begin to clear at around 8.30pm I was able to find the asteroid fairly quickly.

A point of light drifting through the stars in the eyepiece.  It was easily discernible motion at low magnification.  I put the camera in place and took this one minute exposure:

2012DA14

The moving asteroid shows up as a line because of the long exposure.  Then the clouds returned so I felt very happy to have seen anything at all!

2012DA14 ranks as one of the closest astronomical objects I’ve taken pictures of….only spaceweather like the aurora, noctilucent clouds or ISS are closer.  Later that evening I had a go at imaging something much more distant….in fact, it’s the furthest object I’ve ever tried to take a picture of!  Here it is:

3C273

It looks like a star but is really a quasar (and that’s why these objects were initially named Quasi-Stellar Objects) but it is actually the active nucleus of a very distant galaxy.  3C-273 is a mind crushing 2.4 billion light-years away in the constellation Virgo.  That’s about 1,000 times further away than the Andromeda Galaxy.  This quasar is the brightest in the entire sky and one of the nearest to us.  Quasars were more prevalent in the early universe and are an indication how violent the processes at work in the centres of galaxies can be!  Material is falling into a supermassive blackhole and getting shredded and heated in the surrounding accretion disk.  The energy released, in the form of light and other radiation is beamed outwards and we happen to be looking down the beam. Rather like seeing a lighthouse beam sweeping past us.

Checking on my astronomy software…I noticed that another asteroid, called Hera, was also in the frame.  Hera is a foreground object – just under 200 million miles away in the asteroid belt between Mars and Jupiter.

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Chasing an asteroid

Posted: February 14, 2013 in Minor Planets, NASTRO, Observing
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On Friday an asteroid, named 2012DA14, with a mass of about 190,000 tons will zip past the Earth.  For a brief time it will be even closer than the ring of satellites broadcasting weather images and TV signals around the globe.  NASA has great background information and simulations of the event.

2012DA14Flyby

Prior to closest approach 2012 DA14 will be best seen from the southern hemisphere.  The orbit brings the asteroid towards us from beneath the south pole of the planet.  2012 DA14 is expected to be at its closest to Earth – just 27,700 km (17,200 miles) above the surface – at 1924UT (7.26pm GMT).

There is no danger of a collision with the Earth or any satellites.  But amateur astronomers around the world will be trying to catch a glimpse of this rocky visitor near the time of its closest approach.  I’m one of those astronomers hoping for a clear sky on Friday evening so I’ve spent a bit of time preparing myself for the event.

I’m going to try to view the asteroid from Northumberland and at the moment of close approach 2012 DA14 will be below the horizon.  But it is moving very rapidly through the sky and will rise above the horizon in Northumberland at about 25 minutes later.

Here is a chart generated with SkyTools 3 showing the path of 2012 DA14 after it rises in Northumberland on the evening of Friday February 15th.  Note that the times given in the following star charts may be in error by several minutes – the orbit of the asteroid is not precisely determined enough to make timings without giving that caveat.

Asteroid_2012_DA14

To observe the asteroid I’m going to use a small telescope – an 80mm refractor – and choose a part of the sky that I know the asteroid will pass through.  I’ll start looking about 15 minutes before the asteroid is due to arrive at that spot.

The asteroid, predicted to have a brightness of around 7th magnitude at 8pm (just visible with binoculars) will be in the constellation Virgo, close to the border with Leo.  From Hauxley, it probably won’t be possible to see it until it is good altitude above the horizon.  I think I’ll be able to pick it up visually with the 80mm telescope at about 8.20pm as it cruises past the large scattering of stars in Coma Berenices called Collinder 256.  At that time, the asteroid will be tracking across the sky at 37 arcseconds per second.  In other words, it will cover a distance in the sky just smaller than the size of Jupiter every second.  Definitely detectable against the background stars.

By 8.40pm the asteroid will be passing the constellation Canes Venatici – just beneath the familiar seven stars of The Plough.  Larger telescopes will see it tumble past the Silver Needle galaxy (NGC4244) – an edgeways on spiral galaxy glowing at 10th magnitude.  At 9.04pm the asteroid passes close to another galaxy in Canes Venatici;  M106 is a spiral galaxy whose elongated glow will be visible with medium sized telescopes fairly easily.  By this time the asteroid will be shining at 9th magnitude and fading as it recedes from Earth.

After 9.15pm the asteroid is seen against the familiar backdrop of The Plough – probably the most recognisable pattern of stars in our northern sky.  The chart below shows the trajectory of asteroid during a 45 minute period when it should be easier for novice astronomers to locate.

2012da14_plough

At 9.34pm the asteroid passes between two bright stars of The Plough – Alioth and Phad.  This might be the easiest opportunity for inexperienced astronomers to find the asteroid with a telescope.  Although dimmer by a factor of 2 compared to closest approach, it will be much easier to detect with UK based telescopes because it is much higher in the eastern sky.

By 10pm the asteroid is shining at 10th magnitude and travelling across the sky just one-third as fast as it was a couple of hours earlier.    While it remains an easy target for larger telescopes it will continue to slow (relative to the background sky) and fade.  The final chart shows 2012 DA14 as it heads towards Polaris and the north celestial pole of the sky during the early hours of the 16th.

2012da14_draco

Here’s hoping for clear skies, no technical problems with the ‘scope and a hot pizza on a cold night!

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.

The Sun broke through the clouds late this afternoon and I was able to snap about a dozen images of the Sun through the PST before it disappeared.  Without further ado this is what I ended up with after processing several of the best images:

Here are some of my initial thoughts about the PST after one day of use. Well, about 30 minutes of use in total:

  • Focussing is a bit difficult – small image with the supplied eyepiece.  Trying to make the edge of the Sun as sharp as possible but small disk size makes it hard to tell when you’re there! Also, looking at a purely monochrome image takes getting used to.
  • First view through the eyepiece was startling: prominences all around the edge of the disk with one particularly large one.  Sunspots, prominences, filaments and plage visible on the disk.  A wealth of detail – more than is seen in the picture and very sharp when focus is perfect.
  • Disappointed that the PST couldn’t bring an image to focus in the Nikon D80 using the same adaptor/setup I have on my other telescopes.  In the end I dismantled a 2x barlow and plugged it into the T-adaptor.  That moved the focus far enough back and made the image bigger on the chip.
  • The pictures I took showed non-uniform illumination across the solar disk – depending on where the Sun was in the field of view.  Not so noticeable through the eyepiece but it means that several images (at least) with the Sun at different places in the FOV must be stacked to reduce the effect.

Again, I’m hoping for better weather tomorrow…

First light for the PST

Posted: June 16, 2012 in Observing, Sun

There was enough Sun shining through gaps in the cloud to get glimpses of it through my new Coronado Personal Solar Telescope (PST).  Despite the wobbly camera tripod and the interfering clouds, the view was fantastic!  So much detail was visible on the surface of the Sun and there was an incredible prominence visible on the edge of the disk. It sort of resembled an anteater walking along the edge of Sun!

I’d hoped to get some pictures but I quickly realised that my normal method for attaching camera to telescope wasn’t going to work – the focus range of the telescope wasn’t enough to bring the image to focus in the camera.  Think I’ve got a better system sorted now….but it’s raining again.  Maybe tomorrow.

The Northern Crown

Posted: June 9, 2012 in Astrobites, Observing, Stars

The short nights of late spring don’t give much time to do astronomy.  Despite this there are some interesting constellations to be explored!  One of my favourites is Corona Borealis – the Northern Crown.  At this time of the year it is high in the southern sky when it gets dark.  If you’ve not seen this little constellation before, well, it’s easy to find by star hopping from The Plough to the brilliant orange star Arcturus and then onto Corona Borealis.  Like this:

It an easily recognisable constellation – just a small semi-circle of stars.  And one of the few that actually resembles the object it is meant to represent:

The brightest star in the constellation is called Alphekka (or Gemma).  It’s a second magnitude star about 75 light-years away.  Alphekka is an eclipsing binary star and it falls  *very*  slightly in brightness every 17 days as its unseen companion star eclipses it.

The Northern Crown is well known to astronomers for a couple of its odd variable stars!  The first is known as T Corona Borealis, or more informally, The Blaze Star.  It is normally invisible to the unaided eye but it erupted dramatically in 1866 and 1946, becoming the brightest star in the constellation.  The Blaze Star is a recurrent nova; a white dwarf star being fed gaseous material by a red giant companion.

A critical point is aperiodically reached and the material ignites in a thermonuclear explosion visible from Earth.  After a few months the star has returned to its usual dim self.

The second oddball star is called R Corona Borealis (it doesn’t have a more exciting name).  Binoculars or a telescope are needed to see the star because it usually hovers on the border of naked eye visibility at magnitude 6.  At irregular intervals of months or years this star dramatically fades by a factor of 30  – requiring a very big telescope to see.  The best model to explain the unusual behaviour of the star suggests that carbon dust (soot!) builds up in the star’s atmosphere preventing light getting out and causing it to fade.  On the inside of the star the radiation cannot escape and the pressure rises until the carbon dust is blown out again causing the star to return, albeit temporarily, to normal brightness.

I downloaded a more detailed finder chart from the AAVSO showing the location of R CrB:

The numbers next to the stars are actually brightness labels (so 46 means magnitude +4.6).  Naked eye limit from a dark sky are those labelled with numbers less than about 65.  Here’s a light curve showing how the light from the star has brightened and dimmed over the last 20 years:

R CrB tumbled in brightness in 2007 and has been hovering near minimum brightness since.  The star will eventually recover dramatically – will it be in the next few weeks or months?  Time will tell so watch out!

This is the second in a series of articles I’m posting about the transit of Venus on June 6th.  In this one I’ll discuss the 2012 transit and about my plans to observe it from Druridge Bay beach in Northumberland.  I’d hoped to do an article about the history of these events and their impact on astronomy….but I’ve been too busy preparing my telescopes and cameras for this one!

On June 6th the planet Venus, which has adorned the evening sky all year, will slip directly between the Earth and Sun.  For a period of more than six hours Venus will appear silhouetted against the Sun for many observers around the world.  The conditions for seeing a transit are simple: it must be daytime for at least part of the transit.  Here’s a map showing viewing prospects for transit for observers around the world:

At a glance you can see that the UK doesn’t get the best view of transit; we’ll see the end stages just after sunrise on the 6th.  The following picture is a simulation of how the transit may look shortly after sunrise:

The time of sunrise will vary by a few minutes across Northumberland; the further east and north you are the better.  At Druridge Bay sunrise is at 4.28am on the morning of the transit.  The beach is good place to view the transit because the horizon is as low as possible and duration of the transit is maximised.

A clear view of the horizon is essential because any intervening geography may delay sunrise significantly (remember – we only get about 85 minutes of the transit at best from this part of the world!)  NASTRO members are planning to meet at the northern end of Druridge Bay, near Hadston Scaurs, to watch the transit.

Observing the transit will demand the same kind of precautions that are needed for normal solar observation.  Binoculars, telescopes and cameras should be filtered properly to prevent heat damage to the optics (and more importantly – to prevent serious eye damage).  One complicating factor is that at sunrise the light of the Sun may be significantly dimmed by our atmosphere.  This could make it difficult to see the Sun, initially, through filtered instruments.  However, it is still dangerous to stare at the Sun – even if it seems comfortable to do so.  The Sun will brighten rapidly as it climbs higher in the sky.

It’s probably safer to view with experienced observers at your local astronomy club.  In the UK you could take a look at the list of member societies at the Federation of Astronomical Societies to see there are any public observing sessions to attend.

I’ve spent a number of hours in recent weeks getting used to setting up and doing solar astronomy with various telescopes.  I know which eyepieces will give good views of entire Sun or just a small region.  I’ve practised taking pictures with the Nikon D80 on different telescopes with various Barlow lenses and know whether I can focus properly in a given setup and the approximate exposure and other camera settings needed.  All this to minimise wasted time on the morning.  My plan for the transit is as follows.

3.00   Still twilight and reasonably dark.  Get set up: polar align telescopes and other equipment checks.

4.28   Sunrise.  Transit begins!

4.30 – 5.30 Take pictures, watch through the eyepiece.  Appreciate this historic astronomical event unfolding!

5.30   Watch for black drop effect.

5.36   Egress.  Venus begins to leave the solar disk.

5.34 – 5.54   Watch for refraction effects in the atmosphere of Venus.

5.54   Transit ends.

Obviously merely seeing any part of the transit and I’ll consider the day to be a major success.  If I can get pictures of the black drop effect or any images which show the atmosphere of Venus then I’ll be over the moon (or Venus)!

When everything is over, by 6am, we’ll pack up and head to The Trap Inn for a full English breakfast and the probably home.  But not to bed.  A day of image processing and watching pictures from around the world begin to stream in from the internet….

The final part of this series will either be a very short angry tirade about the British weather, or a comprehensive image gallery from our observing session at the beach.  Time will tell.