First clear night for some considerable time last night! As we get into late April, the days are getting much longer and nights shorter and lighter. Despite the early start at work in the morning I was determined to get out and do some astronomy. My plan was to get some decent pictures of the Whirlpool Galaxy. That meant getting long exposures (ideally a few minutes each, or more) which meant setting the autoguider up with the laptop.
The autoguider is a CCD camera attached to the finderscope and the telescope mount which corrects tracking errors in realtime. I hadn't set this system up in over a year; I've mostly been imaging with a small, widefield telescope so haven't needed really precise guiding until last night. I'd hoped to get around 3 hours of imaging done on the Whirlpool. What ended up happening was two hours trying to get the CCD camera talking to the laptop (a new one...with various incompatibilities and the discovery that my CCD camera is not behaving well under Windows 10!). I then managed about half and hour of great tracking...but chose the globular cluster M13 because I really needed to get some sleep by that point.
So here it is; not a disastrous end to a frustrating night. The great Hercules Globular Cluster (M13).
Technical details: Nikon D90, ISO1600 at prime focus of the Mead LX10 (200mm / 8 inch). 3x3 minutes + 1x5 minute stacked exposures.
About an hour after sunset the crescent moon and Venus were putting on a nice show over the western horizon:
The moon is 4% illuminated and is more or less between the Earth and Sun. By contrast Venus is almost on the far side of the Sun; the telescopic view shows Venus to have a gibbous (almost full) phase at the moment. Although Venus and the moon looked close together tonight - that was just a line of sight effect! The moon was just under 372 thousand km away when the picture was taken. Venus was 226 million km (more than 600 times further than the moon). Space is big :-)
This morning was the first period clear after what seems like endless days of rain, sleet and snow. I planned to get some pictures of Mars and Saturn so had to get up at 4.30am. I was set up with the telescope and camera in the garden by 5.
Here's my picture of Mars, Saturn and the globular cluster M 22 through the telescope.
Mars (lower left) and Saturn (upper middle) are the brightest objects in the picture. The little dot to the right of Saturn is actually Titan, the biggest moon. The globular cluster M22 is at lower right in the picture. M 22 is a ball of stars (about 70,000 in all) about 35,000 light-years away.
The picture was a stack of 7 x 60 second images taken with the Nikon D90, ISO800, at prime focus of the 80mm refractor. This field was only 9 degrees above the horizon so I'm pretty happy with the detail I captured.
Here's a wide field shot of the sky taken with the camera mounted on a tripod. Mars and Saturn are about 2 degrees apart and among the stars of Sagittarius.
Here's a Stellarium rendition of that part of the sky.
This is one of the best times of the year for me to capture images of Sagittarius and the Galactic Centre. When the moon gets out of the way in about a week I'm going to try to get some pictures from this region again.
Venus is climbing higher in the sky each evening. You can't miss it - it's the brightest "star" in the sky.
This chart shows the azimuth (direction measured from true north) and altitude (in degrees) of Venus above the horizon at the end of civil twilight (about 40 minutes after sunset). Here we are at the start of April and Venus is just over 10 degrees above the western horizon.
Unfortunately, this isn't going to be a great evening appearance for Venus in UK skies; it'll reach a maximum altitude in the second week of May (not quite 15 degrees) and start to drop back towards the horizon as Spring turns to Summer.
Venus reaches maximum eastern elongation on August 17th when it is 46 degrees from the Sun. From the UK, Venus is just above the horizon and visible for just a few more minutes at the end of civil twilight. This is illustrated on the star chart below; the Sun is 6 degrees below the horizon and Venus is far from the Sun in the sky, but grazing the horizon.
Observers in the southern hemisphere will be getting a great view of Venus at this point!
UK observers will have a better opportunity to see Venus later in the year when it reappears in the morning sky.
A brilliant night with my friends from BEA on Halidon Hill last night. I had my 10 inch Skywatcher Dobsonian on hand and it provided excellent views during the evening. I took this picture of the first quarter moon with the phone camera held at the eyepiece of the telescope:
A personal highlight for me was picking out Mercury from the bright twilight and getting a glimpse of the crescent phase at high magnification. Venus was nearby in the sky and glaringly bright through the telescope.
Other objects on view were the multiple star system Castor in Gemini, the Orion Nebula, the Pleiades and the galaxy pair M81 and M82 in Ursa Major. I also showed off NGC 457 (aka the E.T. Cluster) although it seems not everyone was able to join the dots to see the shape :-)
Halidon Hill is a great spot to do some observing and last night was the second time I'd been there. A great view of just about the entire sky and quite high above the lights of Berwick-upon-Tweed. Here is a picture of the southwest looking towards the Cheviots and the sky above them.
Hope to be back here for more astronomy in the future!
December arrives and so does my yearly tradition of making a planetary elongation chart for the coming year!
A PDF version can be downloaded here.
As usual the lines show positions of the planets with respect to the Sun (the angle on the sky is called elongation). Intersections between lines correspond to conjunctions in longitude and are nice events to observe with naked eye.
For example: Jupiter and Mars are near each other in the morning sky during January 2018. A conjunction occurs on the morning of January 7th with both planets in the constellation Libra.
Stellarium shows the scene at 6.30am on January 7th towards the southeastern horizon nicely. The planets are joined by a last quarter moon.
A long time since my last blog post! Busy at work, at home and studying. To calm my nerves I've been processing pictures of little bits of the heavens. Not my own images - the summer night sky is getting too bright - but data collected by various sky surveys and available online through the ESO Online Digitized Sky Survey.
A number of surveys are available and offer various degrees of sky coverage; from 45% of the sky (in blue filtered light) to 99% (in red and infrared). The web interface allows selection of a target or specific coordinates. The images can be displayed as a GIF or downloaded as GIF or FITS. The FITS file format contains a wider range of pixel intensities than GIF. I use FITS Liberator to select the best "window" to view the FITS data.
The images are scans of photographic plates taken by some very big telescopes. Many of them were obtained with the 1.2 metre UK Schmidt Telescope in Australia during the early 90s. Being scanned from the original plates means there are some interesting blemishes in some of the plates. Hairs, fingerprints and other defects can be found if you look carefully enough :-) They can, of course be photoshopped out these days!
Here is what typical GIF images look like:
There are subtle differences to the images; the blue filtered image shows the structure in the spiral arms more easily because of the hot (bluish), young stars there. The red filtered image shows the background glow of the disk - containing many more low mass, cooler (redder) stars.
These are grayscale images. To make a natural colour image we'd need an image taken with a green filter! However, no images in green were taken.
Just for fun...I wanted to see some colour images so I synthesised my own green image. This was done by averaging the pixel intensities in the red and blue images. For example, if a pixel is very bright in blue (say a value of 3000) and dimmer in red (say, 1000) then the I'd interpolate the green value to be (3000+1000)/2 = 2000. Doing this for every pixel generates a synthetic green image.
Armed with the red-green-blue (RGB) images it's a simple matter to blend the images to get a colour image:
The full res version can be viewed here. And you really should look at it! The amount of detail in the images is breathtaking.
So this has become my most recent astronomical diversion. You can see some of my other results on Flickr.
An interesting planetary conjunction for telescope users on January 12th. Brilliant Venus passes within half a degree of the distant ice giant Neptune.
The southwestern aspect of the sky, just before 7pm, looks like this:
This Stellarium rendition of the sky shows that Mars is not too far away from Venus in the sky as well. And the planet Uranus (needing at least binoculars) is high in the sky in the constellation Pisces.
Zooming in a bit on Venus to simulate the telescopic view:
Venus is 51% illuminated (very nearly half-full) and shining at magnitude -4.4. The distance to Venus is 102.1 million km. By contrast, Neptune is 45 times further away (4.6 billion km) and shining at magnitude +7.9.
It's an interesting scene to visualise on software (like Stellarium, above) but it might much more difficult to get a real picture. Venus is around 80,000 times brighter than Neptune. Exposing to capture the phase of Venus won't be long enough to capture a glimpse of Neptune. However, a greatly overexposed Venus should allow Neptune to be picked up in the same view.
The best view - if you can do it - will be with your own eye at a telescope eyepiece.
Nearly Christmas, so time for the annual planetary elongation chart!
A high quality PDF version with much more information can be downloaded here.
The planets shown are Mercury (m), Venus (V), Mars (M), Jupiter (J) and Saturn (S).
This chart shows the positions of each planet relative to the Sun (middle) all through the year. The vertical axis represents the days and months of the year. The diagonal bands represent constellation boundaries. The wavy yellow band is a region close to the Sun in which it would be difficult to observe the planets. The wavy yellow line represents regions of the sky rendered invisible because of the proximity of the Sun. The shape of that wavy line explains, for example, why Mercury is easier to observe in the March evening sky than the July evening sky (even though it is further from the Sun in July). Also, the chart behaves like a game of PacMan; any planets reaching opposition 180 degrees west of the Sun wrap straight over to the evening sky on the far left. Think of this chart as being like an unwrapped cylinder!
Places where the lines intersect are planetary conjunctions --- often beautiful (but not significant) events where the planets appear close together in the sky. There will be several notable conjunctions during the year. Details below.
The elliptical orbit of the moon means that there is one moment per lunar month when it is closest to Earth. Astronomers call this point the perigee of the orbit. The apparant size of the moon depends on how far from Earth it is, so it appears bigger in the sky at perigee.
When perigee happens at full moon then the moon is obviously bigger and brighter than full moons which don't happen at perigee. In recent years, the phrase supermoon seems to have emerged to describe this situation. It's a little crazy that this phenomenon receives the attention that it does!
Perigee sounds like an easy idea - just the smallest distance between the Earth and moon. However, the Earth and moon are spheres so distance is usually measured from the centre of Earth to the centre of the moon. If you really want to see the biggest possible full moon from the surface of the Earth then a little more investigation is needed!
My copy of SkyMap Pro software tells me that the perigee moon on November 14th 2016 occurs at 11.21am. The perigee distance (moon centre to Earth centre) is 356,509km.
At the time of perigee the moon is below the horizon in Northumberland (and the wider UK). In other words - there's nearly a whole planet Earth between Northumberland and the moon. The moon is actually around 359,000 km from Northumberland at perigee!
The situation improves if we wait a bit.
Here's a plot of the distance between Northumberland and the moon (well, the centre of the moon) over the next few days.
The varying distance is due to the fact the Earth is spinning on its axis. The Earth itself carries Northumberland towards and away from the moon once a day.
In the hours that follow the moon slowly begins to move away from perigee BUT the rotation of the Earth will carry Northumberland closer to the moon. And at a faster rate than the moon is receding. On Monday night, with the moon climbing high into the sky we get our local supermoon: at 12.10 am on Nov 15th the moon will be 351,951 km from Northumberland.
If you look at the graph you'll see there was another minimum before perigee - about 24 hours earlier. The moon was only marginally further away.
Supermoons are overhyped. The oft quoted figure of 10% larger, 30% brighter sounds significant but is very difficult to see in practice because (a) it's comparing apogee full moon with perigee full moon: you never get to see that comparison side by side, (b) the moon illusion complicates the visual appearance just after moonrise (even apogee full moons look big to some people) and (c) the transparency of the atmosphere can markedly change the brightness of the moon and an observer's perception of it!
Even the claim of "no better supermoon until 2034" fails, because the perigee distance referred to in that claim is for moon centre to Earth centre. Actually, for Northumberland (and the rest of the UK) the supermoon on January 1st 2018 will be marginally closer than this one!
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.