Observing can be as simple as looking up at the night sky, allowing your eyes to adjust, and spotting larger and brighter objects with the naked eye or with a pair of suitable binoculars (7×50 or 10×50).
The equipment you use will depend on what you want to achieve, and how well you know the night sky. Even if you don’t know the night sky well, there are a host of apps available to help you locate objects you are looking for or point at an object and identify it. As someone who does not know the night sky as well as some, my favourite app is Star Map Pro which is a full function app that allows you to intuitively explore the night sky. It is a great educational tool as well as being a very visual tool, making it excellent for use by all age groups.
Following that, you can decide on visual or astro photography:
- Visual, as the name suggests, is looking through a telescope using eye pieces of varying magnification. Newtonian telescopes are particularly good for this.
- Astro photography involves fitting a camera to the scope using suitable adaptors (T-ring etc.) to take pictures of targets rather than just looking through an eye piece. Small refractors (e.g. 80mm) are excellent starter scopes given their lack of complexity and simple setup, able to be used straight out of the box in many cases. Once you have experience, the option is to move to larger (and thus more expensive) refractors, Schmidt Cassegrain or Ritchey Chretien. The complexity rises with these latter scopes as some need more maintenance and alignment that others.
For all scopes (except the most expensive), the weight increases with size and you will need to ensure the mount you have purchased can handle the weight of the scope and its counterbalancing weights.
Magnification can be further enhanced for both visual and astro photography by using Barlow lenses which offer 2x, 3x or more magnification.
The Andromeda Galaxy, Hercules Cluster and Orion Nebula, Jupiter, Saturn, and the Moon are examples of objects that can be viewed using any of the above methods, some of them very feint in all but the clearest skies. Planets and clusters of stars are easier to see in most cases, all but the brightest nebulae (such as Orion) will be hard to spot without reasonable magnification. There are far more distant and feinter objects visible as the power of your chosen method increases.
As the earth rotates, you will find that you need to keep adjusting the scope position to keep the object in view. To combat this, you can invest in a motorised mount that tracks the object in the sky, offsetting the effect of the rotation of the Earth.
- Motorised – has motors on each axis that, once the mount is properly polar aligned, can accurately counteract the effect of the rotation of the Earth. Such system do not include computerised systems that allow you to tell the mount to go to a target, you must find the target yourself
- Goto mounts track objects as above, but also have a computerised system that, once properly polar aligned, will accurately go to any object selected using the accompanying hand set. Many astronomers (myself included) do not use the handset, preferring instead to plug a laptop into the mound and use one of the excellent software packages available to control the mount.
Setting up a motorised mount is a little more complicated, but not too bad (see the section on polar alignment for the simplest way to get results). Reasonable results can be achieved with rough polar alignment, but to get reliable results, a good polar alignment is required. Polar alignment ensures the scope is aligned to a line between the centre of the earth and a point close to the pole star (in the northern hemisphere), the point around which stars rotate. By aligning the mount along this line, the mount need only track in one direction. This, coupled with the exact location of the observing site entered as latitude and longitude, tells the guiding system exactly where the scope is, where it is pointing, and if properly aligned, a known and good start point. From here, the goto system can be given a target to slew to. Provided alignment has been accurate, the system should find the target reasonably accurately.
Further accuracy can be gained by doing a one, two or three-star alignment, the latter being the most accurate. To do a star alignment, a bright star is selected, the mount slews to that star, you then use the hand controller (or laptop in more advanced setups) to bring that start into the centre of the viewing lens (or camera if you are imaging). Once the star is in the centre, you tell the system that the star is centred by pressing the appropriate key, and then repeat for the second and third if so desired. Once complete, the mount should be accurately aligned with the current night sky meaning that any slews for the rest of the session should be accurate (as long as you do not move the mount or knock the mount in such a way that it moves on either axis – all movement must be via the motors in the mount, not manual movement in order to maintain accuracy.
Of course, for those who image with cameras rather than just viewing, there are automated options. PinPoint Astrometry works with programs like MaximDL. It uses a reference catalogue such as the Guide Star Catalogue 1.1, the coordinates of the mount and a picture taken from a camera on the mount. Using the coordinates of the mount, PinPoint then compares the star pattern in the picture to its catalogue to work out what part of the sky is being observed and give accurate coordinates. This is commonly called plate solving. For setups with no internet connection, a stand-alone plate solve can take a while, and sometimes will fail depending on the quality of the camera image being worked with. For internet connected setups, the initial plate solve is done in the cloud, giving a reasonably accurate pinpoint location, then the local PC based final plate solve gives homes in to give a very accurate plate solve. From this, the mount can be synchronised and calibrated allowing not only very accurate goto slews, but also the ability to right click on any object in the image and select ‘slew to here’ – and the mount is moved to bring that object dead centre of the image – a very useful function indeed.
In the next post, I will be looking at the mounts I have owned over the years, discussing their strengths and weaknesses. Further posts will cover the telescopes, cameras, polar alignment and remote/robotic control.