Introduction to astronomy

This page gives advice for beginners who are either thinking of buying a telescope, or have just bought one and are now wondering how to use it, and what they could see. If you’re unfamiliar with the characteristics of different types of telescope, its recommended that before buying one, either submit any queries using our Contact us page contact form, or better still come to one of our friendly meetings for advice – see our Programme page.

Buying and using a small beginner’s telescope.

Before buying a telescope, first use your eyes to familiarise yourself with the night sky over the UK. Next progress onto binoculars to learn more about the night sky with the help of this interactive planetarium that’s set to display the sky above Southport, when date and time are specified. Finally buy your telescope with characteristics that best suit the celestial objects that interest you.

The Jodrell Bank Centre for Astrophysics website provides advice on buying and using telescopes and binoculars, and 7 x 50 mm Porro prism binoculars such as these would be a good choice. Wes Stone has also created a good amateur astronomers website that includes a helpful beginners page entitled So you bought a small telescope….  (or planning to buy one), where small is defined as refractors with objective lens diameters between 50 & 90 mm, and reflectors with mirror diameters between 75 & 110 mm.  Advice is given on what features are important, e.g. a sturdy mount to minimise vibration/shaking, and what features should be discounted, e.g. unrealistically high magnification. As a rule of thumb, under typical UK seeing conditions a magnification upto 10-12 X per 10 mm (25-30 X per inch) of aperture is realistic, and with premium optics – v expensive & perfect seeing conditions – very rare in UK, upto 20 X per 10 mm (50 X per inch) may be possible. This link enables you to calculate the resultant magnification, exit pupil, and true field of view, when the aperture diameter, focal length (or focal ratio) of a telescope and eyepiece focal length and field of view are submitted. Having bought your telescope, keeping the optical surfaces of the objective lenses, mirrors, eyepieces and filters clean is important, and advice on how to do this without damaging them can be found here.

What’s up there to look at?

It’s important to appreciate that astronomical seeing conditions at any given observing location vary from night to night, and are classified by the Pickering scale that varies between 1 (v poor) and 10 (perfect). To help judge how stable the atmosphere is, click here to see 10 animated illustrations showing how increasing levels of atmospheric turbulence distort bright star images. The Atmosphere and Observing  confirms much of the UK has poor seeing conditions, so it is helpful to observe celestial objects either located towards the zenith (overhead) or approaching their meridian crossing (highest point above the horizon). The atmospheric light-paths will be at their shortest rather than their longest when they are located low in the sky nearer the horizon.

The easiest and brightest object to start observing for beginners is the moon, and this interactive lunar map should help with identifying its major features. To check current and future phases of the moon, rising and setting times, culmination, including degrees above the horizon, in the Merseyside region, click here.

The ideal time for observing planets is when they are closest to the earth (either inferior conjunction for inner planets or opposition for outer planets), and conversely the worst time is when they are furthest away (either superior conjunction for inner planets or conjunction for outer planets). position of planetsThe diagram illustrates the key relationships of the planets wrt the earth (Image Credit: Wmheric), and this link shows their current positions in the solar system.

For all celestial objects of interest in the Northern night sky during the moth, see Jodrell Bank’s Centre for Astrophysics The night sky this month page compiled by Ian Morison. Wes Stone’s  website also has page links listing what one can expect to see, such as planets, the moon, together with catalogues of suitable double stars (all potentially separable with a good 60 mm refractor), and brighter dark sky objects, especially open star cluster that are easier to recognise through small aperture telescopes. For observing dark sky objects it must be stressed they are generally dim and extended compared with stars and planets, so telescopes with a larger aperture are better, and a 150 mm f 6 Newtonian telescope would be a reasonable choice. By definition, dark sky objects are best observed under remote dark sky conditions well away from city lights.

To improve contrast and enhance surface features on planets, and with larger aperture telescopes, fainter dark sky objects, filters can be threaded onto the eyepiece. When used with smaller aperture telescopes care is needed, because these filters will to varying degrees, reduce planetary image brightness. A good choice for enhancing surface features with small aperture telescopes is the 82A light blue filter, and for larger aperture telescopes the 80A blue filter is better, and will also reduce lunar glare. For regular lunar observing a grey neutral density lunar filter is ideal, and improves contrast without introducing colour bias. For small aperture telescopes (upto 80 mm) the 25% transmission filter is preferable to the 13% transmission one, which is better suited to larger aperture telescopes. This link gives details of colour filters for observing planets, and this link describes specialist filters suitable for improving contrast and/or enhancing details of dark sky objects.

To safely observe the sun it’s important to never look directly at it through a telescope or its finderscope, binoculars, or any type of magnifying lens, because to do so will result in immediate permanent damage to your eye(s). The best, and safest way to observe the sun, is to remove the finderscope and securely place a metallised glass solar filter with a blocking factor of ~100,000 over the aperture, as this afocal photograph taken with an i-phone through a 32 mm eyepiece on a 5″ Maksutov Cassegrain telescope illustrates.

sun-through-makWith a magnification of ~ 50 or more, sunspots can be seen as the dark spots on the photo confirms, also future planetary transits can be seen, with the next transit visible in the UK being Mercury, with ingress around 12.35 pm on 12/11/2019.

Alternatively, using a refractor telescope an image of the sun can be projected onto a white card, and for best results attach a shade collar to the optical tube. Using reflectors risks generating high temperatures inside the optical tube that may damage internal components, especially with closed catadioptric designs such as Schmidt or Maksutov  Cassegrain telescopes. For this reason it’s recommended they’re only used in conjunction with a full aperture solar filter. For more information about observing the sun click here.

For information about observing intermittent events, see A Guide to the Best Meteor Showers in 2017: When, Where and How to Shoot Them for details of major active meteor showers For observing UK displays of the Aurora Borealis  (Northern Lights), visit the AuroraWatch UK  website where you can also choose to sign up to receive e-mail alerts.

What else might I need?

For a downloadable and printable night sky chart available via the Astronomy Now website, see UK Night sky chart, and for planetary co-ordinates (Declination & Right Ascension) see their Almanac. This Almanac defaults to the current date and time, and also includes options for giving details of ISS passes over the UK, transits of Jupiter’s Galilean moons, and its Giant Red Spot across its visible face. It’s well worth buying a suitable power pack for operating “GOTO” telescopes and their computerised drive systems; some also include a spotlight to help with setting up, and importantly,  a red light for reading star maps etc. without compromising your night vision, such as this one. It’s also essential to buy a good sky atlas such as Turn Left at Orion: Hundreds of Night Sky Objects to See in a Home Telescope – and How to Find Them, and for beginners a Planisphere is useful. A virtual planisphere created by the OU is available here; click the clock and set current date & time for a view of the night sky in the planisphere window, then explore the pages and drop down menus for information about objects of interest.