Some of you who have recently joined (welcome aboard!) asked me about putting together some ‘articles’ relevant to beginners astronomy. A sort of guide on jargon, phrases, terminology, things like that. As a start, I am kicking off this section with some useful information. Hopefully, readers will contribute their own thoughts and ideas.
HOW TO START
The best observing instrument, of course, are your eyes. To start, why not take up a small book about the night sky. Get familiar with the patterns of stars that make up the constellations with Star Atlas’s and Charts. It does not make much sense if you want a really big telescope in the future and not know where to point it.
Many stars make imaginary pointers to other well-known stars and celestial objects. On any clear night, simply look up: Orion’s Belt made up of 3 stars in almost a straight line; in a south-west kind of direction from this will bring you to Sirius, the brightest star in the sky; Dubhe and Mirak, the last 2 stars in the Plough’s ‘bowl’, point to Polaris, the Pole Star (celestial North); Cassiopaeia looks like a W or M, and the star clusters around it, and the radiant of the Perseids beside it. All these aides lead to bigger and better things. Like all great endeavours, you first have to start small!
As you learn more, you will want to get something to improve your observing power. If you are new to astronomy as a hobby, you will probably have been told by now that a good pair of binoculars are well worth spending your money on. They are cheap, robust, and are easy to maintain and store. A good size to start from would be 10X50’s. What does this mean? 10 is the magnification, and 50 is the size of the objective lens in millimetres. Thus, 10X50’s allow a larger field of view than 10X40’s with the same magnification. If your price range allows, go for bigger!
Get a star atlas. They come in many sizes, from the MiniGem series that fit in your pocket to almost A3 size. Many will have easy to recognise shapes and colours for the different categories of objects that can be found in a binoculars or telescope. Invest, too, in a small red flashlight. This is important because you will need to see what you are reading at a dark observing site, but not ruin your night vision. It can take your eyes about 20-25 minutes to FULLY adjust to very dark surroundings, and a normal flashlight will ruin that in a flash! A red candy wrapper sellotaped over the flashlight window is childs play.
BE PREPARED
Wrap up warm this time of year. On extremely cold nights, it is important to do so if you intend to stay out for long periods. Boots are a must, with 2 pairs of socks. 2 pairs are better than 1 because not only will they keep your feet warm from the cold ground, but also comfortable while you are standing for long periods. Sometimes 2 pairs of gloves are handy (bad pun… -Ed.). A small thin pair with the fingertips cut off for grabbing eyepieces, pencils etc, while a bigger pair to put over them to keep them warm. A woollen hat instead of a baseball cap. 2 fleeces are thin yet comfortable and warm, inside a warm coat. A scarf for the neck. If you have to wear jeans, wear them over a tracksuit pants.
Take notes when you are observing – you never know what you might see. But, use a pencil. Ink in a pen will freeze quickly, and the pen may burst too. A clipboard with some plain paper attached is ideal for writing on. Bring an easy-chair to sit on to take a break now and again. It is not good to stand and crick your neck skyward for long periods of time!
If you smoke, try not to when you are out in the cold. Smoking is a vasoconstrictor , this means it will restrict blood to your extremities, making them feel colder, quicker. Alcohol and coffee fall into the same category. Bring hot drinks in a thermos instead, like tea or even better, soup. Snacks are allowed too, but try to avoid anything greasy – getting greasy fingerprints on eyepieces etc. is not good!
If you are travelling some distance to your observing site, be prepared for the worst. You may discover you will run out of petrol/diesel and will have to stay the night! Have a sleeping bag or blanket in the car just in case. Spare batteries for your flashlight, a bottle of water (for when you’re thirsty!), and even a book to read are great companions if you get stuck somewhere till daylight comes. Above all this, remember to have the fuel can in the boot of your car topped up, and you wont have to worry at all.
As you go to lectures and observing nights, you will hear astronomers call out objects in the sky by their names or perhaps even their M numbers e.g. The Orion Nebula is also M42, the Crab Nebula is M1 etc. Don’t be distracted from hearing all these odd sounding names and numbers – as you learn more, you will remember them too!
TERMS AND PHRASES
This section just introduces to the beginner to the plethora of words, terms, and phrases you will come across in Astronomy.
Aphelion: see Orbit.
Apogee: see Orbit.
Black hole: the theoretical end-product of the total gravitational collapse of a massive star or group of stars. Crushed even smaller than the incredibly dense neutron star, the black hole may become so dense that not even light can escape its gravitational field. It has been suggested that black holes may be detectable in proximity to normal stars when they pull matter away from their visible neighbours. Strong sources of X rays in our galaxy and beyond may also indicate the presence of black holes. Recent evidence suggests that black holes are so common that they probably exist at the core of nearly all galaxies.
Conjunction: the alignment of two celestial bodies at the same celestial longitude. Conjunction of the Moon and planets is often determined with reference to the Sun. For example, Saturn is said to be in conjunction with the Sun when Saturn and the Earth are aligned on opposite sides of the Sun.
Mercury and Venus, the two planets with orbits within Earth's orbit, have two positions of conjunction. Mercury (or Venus) is said to be in inferior conjunction when the Sun and the Earth are aligned on opposite sides of Mercury (or Venus). Mercury is in superior conjunction when Mercury and the Earth are aligned on opposite sides of the Sun.
Elongation: the angular distance between two points in the sky as measured from a third point. The elongation of Mercury, for example, is the angular distance between Mercury and the Sun as measured from Earth. Planets whose orbits are outside the Earth's can have elongations between 0° and 180°. (When a planet's elongation is 0° it is at conjunction; when it is 180°, it is at opposition.) Because Mercury and Venus are within the Earth's orbit, their greatest elongations measured from the Earth are 28° and 47°, respectively.
Galaxy: gas and millions of stars held together by gravity. All that you can see in the sky (with a very few exceptions) belongs to our galaxy—a system of roughly 200 billion stars. The exceptions you can see are other galaxies. Our own galaxy, the rim of which we see as the “Milky Way,” is about 100,000 light-years in diameter and about 10,000 light-years in thickness.
Neutron star: the extremely dense spinning star that is one of the possible results when a massive star's core has imploded on itself in a supernova. Some neutron stars pulse radio waves into space as they spin; these are known as pulsars.
Occultation: the eclipse of one celestial body by another. For example, a star is occulted when the Moon passes between it and the Earth.
Opposition: the alignment of two celestial bodies when their longitude differs by 180°. Opposition of the Moon and planets is often determined with reference to the Sun. For example, Saturn is said to be at opposition when Saturn and the Sun are aligned on opposite sides of the Earth. Only the planets whose orbits lie outside the Earth's can be in opposition to the Sun.
Orbit: the path travelled by a body in space. The term comes from the Latin orbis, which means circle or circuit, and orbita, which means a rut or a wheel track. Theoretically, there are four mathematical figures, or models, of possible orbits: two are open (hyperbola and parabola) and two are closed (ellipse and circle), but in reality all closed orbits are ellipses. Ellipses can be nearly circular, as are the orbits of most planets, or very elongated, as are the orbits of most comets, but the orbit revolves around a fixed, or focal, point. In our solar system, the Sun's gravitational pull keeps the planets in their elliptical orbits; the planets hold their moons in place similarly. For planets, the point of the orbit closest to the Sun is the perihelion, and the point farthest from the Sun is the aphelion. For orbits around the Earth, the point of closest proximity is the perigee; the farthest point is the apogee. See also Retrograde.
Perigee: see Orbit.
Perihelion: see Orbit.
Planet: a celestial body in orbit around a star. Even in ancient times, it was known that a number of “stars” did not stay in the same position relative to the others. There were five such restless “stars” known—Mercury, Venus, Mars, Jupiter, and Saturn—and the Greeks referred to them as planetes, a word which means “wanderers.” That Earth is one of the planets was realized later. The additional planets were discovered after the invention of the telescope.
In 1995, several of these extrasolar planets were discovered orbiting stars similar to our Sun. Swiss astronomers found a planet orbiting star 51 in the constellation Pegasus, about 40 light-years away. It is the first planet ever discovered to circle a normal Sun-like star.
Pulsar: a source of radio waves, emitted in bursts at regular intervals. Pulsars are believed to be rapidly spinning neutron stars, so crushed by their own gravity that a million tons of their matter would hardly fill a thimble.
Quasar: “quasi-stellar” object. Originally thought to be peculiar stars in our own galaxy, quasars are now believed to be the most remote objects in the universe. Quasars emit tremendous amounts of light and microwave radiation. Recent Hubble Space Telescope images suggest that there may be a variety of mechanisms for “turning on” quasars. Although a number of images show collisions between pairs of galaxies, which could trigger the birth of quasars, some pictures reveal apparently normal, undisturbed galaxies possessing quasars.
Quasars are among the most baffling objects in the universe because of their small size and enormous energy output. Quasars are not much bigger than Earth's solar system, but pour out 100 to 1,000 times as much light as an entire galaxy containing a hundred billion stars. A quasar detected in March 2000 with a redshift of 5.8 is 12 billion light-years from Earth and is the most distant object ever observed to date.1
A super massive black hole, gobbling up stars, gas, and dust, is theorized to be the “engine” powering a quasar. Most astronomers agree that an active black hole is the only credible possibility that explains how quasars can be so compact, variable, and powerful. However, no conclusive evidence supports this assumption.
Retrograde: describes the clockwise orbit or rotation of a planet or other celestial body, which is in the direction opposite to the Earth and most celestial bodies. As viewed from a position in space north of the solar system (from some great distance above the Earth's North Pole), all the planets revolve counterclockwise around the Sun, and all but Venus, Uranus, and Pluto rotate counterclockwise on their own axes. These three planets, therefore, have retrograde motion.
Sometimes retrograde is also used to describe apparent backward motion as viewed from Earth. This motion happens when two bodies rotate at different speeds around another fixed body. For example, the planet Mars appears to be retrograde when the Earth overtakes and passes by it as they both move around the Sun.
Satellite (or moon): a body in orbit around a planet.
Star: a celestial body consisting of intensely hot gases held together by its own gravity. Stars derive their energy from nuclear reactions going on in their interiors, generating their own heat and light. Stars are very large. Our Sun, which is the nearest star, has a diameter of 865,400 mi—a comparatively small star.
A dwarf star is a small star that is of relatively low mass and average or below average luminosity. The Sun is a yellow dwarf, which is in its main sequence, or prime of life. This means that nuclear reactions of hydrogen maintain its size and temperature. By contrast, a white dwarf is near death in the life cycle of a star. White dwarfs come into being in one of two ways: either as the result of the implosion, or supernova, of a massive star, or after the collapse of a red giant.
A red giant is a star nearing the end of its life. When a star begins to lose hydrogen and burn helium instead, it gradually collapses, and its outer region begins to expand and cool. The light we see from these stars is red because of their cooler temperature.
A brown dwarf lacks the mass to generate nuclear fission like a true star, but it is also too massive and hot to be a planet. A brown dwarf usually cools into a dark, practically invisible object. The existence of brown dwarfs, was confirmed in Nov. 1995 when astronomers at Palomar Observatory in California took the first photograph of this mysterious object.
Supernova: the explosion of a star. There are two common types of supernova. Type Ia is the brighter of the two and happens when a white dwarf star draws large amounts of matter from a nearby star into itself, creating a super-powered fusion process ending in the star's collapse. The second, more well-known type, IIa, is the result of the collapse of a massive star. Massive stars are born and develop through the process of atomic fusion of hydrogen into helium, which uses and releases an immense amount of energy. The massive star's heat causes the creation of the star's dense center, made of heavier and heavier elements (even iron) as the process continues. This core of heavy elements causes there to be a gravitational force inside the star. When there isn't enough hydrogen to power the fusion any longer, the star's core collapses inward on itself, releasing a huge amount of energy (the supernova), which may be brighter than the massive star's host galaxy.
