Getting started Martin Crow Crayford Manor House Astronomical Society

Crayford Manor House Astronomical Society  Martin Crow Crayford Manor House Astronomical Society

Aims and goals of the course An introduction to the basics of how to observe the night sky. How to use binoculars and telescopes. How to find things in the sky. The essentials of how to begin the study of astronomy. Martin Crow Crayford Manor House Astronomical Society

Definition of Astronomy Astronomy is pretty much the study of everything physical in the universe. Martin Crow Crayford Manor House Astronomical Society

Where am I? Stars: Shines by its own light. Our Sun is a star. Martin Crow Crayford Manor House Astronomical Society

Where am I? Martin Crow Crayford Manor House Astronomical Society Planets: An object that is only seen through reflected light.

Where am I? Martin Crow Crayford Manor House Astronomical Society Moons: orbit planets and are also objects that are also only seen through reflected light.

Where am I? Martin Crow Crayford Manor House Astronomical Society Asteroids: Rocky objects - orbiting debris. If you can see one like this you’re in trouble!!!

Where am I? Martin Crow Crayford Manor House Astronomical Society Comets: Icy / rocky objects – develop “tails” when in the inner Solar system. Wikipedia

Where am I? Martin Crow Crayford Manor House Astronomical Society Meteors: Dust and debris vaporising as they enter the atmosphere and commonly known as “shooting stars”.

Where am I? Martin Crow Crayford Manor House Astronomical Society Solar Systems: A star and its retinue of planets.

Where am I? Martin Crow Crayford Manor House Astronomical Society Nebula: objects that are within our own galaxy – the milky way. Julian Tworek

Martin Crow Crayford Manor House Astronomical Society Planetary Nebula: objects that are within our own galaxy – the milky way.

Where am I? Martin Crow Crayford Manor House Astronomical Society Open clusters: the are loose clusters of stars located within our galaxy.

Martin Crow Crayford Manor House Astronomical Society

Where am I? Martin Crow Crayford Manor House Astronomical Society Globular clusters: the are dense clusters of stars located around our galaxy and others.

Where am I? Martin Crow Crayford Manor House Astronomical Society Galaxies: A system of stars. The Milky Way is our Galaxy.

Where am I? Martin Crow Crayford Manor House Astronomical Society

Where am I? Martin Crow Crayford Manor House Astronomical Society Universe: Everything that we can see.

Where am I? Martin Crow Crayford Manor House Astronomical Society

Basic glossary contd. Eclipse / Occultation: When one body passes in front of another and obscures it. Parsec: Is light years or approx 206,000 A.U. You also get kilaparsec, megaparsec and gigaparsec Ecliptic: The line of apparent motion taken by the Sun across the sky. Astronomical Unit (A.U.): The mean distance from the Sun to the Earth approx km. Light Year: The distance light travels in one year approx km or approx. 63,000 A.U. Martin Crow Crayford Manor House Astronomical Society

Where am I? Basic glossary contd. Orbit: The path followed by an object due to gravitational attraction. Universal Time (U.T.): Time at the Greenwich Meridian Martin Crow Crayford Manor House Astronomical Society The Seeing: The steadiness of the atmosphere

Where am I? Martin Crow Crayford Manor House Astronomical Society Getting startedThe Mark 1 eye ball

Martin Crow Crayford Manor House Astronomical Society The eye acts like a camera and can be described in similar terms. The lens in the eye has a focal length of around 16 mm and the aperture of the pupil varies between 7 mm to 1.5 mm. This gives focal ratios from f2.3 to f11. The retina is the light detecting structure and consists of some 100,000,000 light sensitive cells of two types : rods and cones. Rod cells cover the entire retina and work well at low light levels. Cones are clustered near the optical axis of the lens and operate best at high light levels. Individual cones are optimised to responded to wavelengths of light and give us colour vision. The cones are about 2 microns in diameter and are packed to a density of about 1000 per square millimetre near the optical axis. The cones match the diffraction limit of the lens providing an angular resolution of about 80 seconds of arc at best. Away from the optical axis resolution is much lower. The peak efficiency of the rods is at 505 nm wave-length and is about 15%. The peak sensitivity of the cones is about 10% at 570 nm this corresponds, not surprisingly, to the peak intensity of the solar spectrum.

Martin Crow Crayford Manor House Astronomical Society The eye detects light by the chemical breakdown of the chemical rhodpsin. This triggers signals to be sent along nerves to the brain for it to interpret. A lot of pre- processing is done at the eye. In addition to filtering noise, the network of nerve cells pre-processes the signals generated by the light- sensing cells so as to detect edges, lines and small differences in colour. So that the signals that travel to the brain are not raw brightness data but partially processed information on the shape, size and colour of objects in the visual field.

Martin Crow Crayford Manor House Astronomical Society Dark adaption Dark adaption is the eyes natural response to very low light conditions. Full dark adaption takes between 20 – 30 minutes to attain. However, even brief exposure to white light will reset the adaption and you will need to start again. To aid seeing in the dark red light can be used as this does not destroy dark adaption. When seeing your surroundings through dark adapted eyes no colour can be perceived. Averted vision When viewing faint objects through a telescope or binoculars turning your gaze slightly to one side can help see detail that cannot be seen by looking straight ahead. This is because when dark adapted the edges of vision are more sensitive than the centre.

Martin Crow Crayford Manor House Astronomical Society Binoculars The best instrument to start doing astronomy is a pair of binoculars. They are relatively inexpensive and very easy to use. Demonstration – how to set up and use. What binoculars to buy. 10 x 50 are ideal. MagnificationObject lens The exit pupil is the diameter of the image at the eye piece of the binocular. This can be calculated by dividing the diameter of the object glass by the magnification. For example: 50 ÷ 10 = 5 mm For the most efficient use of binoculars it helps if the exit pupil match the iris Diameter of the dark adapted eye.

Where am I? Martin Crow Crayford Manor House Astronomical Society Getting to know the sky and find your way around.

Martin Crow Crayford Manor House Astronomical Society

Plough Martin Crow Crayford Manor House Astronomical Society

Plough Martin Crow Crayford Manor House Astronomical Society

Polaris Martin Crow Crayford Manor House Astronomical Society

Cassiopeia Martin Crow Crayford Manor House Astronomical Society

Where am I? Martin Crow Crayford Manor House Astronomical Society

Where am I? Martin Crow Crayford Manor House Astronomical Society