practical telescope demo evening classes week five downstairs in physics green

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Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

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Page 1: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Practical Telescope Demo

Evening Classes

Week Five

Downstairs in Physics Green

Page 2: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Telescopes

Evening Classes

Week Five

Presented by Oisín Creaner

Page 3: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Pupil

Page 4: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

The Eye at Night

The pupil widens to collect more light.

Page 5: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

The Eye at Night

7mm

Page 6: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

50mm x 50mm = 2,500mm2

7mm x 7mm = 49mm2

50mm binocularscollect 50 timesas much light asthe naked eye.

Page 7: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Aperture

Typical values are 5cm for modest binocularsto 30cm or more for large telescopes

Page 8: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Focal Length

Focal

Plane

Page 9: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

A second lens is used to re-diverge the rays.

Page 10: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

A second lens is used to re-diverge the rays.

The eyepiece is placed at the focal plane

Page 11: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Binoculars

Point and look

Adjust for each eye

Useful on land, sea or sky!

Relatively inexpensive

Page 12: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Refractors

Page 13: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Refractors - Pros & Cons

• ADVANTAGES

• Simplicity - no maintenance.

• Suitable for terrestrial viewing.

• No obstruction = high contrast.

• Sealed tube - no air currents.

• DISADVANTAGES

• Very expensive in large apertures.

• Long, heavy & uncomfortable.

• Residual chromatic aberration.

• Long f-ratios unsuitable for photography.

Page 14: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Telescopes

Evening Classes

Week Five

Presented by Oisín Creaner

Page 15: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Reflectors

Page 16: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Newtonian Reflector

Page 17: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Open-end of a reflector

Page 18: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Reflectors - Pros & Cons

ADVANTAGES • Low cost for size• No chromatic

aberration.• Compact &

ergonomic.• Short f-ratios

possible.• Optically simple.• Can be built very

large.

DISADVANTAGES • Obstruction = loss of

contrast.• Only suitable for

astronomy.• Open tube = air

currents.• Mirrors tarnish &

need re-coating.• Need maintance,

esp. collimation.• Off axis coma.

Page 19: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Schmidt-CassegrainReflector

Page 20: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Light-path in a Schmitd-Cassegrain Reflector

Page 21: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Catadioptrics - Pros & Cons

• ADVANTAGES

• Best of both worlds• Large mirrors

available• Suitable for terrestrial

viewing.• Extremely Compact• Sealed tube - no air

currents.

• DISADVANTAGES

• Can be expensive.• Obstruction = loss of

contrast.• Long f-ratios

unsuitable for photography.

Page 22: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Alt-azimuth Mount

Dobsonian

Fork

Point and shoot

Page 23: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Equatorial Mount

Manual

Motorised

GoTo

Photography

Page 24: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Eyepieces

Page 25: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Eyepieces

SWA Apparent field 82°

Plossl Apparent field 52°

Kellner Apparent field 40°

Real field = Apparent field/Magnification

Page 26: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Telescope FL Eyepiece Mag. App.field Real fieldKellner 2000mm 25mm 80x 40° 30 arc minPlossl 2000mm 25mm 80x 52° 39 arc minSWA 2000mm 25mm 80x 80° 1°

1°39 arc min30 arc

min

Page 27: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Barlow Lens

40mm - 20mm

32mm - 16mm

26mm - 13mm

20mm- 10mm

12mm - 6mm

9mm- 4.5mm

Page 28: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

What can I see?

Page 29: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

More like this

Page 30: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Appearance of Venus

(1)Inferior conjunction

(2)Greatest westernelongation

(1)

(2)

Page 31: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Detail on the moon

•Craters

•Maria

Page 32: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Deep Sky Objects

•Clusters

•Galaxies

Page 33: Practical Telescope Demo Evening Classes Week Five Downstairs in Physics Green

Thank You

www.astronomy.ie/handoutswww.stellarium.org

Useful websites