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Slide 1

Astronomy and Space Science I

Astronomy and Space Science I

Dr. Hoi-Fung Chau

and

Dr. Alex Tat-Sang Choy

Jointly Organized by

Hong Kong Space Museum

HKU Physics Department

Co-organized by

CDI of EDB

Slide 2

Astronomy and Space Science

Astronomy and Space Science

Astronomy Basics

Length, time, angles

Celestial sphere, star maps

Solar System

Orbital Motion of the Earth around the Sun

Geocentric models

Heliocentric models

Modern views

Q&A

Slide 3

Length: Power of Ten

Length: Power of Ten

Slide 4

Units of Length

Units of Length

1 ls = distance light travel in 1 second = 299792485 m ≈ 3x108 m

1 ly = distance light travels in 1 year ≈ 9.46x1015 m ≈ 1016 m

1 AU (astronomical unit) = mean distance between the Sun and Earth ≈ 1.49x1011 m

1 pc (parsec) = distance from which 1 AU extends 1 arcsec ≈ 3.26 ly ≈ 3.24x1016 m

1 Mpc = 106 pc ≈ 3.26x1022 m

Slide 5

Examples

Examples

Slide 6

Time Scales

Time Scales

Slide 7

Angles

Angles

Angles are measured in degree (°), arcmin ('), arcsec("); radians (rad, or no unit).

1° = 60' = 3600"

1 rad = 180°/π ≈ 57.3°.

Small angle approximation: angle = arc length/distance

The apparent diameter of the Sun and the Moon are about 0.5°.

Resolution limit of a 4" telescope ≈ 1".

Note: Do not confuse arcsec with inch, both use the same symbol.

Slide 8

Objects with Large Angular Sizes (roughly to scale)

Objects with Large Angular Sizes (roughly to scale)

Andromeda Galaxy (M31)

180’ x 63’.

M54, extragalatic

globular star cluster, 12’

M4, globular star cluster, 36’

Orion Nebula (M42), 85’ x 60’.

Pleiades, open star cluster, 180’.

Moon, 30’.

Sun, 30’.

Slide 9

More Examples

More Examples

Hubble Deep Field, ≈ 1.5’.

Polaris A’s apparent size = 0.002”.

Polaris A to Polaris Ab is 0.2”;

Polaris A to Polaris B is 20”;

Polaris A to Dubhe ≈ 30°.

Io, Jovian satellite, 1”.

Crab Nebula

Supernova

remnant,

6’x4’.

Ring nebula,

planetary

nebula,

1.4’ x 1’.

Slide 10

Celestial Sphere

Celestial Sphere

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