Constellations-EV etc.

The Night Sky

Celestial Sphere

Celestial Sphere

- an imaginary hollow sphere around the Earth, which all objects are either attached to or move across

- has a specific shape but no specific size.

Celestial Equator

- a circle on the celestial sphere concentric with Earth’s equator

- projection of Earth’s equator onto the celestial sphere.

Ecliptic

- a circular path across the celestial sphere along which the Sun moves during the year.

- path that the Sun appears to follow across the sky when viewed from Earth

Ecliptic

Constellation

Constellation

- part of the sky containing a figure.

- group of stars that appear to form a pattern in the sky.

- 88 recognized by International Astronomy Union

Asterisms

- small distinctive groups of stars within the constellations.

- often used as a guide to other stars.

Asterisms

A. Zodiac

• band of 13 constellation along the ecliptic.

12 zodiac signs, 13 zodiac constellation

Constellation of the zodiac

- Sun passes through each one on dates very different from traditional astrological dates, partly due to precession ( Earth’s wobble)

Effects of Latitude

Effects of Latitude

Solar analemma- a graph or plot that shows the position of the Sun in the sky at a single location and at the same time of the day throughout a year.

Naming Sky Objects

• Bayer System

- 1603 by German astronomer Johann Bayer

- distinguish up to 24 stars in each constellation, labelling them with Greek letters in roughly decreasing order of brightness.

Naming Sky Objects

• Flamsteed System

- 1712 by English astronomer John Flamsteed.

- numbering stars in order of their right ascension – from west to east across each constellation.

Bayer & Flamsteed

Naming Sky Objects

Tools & Techniques

• Latitude & Longitude

- Observers at the same latitude but on opposite sides of the world see the same sky

- changing your latitude by moving north to south, new constellations appear & entire night sky becomes inverted

Angles in the Sky

• Azimuth - the direction of a celestial object from the observer, expressed as the angular distance from the north or south point of the horizon to the point at which a vertical circle passing through the object intersects the horizon.

• Zenith - the point on the celestial sphere vertically above a given position or observer.

Angles in the Sky

- position of an object in the sky is often expressed – altitude & azimuth

Measuring AltitudeTo determine an object’saltitude, stretch one armabove your head to make a90° angle with the

horizon. Then point your

other arm at the object &

judge its angle above the

horizon.

Measuring azimuth

To determine an object’s azimuth, extend one arm in the direction of due north and swing the other arm round to point at the object. East is 90°to the right;

northeast is 45°.

Angles in the Sky

Sizing things up

- smaller sizes can be measured using your hands, a method that helps you relate a map of a constellation to the real stars in the sky.

Sizing things up

Star-hopping

- Many constellations contain stars that act as pointers to other parts of the night sky.

Star-hopping

Star-hopping

Binoculars

Focusing binoculars

Focusing binoculars

Using binoculars