Constellations

Patterns in the Sky The Constellation Orion

There are 88 Constellations. 12 are based on the Zodiac. Constellations: a group of stars that seem to form recognizable patterns in the sky Light-year: the distance that light travels in one year, about 9.5 x 10 to the exponent 12 There are 88 Constellations. 12 are based on the Zodiac. Orion, Leo, Aries, Taurus, etc. Asterisms: Recognizable patterns of stars that are not one of the constellations are called Asterisms: Big Dipper, Little Dipper, Summer Triangle

The Celestial Sphere

Are stars still present in the sky during the day time? Yes, we just can’t see them because their dim light is overwhelmed by the brightness of the sun during the day. Apparent magnitude = the brightness of a star as seen from Earth

The Milky Way The band of light called the “Milky Way” traces the galactic plane as it appears from our location in the outskirts of the galaxy. From: http://skyphoto.com/milky/Default.htm © Jerry Schad

The Circling Sky Earth rotates from west to east. The celestial sphere appears to rotate east to west. Apparent path of a particular star

The Dome of the Sky: Definitions in your local sky

Latitude : Measures positions north or south of the equator Latitude : Measures positions north or south of the equator. (Note: This is an angle) 0o = the equator. 90o N= the north pole. 90o S = the south pole. Longitude : Measures positions east or west of the Prime Meridian. (This is an angle) The Prime meridian is an imaginary line that passes through Greenwhich, England.

Latitude and Longitude

In the Northern Hemisphere, stars near the North Celestial Pole are always above the horizon. Therefore, these stars are called Circumpolar Stars. In the Northern Hemisphere, stars near the south celestial pole remain below the horizon and so are never seen by a northern observer. In the Southern Hemisphere, stars near the north celestial pole are never visible to the southern observer.

Different sets of constellations are visible in northern and southern skies.

Northern Hemisphere Southern Hemisphere Counter-Clockwise Rotation Clockwise Rotation Northern Hemisphere Southern Hemisphere The Altitude of the celestial pole (Polaris or the North Star) = your latitude

Seasonal Changes in the Sky The night-time constellations change with the seasons. This is due to the Earth’s orbit around the Sun.

The Sun’s Path Through The Daytime Sky Changes With Seasons The sun traces out a characteristic figure 8 pattern over the course of a year at the same time of the day. This “Figure 8” is called an analemma. Composite photograph Images taken always at same time of day. (8:30 am. EST) Pictures taken at 10 day intervals over an entire year. North South Summer Fall Spring Winter Path of sunrise for a particular date. Dennis di Cicco

Seasons- Geocentric View The apparent path of the Sun on the celestial sphere, showing how the seasons arise. Figure from Astronomy Today, 3rd ed., Chaisson & McMillan, Prentice-Hall, ©1999

The Moon, Our Constant Companion As the Moon moves through the sky, both its appearance and the time at which it rises and sets change with the cycle of Lunar Phases.

Lunar Phases Demonstration The Moon The Earth

Lunar Phases Note: Look at top view to understand rise and set times.

We always see the same face of the Moon. The Moon rotates as it orbits the Earth. The rotation rate is synchronized with the orbital period. This is called a “Synchronous Orbit”.

Eclipses In order for an Eclipse to occur: The nodes of the Moon’s orbit must be nearly aligned with the Earth and the Sun. The phase of the Moon must be either new or full.

The Ecliptic Plane is represented by the surface of the pond. Lunar Eclipse Solar Eclipse Solar Eclipse Lunar Eclipse Nodes occur at points where the orbit crosses the surface of the pond

Lunar Eclipse = the phenomenon in which the shadow of the Moon falls on the Earth′s surface. (Sunlight is partially blocked) (Sunlight is fully blocked)

Three Types of Lunar Eclipses

Solar Eclipse = the phenomenon in which the shadow of the Moon falls on Earth′s surface.

Multiple Exposure Photograph of Progression of a Solar Eclipse Totality- lasts only a few minutes. The Solar Corona becomes visible.

Tides The Moon′s motion is responsible for the tides. They are caused by the force of gravity; the amount or gravitational force is the force of attraction between all masses in the universe.