Astronomy vs. Astrology Astronomy: Astronomy: The scientific study of matter in outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena. Astrology: Astrology: 1. The study of the positions and aspects of celestial bodies in the belief that they have an influence on the course of natural earthly occurrences and human affairs. 2. Obsolete Astronomy.

You Know Astronomy! Observing the motions of Sun, Moon, Stars Observing the motions of Sun, Moon, Stars Observing the appearance of the Sun, Moon, Stars Observing the appearance of the Sun, Moon, Stars Observing the passage of time Observing the passage of time

Scale of the Cosmos “Powers of 10” video “Powers of 10” video Class discussion Class discussion Scale of the solar system video and handout etail.cfm?guidAssetID=8AB502BD-C376-4D AD21C4D012C Scale of the solar system video and handout etail.cfm?guidAssetID=8AB502BD-C376-4D AD21C4D012C Class discussion Class discussion

Celestial Motions Sun, Moon and Stars appear to rise in the East and set in the West daily Sun, Moon and Stars appear to rise in the East and set in the West daily Actual motion is the rotation of the Earth from West toward East daily Actual motion is the rotation of the Earth from West toward East daily Solar Day-Noon to Noon Solar Day-Noon to Noon Time Zones Time Zones

Celestial Sphere It is useful in discussing objects in the sky to imagine them to be attached to a sphere surrounding the earth. It is useful in discussing objects in the sky to imagine them to be attached to a sphere surrounding the earth. At any one time we see no more than half of this sphere At any one time we see no more than half of this sphere The point on the celestial sphere that is directly over our heads at a given time is termed the zenith. The point on the celestial sphere that is directly over our heads at a given time is termed the zenith.

Celestial Coordinate Systems We can define a useful coordinate system for locating objects on the celestial sphere by projecting onto the sky the latitude-longitude coordinate system that we use on the surface of the earth. We can define a useful coordinate system for locating objects on the celestial sphere by projecting onto the sky the latitude-longitude coordinate system that we use on the surface of the earth. North and South Celestial Poles = the earthly poles projected on to the celestial sphere North and South Celestial Poles = the earthly poles projected on to the celestial sphere Celestial Equator = equator projected on to the celestial sphere Celestial Equator = equator projected on to the celestial sphere Longitude and Latitude on earth can correspond to coordinates in the sky Longitude and Latitude on earth can correspond to coordinates in the sky

Ecliptic Imaginary path that the Sun follows on the celestial sphere over the course of a year Imaginary path that the Sun follows on the celestial sphere over the course of a year The ecliptic is important observationally, because the planets, the Sun (by definition), and the Moon are always found near the ecliptic. This is because all of these objects have orbits that lie nearly in the same spatial plane. The ecliptic is important observationally, because the planets, the Sun (by definition), and the Moon are always found near the ecliptic. This is because all of these objects have orbits that lie nearly in the same spatial plane.

Diurnal Motion The apparent daily motion of the stars around the celestial poles The apparent daily motion of the stars around the celestial poles One complete circle is a sidereal day which is 23 hours, 56 minutes and 4.09 seconds One complete circle is a sidereal day which is 23 hours, 56 minutes and 4.09 seconds

Circumpolar Stars Stars that do not set during their diurnal motion Stars that do not set during their diurnal motion Most stars are hidden beneath the horizon and will rise and set each night, circumpolar stars never set, they stay above the horizon and seem to rotate around the north celestial pole Most stars are hidden beneath the horizon and will rise and set each night, circumpolar stars never set, they stay above the horizon and seem to rotate around the north celestial pole

SEASONS Why do we have seasons?

Seasonal Fact vs. Fiction Seasonal Fact vs. Fiction First, Fiction: some people believe that seasons are because earth is closer to the sun during summer. Wrong! Perihelion = closer to sun, 147 million KM or 91 million miles. This occurs during January! Aphelion = further from the sun, 152 million km almost 95 million miles, during June.

Seasons really happen because… Intensity and duration of sunlight due to the tilt of the earth’s axis Intensity and duration of sunlight due to the tilt of the earth’s axis The Earth is Tilted on it’s axis by 23.5º The Earth is Tilted on it’s axis by 23.5º During certain times of the year, we receive more direct sunlight since we are tilted toward the Sun (Summer) During certain times of the year, we receive more direct sunlight since we are tilted toward the Sun (Summer) Other times we receive less direct sunlight since we are tilted away from the Sun (Winter) Other times we receive less direct sunlight since we are tilted away from the Sun (Winter)

Intensity of sunlight

Duration of sunlight For Northern Hemisphere: Winter ~ 9 hours of daylight Summer ~ 15 hours of daylight Link: bin/aa_durtablew.pl

Seasons

Equinoxes and Solstices Vernal Equinox = March 20 or 21 Vernal Equinox = March 20 or 21 Autumnal Equinox = September 22 or 23 Autumnal Equinox = September 22 or 23 Equinox “Equal Night” Equinox “Equal Night” Summer Solstice Longest Day = June 20 or 21 Summer Solstice Longest Day = June 20 or 21 Winter Solstice Shortest Day = December 21 or 22 Winter Solstice Shortest Day = December 21 or 22 These rules are for Northern Hemisphere ! These rules are for Northern Hemisphere !

Seasonal Sun Does the sun appear at the same location in the sky at “noon” from season to season? Does the sun appear at the same location in the sky at “noon” from season to season? No! How does it change? No! How does it change? Tilt of Earth affects the location of Sun Tilt of Earth affects the location of Sun

Seasonal Sunset The tilt also affects the location of the sunrise and sunset The tilt also affects the location of the sunrise and sunset Sun’s position moves Southward approaching the Winter Solstice Sun’s position moves Southward approaching the Winter Solstice It moves Northward approaching the Summer Solstice It moves Northward approaching the Summer Solstice Think about the motion during the course of the year Think about the motion during the course of the year

Larger Motions Notice the night sky during different times of the year Notice the night sky during different times of the year Different star groupings are visible at night during different times of the year Different star groupings are visible at night during different times of the year Why? We are orbiting the Sun! Why? We are orbiting the Sun! Year-time for one complete orbit around the Sun by the Earth Year-time for one complete orbit around the Sun by the Earth

Other Larger Motions During the course of the year both the Sun and Moon appear to be moving Eastward compared to the background stars During the course of the year both the Sun and Moon appear to be moving Eastward compared to the background stars Sun –due to Earth’s orbit Sun –due to Earth’s orbit Moon –due to its orbit Moon –due to its orbit

What’s Your Sign? Constellations- Apparent 2-D pictures Constellations- Apparent 2-D pictures Zodiac-12 constellations that are special Zodiac-12 constellations that are special Lie along Ecliptic, the apparent path of the Sun through the sky due to the tilt of the Earth Lie along Ecliptic, the apparent path of the Sun through the sky due to the tilt of the Earth

Sun in Leo When we identify the Zodiac constellations we reference the position of the Sun When we identify the Zodiac constellations we reference the position of the Sun Can we actually see Leo from the earth during the month of August? Can we actually see Leo from the earth during the month of August? No, the Sun is much too bright! No, the Sun is much too bright! We need to wait until later Winter to see Leo in the nighttime sky We need to wait until later Winter to see Leo in the nighttime sky

Now think about the moon… Picture in your mind the moon. What do you see? Picture in your mind the moon. What do you see? Do you think everyone is visualizing the same thing? Why or why not? Do you think everyone is visualizing the same thing? Why or why not?

Phases of the Moon Why do we see the phases of the Moon ?

Answer The relative positions of the Earth, Moon, and Sun The relative positions of the Earth, Moon, and Sun Waxing- Moon is getting brighter (New to Full) Waxing- Moon is getting brighter (New to Full) Waning-Moon is getting darker (Full to New) Waning-Moon is getting darker (Full to New) Month-one complete phase cycle of the moon Month-one complete phase cycle of the moon

Moon Bow and Arrow The lighted portion of the Moon always points toward the Sun The lighted portion of the Moon always points toward the Sun The angle between the Sun and Moon changes as the Moon goes through its phase cycle The angle between the Sun and Moon changes as the Moon goes through its phase cycle

What time does the moon rise? New moon? 6 am 1 st quarter? 12 pm Full moon? 6 pm 3 rd quarter? 12 am

How long between each phase? 1 week 1 week If the moon rises at 6 pm on day 1, then what time does the moon rise on day 2? 6:50 pm 6:50 pm

Eclipses Sun, Moon, and Earth are lined up. Sun, Moon, and Earth are lined up. Eclipses are caused by shadows cast on objects Eclipses are caused by shadows cast on objects Solar Eclipse-Moon blocks light from the Sun and casts a shadow on the Earth. Solar Eclipse-Moon blocks light from the Sun and casts a shadow on the Earth. Lunar Eclipse-Earth blocks light from the Sun and casts a shadow on the Moon. Lunar Eclipse-Earth blocks light from the Sun and casts a shadow on the Moon.

Solar Eclipse Moon must be between the Sun and Earth Moon must be between the Sun and Earth Moon must be in what phase for a Solar Eclipse to occur? Moon must be in what phase for a Solar Eclipse to occur? New New Eclipses don’t occur every month due to tilts of both Earth’s and Moon’s orbit Eclipses don’t occur every month due to tilts of both Earth’s and Moon’s orbit

Solar Eclipse Panorama Astronomy Picture of the Day

Lunar Eclipse Earth must be between Sun and Moon Earth must be between Sun and Moon Moon must be in what phase ? Moon must be in what phase ? Full Full More people can see it since Earth’s shadow is larger More people can see it since Earth’s shadow is larger

Lunar Eclipse Montage

Human Anatomy You have all the tools that ancient astronomers had! You have all the tools that ancient astronomers had! Eyes Eyes Hands Hands Brains Brains

Summary You know much already about observational Astronomy You know much already about observational Astronomy Anyone can be an Astronomer Anyone can be an Astronomer Heavenly objects follow predictable motions. Some units of time are defined by these motions Heavenly objects follow predictable motions. Some units of time are defined by these motions Appearance of objects can change for a variety of reasons Appearance of objects can change for a variety of reasons