coordinate systems more than x marks the spot. coordinate systems global – for the earth global...

Coordinate SystemsCoordinate SystemsMore than X marks the spotMore than X marks the spot

Coordinate SystemsCoordinate Systems Global – for the EarthGlobal – for the Earth Local – applies to youLocal – applies to you Celestial (Equatorial or Polar)Celestial (Equatorial or Polar)

- for the sky- for the sky Sky MovementSky Movement

• DailyDaily• YearlyYearly• 26,000 years26,000 years

Altitude and AzimuthAltitude and AzimuthPoints of referencePoints of reference

ZenithZenith: Straight : Straight overheadoverhead

MeridianMeridian: Line : Line from north to from north to south, passing south, passing through the through the overhead zenithoverhead zenith

NorthNorth: That point : That point on horizon toward on horizon toward the the North Pole.North Pole.

Local Coordinate System Local Coordinate System Altitude and Azimuth (Alt-Az)Altitude and Azimuth (Alt-Az)

AltitudeAltitude Angle from the Angle from the

horizon upward.horizon upward.

Measured in Measured in degrees from 0 degrees from 0 degrees at the degrees at the horizon to 90 horizon to 90 degrees straight degrees straight overhead at the overhead at the ZenithZenith..

0º

90º

45º

Altitude and AzimuthAltitude and AzimuthAzimuthAzimuth

Angle measured Angle measured clockwise from clockwise from north.north.

Measured in Measured in degrees, from: degrees, from: • 00oo north, north, • 9090oo east, east, • 180180oo south, south, • 270270oo west, west, • back past 359back past 359oo, to , to

00oo north again north again

Altitude and AzimuthAltitude and AzimuthWhat can you use it for?What can you use it for?

Use it for casual references to objects in Use it for casual references to objects in the sky (e.g. announcements of comet the sky (e.g. announcements of comet positions).positions).

Use it with alt-az telescope mounts which Use it with alt-az telescope mounts which have digital setting circles that read in alt-have digital setting circles that read in alt-az:az:

Celestial Coordinate SystemCelestial Coordinate SystemRight Ascension and DeclinationRight Ascension and Declination

TermsTerms Celestial sphereCelestial sphere: an : an

imaginary sphere, imaginary sphere, with Earth at the with Earth at the center, having an center, having an infinitely large radius.infinitely large radius.

All stars and celestial All stars and celestial objects are projected objects are projected onto the inside onto the inside surface of this great surface of this great sphere.sphere.

Right Ascension and DeclinationRight Ascension and Declination North celestial poleNorth celestial pole (NCP) (NCP)

and and south celestial polesouth celestial pole (SCP): where Earth’s polar (SCP): where Earth’s polar axis, if extended to the axis, if extended to the celestial sphere, would celestial sphere, would intersect.intersect.

Celestial equatorCelestial equator: a plane : a plane from Earth outward to a from Earth outward to a line around the celestial line around the celestial sphere halfway between sphere halfway between the NCP and the SCP.the NCP and the SCP.

EclipticEcliptic: the plane in which : the plane in which the Earth orbits the Sun, or the Earth orbits the Sun, or the Sun appears to orbit the Sun appears to orbit the Earth.the Earth.

Right Ascension and DeclinationRight Ascension and Declination

Declination:Declination:

• Similar to latitude.Similar to latitude.

• Measured in Measured in degrees, degrees, perpendicular to perpendicular to the celestial the celestial equator (north-equator (north-south direction).south direction).

• North is positive, North is positive, south is negative.south is negative.

Right Ascension and DeclinationRight Ascension and Declination

Right Ascension:Right Ascension:

• Similar to longitude.Similar to longitude.

• Measured in hours, Measured in hours, minutes and seconds minutes and seconds around the sky, around the sky, measured parallel to measured parallel to equator, eastward.equator, eastward.

• From 0 hr 0 min 0 From 0 hr 0 min 0 sec to 23 hr 59 min sec to 23 hr 59 min 59.999… sec.59.999… sec.

Right Ascension and DeclinationRight Ascension and Declination Where is the celestial Prime Meridian located and why?Where is the celestial Prime Meridian located and why?

Located at an Located at an important spot, where important spot, where celestial equator and celestial equator and ecliptic cross.ecliptic cross.

This is where Spring is This is where Spring is defined to begin.defined to begin.

Why? In order to keep Why? In order to keep the calendar the calendar consistent with the consistent with the seasons.seasons.

Greenwich Royal Greenwich Royal ObservatoryObservatory• Prime meridian Prime meridian

appears in appears in foreground.foreground.

Main instrument is Main instrument is a a transittransit telescope telescope• It moves only in It moves only in

altitude.altitude.• Installed by George Installed by George

Airy in 1850.Airy in 1850.

Right Ascension and DeclinationRight Ascension and Declination Where is the celestial Prime Meridian located and why?Where is the celestial Prime Meridian located and why?

Right Ascension and DeclinationRight Ascension and DeclinationHow can you use it?How can you use it?

Knowing the coordinates of an object you want to see, from Knowing the coordinates of an object you want to see, from a a star cataloguestar catalogue……


Locate the object at the coordinates on the Locate the object at the coordinates on the star chart…star chart…


From the star chart, pick out recognizable From the star chart, pick out recognizable constellation or star patterns in the area, and pick constellation or star patterns in the area, and pick out marker stars to the object. out marker stars to the object.


Now find a similar star pattern in the sky…Now find a similar star pattern in the sky…


And follow the imaginary lines you mentally drew on And follow the imaginary lines you mentally drew on the star chart.the star chart.

Meridian

NORTHNORTH

SOUTHSOUTH

EASTEAST

WESTWEST

Zenith

Polaris (NCP)

The declination of my zenith is

equal to my latitude!

Declination and locationDeclination and location

Declination of zenith = latitudeDeclination of zenith = latitude AND… AND… Latitude = angle of Polaris above Latitude = angle of Polaris above

northern horizonnorthern horizon

Sky Movement - DailySky Movement - DailySolar Day & Sidereal DaySolar Day & Sidereal Day

In a 24 hour solar day, In a 24 hour solar day, last night’s star last night’s star arrives at tonight’s arrives at tonight’s meridian 3 min 55.9 meridian 3 min 55.9 seconds earlier than seconds earlier than last night.last night.

Stars cross the Stars cross the meridian 3 m 55.9 s meridian 3 m 55.9 s earlier each night.earlier each night.

Sidereal day is 23 hr Sidereal day is 23 hr 56 min 4.1 sec long.56 min 4.1 sec long.

Sky Movement - DailySky Movement - DailySolar Day & Sidereal DaySolar Day & Sidereal Day

Sky Movement - AnnualSky Movement - Annual

As a consequence, each night the stars As a consequence, each night the stars appear about 59 arc-min (~1appear about 59 arc-min (~100) farther ) farther west at the same time as the night before.west at the same time as the night before.

Over one year, the entire sky will Over one year, the entire sky will completely slip past.completely slip past.

Therefore, what is up tonight depends not Therefore, what is up tonight depends not only on what time of night it is, but on only on what time of night it is, but on which night of the year it is. Last month’s which night of the year it is. Last month’s stars are 2 hours farther west.stars are 2 hours farther west.

Sky Movement - AnnualSky Movement - Annual9:00 pm,9:00 pm, May 15, 2005May 15, 2005

Sky Movement - AnnualSky Movement - Annual 9:00 pm,9:00 pm, June 15, 2005June 15, 2005

Sky Movement - AnnualSky Movement - Annual 9:00 pm,9:00 pm, July 15, 2005July 15, 2005

Sky Movement - AnnualSky Movement - Annual

Manage both:Manage both: time of night, andtime of night, and night of the yearnight of the year

with a with a PlanispherePlanisphere..

Using your star wheelUsing your star wheel

Set date and Set date and timetime

Hold overheadHold overhead Align horizonsAlign horizons Read Read

constellationsconstellations

Sky Movement – 26,000 yearsSky Movement – 26,000 years

The Roman calendar, as established by The Roman calendar, as established by Julius Caesar, had problems:Julius Caesar, had problems:• Started at Winter Solstice on January 1, 45 BC.Started at Winter Solstice on January 1, 45 BC.• Year was 365 ¼ days long, with leap year Year was 365 ¼ days long, with leap year

corrections. Decimals had not been invented corrections. Decimals had not been invented yet; yet;

• Year is actually 365.242199… days.Year is actually 365.242199… days.

So, after a few centuries, people noticed So, after a few centuries, people noticed the seasons (equinoxes) were moving the seasons (equinoxes) were moving slowly in relationship to their calendar. slowly in relationship to their calendar.

Precession of the EquinoxesPrecession of the Equinoxes

Earth’s drifting Earth’s drifting polar axis causes polar axis causes the North Celestial the North Celestial Pole to move in a Pole to move in a circle around the circle around the sky, once every sky, once every 26,000 years.26,000 years.

ThubanThuban was the was the pole star when the pole star when the Great Pyramid was Great Pyramid was built in Egypt.built in Egypt.

Summer Solstice, 400 BCSummer Solstice, 400 BC

Summer Solstice, 2005 ADSummer Solstice, 2005 AD

Spring Equinox, 2005 ADSpring Equinox, 2005 AD

Spring Equinox, 2600 ADSpring Equinox, 2600 AD

Leap YearsLeap Years Gregorian solar year: 365d 5h 48m 20s; still has Gregorian solar year: 365d 5h 48m 20s; still has

25.967s/SY error.25.967s/SY error. Summer solstice moves later on calendar each year. Summer solstice moves later on calendar each year.

Slightly over-corrected each leap year.Slightly over-corrected each leap year. Cumulative annual error is corrected each century by Cumulative annual error is corrected each century by

not having a leap year, unless that year is divisible by not having a leap year, unless that year is divisible by 400 (1600 and 2000 were leap years).400 (1600 and 2000 were leap years).

Why bother with such tedious Why bother with such tedious accuracy ?accuracy ?

Nearly all major advances in astronomy Nearly all major advances in astronomy occurred when observation did not agree occurred when observation did not agree with prediction, and people needed a with prediction, and people needed a better theory for better predictions.better theory for better predictions.

Astronomy advanced as instruments Astronomy advanced as instruments became precise enough to measure the became precise enough to measure the flaw in prevailing theory. flaw in prevailing theory.

By the middle of the 19th Century we By the middle of the 19th Century we could predict the movement of stars and could predict the movement of stars and planets within a fraction of a second, planets within a fraction of a second, except….except….

What does this lead up to?What does this lead up to? The perihelion of Mercury (point closest to The perihelion of Mercury (point closest to

the Sun) was observed to be advancing in the Sun) was observed to be advancing in longitude by about half a minute of arc per longitude by about half a minute of arc per century faster than prevailing celestial century faster than prevailing celestial mechanics predicted. mechanics predicted.

Which is where Newtonian Theory ends, Which is where Newtonian Theory ends, and Relativity Theory begins.and Relativity Theory begins.

Scientific advancement is a journey, not a Scientific advancement is a journey, not a destination. Our trip continues with each destination. Our trip continues with each new discovery.new discovery.

Web StuffWeb Stuff

http://astro.unl.edu/classaction/coordsmotion.html

Credits: BooksCredits: Books

All About TelescopesAll About Telescopes, Edmund Scientific, 1975, Edmund Scientific, 1975

CalendarCalendar, David Ewing Duncan, 1998, David Ewing Duncan, 1998

Cambridge Illustrated History of AstronomyCambridge Illustrated History of Astronomy, , Michael Hoskins, ed., 1997Michael Hoskins, ed., 1997

Instruction ManualInstruction Manual, Meade Instruments Corp, , Meade Instruments Corp, 19961996

Observer’s Handbook 2005Observer’s Handbook 2005, RASC, 2004, RASC, 2004

Sky 2000.0Sky 2000.0, Will Tirion, 1981, Will Tirion, 1981

The Practical AstronomerThe Practical Astronomer, Colin a Ronan, 1984, Colin a Ronan, 1984

Credits: Web sitesCredits: Web sites

For magnetic declination for any latitude and For magnetic declination for any latitude and longitude:longitude:

http://www.geolab.nrcan.gc.ca/results/mirp_result.70.241.78.92_e.shtml

For seasons and ecliptic tilt:For seasons and ecliptic tilt:http://en.wikipedia.org/wiki/Season

For history of Royal Observatory at For history of Royal Observatory at Greenwich:Greenwich:

http://www.nmm.ac.uk/

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