Week 1: Night Sky & Coords Please complete the Student Info and - - PowerPoint PPT Presentation

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Week 1: Night Sky & Coords Please complete the Student Info and - - PowerPoint PPT Presentation

Sep 16, 2023 14 likes •397 views

Week 1: Night Sky & Coords Please complete the Student Info and Pre-course Asssessment, if you havent yet Name our Llama! HW1 due in 1 week Read indicated sections of Ch. 2 & 3 by Tuesday ASTR/PHYS 2500: Foundations Astronomy Fall

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Week 1: Night Sky & Coords

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Please complete the Student Info and Pre-course Asssessment, if you haven’t yet Name our Llama! HW1 due in 1 week Read indicated sections of Ch. 2 & 3 by Tuesday

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

The Night Sky & Astronomical Coordinates

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Star trails over the Gemini South telescope

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Gemini Monoceros Canis Major Lepu s Eridanus Taurus

Orion

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Constellation versus Asterism

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Ursa Major & Minor (Big and Little Bears) Big & Little Dippers Polaris (North Star)

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These star patterns are of little use to modern astronomers

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Coincidental Associations

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But, constellations act like political boundaries on a map

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But, constellations act like political boundaries on a map

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But, constellations act like political boundaries on a map

Useful for naming objects: Brightest stars in a constellation are ordered from brightest to faintest with Greek letters (e.g., brightest star in Centaurus is called alpha Centauri) Similar convention in radio and X-ray, e.g., the radio supernova remnant Casseopia (Cas) A, the black hole systems Cygnus X-1 and X-3, the supermassive black hole at the center of the Milky Way, Sagittarius (Sgr) A* Nearby galaxies and galaxy groups and clusters also take constellation names (Andromeda Galaxy, Coma Cluster, Virgo Cluster)

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Constellations aren’t that useful in practice though, because the sky is constantly “moving”

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https://www.youtube.com/watch?v=IJhgZBn-LHg

VSauce: How the Earth Moves

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy 11

side view

Everything moves and is a tad cockeyed

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

MOON PHASES!!!!

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You wake up outside, no idea how long you were unconscious for. You look to the horizon and see this Moon. Is it waxing or waning? What time is it (roughly)? What direction are you looking? What time will the Moon rise a week from now?

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Coordinates on the Sky

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Coordinates on the Sky

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Coordinates on the Sky

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The Celestial Sphere

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https://www.youtube.com/watch?v=1Toya19H12w

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If the north star is directly above our illustrious llama (i.e., at their zenith), where are they on the Earth?

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North Pole!

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If you’re 30 degrees north of the equator:

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At the Equator, where you can see the entire sky:

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Southern Hemisphere, same as in the north but relative to the South Celestial Pole

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Max altitude of the Sun determined by where we are on Earth and where the Earth is in its orbit

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http://www.youtube.com/watch?v=Xm_Cn8-DCNc Where and when are we?

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Right Ascension & Declination

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Angular Sizes / Distances on the Celestial Sphere

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Right Ascension

  • tells time, marking when stars cross an

Hour Angle of 0h

  • can be quoted either in degrees or

hours/minutes/seconds where 24h = 360o

  • differences of RA DO NOT correspond

to angular differences except when Dec = 0o

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

If the Sun has an Hour Angle of +3h, what time of year will the Sun set in 3 hours no matter your latitude on the Earth? If the Sun has a declination of +15o, where on the Earth is the Sun on the horizon no matter its Hour Angle?

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The Ecliptic: Sun’s path on the Celestial Sphere

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The Ecliptic

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Hey you, what’s your sign?

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Astrology is bunk!

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Earth’s axis wobbles like a top: called Precession

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Earth’s axis wobbles like a top: called Precession

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Fall 2020: Week 01 ASTR/PHYS 2500: Foundations Astronomy

Because of precession, the RA & Dec of a star are always changing! To keep sane, astronomers use coordinates from a particular time, referred to as the Epoch; at present, we use Epoch J2000, the RA/ Dec objects had at midnight on January 1st, 2000. To actually locate a star or object when observing, the coordinates must be “precessed”. This “precession of the equinoxes” has a rate of ~50” per year (modest optical telescopes tend to have angular resolutions of ~1” and fields of view of a few arcminutes across, so this rate is quite significant!

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Imagine that a team of highly advanced -- but extremely mischievous aliens -- has changed the tilt of Earth’s rotation axis, relative to its

  • rbital plane, from 23.5° to 0°.

Which of the following features of the celestial sphere would be altered? How?

  • A. local altitude of the North Celestial Pole
  • B. the constellations along the ecliptic
  • C. length of the year
  • D. altitude of the Sun at noon on June 21st
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Why star rise/set times change

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About how many degrees does the Earth move in its orbit each day?

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Julian calendar was used for over 1000 years (leap day every 4 years). Every 400 years, the calendar is offset from the seasons by 3 more days. Gregorian Calendar (what we use today)

Calendars aren’t trivial, because an orbit around the Sun takes 365.2422 days

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Constellations aren’t that useful in practice though, because the sky is constantly “moving”

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https://www.youtube.com/watch?v=IJhgZBn-LHg

VSauce: How the Earth Moves

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Why isn’t there a solar eclipse every month? Why do the Sun and Moon appear to be the same size on the sky?

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What causes precession (i.e., how is Earth’s angular momentum able to change)? What causes seasons? What effects result from this cause that leads to colder/hotter temperatures?

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