Definitions:

A.M. – Anti Meridian (after meridian)

Absolute Magnitude (M) – A scale for measuring the actual brightness (or intrinsic brightness) of a celestial object without accounting for the distance of the object. The apparent magnitude measures how bright an object would be if it were placed at a standard distance of 10 parsecs from Earth. If the distance is known, the absolute magnitude can be calculated using the formula M = m + 5 – 5 log d.

Apparent Visual Magnitude (m) – The apparent brightness that a star appears to have, as measured by an observer on Earth. (How bright a star appears to the naked eye.) The smaller the magnitude of the star, the brighter the star. Each magnitude is brighter by a factor of 2.5. If the distance is known, the absolute magnitude can be calculated using the formula m = M + 5 – 5 log d.

Age of Solar System (Earth & Planets) – 4.6 billion years

Alpha Centauri – Nearest star system, it’s a triple star system, 4.3 ly from earth.

Alpha Star (a) – brightest in a constellation

Andromeda (M31) – next largest galaxy. Larger than the Milky Way, has approx. 200-300 billion stars, spiral galaxy, about 2.2 million ly away, magnitude of +6 (barely visible to the naked eye). In 7 billion years, the Andromeda and Milky Way will merge. Their spiral arms will collide (just the dust and gas, not the stars) and it will form new stars.

Asterism – (from Webster’s) a constellation, a small grouping of stars

Asteroid Belt – Resides between Mars & Jupiter, Rocks & Boulders, Cerres is the largest asteroid, made up of debris left over from formation of planets. Never had a chance to coalesce (accrete) into a planet because of the intense gravitational pull of Jupiter. 10 or 12 moon size objects were in the asteroid belt but collided and broke themselves down.

• • When Asteroids collide, they break down. Radiation causes their dust and particles to spiral towards the
  • It is continuously creating dust – an ongoing Sun.
  • It takes about 100,000 years for this dust to reach the Sun (or 15.25 hours to an 80 year old) (1x10⁵/4.6x10⁹) 80 = 1.739x10^-3 years
  • Effects: this dust cloud covers the inner solar system (Earth, Venus, Mercury, Mars)process that is referred to as Dynamic Equilibrium
  • Created roughly 100,000 years ago.

Astronomical Unit (AU) – Average distance between the sun & earth. 1au = 150,000,000 km (1.5x10⁸) or 94 million miles.

Autumnal Equinox – September 21^st, beginning of fall

Beta (B) – second brightest star in a constellation

Black Hole – A region of space where the pull of gravity is so great that nothing – not even light – can escape. A possible outcome of the evolution of a very massive star. 50 to 100 times the mass of the Sun, matter collapsing in on itself - no known force can stop it’s collapse, has enormous gravitational pull. (If after a supernova there is enough material left over, a black hole can form. Gravity continues to compress the material until the central core collapses forever. As the core shrinks, the gravitational pull in its vacinity eventually becomes so great that not even light can escape. The resulting object emits no light, no radiation, no information at all.)

Celestial Coordinates – declination & right ascension measure where a celestial body is located in the night sky

Celestial Equator – represents the intersection of Earth’s equatorial plane with the celestial sphere

Celestial Meridian – the upper half of the celestial sphere from due North to due South, the best time to view an object is when it is along this meridian (because there is less dust which makes object appear fuzzy – dust settles at the horizon)

Celestial Sphere – A crystal globe that appears to encompass the Earth

• the stars look as if they are permanently attached to the sphere (the stars do change positions because of the solar system’s orbital motion about the center of the galaxy, but the stars are so far away it’s difficult to detect their movement)
• the planets, sun and moon change positions on the sphere every few days

Conjunction – When to objects are on opposite sides of the Sun (when an object is near to the sun in the sky

Constellation – grouping of the brightest stars which ancient astronomers named after mythological beings, heroes, and animals.

Daily Star Tracks – objects on the celestial sphere appear to move along a circular path once every 24 hours, this path is centered above the NCP and parallel to the celestial equator.

Declination – measures how far N or S of the equator an object is – represented by the Greek letter for gamma (measured in + 0 to 90 degrees north or – 0 to 90 degrees south)

Distance Modulus –

Dynamic Equilibrium – when something in the Universe is replenished as quickly as it is used.

• Examples: Oxygen – the amount of O₂ stays constant in our atmosphere. It as it burns off/is used, plants create it through photosynthesis

Eastern Horizon (EH) – Extends from due North through due East, to due South; each day the sun, planets & moon rise somewhere along this horizon. The stars rise at the same place along the eastern horizon each day.

Ecliptic – the path the sun traces across the sky or the sun’s circular path on the celestial sphere. It is a mirror image of the Earth’s orbit around the Sun. It takes the Sun 365 days (1 year) to complete it’s trek. The ecliptic is inclined 23.5⁰ to the celestial equator (the earth and other planets are within 7^o of the ecliptic)

Ecliptic Plane – the apparent path of the sun relative to the stars on the celestial sphere, over the course of a year in which the planets orbit the sun within 5^o except Pluto which orbits it at 17^o

Electromagnetic Radiation – another term for light, it transfers energy and information from one place to another.

Event Horizon – the point at which a black hole’s gravitational pull draws things in – there is no known escape.

Horizon Circle – where the celestial sphere appears to meet the ground (where the sky meets the ground), horizon points: due north (90^o from due west), due east (90^o from due north), due south (90^o from due east), due west (90^o from due south)

Kuiper Belt – field outside the orbit of Neptune that is made up of billions of ice boulders. It contains approximately 62 objects that have diameters of 100-400km. Scientists believe these objects are the building blocks of planets that were disrupted from that process by Jupiter’s gravitational force. It is also believed this field is where short-period (reoccurring every 200 years or less) comets originate. Extends approximately 50au’s from the Sun.

Kuiper Belt Objects - masses of rock & ice (the building blocks of planets) that were disrupted from their routine by Saturn’s gravitational pull that now orbit between 30 and 100 au from the sun. Pluto is thought to be the largest known KBO.

Light year (ly) – the distance light, moving at a speed of 300,000 km/s, travels in one year. We use it to measure the distance between stars. (3x10⁵ km/sec or 9.5x10⁹km/year)

M42 – (Orion’s Nebula) stellar nursery 15 million miles from Earth. Magnitude 6, barely visible from Earth.

M31 – Andromeda Galaxy – barely visible with naked eye Magnitude 6

Magnitude Scale:

• Apparent Visual Magnitude (m) - The lower the number, the brighter the star, increases by 2.5 (from +1 to +3 = 2^2.5). This also corresponds to a physiological response – the eye sees the next magnitude as 2.5 times brighter. The scale uses zero & negative numbers. Ex: the Sun has a m of –27, the moon –13, Venus –5, Sirius –1.5

• Change in magnitude = M₂ – M₁

• Absolute Visual Magnitude (M) – Puts all stars at an equal distance (10pc) to test how bright they are compared to each other. This shows true or intrinsic brightness. Stars with more energetic surfaces are brighter.

Milky Way Galaxy – 10 billion years

Metamorphism – The process of heating and melting an object which re-organizes it into a new chemical compound as compared to it’s original makeup.

Milky Way Galaxy – our galaxy, spiral galaxy, 30,000 ly across, approx. 150 billion stars, 10 billion years old.

Nadar Meridian – the lower half of the celestial sphere, from due North to due South

North Celestial Pole – Directly over the North Pole

Obliquity – the Earth’s axial tilt 23.5^o, causes the change in seasons, the Sun & moon’s gravity is causes the Earth to wobble & the obliquity to change

Opposition – when two planets are on the same side of the sun.

P.M. – Post Meridian

Parsec (pc) – 3.26 parsecs = 1 light year; The distance at which a star must lie in order for its measured parallax to be exactly 1 arc second.
1 pc = 206,000 au

Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto (not a planet)

Polaris (North Star) – Brightest star in Alpha Minor, in Abilene it can be found 23^o due North (because Abilene’s longitude is 23^o.

Proxima – nearest star to Earth (hence the name)

Right Ascension (RA) – corresponds to longitude on Earth, measured East and West along the equator, you measure starting at the equinox, going east along the celestial equinox, measured in hours and minutes instead of degrees because it is used to correspond to time, moves toward the East because stars appear to rise in the East.

Sgr A* - Object at the center of the Milky Way Galaxy. Thought to be a massive black hole, but if it is a black hole the size of it’s event horizon is only 0.02 au. It contains approximately 1 to 2 million solar masses & is 23,000 ly from Earth

Sidereal Time – telling time by tracking the vernal equinox (which is an "empty spot" in the sky just below the great square of pegasus). Sidereal time begins at 0:00st at the Zenith. Matches solar time on Sept. 21^st (the autumnal equinox) and is exactly 12h opposite solar time on Mar. 21^st (vernal equinox)

Solar Time – clock time, telling time by the sun; it begins at 12:00pm, midnight when the Sun is at the Nadir. (12p sun is straight up in the sky)

South Celestial Pole – Directly over the South Pole

Summer Solstice – June 21^st, beginning of summer, longest day of the year (Sun is at it’s highest)

Universe – 13 to 15 billion years

Transit Event – When an object in the sky crosses the Ecliptic or crosses the Sun’s path

Vernal Equinox – March 21^st, beginning of spring

Western Horizon (WH) – Extends from due South through due West to due North; each day the stars, sun, planets & moon rise somewhere along this horizon

White Out – when it’s too cloudy out to use stars the as a point of reference

Winter Solstice – December 21^st, beginning of winter, shortest day of the year (Sun is at it’s lowest)

Zenith – highest point along the celestial sphere

How the Universe formed:

• Big Bang
• Massive stars formed from Hydrogen/Helium – these stars are thought to be 50 to 100 times larger than the mass of the sun. These stars evolve quickly ending their lives after 1 million years. (The sun by comparison will live 10 billion years)
• Black holes formed after the massive stars – around which Galaxies formed.

Universe from the perspective of an 80 year old.

Signs of the Zodiac

These stars are visible during the day time (for the corresponding month) wait 6 months and they are visible at night.

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