AS101 - OC1 Module 1 Notes

Lesson 1: - Voyager 1 and 2 were launched around 45 yrs ago. The alignment took planning. The probes flew past each other and - Voyager 1 - saturn jupiter and titan (jupiter’s biggest moon) - Voyager 2 - saturn and jupiter + follow trajectory of neptune and uranus - Voyager 2 was launched first - Voyager 1 is currently the farthest human made object from Earth at 23.4 billion km away - Voyager 2 is not too far from that, being 19.5 billion km away. The only pics we have of neptune and uranus are from the Voyager 2 as it passed by them very fast - Uranus: January 24, 1986 - Neptune: August 25, 1989 - CERN: high-energy, physics lab near Geneva Switzerland - Diameter of earth is approx 13 000 km - 150 000 000 = 150 million km, this is 1,5 x 10^8 km in scientific notation -> aka 1 AU (astronomical unit) - Neptune is the outermost planet in the solar system (40 AU away from Earth) - Inner planets are closer together compared to the four outer gas balls - Nearest star is Proxima Centauri - If we made Earth the size of a dust particle, the sun would be 2.5 cm away and the size of a period. The smaller planets (Mercury, Venus and Mars) would be smaller dust and the larger planets (Jupiter, Neptune, Saturn and Uranus) would be slightly bigger dust particles - Light year: distance light travels in 1 year - Sirius -> brightest star in constellation Canis Major (Great Dog) - At 1700 lightyears away, we see a bunch of stars ( some larger and smaller than the sun) Not even a telescope can help us see these - Milky Way is a spiral galaxy, has a swirl that has over a 100 billion stars spread over 100 000 lightyears (ly) in diameter - Before 90 years ago, people thought this was all space was, a man named Edwin Hubble convinced us all otherwise - In 4 million ly, there are 7 galaxies including our own. The closest to us is Andromeda which is 2.5 million ly away and is moving towards us - At 1.7 billion ly away, we would see a cluster of galaxies with voids of space between them. We do not know if those voids are actually empty or not - 13.8 billion years since the big bang

- Cosmic Calendar: concept designed by Carl Sagan. This is the idea of spreading the life of the universe over 1 calendar year (each month would be a bit over 1 billion years) - Carl Sagan was a well known astronomer in the 1900s - January 1st at midnight: big bang occurs - Mid Feb to early March: Milky Way Galaxy starts to come together - Mid August: solar system starts to form - End of September: primitive life forms on Earth - Mid December: complex living structure (invertebrate life) are formed - December 24/25: Dinosaurs roam the planet - Yesterday (65 million years ago)/ December 30: Dino era ends :( - December 31st (11 seconds ago): Egyptian Pyramids built - December 31st (1 second ago): Copernicus convinced people that Earth revolves around the Sun - December 31st (0.14 second ago): Elizabeth 2 becomes queen - December 31st (0.023 second ago): Canada won Gold in the 2002 Olympics for Mens and Women’s hockey - December 31st (0.04 second ago): I was born - A pattern of stars in the sky is called a constellation - Constellations appear to be 2D to us, but they are actually 3D and each star is a different distance away from Earth - The moon is the more prominent object in our sky, it is 30x the diameter of the Earth away from us (384 000 km away), the moon’s diameter is 3476 km (¼ of Earth’s size) - It takes 1.6 seconds for light to travel between Earth and the Moon - With the naked eye, we can see about 3000 stars in the sky (all from our galaxy) - Even with a telescope, it is hard to see stars from other galaxies - Polaris = North Star - Earth’s rotational axis is pointed towards Polaris - 2000 it did not point to any star and in another 2000 it won’t again - This is called precession: the analogous spinning around an axis - The Earth is on 23.4 degree tilt, while it rotates around its axis, the tidal forces make it wobble creating a slow rotational spin around the bottom of the axis (creates a cone shape since top axis moves but bottom stays stagnant) - One precession cycle is 26 000 years and Earth maintains the 23.4 degree tilt - Right now, we are 0.5 degrees of Polaris - Objects in the sky appear to go East to West, however, they actually go West to East in front of the sun (hence day and night) - The stars and constellations we see are dependant on where on Earth we are - The things we see in Canadian skies are never visible in Australian skies - Astronomers measure distances across the sky in angles in units of degrees, arcminutes and arcseconds

Lesson 2: - The stars are still out during the day, the light from the sun just covers it all up - The sun moves east to west throughout the day - The Earth moves along its ecliptic path on its rotational axis (of 23.4°) and makes 1 full revolution per day. - This makes our seasons. The change in solar energy received by the northern and southern hemispheres. - During Summer Solstice, the angle the sun hits Earth is steeper, so light spreads less and results in summer - While the Earth rotates around the sun, it also rotates on its north-south axis (rotational axis) - This axis is NOT perpendicular to the ecliptic plane bc the axis is tipped 23.4° - The rotational axis always points towards the same spot no matter the location around the sun (currently Polaris) - From the summer solstice to winter solstice, the sun moves south of your zenith - From winter solstice to summer solstice, the sun moves north of your zenith - On the vernal equinox (march 21) the sun’s path is coincident with the celestial equator - From this day onward, the sun rises a little more north from the previous day, but remains parallel to the celestial equator - The day of summer solstice, the sun follows the line of 23.4 latitude (AKA tropic of cancer) - From this day onward, the sun will move south until september 21 (autumn equinox) - At winter solstice, the sun will reach the tropic of capricorn - The moon takes 1 month to orbit the Earth - The orbit is not quite circular (the distance varies from 356000 km to 406000 km) - The lunar cycle is the phases of the moon that we see from the sun’s light reflecting onto the moon - The orbital period is almost exactly 29.5 days - Sidereal period is one revolution relative to the stars (this is a 27 day period)

LUNAR CYCLE AND PHASES: - Moon between sun and Earth -> results in new moon bc sun shines on moon side phasing it (no light shines on what part is facing earth) - A new moon also rises each day at 6am and sets at 6pm - Tiny sliver visible is a waxing crescent - Half the moon visible is a first quarter moon (bc ¼ through the phases) - Small sliver not visible is waxing gibbous - Full moon visible is called a full moon - Rises at 6pm and sets at 6am - When small sliver is missing on the right side it is called a waning gibbous - Left half of the moon being visible is called the third quarter - Left tiny sliver visible is called a waning crescent - The “Almost new moon” is when the new moon happens at midnight and we can't see it but when the sun rises we can still see it. Since it’s been 6 hours since the moon rose, it isn't exactly a new moon so we call it an almost new moon - Based on this info, there should be 2 eclipses each month (solar eclipse at each new moon and lunar eclipse at full moon) - This does not happen because the moon is inclined 5° to the ecliptic plane - So an eclipse only occurs when it comes in line with the plane at specific spots called NODES - For an eclipse to occur: the moon must be at a node, be a new/full moon and line up with the Earth and Sun 3 types of lunar eclipse: - Penumbral: This is when the moon only passes through the penumbra, so the sunlight is only partially blocked. This results in a slightly darkened appearance of the moon. - Partial: This is when part of the moon passes through the umbra and the rest through the penumbra. This results in a part of the moon is darkened, but the rest is only slightly darkened with no border between the two parts. - Total: This is when the moon entirely passes through the umbra. This results in a completely darkened moon. PENUMBRA: space of partial illumination on both sides of the earth from the sun’s light UMBRA: space of no illumination, solar light being blocked by Earth

Interesting facts: - The moon’s diameter is 400 times smaller than the Sun’s BUT the sun is 400 times further from Earth - This results in both appearing the same size in our sky - This means during a solar eclipse, the Moon perfectly covers the sun and we see the edge of the sun peeking around which reveals the diamond ring effect - If a solar eclipse happens when the moon is at its apogee (furthest from Earth), the moon’s size is a bit smaller and we have an annular eclipse (May 20, 2012) Planet wandering: - We can see the 5 closest planets to Earth with our eyes - Mercury (at sunrise or sunset), Venus (near the horizon), Mars (reddish star in the sky), Jupiter (at night and bright) and Saturn - Planet means “wanderer” (greek) - Order of planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune - “My Very Educated Mother Just Served Us Nachos” - Relative to the stars, the Sun and Moon move eastward - Retrograde: when the planets appear to change direction and move westward relative to the stars - Early astronomers (pre-Copernican) couldn’t explain this motion - Aristarchus (Greek, 260 BC) first suggested Earth revolves around the sun, but the idea was so foreign, it wasn’t considered until 1800 years later when Copernicus promoted the idea - Inner planets move faster in orbit, they catch up to and pass the outer, slower-moving planet. The outer planets “appear” to move backwards in the sky - Retrogrades also appear for Venus and Mars but its nearly impossible to see because this motion happens when Earth, the planet and the Sun are all aligned so the Sun’s glare prevents us from seeing the westward movements - The retrograde motion for these happen during the transition from “evening” star to “Morning” star - Retrograde is an optical illusion created when Earth passes slower moving planets further away in orbit - During the passing, when the outer planet is aligned with Earth and the Sun, it will be in the middle of its retrograde motion and closest distance to Earth

Stellar parallax: - Parallax: lateral shift in object’s position relative to the background - Stellar parallax: happens when we look at nearby stars from 2 vantage points (first when Earth is at 1 extreme and second when Earth is at opposite extreme 6 months later) - The nearby star appears to shift laterally against the background of stars behind it - Stellar parallax allows us to measure distances to nearby stars AND provides evidence that the Earth does indeed revolve around the sun - Stellar parallax is not seen by the naked eye because the shift is too small for us to see since the far away background is sooo far from us

Telling time: - We use sorta use apparent solar time (sun’s position in the sky to local meridian) to tell time - Sun above local meridian = noon - Before sun is at local meridian = ante noon (ante means before) - After sun passed local meridian = post noon (post means after) - Earth’s orbit is not perfectly circular and has a tilt so each solar day is slightly different from 24 hours - We use average solar time because using apparent solar time would require changing the clock every day - Apparent solar time varies from longitude as well, so everyone would have a different time - Sandford Flemming (Canadian) created a 24 hour timezone system to solve this problem Calendars: - Tropical year is 365.25 days long, if we use the Egyptian concept (365 days), every 4 years the seasons will drift - Julius Caesar introduced that every 4 years, an extra day will be added (leap year) - HOWEVER the tropical year is 11 minutes short of being 365.25 days long - Resulting in spring equinox moving back 11 minutes each year - In 1582, Pope Gregory XIII set the spring equinox to March 21 and adjusted the leap year system (each century which would normally be a leap year would be skipped unless divisible by 400) - This is called the Gregorian Calendar