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by: Erin Bleck

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# Astronomy Week 2 EESC1150

Erin Bleck
Harvard University
GPA 3.91

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These notes cover Week 2 of the Astronomy course taught by Professor Kuchar.
COURSE
Astronomy
PROF.
Dr. Thomas Kuchar
TYPE
Class Notes
PAGES
3
WORDS
CONCEPTS
sun, Year, changes, stars, Vocabulary
KARMA
25 ?

## Popular in Earth and Environmental Sciences

This 3 page Class Notes was uploaded by Erin Bleck on Sunday July 17, 2016. The Class Notes belongs to EESC1150 at Boston College taught by Dr. Thomas Kuchar in Summer 2016. Since its upload, it has received 45 views. For similar materials see Astronomy in Earth and Environmental Sciences at Boston College.

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Date Created: 07/17/16
Notes January 26, 2016 - Horizon coordinates o Dome interpretation of the sky o Meridian – imaginary line along the dome that runs north to south  The north star crosses the meridian (find this, then you know which way is north)  *North is not a position in the sky, it’s a position on the horizon o Azimuth = N, S, E, W (degrees)  N = 0  E = 90  S = 180  W = 270 Nightly Motions - Horizon is set by where you’re located on the Earth - Everything in the sky appears to rise in the east and set in the west due to the counterclockwise motion of rotation and orbit of the Earth - The horizon (what we see and can’t see) rotates along with us as the Earth rotates - If something goes below the horizon, we cannot see it - Because of how we’re oriented with the celestial sphere, stars can make complete circles (circumpolar stars; stars that are closer to Polaris), rise and set, or not appear at all - Nightly motion of the stars o For stars (this includes the Moon, planets, even the Sun) that appear in the southern half of the sky:  Stars first rise near the eastern horizon, move upward and toward the south, and then move down and set near the western horizon (what the Sun does every day)  There are exceptions o (picture on presentation) the direction is west (as stars are moving down or appear to be setting) o (picture on presentation) the direction is north (we see stars making almost complete circles) o Looking north: stars appear to move counterclockwise around the stationary North Star (Polaris)  Stars that neither rise or set = circumpolar stars  Circumpolar stars seem to move counterclockwise around the stationary North Star  These constellations and stars are visible any night of the year in the northern sky because they never rise or set (never go below the horizon)  Ex. Ursa major, Ursa minor, Draco, Cepheus, Cassiopeia Notes January 28, 2016 - Stellarium.org Yearly Changes - Need to keep in mind the Earth’s orbit around the Sun (not just the rotation on its axis) - The zodiac o The constellations that mark the path of the Sun (i.e., stars blocked by the Sun) in the sky throughout the year o Ecliptic – the line through the zodiac that Sun follows (Earth-centric perspective)  The line through the zodiac that marks the plane of the Earth’s orbit (Sun- centric perspective) o Repeats from year to year o There are 13 constellations and we go through one constellation a month (there used to be only 12)  Aquarius  Pisces  Aries  Taurus  Gemini  Cancer  Leo  Libra  Virgo  Scorpius (constellation name is different from the astrological name = Scorpio)  Ophiuchus (new one)  Sagittarius  Capricornus (constellation name is different from the astrological name = Capricorn) - Your birth sign o Roughly, it is the constellation that the Sun is covering up during the day you are born o That is if you were born over 2000 years ago  The traditional dates were drawn up when the constellations were set up  over 1000s of years, the sky has shifted, so it looks different  The arrangement of stars is still the same, but what we see those stars has shifted  A little bit more than one constellation over 1000s of years  Ex. Aquarius originally was January 20 to February 19 o Now, the Sun passes through Aquarius through February 18 to March 3  This shift is due to precession (Week 4) - (picture in presentation) o 1. Sun blocks Scorpius  Look to see where the person is  Look to see the Sun  Look to see the constellation that the Sun is covering (this is why not Taurus) o 2. It is midnight o 3. Cancer o 4. Pisces o 5. 12 hours later after midnight, Scorpius will be in Taurus’s position o 6. 18 hours later after midnight, the Sun will be in the West (6pm) o 7. 18 hours later after midnight, Scorpius will be West (because it is the same as the Sun)  The whole sky is moving together o 8. 2 months from now, Cancer will be high in the southern sky at midnight o 9. 2 months from now, Capricornus will be high at noon (being blocked by the Sun) o 10. What will the person’s astrological sign be? Capricorn (Sun has to block the constellation) - As the Earth moves around the Sun, the time that stars rise changes a bit (actually gets earlier) each day so that other constellations can be high in the sky certain months o Stars rise just a bit earlier each day due to Earth moving in its orbit (and this is why we get different constellations rising and setting with the Sun each month) Path of the Sun - Throughout the year, we see the Sun low in the sky (winter) and then high in the sky (summer) o The tilt of the Earth’s axis changes the Sun’s position in the sky - When the Sun is past the meridian = PM or post meridian - When the Sun is before the meridian = AM or ante meridian - When the Sun is on the meridian = noon o Highest point of the day - The Sun’s position moves up when it’s becoming summer and moves down when it’s becoming winter - Dec. 21 = Winter Solstice = the Sun’s at its lowest point in the sky o From this day on, the Sun will get higher each day o Not as long of a path from East to West because it’s low in the sky - June 21 = Summer Solstice = the Sun’s at its highest point in the sky o From this day on, the Sun will get lower each day o A much longer path from East to West because it’s high in the sky - Mar. 21 and Sept. 21 = Equinox (Vernal and Autumnal) = the Sun’s in the middle position between its lowest point and highest point o Rises exactly east and sets exactly west only on these two days of the year - For the Sun to make one complete circuit from highest point to highest point again takes one year (from summer to summer)

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