Astronomy Midterm

Midterm lol

What is Science?

the attempt to describe, understand, and predict the physical Universe around us

What is astronomy?

it the study of celestial objects and the Universe as a whole. It included the study of the Earth, but specially in the context of an example of a planet as a whole.

One star =

the sun

How many major planets

8

Four smaller, rocky terrestrial planets:

Mercy, Venus, Earth, Mars

Four larger jovian planets, gas giants, or ice giants:

Jupiter and Saturn For Gas

Uranus and Neptune for Ice

Nine Dwarf plantes (100 suspected)

e.g Ceres, Pluto, Eris, Hamea, Makemake

1-2 million of rocky…

Asteroid Belt asteroids

millions of icy…

Kuiper Belt comets

Trillions of icy…

Oort Cloud comets

Countless meteoroids and…

dusty grains

SSSBs

Smaller Solar System Bodies

Trans-Neptunian Objects

TNOs

The Scientific Method

1. Make detailed observations or experiments of

nature, collecting a body of data. Look for

patterns & relationships among measurements.

2. Create a new hypothesis to explain all existing

data and relationships/rules/patterns within it

3. Use hypothesis to make predictions of new,

different observations or experiments-- ideally

testable and falsifiable predictions

4. a) if the prediction is accurate, the hypothesis is

supported (but not proven true). Go to Step 3.

b) if the prediction is clearly inaccurate, the

hypothesis is rejected. Go back to Step 2

Proportionality (“ ∝ ”) describe

the behavior of one variable as another changes, with all else constant

directly proportional means

the change in one variable is duplicated by the other: same numerical change and same direction

inversely proportional means

the change in one variable is reversed in the other: same numerical change, but opposite direction

If the powers on the two variables don’t match…

the variable with the smaller power must change more rapidly to “keep up”

directly prop → same row on

opposite sides of ∝ symbol…

inversely prop = opposite rows on…

opposite sides of ∝ symbol…

A measurement is a…

symbolic description of some property (some “thing”) of the real world.

A measurement has up to three integral pieces:

1. a numerical value (always)

2. units (usually)

3. a specific direction = a “vector” (sometimes)

Equation for momentum (p)

p = m(v)

equation for kinetic energy

KE = (1/2)(m)(v²)

No measurement is ever perfectly exact; there is always uncertainty or measurement “error” so then…

measurement and any calculation based on a measurement must include its uncertainty

The uncertainty can be explicitly stated…

(±X), or just implied through the practice of significant figures

Celestial bodies have two basic motions

Rotation and Revolution

Rotation =

Spin: turning about there own center/axis

Revolution =

Orbit: motion around another body under the influence of gravity

If using the Sun as your Celestial Reference to use as your zero point:

you get Solar, Tropical, or Synodic period

If using the Distant Star as your Celestial Reference to use as your zero point:

you get a sidereal period

Siderreal period =

true 360 degrees of spin/orbit

Based on the Earth’s Orbit around the sun, a tropical year is

365.24219 = 365d 5h 48m 45s (our calendar)

Based on the Earth’s Orbit around the sun, a sidereal year is

365.25636d = 365d 6h 9m 10s (true orbit)

Based on the Earth’s spin about its polar axis, a mean solar day is

24.00000 hr = 24h 00m 0.00s (civil clocks)

Based on the Earth’s spin about its polar axis, a sidereal day is

23.93447hr = 23h 56m 4.091s (ture spin)

Based on the cycle of the Moon’s phases, caused by

its orbit around the Earth, synodic month is

29. 5 days (origin of our calendar months)

Based on the cycle of the Moon’s phases, caused by

its orbit around the Earth, sidereal month is

27.3 days (true orbit)

Astronomy is _____ dimensional

THREE

We measure the sky in….. and not….

angles and not lenghts

1 degree =

60 arcminuetes = 60’

1 arcmin =

60 arcseconds = 60”

declinations measures

N-S (like latitude) in degree unites

Right Asension measures

E-W (like longitude), but in time units (h,m,s) where 24h = 306 degrees

Point overhead =

zenith

point underfoot =

nadir

great circle halfway between =

horizion, cuts whole sky into 2 halves

Line from due N, to zenith to du S '=

local meridian, local sky cut in E-W halves

Angled up from horizon =

altitude or elevation

angel clockwise from N along horizon =

azimuth = “direction”

declination of your zeinth =

your latitude on Earth

altitude of North Celestial Pole =

your latitude on Earth

longitude requires accurate…

clocks and celestial objects

circumpolar

alwayas visible or never rising.

seasonal

rise and set every 24 hrs

living closer to the equator =

larger seasonal band;

Living closer to the poles =

larger circumpolar zones

Polaris is…

not exactly at NCP (~45degree’s off)

an observer at the equator can see the complete sky..

but each sky object for exactly 12 hr

at the equator..

the entire sky is one seasonal zone; there are no circumpolar zones

an observer at the pole only every sees

½ of the CS but every object in the same hemisphere is visible for 24h at fixed altitude

at the pole, the whole sky is

two circumpolar zones; no seasonal zone

Local sky from S. hemisphere, Southern sky visible objects for

12-24h

Local sky from S. hemisphere, Northern Sky Objects visible for

12-0h

Local sky from S. hemisphere, is a mirror image of

the northern Hemisphere observer

sunrise and sunset points…

shift along the horizon across the year

Sun rises due… and sets due…

rises due east and sets due west

for latitudes on 3/21 & 9/21 =

“vernal and autumnal equinoxes”

Rises NE, sets NW 3/22-9/20; max shift +23.5 degree to N on 6/21 =

summer solstice

Rises SE, sets SW 9/22-3/20; max shift of -23.5degree to S on 12/21 =

Winter Solstice

Artic circles (w/in 23.5degree of poles) have…

6 month summer/winter periods with no sunset/no sunrise

Apparent path of the Sun on a Cel. Sphere overa year is called

the ecliptic

ecliptic plane =

Earth’s Orbital plane

Ecliptic tilted 23.5degree relative to

celestial equator

declination of zenith

= observer’s latitude

Sun of N of Cel. Equator Mar-Sep;

overhead for a norther tropical latitude

Sun south of Cel. Equator Sep-Mar;

overhead for a southern tropical latitude

no scientific theory is ever

absolutely proven true.

But a single good experiment can definitively prove

prove a theory to be false with a failed prediction.

speed of light in a vacuum

c = 3.00 x 10^5 km/s,

absolutely nothing can travel faster than

the speed of light

Earth is closets to the sun on

January 4th

Earth is furthest on

July 4th

Efficiency of solar heating depends on the angle at which

the Sun's rays strike level ground

Shallower angle from ground =

less efficient rays

two physical effects on sunlight on your local ground:

1. by varying the number of hours of daylight (Fig. 2.14 in text) and

2. by varying the directness of the Sun's rays (Fig 2.15 in text)

Eight Phases of the Moon (in order)

new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent (and then back to new).

the orbit (of moon) takes roughly

one month

in a state off synchronous rotation.

how the Moon always keeps one side facing the Earth by having its spin period about its polar axis match its orbital period around the Earth

the Moon is evenly divided into

daylit and dark sides by the greatcircle of the terminator,

the Moon is evenly divided into

and into near and far sides by the great circle of the limb as seen from our point of view from the Earth.

The phase of the Moon is determined by how much of

the daylit half is currently on the near side facing the Earth.

all solar eclipses happen at

new moon

all lunar eclipses happen at

full moon

three types of lunar eclipses

penumbral, partial, and total

types of solar eclipses

partical, total, annular

Yutu the lunar rabbit

is all ways watching you!

Partial Solar Eclipse

poor alignment

annular solar Eclipse

“ring shaped”

Good alignment BUT Moon too small to cover sun

total Solar Eclipse

Good Alignment and Large moon enough to cover the sun