Astr 1210 Quiz 1

Small angle formula

angle(θ)(radians)=Size/distance

Degrees=

radians x 180/π

Angle(arcsec)=

1/distance(parsec)

Distance(parsec)

1/angle(arcsec)

Angle of parallax(radians)=

Distance between observers or to center of Earth/vertical distance

Parallax

the apparent displacement of an object due to the position of the observer

Angular size of Moon/Sun

1/2°

Movement of objects through the sky

Rise in East, set in West

Origin of Constellations

Discovered by a society at 36° N latitude(Babylonia)

Circumpolar

Stars visible year-round (none at equator)

Polaris

closest star to North Pole(North Star)

(T or F) All constellations can be seen from the equator at some point in a year

T

How many stars are visible?

6000

Which way do stars move?

Clockwise in Southern Hemisphere(or facing South)/Counter-clockwise in Northern Hemisphere(or facing North)

How long are constellations recognizable?

About 500,000 years

(T or F) Stars visible vary by time of day

T

How many official constellations are there?

88

Pointer star of Little Dipper

Polaris

Apparent magnitude

Brightness of stars(lower is brighter)

Relative magnitude

magnitude=2.5^difference in magnitude

Zodiac

set of 12 constellations through which the Sun appears to move over a year (originated 2500 years ago, now 10% off)

Ophiuchus

13th constellation left out of Zodiac

Aries

Zodiac of vernal equinox

Almagest

most important astronomy text prior to the Renaissance

Asterism

small part of a constellation (ex: Little Dipper)

Prime meridian

Longitude which passes through Greenwich, England (0°)

Arcsecond

1/60 of an arcminute or 1/3600 of a degree

Arcminute

1/60 of 1° 

Constellation

a region of the sky with well-defined borders

Speed of Earth’s orbit

100,000 km/hour

Our solar system’s orbit of the Milky Way

800,000 km/hour, every 230 million years

Speed of Earth’s rotation

1000 km/hour (counterclockwise)

Speed of Milky Way towards Andromeda

300,000 km/hour

Speed of solar system relative to other stars

70,000 km/hour

Position of solar system in Milky Way

Halfway between the center and visible edge (26,000 LY from center)

Ecliptic plane

flat plane on which Earth orbits around the Sun

Local solar neighborhood

neighboring stars

Axis tilt

23\.5° from perpendicular to ecliptic plane (towards Polaris)

When was our solar system formed?

4\.5 billion years ago

Early universe only contained:

hydrogen and helium

Supernovae

large explosion which occur when a star dies

When was the Big Bang?

14 billion years ago

Local Group

Group of 40-70 galaxies including the Milky Way (Milky Way is one of the two biggest)

Galaxy

collection of stars held together by gravity and orbiting a common center

Supercluster

Largest known structures in the universe-cluster of galaxy clusters

Oort Cloud

theoretical cloud of small icy objects on the outskirts of our solar system

Galaxy cluster

group of galaxies help together by gravity

1 light year

10 trillion km

Alpha Centauri

Nearest star system to us (4.4 light years away)

Speed of light

300,000 km/second

AU

Earth’s distance from the sun (150 million km)

Width of Milky Way

100,000 light years

How many stars are in the Milky Way?

100 billion

Number of stars in the observable universe

100 billion x 100 billion

Distance of Sirius from Sun

8 LY

Distance of Jupiter from Sun

5\.2 AU

Sun’s diameter

1 million km

Distance of Mars from Sun

1\.5 AU

Distance of Pluto from Sun

39\.5 AU

Vega

Star towards which our solar system is moving at 70,000 km/hour

Distance to Orion Nebula

1500 LY

Nearest stellar neighborhood

Proxima Centauri(4.2 LY away)

Distance between Earth and Moon

384,400 km

Perihelion

Nearest point in a planet’s orbit to the Sun

Aphelion

Farthest point in a planet’s orbit from the Sun

Summer solstice

When the Northern hemisphere is most tipped towards the Sun (June 21)

December solstice

When the Northern hemisphere is tipped furthest away from the Sun (December 21)

Vernal equinox

When the Northern hemisphere becomes tipped towards the Sun + the moment when the Sun’s path crosses the celestial equator (March 21)

Autumnal equinox

When the Northern hemisphere starts to be tipped away from the Sun (September 22)

Precession

a gradual wobble of the Earth’s axis’ orientation in space caused by gravity, affects timing of the seasons

Equinox

Day where most locations have equal amounts of daylight and night

Cause of seasons

Change in Earth’s axis tilt relative to the Sun and its effect on the angle at which sunlight hits the ground

How much does Earth’s distance from the Sun vary over a year?

3% (closest in January)

Cycle of Earth’s precession

26,000 years

What is the purpose of leap years?

To keep the dates of solstices/equinoxes about the same

When does the equator get the least direct sunlight?

The solstices

When is the Sun at peak height in the sky for someone on the equator?

Equinoxes

Tilt of the Moon

5° from ecliptic

Globular cluster

cluster of stars

Betelgeuse

Star 1000x the size of the Sun, 8 million years old

What causes apparent retrograde motion?

Earth surpassing other planets in its orbit

What planets are visible from Earth?

Mercury, Venus, Mars, Saturn, Jupiter

How old is the Sun?

4 billion years

Distance=

velocity x time

How far are we from Andromeda?

2\.5 LY

Angular size:

the angle created by an object’s linear boundaries when they reach the ground

Ecliptic path

path that the Sun traces around the Earth/Celestial sphere over its orbit (mirrors ecliptic plane)

Lunar eclipse

When the Earth aligns between the Sun and Moon; two total eclipses every 3 years

Solar eclipse

When the Moon aligns between the Earth and Sun; total eclipse every 18 months

Umbra

Earth’s full shadow

Penumbra

Earth’s partial shadow

Penumbral lunar eclipse

When the Moon only passes within Earth’s penumbral shadow

Partial lunar eclipse

When the Moon is partially covered by Earth’s umbral shadow

Moon phases

waxing crescent, first quarter, waxing gibbous, full, waning gibbous, third quarter, waning crescent, new (appears reversed in Southern hemisphere)

Length of cycle of phases

1 month/29.5 days (counterclockwise when facing Sun)

Moon rise/set times

Full: Rise-Sunset

Set-Sunrise

* Varies counterclockwise(sunset, —, midnight, —, sunrise, —, noon, —)

Earthshine

subtle illumination of moon’s face by sunlight reflected off Earth

How long does solar totality last?

A few minute

How long does lunar totality last?

About an hour

Annular solar eclipse

Solar eclipse where moon is directly in front of Sun but not large enough to cover it completely