Astronomy Lab Midterm

What is 0.000001?

1.0 x 10⁻⁶

What is Scientific Notation?

a x 10ⁿ

What is 1,000,000?

1.0 × 10⁶

What is 8,200 to Scientific Notation?

8.2 × 10³

What is 4.5 × 10⁶ to Standard Notation?

4,500,000

Astronomical Unit

Average distance from the Earth to the Sun; approximately 149.6 million km (93 million miles)

Light year

Distance that light travels in one year; 9.46 trillion km (5.88 trillion miles)

Parsec

Distance at which an object would have a parallax angle of 1 arcsecond when viewed from Earth; 3.26 light years

How much is 1cm?

0.01m

How much is 1km?

1,000m

Degree

The full sky is 360° across

Arcminute

Each degree is divided into 60; allows for more precise measurements

Arcsecond

Each arcminute is divided into 60; used for very small objects

Sources of Uncertainty for Astronomy

• Instrument Precision

• Observer error

• Environmental factors

  • -+ (represents possible margin of error)

How many cm in a meter?

100cm

What is 2.54cm to mm?

25.4mm (2.54 × 10)

What is 1500m to km?

1.5km (1500 divided by 1000)

The average distance from Earth to Mars is about 225million km. What is the distance to AU?

Roughly 1.5 AU (225million divided by 149.6million)

Star A is 45 arcminutes away from Star C and Star B is 5 degrees away from Star C. Which star (Star A or Star B) is farther from Star C?

Star B is farther than Star C (60 × 5 = 300 arcminutes)

What do the different sizes of the dots on a star chart represent?

The magnitude (brightness) of stars

What does the circular border around the star map represent?

The horizon

Why do you think there is a different chart for every month?

The orbit of the Earth around the Sun places different regions of the sky in our night-time view

What is the horizon?

The boundary between the sky and the ground

What is the meridian?

An imaginary half-circle connecting south, zenith and north

What is the ecliptic?

The path of the sun in the sky

Constellation

A group of stars forming a recognized pattern in the sky (e.g. Ursa Major)

• Defined by the International Astronomical Union (there are 88 of them named)

Asterism

An identifiable group of stars that is not recognized as a constellation (e.g. Big Dipper)

Zodiac Constellations

12 constellations that the Sun blocks out at a given time of the year

• Situated along the elliptical line

Why do you think there is a difference in what constellations you are able to observe at different hours?

Earth’s daily rotation and the annual orbit of the Sun

What is significant about the 12 constellations of the zodiac, astronomically speaking?

They lie along the elliptic (the path of the Sun), and also mark the path where the Moon and stars are found

Do all stars appear to rise and set in Costa Mesa?

No, but because we are at an angle, some stars appear to rise in the East and set in the West (past the horizon), while others appear to not set at all (not passing the horizon)

Do all stars appear to rise and set in the North Pole?

No, because all visible stars here are circumpolar, circling the sky parallel to the horizon; more accurate portrayal of stars and their motion

Circumpolar stars

Stars that never rise or set below the horizon; remain visible at all night and all year-round

What is the azimuth of this star? (insert image)

120 degrees

If you measure the North Celestial Pole (NCP) to be 0 degrees above the horizon, your location is…?

The equator

Which planet is most similar in size to the earth?

Venus

What happens to the length of the year of the planets around the Sun as the distance from the Sun increases?

It increases

Aphelion

The point of the Earth’s orbit farthest from the Sun; slower

Perihelion

The point of the Earth’s orbit closest to the Sun; faster

This ellipse has an eccentricity of about…? (insert image)

0.75 (since “a” like 75% on the semimajor axis)

What did we use for our refracting telescopes in class?

Lenses

Refraction

Bending of a light path as the light moves from one medium to another

• Changes the angle light makes with the surface

Reflection

Light changing direction at the surface of an object

Convex

Thicker in the middle, thinner on the outer edges; light rays are bent so they can come closer together (converge)

Concave

Thinner in the middle, thicker on the outer edges; light rays are bent so they diverge, moving farther apart (diverge)

Magnification

Ratio and height of the image object to the height of the original object

If it is summer in Costa Mesa, California. What season is it in the southern hemisphere?

Winter

What season is it when the sun’s altitude is high, the angle is more direct, and sunbeam spread is more concentrated?

Summer

What is the declination of a star that is located on the celestial equator?

0 degrees

Altitude

Measures how high an object is above the horizon

• 0° at horizon

• 90° at zenith

What is the altitude of an object located at the zenith?

90°

What is the altitude of an object located at the horizon?

0°

What is the altitude of an object located halfway from the horizon?

45°

What is the altitude of an object located 2/3 up from the horizon?

60° (90 × 2 = 180) (180 divided by 3 = 60)

Azimuth

Measures the direction along the horizon

• 0° North

• 90° East

• 180° South

• 270° West

What is the azimuth of an object located in the southeast?

135°

• Reason: Southeast is exactly in between South and East, which equals around 45°. So, if you take 90° and add 45°, you get 135°

What is the azimuth of an object located in the northwest?

315°

• Reason: Northwest is exactly in between North and West, which equals around 45°. So, if you take 270° and add 45°, you get 315°

What is the azimuth of an object located in the south-southwest?

202.5°

• Reason: South is 180° while Southwest is 225° (180 + 45), so if you add both and divide by two, you get 202.5°

What is azimuth of an object that is transiting (at its highest point in the sky)?

0°

Latitude

Measures north-south position from 0° (equator), up to +90° (North Pole) or down -90° (South Pole)

Longitude

Measures east-west position from 0° (Prime Meridian), ranging from -180° to +180°

What is the latitude and longitude of Costa Mesa?

Roughly 34° N and 118° W

Where is the celestial equator located in your local sky if your latitude is 0° (you are on the Earth’s equator)?

90° in our local sky

Where are the north and south poles located in your local sky if your latitude is 0°? (you are on the Earth’s equator)? Could you see Polaris?

Both at 0° from our local sky; yes, you could see Polaris, but just barely as it is only visible in northern horizon near the NCP

What is the altitude of the north celestial pole?

0°

How does the north celestial pole’s altitude compare with the latitude of the Earth’s equator?

They compare the same at 0°

Where is the celestial equator located in your local sky if your latitude is 90° (you are on the Earth’s North Pole), what is its altitude?

0°

What is the altitude of the North Celestial Pole?

90°

How does the altitude of the North Celestial Pole compare to the latitude on the Earth’s North Pole?

They compare the same at 90°

The altitude of the NCP and Polaris are equal to what on Earth?

Your latitude

What is the altitude of the North Celestial Pole in Costa Mesa?

Roughly 34° above the horizon

What is the altitude of the celestial equator when it crosses the meridian?

56°

• Reason: 90° (degrees of the celestial equator from the NCP) - 34° (Costa Mesa latitude) = 56°

What path would a star (located on the celestial equator) make if it were at the latitude equator?

0°; Star would rise in the east, pass through the zenith and then set in the west

What path would a star (located on the celestial equator) make if it were at the North Pole?

90°; Star is circumpolar and is exactly at your latitude

• Does not pass through zenith

What path would a star (located on the celestial equator) make if it were in Costa Mesa?

34°; Star would rise in the East and only reach an altitude of about 56° above our horizon (below the zenith) before setting West

Right Ascension

Like longitude but measured in hours, minutes and seconds

• 0h - vernal equinox

• 12h - autumnal equinox

• 24h - vernal equinox, one full circle around the sky

Declination

Like latitude, measured in degrees, arcminutes and arc seconds

• +90° = north celestial pole

• 0° = celestial equator

• - 90° - south celestial pole

Costa Mesa vs Victoria - What do you notice about the azimuth values and altitude values of Polaris compared to Arcturus?

The altitude and azimuth of Polaris remains very consistent, only changing by a few degrees between locations. Meanwhile, the altitude and azimuth of Arcturus is less consistent, changing degrees far more drastically between locations

Costa Mesa vs Victoria - What do you notice about the right ascension values and declination values of Polaris compared to Arcturus?

The RA and declination values of both Polaris and Arcturus remain very consistent, with the exception of a few seconds between locations

Which star is closest to the North Celestial Pole?

Polaris

Which star is closest to the celestial equator?

Regulus (it lies on the ecliptic)

What happens to the horizontal and equatorial coordinates as a star moves across the sky?

The equatorial coordinates (altitude/azimuth) remains fixed while the horizontal coordinates (right ascension/declination) change constantly as the star moves across the horizon

What are some advantages of equatorial coordinates over horizontal coordinates?

Equatorial coordinates provide more accurate results that can be measured multiple times from:

• any location

• any time

• any season

What causes the seasons?

Earth’s tilt (23.5°); different regions receive more or less direct sunlight at different times of the year

What also causes the seasons?

Earth’s orbit around the Sun; throughout the yearly orbit, the tilt remains constant

What is NOT a cause for the seasons?

Earth’s distance from the Sun

Direct Sunlight

When the Sun is high in the sky, sunlight is concentrated in a small area:

• more intense

• warms surface more efficiently

Which season is there more direct sunlight?

Summer (when a hemisphere is tilted toward the Sun)

Indirect Sunlight

When the Sun is lower in the sky, sunlight is spread over a larger area:

• less concentrated

• less intense

• provides less heat

Which season is there more indirect sunlight?

Winter (when a hemisphere is tilted away from the Sun)

Spring

Vernal Equinox (March 21st)

• Sunlight is moderate, neither as concentrated as in summer or as spread as in winter

Summer

Solstice (June 21st)

• The Northern Hemisphere is most likely tilted toward the Sun

• Sun appears higher at noon

• Sunlight is more concentrated; hits ground at steeper angle, more intense warmth

• Longer days

Fall

Autumnal Equinox (September 21st)

• Sunlight is moderate, neither as concentrated as in summer or as spread as in winter

Winter

Solstice (December 21st)

• The Northern Hemisphere is least likely tilted from the Sun

• Sun appears lower in the sky at noon

• Sunlight is spread over a larger area; less concentrated, less warm

• Shorter days

The Northern and Southern hemispheres experience…?

Opposite seasons

• They reverse after six months

What are the seasons at the equator?

Gets consistent sunlight year-round, so seasons are minimal

What are the seasons at the Mid-latitudes (e.g. US, Europe)?

Experience noticeable seasonal changes due to varying sunlight angles

What are the seasons at the poles?

Get continuous sunlight in summer and no sunlight in winter, leading to extreme seasonal variations

Precession

The changing of Earth’s axis over a very gradual period (wobble motion) due to the gravitational pull of both the Sun and the Moon

The most direct sunlight is…?

Perpendicular to the earth's surface (90° angle)