Astrology 8.4

Why does the North Star (Polaris) appear to stay in the same position all year?

It is located almost directly above Earth's axis of rotation at the North Pole.

Can you see Polaris from the Southern Hemisphere?

No; south of the equator, Polaris drops below the northern horizon and is not visible.

What is 'precession' in the context of the North Star?

It is a 26,000-year wobble of Earth's axis that causes the axis to point toward different stars over long periods.

Which star will eventually replace Polaris as the North Star in a few thousand years?

Vega.

How do you find Polaris using the Big Dipper?

Draw an imaginary line through the two 'pointer stars' (Dubhe and Merak) at the edge of the Big Dipper's bowl; they point directly to Polaris.

What does the altitude of Polaris in the sky tell an observer?

The height of Polaris above the horizon is equal to the observer's latitude.

Is there currently a 'South Star'?

No; there is no bright star currently aligned with the southern axis of Earth.

How bright is Polaris compared to other stars?

It is a 'middling-bright' star, ranked as the 50th brightest visible from Earth.

In which constellation is Polaris located?

It marks the end of the handle of the Little Dipper in the constellation Ursa Minor.

What is the fundamental cause of the seasons?

Earth's 23.5-degree axial tilt as it revolves around the Sun.

Why do the Northern and Southern Hemispheres have opposite seasons?

Because when the North Pole is tilted toward the Sun, the South Pole is tilted away (and vice versa).

What happens to the Sun's midday height during summer?

The Sun reaches its highest point in the sky for the year.

What happens to the Sun's midday height during winter?

The Sun remains much lower in the sky, even at solar noon.

Why is direct sunlight hotter than indirect sunlight?

Light at a high angle concentrates solar energy over a small area, while light at a lower angle spreads the same energy over a larger area.

True or False: Earth is closer to the Sun in the summer.

False; in the Northern Hemisphere, Earth is actually slightly closer to the Sun during winter.

What is an 'equinox'?

Days when Earth is tilted neither toward nor away from the Sun, resulting in approximately 12 hours of day and 12 hours of night globally.

When are the approximate dates for the equinoxes?

Around March 21 (Vernal/Spring) and September 22-23 (Autumnal/Fall).

What happens to daylight at the North Pole during the summer solstice?

It experiences 24 hours of continuous daylight.

What happens at the North Pole during the winter solstice?

It experiences 24 hours of continuous darkness.

On which days of the year does the Sun rise due East and set due West?

Only on the equinoxes.

Where does the Sun rise and set during summer in the Northern Hemisphere?

It rises North of East and sets North of West.

Where does the Sun rise and set during winter in the Northern Hemisphere?

It rises South of East and sets South of West.

How does the Sun's path change from summer to winter?

The arc of the Sun moves lower in the sky and shifts southward along the horizon.

When viewed from North of the Tropic of Cancer, what direction does the Sun rise and set?

It always rises at an angle up and to the right and sets at an angle down and to the right.

What is 'solar noon'?

The moment when the Sun reaches its highest point in the sky for that day.

Why does Manhattanhenge happen only twice a year?

Because the Sun's setting point on the horizon moves daily; it only crosses the specific angle of the street grid twice.

Why does Manhattanhenge not occur on the equinoxes?

Manhattan's grid is rotated about 30 degrees East of geographic North, shifting the alignment dates.

What are the two versions of Manhattanhenge?

'Full Sun on the Grid' and 'Half Sun on the Grid.'

What is 'Reverse Manhattanhenge'?

When the rising Sun aligns with the grid during the winter months (January and November).

Why is Chicagohenge different from Manhattanhenge?

Chicago's grid is aligned with cardinal directions, so its alignment occurs exactly on the spring and autumn equinoxes.

Does the Moon generate its own light?

No; we see it because it reflects sunlight.

What causes the phases of the Moon?

As the Moon orbits Earth, we see different amounts of its sunlit half depending on its position relative to Earth and the Sun.

How much of the Moon is always lit by the Sun?

Half of the Moon is always lit, except during a lunar eclipse.

What is the difference between 'waxing' and 'waning'?

Waxing means the lit part we see is getting larger; waning means it is getting smaller.

What is a 'gibbous' moon?

A phase where the Moon is more than half lit but not yet full.

Why does the same side of the Moon always face Earth?

Because the Moon takes the same amount of time to rotate once on its axis as it does to orbit Earth once.

What is a solar eclipse?

When the Moon passes between the Sun and Earth, blocking the Sun's light and casting a shadow on Earth.

During which Moon phase can a solar eclipse occur?

Only during a New Moon.

What is a lunar eclipse?

When Earth passes between the Sun and the Moon, casting Earth's shadow on the Moon.

During which Moon phase can a lunar eclipse occur?

Only during a Full Moon.

What is the difference between a total and partial eclipse?

A total eclipse occurs when an object is in the 'umbra'; a partial eclipse occurs in the 'penumbra.'

Why don't we see an eclipse every month?

The Moon's orbit is tilted about 5 degrees relative to Earth's orbit around the Sun, so the shadows usually miss their targets.

Why does the Moon look red during a total lunar eclipse?

Earth's atmosphere bends and scatters sunlight, projecting red light onto the Moon.

What is the 'path of totality'?

The specific track on Earth's surface where the Moon's darkest shadow (umbra) passes during a solar eclipse.

What part of the Sun is visible during a total solar eclipse?

The corona, which is the Sun's glowing outer atmosphere.

What is Earth's axis?

An imaginary line running through the center of Earth connecting the poles.

What is the difference between rotation and revolution?

Rotation is spinning on an axis; revolution is orbiting around another object.

What causes day and night?

Earth's rotation on its axis every 24 hours.

What is the name and shape of Earth's orbit?

It is an 'ellipse,' which is the shape of a squashed circle or oval.

How long does it take the Moon to orbit Earth?

About 28 days or one month.

How does the Moon's size appear to change during the 'waning' phase?

It appears to get smaller as it moves toward a New Moon.

What is azimuth?

A point along the horizon used to identify direction in degrees.

What is altitude or elevation in astronomy?

The angular height of a celestial object above the horizon.

What is the zenith?

The point in the sky directly overhead (90 degrees).

What is the nadir?

The point in the sky directly below the observer.

What is the umbra?

The inner, darkest part of a shadow.

What is the penumbra?

The outer, lighter part of a shadow.

What are circumpolar stars?

Stars near the poles that appear to circle them and never set.

What is the best way to remember eclipse names?

Think about what gets darker; in a lunar eclipse, the Moon gets darker; in a solar eclipse, the Sun gets darker.

What is the only Moon phase in which a solar eclipse can occur?

The New Moon.

What is a partial solar eclipse?

When only part of the Sun is covered by the Moon.

What is a total solar eclipse?

When all of the Sun is covered by the Moon.

What determines whether you see a partial or total solar eclipse?

Which part of the Moon's shadow you are in.

Why isn't there an eclipse every month?

Because the Moon's orbit is tilted relative to the Earth's orbit around the Sun.

How long do lunar eclipses typically last?

Usually a couple of hours.

What is Manhattanhenge?

A phenomenon where the setting Sun aligns perfectly with the east-west street grid of Manhattan.

When does Manhattanhenge typically occur?

Twice a year, usually around late May and mid-July.

Who is credited with taking the first photo of Manhattanhenge in 2001?

Neil deGrasse Tyson.

What is Chicagohenge?

A solar alignment with Chicago's street grid that occurs on the spring and autumn equinoxes.

Why does Chicagohenge happen on the equinoxes but Manhattanhenge does not?

Chicago's grid is aligned with cardinal directions, while Manhattan's is rotated.

What is the 'Reverse Manhattanhenge'?

When the rising Sun aligns with the Manhattan grid during winter months (late November/early January).

Where is one of the best viewing spots for Manhattanhenge?

34th Street and 5th Avenue, facing northwest.

What lens is recommended to capture the Sun and surrounding buildings?

A wide lens (24-50 millimeters).

What lens is recommended to zoom past crowds and capture the Sun alone?

A telephoto lens (70-300 millimeters).

What camera setting is recommended for optimal exposure during Manhattanhenge?

High aperture (F/16) and low ISO (e.g., 100).

What makes the Sun appear to move from East to West across the sky?

Earth's rotation.

At what rate does the Sun appear to move across the sky?

15 degrees per hour.

What is the 'meridian'?

An imaginary line from north to south passing through the zenith.

When does the Sun rise due East and set due West?

On the equinoxes.

What is the 'celestial sphere'?

An imaginary sphere surrounding Earth onto which all celestial objects appear projected.

How many degrees of daylight are in a complete 24-hour circle?

360 degrees.

What are the primary reasons for the seasons?

Earth's 23.5-degree axial tilt and its revolution around the Sun.

Does Earth's distance from the Sun cause the seasons?

No.

What happens to shadow length at noon as the seasons change from summer to winter?

Noon shadows become longer in winter.

Why is summer hotter than winter?

Sunlight hits the Earth more directly (at a higher angle), concentrating energy over a smaller area.

What is the angle of sunlight hitting the Earth directly?

90 degrees.

When is the Northern Hemisphere tilted most toward the Sun?

During the Summer Solstice (around June 21).

When is the Northern Hemisphere tilted most away from the Sun?

During the Winter Solstice (around December 21).

If you are far from the equator, has the Sun ever been directly over your head?

No; it only goes directly overhead within 23.5 degrees of the equator.

What is a 'gnomon'?

The vertical pole on a sundial that casts the shadow.

Why does the Sun look more orange/red at sunrise or sunset?

Sunlight travels through a longer path of atmosphere, scattering blue light and leaving redder hues.

How long does the Moon take to make a full orbit around Earth?

Approximately 27 to 29.5 days.

What are 'Moon phases'?

The changing appearance of the Moon's lit portion as seen from Earth.

What does 'waning' mean?

When the visible lit part of the Moon appears to be getting smaller.

What does 'waxing' mean?

When the visible lit part of the Moon appears to be getting larger.

What phase follows the Third Quarter Moon?

Waning crescent.

What is a natural satellite?

A naturally occurring body that orbits a planet.

How many natural satellites does Earth have?

One (the Moon).

What determines the shape of the Moon we see?

The Moon's position in its orbit relative to the Sun and Earth.

What is another name for the North Star?

Polaris.