Astronomy: Actvity 1

2.1 The Sky Above, 4.1 Earth and Sky

Recall that the Sun travels along the ecliptic over the course of the year.

How many times each year does the Sun pass through your zenith if you live on the Equator?

2 times each year.

(Since the celestial equator is directly over Earth's equator and the Sun travels along the ecliptic, the sun will be directly overhead at the points where the ecliptic and celestial equator cross, which happens TWO TIMES each year. This occurs during the equinoxes.)

QUESTION 1:

There is a clear trend in the altitude of the NCP above the northern horizon as view from different northern latitudes. What is this trend?

The NCP is high above the horizon at higher latitudes, and its altitude above the horizon is equal to the latitude.

QUESTION 2:

At what latitude are you currently?(Milwaukee)

43 degrees

QUESTION 3:

If the night sky was clear and you went out to find the star Polaris(NCP), how many degrees would it be above the northern horizon?

43 degrees above.

QUESTION 4:

Is the motion of the stars around the Polaris(NCP) due to the rotation(daily motion) or revolution(yearly motion) of Earth?

Rotation of the Earth.

The stars appear to move around the Polaris because the Earth is rotating between them.

QUESTION 5:

Where on Earth are you if the northern stars move in horizontal circles across the sky, never rising or setting?

At the North Pole.

Polaris(NCP) is directly overhead, and the other stars move in horizontal circles around it.

QUESTION 6:

where on Earth are you if all the stars rise and set, moving perpendicular to the horizon as they do so?

At the Equator

Polaris(NCP) is on the horizon, and the others stars rise and set perpendicular to the horizon.

Where on Earth are you if the Sun passes directly overhead twice per year?

At the Equator.

This happens when the Sun is at the two points where the celestial equator and ecliptic cross.

If we assume the 12 constellations of the zodiac were evenly distributed along the ecliptic, about how long would the Sun “stay” in each of those constellations?

About 1/12 of the year, or one month.

Imagine that at noon on the northern summer solstice there is a total eclipse of the Sun, and you can see the background stars in the middle of the day. The sky might look something like the sketch in image shown.

Notice that the Sun is in the constellation of Gemini. On the same day 6 hours later, in which constellation would the Sun be?

Gemini

Is the apparent motion of the Sun against the background constellations due to the rotation (daily motion) or revolution (yearly motion) of Earth?

Revolution(yearly motion) of Earth around the Sun.

The image shows how the position of the Sun is relative to the stars’ changes over the course of a year.