Astronomy Merit Badge 3

Here's what we covered last time (week 3):

- The Earth rotates and revolves around the sun. The apparent motion of the sun, moon and stars each day is due primarily to rotation. If you look north at night, you will see the stars slowly rotate around the axis of the Earth's rotation (which is the point of requirement 4c, which was your homework last week).

- Our revolution around the sun causes the stars to be shifted a little each night, so we see different parts of the universe at different times of the year.

- One of the things we see in the summer sky is the milky way. It is actually the center of the galaxy we live in (the milky way galaxy).

- The moon revolves around the Earth, which gives it the appearance of "phases". When the moon and sun are on opposite sides we see a full moon, when they are on the same side it's a new moon.

- When the new moon is directly between Earth and the sun it can cast a shadow on the Earth, which is a solar eclipse. Since the moon is relatively small, it's shadow only falls on a small part of the Earth's surface, so not everyone gets to soo an eclipse. An eclipse lasts jsut a few minutes.

- When the Earth is directly between the Moon and the Sun it can cast a shadow on the Moon, which is lunar eclipse. Since the Earth is much bigger than the moon, it's shadow covers the entire moon, for hours. Everyone on the night-time side of Earth during a lunar eclipse can see it.

- There are 8 officially recognized planets. There are 5 (excluding Earth) that are visible to the naked eye:
The other two can only be seen with a telescope, which is why they were discovered so late:
    Uranus (discovered in 1781)
    Neptune (discovered in 1846)

- Requirement 5b says to list the times when the 5 most visible planets are visible. That information can be found on the web at

- The sun is a star.

- Our sun provides us with heat and light. The difference in weather from summer to winter is caused by the fact that the Earth is tilted. When we are tilted away from the sun, the sun is lower in the sky and not up for as long, so we get less heat and light, while the southern hemisphere gets more (so they have warmer weather in the winter). In the summer the opposite is true.

- Stars like our sun are made mostly of hydrogen and get energy by coverting the hydrogen into helium.

- Sunspots are cool spots (relatively cool, only 7000 degrees!) on the surface of the sun.

- Our sun is a yellow star. Other stars can be different colors, depeding on their temperature. Blue stars (like Rigel) are the hottest. Yellow stars (like our sun or Capella) are cooler, and red stars (like Betelgeuse) are the coolest.