Mars

Mars is the most similar planet to the Earth in our solar system. It is about half Earth's size (4000 miles in diameter), has 1/3 the gravity on the surface, a thin atmosphere with clouds, a similar day length, polar caps, huge volcanoes, dry river valleys, a gigantic canyon (Valles Marinis) that dwarfs our Grand Canyon, sand dunes, and ancient, dry river valleys. Mars is also quite different from Earth. It has two tiny moons (Phobos and Deimos) that orbit very close to Mars, it is heavily cratered, probably does not harbor life, Mars is very cold (the warmest it ever gets is about 80F), and there are huge dust storms that can occur whenever Mars is closest to the Sun. Telescopically, Mars is a fascinating object to observe, if you are patient.

Mars is a superior planet which means that it orbit is larger than ours and that it is moving more slowly than Earth.  Earth overtakes Mars in its orbit around the Sun about every 26 months. The orbit of Mars is not very circular, whereas Earth's orbit is. This means that the distance between Earth and Mars when Earth passes Mars (called "opposition") can be only 35 million miles (as it is in 2003) or as much as 64 million miles (as in the 1995 opposition). Between oppositions, the two planets are very far apart and it is tough to see any detail on Mars at all. It is clearly best to observe Mars at opposition and we are in luck.  Mars comes to opposition this semester for the first time in more than two years.  The down side is that even at opposition, Mars still appears tiny in a telescope. 

Objectives:

1. To observe and map the surface of Mars, and note any surface and/or atmospheric features.

2. To observe the apparent motion of Mars against the starry sky.

Requirements:

1. A detailed sketch of Mars made at the telescope.  Try to identify the features that you see with the map provided to you. 

2. A map that shows the motion of Mars against the stars.

3. Answers to the questions that appear at the end of this lab.

Directions:

1. Find Mars in the sky.

2. Make a sketch of Mars and surrounding stars. Note north, south, east and west on your map. 

3. Repeat every week from February 18th until March 11th.

1. Set up a telescope and align it with the north celestial pole.

2. Carefully shade the circle of an observing form a uniform, neutral grey. This is so that light

features can be sketched by erasing and dark features can be sketched by drawing darker.

3. Locate Mars with the telescope and switch to high power. Mars is small but can take a lot of

magnification. Try to use at least 200x for an 8-inch telescope.

4. Observe Mars (without sketching) for about five minutes to let your eyes adapt to the subtle

details on the surface.

5. Quickly sketch in the MAJOR details that you see on the surface.

6. Fill out the observing form (time, date, magnification, weather, seeing, etc.)

7. Now carefully fill in all of the tiny details that you can glimpse. Make notes of interesting features you see. Even the tiniest detail that you are sure of should be included. Look for the small, bright polar cap, and dark markings on the orange planet.

8. Look at the map of Mars provided by your instructor. Try to identify any features that you see.

Questions:

1. What two ingredients are the polar caps made of?

2. How much is the rotational axis of Mars tipped? How about Earth’s rotational axis? What effect does this have on the planets?

3. Did you see the polar caps? What did they look like? What does this tell you about which season it is on Mars?  Hint: Think of how the Earth would look from the Sun's perspective during our year. 

4. What causes the dark features seen on the planet?

5. How long is a day on Mars? If you looked at Mars two nights in a row, at the same time, what would you expect to see on Mars compared to the first night?

6. How long is a year on Mars? How often does Earth pass Mars? What is this event called?

7.  What phase did Mars appear in the telescope?  What phase would Mars appear to be when it is on the far side of the Sun?  How do all superior planets appear in the telescope from Earth?

8. Explain the motions of Mars that you observed during the months that you observed it. Be specific.  Was Mars exhibiting pro-grade or retrograde motion when you saw it?  Why?

9. If you were on Mars, what would Earth look like in a telescope (hint: think how planets that orbit inside of our orbit appear from Earth through a telescope).  What phase would Earth be?

10.  Why is it so hard to see details on Mars through a telescope?