The apparent Magnitude of Mars, as observed from Earth, can vary from +1 to -1 in the course of a few months?

Question

Why is this..?

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Answer 1

There is one more reason why the magnitude of Mars can change.

Mars experiences gigantic dust storms from time to time. These can cover the whole planet and reduce the reflectivity of the planet's surface substantially, resulting in a change of visual magnitude.

To the frustration of Mars observers, these storms can obliterate all surface features normally visible through a Telescope.

The magnitude changes caused by these storms can occur in a matter of hours or days, rather than the slower changes due to the planet's distance from us.

Adolph

Answer 2

Because Earth is orbiting the Sun much closer and therefore faster than Mars,  this happens when Earth overtakes it and moves away from Mars quite rapidly, causing the magnitude to fade relatively quickly.

The magnitude fades quickly because Mars is a small planet and its angular size (this year) decreases from 17" to 4" in a space of about 12 months due to the increasing distance from Earth.

It takes about 26 months for Earth to lap Mars in this race.

Hope this is clear enough for you.

Answer 3

It's all to do with reflected sunlight, and angle of view.

Answer 4

The apparent magnitude of Mars varies mainly due to the change in its distance from the Earth. Its distance can vary from about 56 to 400 million km over the course of a year. The phase of Mars also plays a small part in its brightness. Sometimes we see a "full" Mars and sometimes it is only about 85% illuminated. Also its distance from the Sun varies, so it becomes more brightly or less brightly illuminated by the Sun depending on its position in its own orbit.

There is an animation at the link below which illustrates how much Mars' distance from Earth varies:

http://www.windows.ucar.edu/tour/link=/m...