# Question about the Sun's Motion

My name is Chris, I am a junior and I'm taking an Astronomy class in my high school. For a homework assignment, I have to explain how the Sun would move across the sky from September 1st through September 30th (assuming that the weather allows viewing)

For example: In this picture the

sun is facing west. If I were to take a picture of this same area at the same time every day for the whole month, How would the sun change? Would it go east? Would it go lower in the sky?

I, being a new student to Astronomy, honestly have no clue.

• Lets start with something simple. What season is it and what is happening to the length of daylight?
– LDC3
Oct 11, 2014 at 4:12
• To have an Astronomy class in high school, you are clearly the luckiest person alive. Oct 11, 2014 at 14:49
• Chris / @Kultid_Games , did you figure it out? Oct 11, 2014 at 22:42
• @HDE226868 Yes actually I have. And yeah my teacher is pretty awesome too actually, so I guess I'm lucky on two level :D He is 63 (I had him for Chemistry last year too) and he always talks about rock concerts and stuff.) But thank you :D Oct 11, 2014 at 22:54
• Here's a nice analemma showing the sun's psition over the Temple of Apollo in Corinth at 9am over the course of a year. September falls in there somewhere: apod.nasa.gov/apod/ap130922.html A Martian analemma looks quite different: apod.nasa.gov/apod/ap061230.html Oct 12, 2014 at 2:02

Over the year, the sun follows a path known as an annalemma. This is a figure eight shape and is caused by the combination of the Earth's rotation around the Sun and its tilt relative to the plane of the equator.

The analemma can be observed by pointing a camera at the sun, and at the same time each month, take a picture and over lay the images:

Taking a picture every day for a month (in September) would mean that you'd see it lower in the sky, curving slightly as it followed the figure of eight shape of the analemma.

### Note:

An analemma can be different on different planets. For example, a Martian analemma is different because its tilt and shape of orbit is different to that of Earth's:

• Mercury: Because orbital resonance makes the day exactly two years long, the method of plotting the Sun's position at the same time each day would yield only a single point. However, the equation of time can still be calculated for any time of the year, so an analemma can be graphed with this information. The resulting curve is a nearly straight east-west line.
• Venus: There are slightly less than two days per year, so it would take several years to accumulate a complete analemma by the usual method. The resulting curve is an ellipse.
• Mars: teardrop
• Jupiter: ellipse
• Saturn: technically a figure 8, but the northern loop is so small that it more closely resembles a teardrop
• Uranus: figure 8 (Uranus is tilted past "sideways" to an angle of 98 degrees. Its orbit is about as elliptical as Jupiter's and more elliptical than Earth's. )
• Neptune: figure 8

A good way to visualize the apparent movement of the sun across time is using the free stellarium program. First input your location and time you would like to view because location will determine what the apparent movement of the sun. For example, if you live in Seattle WA and facing the west observing the position of the sun for the periods of September 1 - 30 you will notice the sun appears to move downward and to the left in the sky (see screenshots).

The cause of this phenomenon is the tilt of the Earth's axis. As the Earth revolves around the Sun, the tilt changes, the seasons progress, and more or less sunlight hits a given region of Earth, depending on where it is and which way the axis is tilted. This tilt means that the Sun appears to be at a different angle in the sky, which in turn means that in winter, the Sun appears lower in the sky. In summer, the Sun appears higher in the sky. So as September progresses, the Sun should start getting lower and lower. This graphic sums it up: