During the months on the "upper half" of the annual cycle, I like to try to do my morning Sun Salutations outdoors, towards the direction of the rising sun.
Because I live in the northern hemisphere, these are the months between the March equinox and the September equinox, when hours of daylight are longer than hours of darkness, and when it is generally warmer outside than it is during the months on the "lower half" of the annual cycle. Even during the lower half of the year, I like to try to do my Sun Salutations outdoors if possible, on occasion and weather permitting, but as days get longer and warmer during the upper half of the year it is especially enjoyable to take advantage of those conditions and practice outdoors if at all possible.
Doing your Sun Salutations outdoors has numerous benefits. If the sun is already above the horizon, you can close your eyes as and feel the sun on your face and see its warm glow through your eyelids. Additionally, if you orient yourself and your Yoga mat towards the sun each morning, you will be able to follow its daily motion as it rises further and further north (during the "upward" progress from winter solstice up to summer solstice) or further and further south (after summer solstice, when the sun turns around and rises further and further south on its way "down" to the winter solstice).
In this way, you will actually become a sort of human gnomon or menhir, and will gain a good first-hand feel for the sun's annual motion along the horizon. Here's a link to a postfrom the early days of this blog which discusses this principle as part of an examination of the concept of "cross-quarter days" (one of which is coming up soon!) -- and here's a link to one more early post which contains a little sketch I made showing the same concept from a slightly different angle.
If the sun is already up in the sky and casting shadows, then you can easily align yourself in the direction of the sun by seeing that the shadows made by your arms and legs as you do your salutations are going "straight back" and not off at an angle from the point your hands or feet are touching the mat.
Below is a composite image showing my Yoga mat as it moves through the year, pointing towards the sunrise in the east:
The top of the image is pretty much due east, and thus north is towards the left and south towards the right. At present, my mat is oriented as shown in the top image in the composite, facing towards "north of east" -- but not too long ago (prior to the March equinox) it was oriented as shown for "south of east." As most readers already know, the sun's rising-point moves back and forth along the eastern horizon between a northernmost point (reached at the June solstice) and a southernmost point (reached at the December solstice), passing through the "due east" rising point twice each year at the equinoxes (once on its way north, in March, and once on its way back south, in September).
By lining up your Sun Salutations to face the sun each morning, you will be aligning yourself with this annual motion as well!
Note that we already do many things that correspond to the cycles of the heavens, often without even thinking about it. For instance, most of us take our sleep during the hours that our side of the earth is turned away from the sun, thus aligning our waking and our sleeping hours with the sun's progress across the sky or (figuratively speaking) "under the earth." Most of us observe our own birthdays, and the birthdays of our friends and family, which is a way of noting when the earth in its annual motion around the sun has returned to the same relationship it had on the day upon which we (or our friend or family member) was born. And there are many other examples, of course, that most of us can come up with, once we begin to consider the subject.
If you read translations of some of the ancient Sanskrit texts, including the great epics of the Mahabharata and the Ramayana, you will see that the characters in those stories perform morning rituals at the sun's rising each day.
Additionally, there are passages in the Pyramid Texts which describe the gods giving their salutations to Ra. In Utterance 579, for instance, the text at one point says: "They praise thee; they come to thee with salutations, as they do homage to Re, as they come to him with salutations" (1952 translation by Samuel A. B. Mercer).
For more on the Yoga Sun Salutations, see this previous post (linked in the first line, above, as well).
For those in the northern hemisphere, where the days are getting longer and warmer as we head towards our summer months, I hope that you can have the opportunity to do some Sun Salutations outside, oriented towards the sunrise, if at all possible!