Nan at Night by Nan Hoyt
-Thursday the 3rd: Every night, a single star maintains its position in our sky: Polaris, the North Star. All the other stars appear to wheel around Polaris. This apparent motion is caused by Earth’s rotation on its axis, which aims toward Polaris.
-Friday the 4th: Happy Independence Day! Earth is at aphelion today, which marks its farthest point from the sun for the year. We are more than one million miles farther from the sun than the average distance of about 93 million miles.
-Saturday the 5th: Mars and Saturn are dancing close together for the next several nights. Look for them low in the west at nightfall. Tonight, they are to the upper left of the crescent moon, with the star Regulus lining up between the moon and the two planets.
-Sunday the 6th: Saturn and Mars stand close to the right of the crescent Moon this evening. Saturn is brighter and a little closer to the moon. Regulus, the brightest star of Leo, completes the array to the lower right of the planets.
-Monday the 7th: Jupiter, the largest planet in the solar system, is low in the southwest at first light tomorrow. It looks like a dazzling star. The smallest planet, Mercury, is on the other side of the sky, quite low in the east-northeast shortly before sunrise.
-Tuesday the 8th: Jupiter, the biggest planet in the solar system, is putting in a big appearance this month. It is visible from dusk until dawn, and it’s brightest for the year. Look for it low in the southeast at nightfall. It looks like a dazzling cream-colored star.
-Wednesday the 9th: Mars passes Saturn over the next couple of nights. They are low in the west at sunset. Mars is below brighter Saturn this evening. The moon is half-lit in its 1st quarter stage.
-Thursday the 10th: Mars and Saturn continue to perform a duet as Mars overtakes Saturn. Look for Mars to the lower left of Saturn in the western sky at twilight.
When we think of the Earth orbiting around the sun we often visualize a perfect circle. In actuality the orbital path is slightly distorted which results in the Earth being somewhat closer to the sun at one time of year and farther away at another. It may surprise you that we are reaching our farthest point from the sun this Friday, July 4th during what seems like the warmest time of the year. This phenomenon is termed aphelion and occurs once a year, usually near the summer solstice in the Northern Hemisphere. On January 2nd of this year we reached perihelion, which is our closest approach to the sun. Perihelion usually occurs sometime near the winter solstice in our Hemisphere. What we often forget is that “down under” the equator it is winter while we experience our (sometimes) blazing hot summers. The seasons of our planet are determined by the “tilt” of our planet on this particular orbit. During the summer months in the Northern Hemisphere, the northern half of the Earth is “tilted” toward the sun, even though we are at our farthest point from our star. Consequently, in the winter, we are tilted away even though we are closest to the Sun in the Northern Hemisphere. Astoundingly, in the 1700’s astronomers were able to first accurately measure this Earth-Sun distance and called it an Astronomical Unit (or AU). “They did so by observing Venus crossing the face of the Sun from different points around the Earth. Comparisons of these different views allowed them to hone in on the value of the AU – which turns out to be about 93 million miles.” The AU is still an important form of measurement used to describe distances within our solar system today, such as Jupiter orbits the sun at 5 AU. The AU is actually an average distance calculating the midway point between the Earth’s position at perihelion and aphelion. The ability of scientists long ago determining these concepts with the tools of their time is always a humbling concept for me. We can admire the patience and determination needed to arrive at these huge ideas and maybe slow down a little this summer and reflect on those same stars that still shine down on us.
