It’s the first day of summer here in the Northern Hemisphere, and the first of winter in the Southern Hemisphere. Why the difference? It’s all about Earth’s tilt!
Earth’s axis is an imaginary pole going right through the center of Earth from “top” to “bottom.” Earth spins around this pole, making one complete turn each day. That is why we have day and night, and why every part of Earth’s surface gets some of each.
Earth’s axis is always tilted 23.5˚ with respect to the Sun. Today, the north pole is tipped toward the Sun, and the south pole is tipped away from the Sun. The northern summer solstice is an instant in time when the north pole of the Earth points more directly toward the Sun than at any other time of the year.
The solstice—meaning “sun stands still” in Latin—occurs at 10:54 a.m. CDT.
35.8 million miles is definitely not what most of us would consider “close.” But in planetary terms, close is definitely relative! On July 31, Mars will be 35.8 million miles from Earth, which is the closest it has been to Earth in 15 years. What does this mean for sky watchers? It means the Red Planet will appear super bright, and with its orange-red color, will be hard to miss in the nighttime sky. From July 27-30, the point in Mars’ orbit will come closest to Earth, and will be closest to Earth before sunrise Eastern Time on July 31.
What defines a “close approach?” The minimum distance from the Earth to Mars is about 33.9 million miles and does not happen very often. Because Earth and Mars have elliptical orbits and are slightly tilted to each other, all close approaches are not equal. When Mars slowly approaches what astronomers call opposition, it and the Sun are on opposite sides of the Earth. Earth and Mars align in opposition about every two years (fun fact: this is why most NASA missions to the Red Planet are at least two years apart – to take advantage of the closer distance). Opposition to Mars is at its closest to the Sun every 15 to 17 years, when excellent views of the Red Planet from Earth can occur. This is what is happening on the early morning hours of July 31.
Is 35.8 million miles the closest Mars has ever been to Earth? Nope. In 2003, Mars was 34.6 million miles from Earth and the closest it had been in nearly 60,000 years. This type of proximity won’t occur again until 2287. But, there will be another close approach in October 2020 when the distance between the Red Planet and Earth will be 38.6 million miles.
Now that we’ve gotten all of that out of the way, what does this mean for you, the novice astronomer or general sky-watcher? It means that if you have clear skies where you live, go outside on the overnight hours of July 30 or early morning hours of July 31 and look up. The planet will be brighter than usual and will have an orange or red haze. You can also look through a telescope. If weather is bad where you are, NASA will be streaming live from the Griffith Observatory.
Want to find out more about this year’s total solar eclipse — like what totality means and why the path of totality is so much smaller than the overall eclipse? Wonder how long it takes photons from the sun to reach Earth? Curious about dark matter and what we know about it? All are possibilities in the newly revamped Watch the Skies blog.
Hello and welcome back! We will be posting content more regularly, although it will be somewhat changed from before. You can look forward to new articles explaining different astronomy topics, breaking down complex science and jargon in a way that people can understand.
We’ll kick things off this week with some solar eclipse science. So come back then to learn more about just how wonderful and strange our universe can get!
Kevin Matyi is a summer intern in the Office of Communications at NASA’s Marshall Space Flight Center.
The graphic below illustrates the five planets as they are visible, with the naked eye, from Huntsville, Alabama. It shows their positions in the sky around 6:30 AM during the week of January 18 and continuing for the next few days. Mercury will be close to the Sun, over in the East, and Jupiter will be over in the West, with Venus, Saturn, and Mars between the two. Pluto is near Mercury, but is invisible to the eye, requiring a telescope for viewing.
The last time an alignment such as this occurred was about 10 years ago. This pre-sunrise configuration will be similar for other northern latitudes.
In the graphic, the yellow line is the ecliptic, which is the plane of the Earth’s orbit. The orbits of the major planets lie close to this plane, which is why they appear close to the ecliptic in the night sky.