A Supersun (And Why It Doesn’t Mean Summer Weather)

Posted on Wed, January 3, 2018
  • by: Geneviève de Messières, Astronomy Education Program Manager

If you looked up at the sky on January 1, you might have witnessed something spectacular--the Moon kicked off the year with the biggest full moon of 2018. A full moon occurs when the Sun, Earth, and Moon line up so the Earth-facing side of the Moon is fully lit. On Monday, the Moon reached its full phase within hours of the moment when it was closest to the Earth (a moment which astronomers call “perigee.”) The Moon appeared 7.3 percent wider than during an average full moon, and just a bit brighter, earning it the informal title “supermoon.” It was lovely and brilliant to behold in a frosty sky, but it didn’t seem much brighter to me than any other full moon.

Bookending the month of January, another full moon will occur on the morning of January 31, 2018.  That one earns its headlines too.  It will be another supermoon, a Blue Moon, and a total lunar eclipse

The year’s first full moon is sometimes known as the Wolf Moon. This year’s Wolf Moon occurred on January 1, 2018. Photo by Geneviève de Messières.

But, enough about the Moon already! What about the Sun; did you know that it can be super, too?

If you’re shivering under a mass of Arctic air like many in the United States right now, it might not feel like the Sun is doing its part to keep you warm. However, it’s actually closer to you now, at the beginning of January, than at any other time in 2018 , and that deserves a headline, too. Around midnight last night, the Earth reached its closest approach to the Sun, in its not-quite-round orbit around our star. That moment of closest approach in the Earth’s orbit is called perihelion. And if a perigee full moon is called a “supermoon,” it’s only fair that the perihelion Sun should be called a “supersun!”

The “supersun” of January 2, 2018, photographed at noon EST with safe solar telescopes at the Phoebe Waterman Haas Public Observatory. Pictured, the blank surface of the Sun. The Sun is approaching a period of low activity. It currently has no sunspots. Photo credit: National Air and Space Museum

The “supersun” of January 2, 2018, photographed at noon EST with safe solar telescopes at the Phoebe Waterman Haas Public Observatory. Pictured is the lower atmosphere of the Sun, as seen with a calcium-K telescope. Photo credit: National Air and Space Museum.

Don’t break out the beach towels just yet, though. At perihelion, the Sun is about 2 percent closer and looks about 2 percent wider than average. The Earth is getting a tiny bit more light in January than in July. However, the main reason we’re getting frostbite here in the Northern Hemisphere is that the Earth is spinning on a tilted axis. 

Earth has seasons because its axis of rotation is tilted. Credit: NASA.

In January, the Northern Hemisphere is tilted away from the Sun. The Sun is low in the sky, and for fewer hours per day. Meanwhile, the Southern Hemisphere is experiencing summer: the Sun is high in the sky at noon, and it’s up for many hours per day.

The supersun may not have anything to do with the seasons, but it is a few million miles closer. We can use safe solar viewing devices to see it just a bit better, and that makes it super to me.


Related Topics