Transit of Mercury

Frequently, we observe solar and lunar eclipses here on our blue marble we call Earth. Solar eclipses are when the moon passes in front of the sun. Lunar eclipses are when Earth cuts between the sun and moon, with the moon covered in our shadow. Less commonly observed are planetary transits. Because we live on the third rock from the sun, we only get to see Mercury and Venus pass in front of it. Because orbits wobble and planes aren't aligned, this is something that is only seen a few times per century.

Transit of Mercury as seen with the unaided eye

Mercury transited the sun on November 11. Because the sun is so bright and Mercury is so small, a telescope with solar filter is a requirement to witness the event. I took a field trip to Philadelphia's Franklin Institute to see it for myself with their telescope. Because seeing Mercury normally requires a clear horizon at sunrise or sunset, most folks don't get to see it. This was my first time, and now I've finally seen all six naked eye planets- I included Earth, which I see every day.

Franklin Institute's telescope with solar filter

I got a shot of Mercury being live-streamed on the big screen

Sadly, I wasn't able to get my own pictures of Mercury, but I did get pictures. NASA was live-streaming and has a video up on their Youtube page. If you want to see a Mercury transit live and in person, you'll have to wait until 2032. You'll need to be in Africa, eastern Europe, or western Russia to see it. Otherwise, the next transit here in the states won't be until 2049. But if you think that's bad, the next transit of Venus won't happen until 2117.

NASA posted this picture of a prior transit on their Facebook page.
The little black spot on the bottom is Mercury. The one on
the top is a sunspot.

Lunar Lunacy

Next Wednesday (January 31) the world will be treated to a trio of rare lunar occurrences, all at the same time. A blue moon, super moon, and total lunar eclipse all fall on the same date. What are all of these? Let’s break it down one item at a time.

Humans love to name things, and a blue moon is simply when a second full moon happens in a single calendar month. Our first full moon was on New Year’s Day, which in itself is one of those rare events that people seem to think means something. Sometimes the moon actually does appear to be blue, but that is usually due to atmospheric issues like pollution.

A super moon is when the moon reaches its closest approach to Earth (the moon’s perigee). Our orbit around the sun isn’t round, it’s slightly elongated. The moon’s orbit of us is the same. When the moon is near or at perigee, it appears slightly larger than usual. It’s barely even noticeable to the human eye.

Diagram showing the moon's elliptical orbit (NASA image)

A lunar eclipse is when the moon passes through Earth’s shadow. This event only happens during a full moon, when the sun fully lights the side of the moon facing Earth. This puts Earth between the sun and moon. A solar eclipse requires a new moon, and places the moon between sun and Earth. During a lunar eclipse, the moon sometimes appears red. It’s also known as a blood moon. Next week we are treated to the rare super blue blood moon. That’s a mouthful!

Diagram showing the sun, earth, and moon positions during
an eclipse (Smithsonian Air and Space Museum)

NASA photo of a blood moon

The best lunar eclipse I’ve ever seen was in 2015. The eclipse began before moonrise, so by the time it came up over Mount Rainier it was already red. This time, I'll get to see it on my way to work, assuming we have clear skies.

Lunar eclipse over Mount Rainier

Partial phase of a lunar eclipse

Cosmic Ballet, Part 2

Despite dire warnings not to travel to Oregon for the solar eclipse, I went any way. Traffic was not as bad as predicted. My gamble that everyone going to Oregon would have left over the weekend paid off. My gamble that homeward-bound traffic would be going the opposite direction of where I was headed paid off. I even managed to get some pictures for those of you who weren't lucky enough to witness totality, which was a first for me.

Before totality, small chunk of sun missing from top right

The eclipse caused these funky curved shadows

Using your hands to make a pinhole viewer

Totality! The black circle is the moon, the white ring is the sun's corona

The sky was dark enough that some stars were visible. I think this is Venus.

The eclipse got underway just after 9 AM Pacific time, immediately preceded by a flock of birds flying overhead away from the sun. Was that related to the eclipse? I don't know. I don't recall seeing any birds until after the eclipse was over. It took a while to notice any changes in lighting, but as totality got closer it was like someone turning a dimmer switch until it got dark. At that point, the eclipse glasses came off, the pop of some fireworks, and the crowd at the nearby football field let out a cheer. It was oddly quiet and oddly dark for about a minute until there was a flash of light where the top of the sun came out from behind the moon and the dimmer switch turned the other way and daylight returned.
The next total solar eclipse to hit the US is in April 2024. At that time, I hope to be in the field studying how animals react to an eclipse. Not much is known because they are such an infrequent event. Many animals run on a solar (day-night) cycle and scientists like myself wonder what they do when night suddenly happens during the day for a brief period.
Stay tuned for more stories from the road following Nature Minute's great American road trip!

The Cosmic Ballet Continues

This Monday the United States will witness the rare and majestic total solar eclipse. Not all areas will see a total eclipse, but all of North America will see at least some of the sun disappear. While not a rare event, it is unusual for a total solar eclipse to cover such a large populated area. It seems like usually they happen only over the remotest part of the Pacific Ocean or exclusively at the South Pole. This eclipse will the first total solar eclipse to hit the US since 1979. That might not be too terribly long ago, but think about this: in 1979 there were still people alive who could remember the last time the Chicago Cubs won the World Series (1908) or fought in the war against Spain in 1898.

What is a solar eclipse? When the moon passes between the sun and Earth and casts a shadow on us, that’s a solar eclipse. They can only happen during a new moon, which is when the sun’s rays hit fully on the “dark side” of the moon, so it’s the only time you’ll ever see a new moon. New moons happen every 29 days, just like a full moon, but we don’t have a solar eclipse every month because of how the sun, moon, and Earth dance with each other.

Geometry of a solar eclipse- not to scale (from Nustem)

You’ll notice the sun is a lot higher in the sky now than it was in January. Because Earth is tipped about 23̊ as were orbit the sun while spinning in our tipped circle (which also wobbles) the sun appears to ride a squashed and stretched figure 8 across the sky called the elliptical. The moon does the same, but their ellipticals don’t always match. When they do, you get an eclipse.

Distance is also important. Neither Earth’s orbit nor the moon’s is circular; both are slightly elongated (an ellipse, hence the term elliptical) so sometimes the moon close enough to block out the sun during an eclipse and sometimes it fits inside the sun like a ring. This is called an annular eclipse. Like during a total eclipse, only a narrow band will see the annular eclipse, while everyone else gets to see a partial eclipse or nothing at all.

Annular eclipse (from Universe Today)

Partial eclipse (from Huffington Post)

Always practice safe eclipse viewing! Follow these tips from NASA. Never look directly at the sun, even during an eclipse. The only exception is during totality, and that is ONLY if you have totality where you are at, and it only lasts about a minute and a half. Use eclipse glasses- if you put them on and try to see anything but the sun, you should only see blackness. Sunglasses will not do the job. Never look at the sun through binoculars or a telescope, unless you have a solar filter. If your solar filter screws on to the eyepiece, it is junk- throw it away! If you don’t have any safe viewing equipment, make a pinhole viewer by poking a hole through a piece of cardboard and let the sun shine through. During the partial phase, you will see a spot of sunlight missing a chunk in the middle of the cardboard’s shadow.

I will be in Salem, Oregon for the eclipse, immediately preceding a very special Nature Minute road trip. Sorry, no live-blogging. I can’t blog while driving, and besides, there’s no wifi in the wilderness. Check back in September or follow along on Facebook for pictures and tales from the road.

This week's credits: Nustem, Huffington Post, Universe Today, and NASA