BAN #337: Happy aphelion!, Brains On Bicentennial

[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]

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Upcoming Appearances/Shameless Self-Promotion

Where I’ll be doing things you can watch and listen to or read about

My friend Sanden Totten (who was on the writing team when I worked on Bill Nye Saves the World) has a fantastic science podcast for kids called “Brains On”, which just celebrated their 200th episode. Wow.

They have a segment where the Sun has guests on for a talk show, and our nearest star invited me to talk about why space is dark and cold even though she is bright and hot. I gave it my best shot. My segment starts around 22 minutes in. Hopefully I… shed some light on this.

“Brains On” really is terrific, so if you know some young-uns who want to learn about science (or maybe don’t know they want to learn about science yet) then you should tell them about it. Sanden is a wonderful person and a great science writer.

Congrats to the whole team on their bicentennial episode!

Blog Jam

What I’ve recently written on the blog, ICYMI

[A part of the mighty Andromeda Galaxy, the nearest big galaxy to us and part of the Local Group. From Thursday’s article.  Credit: Local Group Survey Team and T.A. Rector (University of Alaska Anchorage)]

Y’all read my blog, right? If you don’t it makes my editors cry. Don’t make them cry: Click these links and read ‘em!

Monday 28 June, 2021: Baby stars throw big tantrums. Very, very big tantrums. And they do it a lot.

Tuesday 29 June, 2021: Spacetime shakes: For the first time, astronomers see a black hole eating a neutron star

Wednesday 30 June, 2021: Tiny but mighty: Astronomers find the smallest but most massive white dwarf ever seen

Thursday 1 July, 2021: The motions of 66 nearby galaxies have now been reliably measured. Not stars. *Galaxies*.

Friday 2 July, 2021: A deep, deep photographic dive into Cygnus the Swan

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

Today (July 5, 2021) at 22:27 UTC (6:27 p.m. Eastern US time) the Earth will reach aphelion, the point in its mildly elliptical orbit when it’s farthest from the Sun. At that time, we will be 152.1 million kilometers from the Sun (roughly speaking, and measured center-to-center, which matters because while the Earth has a radius of ~6,400 km the Sun has a radius of 700,000), compared to the usual 150 million.

You probably won’t notice the Sun looking any smaller than usual, because a) the difference is tiny, only a couple of percent, and 2) it’s not like you spend a lot of time (I hope!) staring at the Sun to gauge its size change.

There is a difference, noticeable if you take photos of the Sun — again, not something most people do, but with the right equipment and experience it can be done. It’s something astrophotographer Anthony Ayiomamitis, for example, has done:

[The Sun from Earth at aphelion (left) and perihelion (right). Credit: Anthony Ayiomamitis]

He took these two pictures six months (half an Earth orbit) apart, and you can see the Sun is a wee bit smaller at aphelion.

This causes some confusion for some people, since in the northern hemisphere this happens in the summer. But it goes to show you our seasons aren’t caused by our distance from the Sun! If you think about it you know they can’t be anyway; in the southern hemisphere their seasons are opposite ours, which can’t be due to solar distance.

There is a small temperature change because of the distance change, but it’s only a couple of degrees. I actually did the math on this one at my old Bad Astronomy site, if you’re curious.

Another misconception is that Earth’s orbit is really elliptical, because diagrams usually show it from an angle, which exaggerates the ellipticity (like looking at the rim of a drinking glass at an angle). I actually drew Earth’s orbit to scale using Wolfram Alpha and put it next to an actual circle of the same diameter. Can you see the difference? Can you tell which is which?

[Drawings of a circle and an ellipse representing Earth's orbit. Can you tell which is which? Credit: Wolfram Alpha/Phil Plait]

Spoiler: The one on the left is a circle, and the ellipse on the right. Hopefully that gives you a sense of scale!

Incidentally, at aphelion it takes light 8.42 minutes to reach us from the surface of the Sun. At perihelion it’s more like 8.2 minutes. That 5 million kilometer difference is covered by a photon in about 17 seconds. Light is fast.

Also, if you’re curious, I pronounce it APP-hee-lee-un. It can be argued it should be “uh-FEEL-ee-un” but to me that loses its meaning, blurring the prefix and the root word together. I won’t say which is right, but I am, and I will be taking no further questions.

Et alia

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