Subscribers make my holidays merry

The holiday season is here once again! Now, you could go out and brave the crowds (who does that any more?) or throw your money at billionaires who want to squeeze every dime they can from you while providing worse products and service every time…

…or you could give the science nerd in your life a subscription to this very actual Bad Astronomy Newsletter at a 20% discounted price!

Starting today and running through noon (Eastern US time) December 19, 2025, I’m taking 20% off the usual $60 per year/$6 per month Premium subscription price, making it just $48 per year or $4.80 per month.

To give this as a gift, go to the signup page and enter their email address. After that you’ll be sent to a page that lets you choose some options. First, click the “Gift” button, then choose whether you’d like this to be for one month or for one year. After that it’s the usual kind of thing for an online purchase. 

But wait! There’s more!

If you’re a free subscriber (so you get the newsletter once per week on Mondays), you can also upgrade to Premium at this discounted price! Just go to the signup page and enter your own email address; after that follow the instructions in the paragraph above. Easy peasy, chicken dinner.

Premium subscribers get three issues per week (on Monday, Tuesday, and Thursday), no ads, and can also leave comments for any issue archived on the newsletter website.

[Note this discount will only apply for your own subscription if you’re upgrading from the free level. Also, the discounted price will apply for one term of the subscription, meaning one month or one year depending on which you choose. After that, it goes back to full price again. If this is a gift it is only for the term chosen; if it’s an upgrade it will auto-renew every term.]

Thanks for doing this. It’s an honor and a pleasure to write this newsletter for all y’all, and it’s honestly hugely uplifting to have you supporting me as well — this newsletter is the main source of my income. I really appreciate it.

Hey, c’mon, you didn’t think I wouldn’t have some actual astronomy for you in this issue, did you?

Behold, NGC 6302!

WHOA. This image was taken using the mammoth Gemini South telescope, an 8.1-meter behemoth in Chile. The image used filters that select for light emitted by oxygen (displayed as blue and green) and hydrogen (green and red). Click it to get it in much higher resolution. 

NGC 6302 is a planetary nebula, the gas cast off by a Sun-like star as it dies. The process is complicated — what isn’t, in astronomy? — but in a nutshell, as the star runs out of fuel in its core it swells up and becomes a red giant. It starts to blow a dense wind of gas outwards. Eventually, it loses a lot of its upper layers to that wind, exposing the much hotter core. The wind then shifts to become lower density but much faster, colliding with the slower material and sculpting it into various shapes. The hot core, now a white dwarf, zaps the gas with ultraviolet light, causing it to glow. We call this object a planetary nebula not because it has anything to do with planets, but because in small telescopes they can look like small, pale disks, resembling a planet. It’s an old term and not terribly accurate, but we still use it out of inertia.

A star like the Sun should make a roughly spherical planetary nebula when it dies, but if the star is in a close binary system, orbiting another star, a lot of the material is thrown off along the plane of the orbit. This creates a thick disk around the stars, and as more material is blown off it slams to a stop when it hits the disk. But material ejected in the up-and-down direction is still free to flow away, and that’s what forms the gorgeous wings to this cosmic butterfly. We call this a bipolar nebula.

I actually wrote more about NGC 6302 on The Old Blog™ in 2020 when a Hubble Space Telescope image of it was released, so go ahead and read up on it there. 

I studied planetary nebulae for my Master’s Degree, and a different form of one for my PhD as well; they’re one of my very favorite cosmic objects. Quite a few are visible in small telescopes, and I still get a thrill going out and pointing my own ‘scope at the Ring Nebula, or the Dumbbell Nebula, or any of several others that are easy to spot.

I may be a professional astronomer by training, and a science communicator by trade, but deep down I’ll always be an amateur astronomer, standing at an eyepiece and marveling at what the Universe provides for us as a treat. It’s always beautiful, and understanding what I’m seeing adds a dimension and depth to it. I’m always happy to be able to share that with you, too. That may be the best part of all of this.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!