BAN #91: Treasures of the celestial equator

February 25, 2019 Issue #91

February 25, 2019

Subscribers are at a declination of 90° in my metaphorical sky.

Pic o’ the Letter

A cool or lovely or mind-bending astronomical image/video with a short description so you can grok it

Orion is one of the most well known constellations in the sky, and that’s no coincidence. When we look in that direction we look into a nearby spiral arm of the Milky Way, and it’s loaded with star-forming nebulae and bright stars. It helps that it makes such a recognizable pattern, of course, but even without that coincidence it would be an amazing place to dig around for cosmic treasures.

Like, say, M78 and environs:

Spectacular, isn’t it? This image is a combination from multiple data sources, including the huge 8.2-meter Subaru telescope. M78 is the beautiful blue gas cloud in the center. It’s blue because it’s reflecting the light from a couple of nearby massive stars. The stars, called HD 38563A and B, are both very massive blue supergiants, blasting out vast amounts of light, easily capable of illuminating such a glorious display of gas and dust.

Just below M78 is NGC 2071, lit by the star HDE 290861, which is also a blue supergiant, though not quite as hot as the pair lighting up M78.

This whole complex is bright enough to spot in binoculars, though of course looks best through a bigger telescope. I’ve been thinking about it, and weirdly I don’t remember ever seeing this for myself with my own telescope! That’s peculiar; it sits just above Orion’s belt, not too far from the far more famous Orion Nebula, and while fainter shouldn’t be too hard to pick out. It’s up in the winter — so, right now — and if we get a clear night here in Colorado that isn’t cold enough to freeze the CO2 out of the air I may have to give this one a go.

Apropos of nothing I was mildly amused to see that M78 sits almost exactly on the celestial equator, the projection of the Earth’s equator on the sky (much like Polaris sits near the Celestial North Pole, the projection of our own on the sky). That means it’s visible literally everywhere on Earth, from pole to pole (even though it sits just barely north of the equator, you could technically see it from the South Pole because the Earth’s atmosphere bends light near the horizon, making objects actually just below the horizon visible just above it).

Curious, I poked around, and to my even greater amusement found another Messier catalog object even closer to the equator: the gorgeous spiral galaxy M77, or Cetus A. Its declination — the latitude on the sky — is just under 4 arcminutes from the equator. That’s small; the size of the Moon on the sky is 30 arcminutes! So it sits very nearly exactly on the equator.

Again, there’s no magic or anything here; besides the horizon thing this is mostly just a curiosity. But I’ve always been fascinated by maps, and how we slap borders around things sometimes. Most of the time it’s arbitrary (subscribers may harken back to BAN Issue 80 where I talk about how Colorado isn’t really rectangular), but in this case it’s actually based on physical delimiters. If the Earth didn’t spin it wouldn’t have poles or an equator, but it does spin, so those places exist.

And sometimes by coincidence there are very pretty astronomical objects that sit near them.

Blog Jam

What I’ve recently written on the blog, ICYMI

[NGC 6769 and 6770; see Friday’s post. Credit: NASA/ESA/ESO/Judy Schmidt]

Monday Feb. 18, 2019: No, 'Oumuamua is not an alien spaceship. It might be even weirder. (This one went really viral, picked up by several news aggregators.)

Friday Feb. 22, 2019: Prelude to galactic catastrophe (oh my yes you want to click this)

Et alia

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