I'm a bit late to the Equinox party but wanted to share this @StellariumDev simulation showing three lines that intersect at two points on the sky: the celestial equator (red), ecliptic (yellow), and equinoctial colure (purple). At the equinox time, the Sun was at that point. The other such point is at the September equinox, which this year happens on 23rd September at 06:50 UTC. Here's the simulation from that date. Note that the positions of the equator and colure are the same, but the angle of the ecliptic line changes.

It's Paper Day ×2! My research groups have two papers on light pollution in today's issue of @NatureAstronomy, one each from terrestrial and orbital sources of skyglow. A 🧵 about the pair: In the 1st, a Perspective with @salvabara et al., we argue astronomers should be concerned about the aggregate effects of satellite megaconstellations on astronomy. And we suggest that they are significant beyond impacts to our science.

Free full-text: rdcu.be/c727o

It will be interesting to see how bright this version turns out to be, particularly once they reach station.

https://twitter.com/Gizmodo/status/1630249667765125122

.@SpaceX published info about v2 Mini on api.starlink.com/public-files/G…

In this section, it confirms "SpaceX also started using dielectric mirror film on many surfaces of the satellite, which reflects light away from the ground and leads to less reflectivity."

Today's H-alpha Sun at 2000 UTC. Had to dodge clouds to get one chance at a cleat shot. Seeing wasn't great and focus was a bit soft. But: more bright emission from departing AR 3229 near the NE limb. Turns out that yesterday "a magnetic filament connected to sunspot AR3229 erupted on Feb. 24th, producing a chain reaction of events that could lead to a geomagnetic storm on Earth." (per @spaceweather)

Today is the 10th anniversary of the fall of the Chelyabinsk bolide, the largest known natural object to have entered Earth's atmosphere since 1908. It damaged over 7,000 buildings, shattered windows, and caused $33 million in property loss.

And we didn't see it coming. A 🧵: Long story short: an asteroid nearly 20 meters in diameter whose orbit intersected that of the Earth came down over Russia one early February morning. It exploded 30 km above the ground. The event released the energy equivalent of 400–500 kilotons of TNT.

📷: Aleksandr Ivanov

When I was an undergrad, counseling before student loans were disbursed used to go like this: "Congress has determined that the obligation to pay for higher education falls on the following entities in the following order: 1, the student; 2, the family; 3, the taxpayer."

https://twitter.com/ronlieber/status/1344363653236191238

That's what I was literally told by my university bursar's office in the mid-90's: you will fork over everything you have first, then your family will fork over whatever the federal government determines it's capable of paying. After that's exhausted you can have some free money.

The “Winter Hexagon” @SkyandTelescope piece reminds me to make a finder chart for what I’ve heard called the ‘Winter Spiral’ that starts at M42, unwinds across most of the same bright stars and ends up back at Betelgeuse. I’ve used it in outreach programs for years. It’s not perfect, but it’s close: the path of the spiral (M42, Rigel, Sirius, Procyon, Capella, Aldebaran, Betelgeuse) follows the OBAFGKM stellar classification system pretty well, and is a good tool for illustrating the Main Sequence. (📷: Wikisky/Wikipedia)

Venus has finished its brief but very photogenic dance with the Pleiades, but don’t put those telescopes away just yet! We’re headed into prime time to see an elusive phenomenon called the Ashen Light. Here's what it may be, and why it's important. (thread) (📷: Scott Tucker) Humanity didn't get a close-up view of Venus until the invention of the telescope around the turn of the 17th century. When they did, they noticed something odd: it goes through phases, like the Earth's Moon. Galileo Galilei was the first to publish this fact, in 1623.

What does light pollution in the U.S. have to do with the COVID-19 outbreak? For one thing, LP might be reduced over time if restrictions on federally funded outdoor lighting are enacted along with a possible infrastructure bill coming next month. (thread) thehill.com/policy/transpo… The U.S. federal government funds a huge number of construction projects each year, whether directly (think federal buildings and highways) or indirectly (think grants to states). And it puts all manner of restrictions and requirements on how that money can be spent.