Greetings, Stargazers.
My May column is often a time I get to list upcoming summer star parties, but for another month, these will have to wait. I really do hope that we can get together soon, but at least it is good to know that solo stargazing is always possible.
A funny thing I’ve noticed is that most of the questions I get about astronomy are about things in the sky that I think interfere with stargazing. Did you see that most recent supermoon? Yes, it was so bright that I couldn’t see anything else. Wasn’t that a great meteor shower? Yes, but I was trying to take long exposure photographs of an open cluster and ended up with streaks going across my pictures! (Really, I do like these things, too, and try to include them in What’s Up in Durango Skies.)
Along those lines, I was recently interviewed about the Starlink satellites that SpaceX is launching. These are like most other low-Earth-orbit, or LEO, satellites, in that they can easily be seen in the sky just after sunset or just before sunrise. This happens when you are in darkness because the sun is below your horizon, but the satellites are high enough to still be in direct sunlight. During the middle part of night, the satellites are in the shadow of the Earth and so will not be visible. If you have never seen a satellite, they can be almost any brightness but will always move steadily across the sky. (If it blinks, it’s an airplane.)
Satellite watching is a hobby that has been around since Sputnik. On most nights, I will see several, but because this hasn’t been my primary interest, I usually won’t try to find out which ones they are.
On the other hand, the International Space Station is big and bright and makes regular passes overhead. For star parties, it is often worth checking to see if a pass will be visible.
A particularly memorable type of satellite event to watch for is an iridium flare. The set of iridium communications satellites are in nearly polar orbits, flying in north to south paths overhead. These satellites have large, flat antennae that can reflect sunlight and cause an extremely bright flash of light if they catch the sunlight just right. When they flash, they can be even brighter than Venus. These flashes are so impressive that websites and mobile apps have been set up to alert you to them.
Starlink will be a constellation of satellites intended to provide global, low-cost, broadband internet access. Rather than a single, big, expensive satellite, the idea with Starlink is to have lots of small, low-cost satellites provide the service.
These satellites are being launched 60 at a time on Falcon 9 rockets and will appear as a string of dots moving across the sky, until they eventually reach their final, spread-out positions.
The first launch was a year ago, and as of the April 22 launch, 422 Starlink satellites are in 340-mile altitude orbits. Plans are for up to 12,000 total satellites at three different altitudes, but this number could increase to as many as 42,000 satellites. This could mean hundreds visible at one time to an observer on Earth. (Before you try to sell the idea of arranging them to fly in formation to spell out your favorite product name, realize that the space advertising idea pre-dates the space age.)
To reduce the Starlink impact on astronomical observations, recent improvements have included changing the exterior to a dark coating to make them less reflective, and upcoming flights will add what’s called a sun visor to block sun reflections heading toward Earth. We will all have to wait to see if these improvements help.
This monthThe once-promising Comet Atlas turned out to be even less than ho-hum. But Venus is still bright, and the summer Milky Way is always great.
On the morning of May 12, the moon will join Jupiter and Saturn to make a nice grouping in the southern sky.
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.
