Bob Moler's Ephemeris Blog

This is Bob Moler with Ephemeris for Monday, April 11th. Today the Sun will be up for 13 hours and 17 minutes, setting at 8:22, and it will rise tomorrow at 7:03. The Moon, 2 days past first quarter, will set at 5:37 tomorrow morning.

On April 1st SpaceX launched their Transporter 4 mission taking forty small satellites into sun synchronous orbits. Sun synchronous orbits are cool The plane of the orbit precesses 360 degrees over the period of a year so as it orbits it flies over the same part of the Earth at the same time of the day, so the sun angle on the ground is the same. This is great to see changes on the ground over time. To do that, the orbit has to have an inclination of 97 degrees. Which is hard to do launching from Cape Canaveral, the rocket must be sent toward the south-southwest, but must not cross southern Florida. So the rocket launches to the southeast and bends its path southward, keeping offshore. The second stage completes the turn to achieve the 97 degree inclination.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hours). They may be different for your location.

Addendum

Screenshot of the animation from SpaceX launch webcast of Transporter 4. Launches of polar orbiting satellites are generally made from Vandenberg Space Force Base in California, which have a clear shot to the south and south-southeast. Curving the launch trajectory like this exacts a penalty in the amount of payload mass that can be put into orbit. Credit: SpaceX.