Home > Concepts, Ephemeris Program > Ephemeris: 08/15/2024 – What’s the matter with dark matter?

Ephemeris: 08/15/2024 – What’s the matter with dark matter?

August 15, 2024

This is Bob Moler with Ephemeris for Thursday, August 15th. Today the Sun will be up for 14 hours and 1 minute, setting at 8:47, and it will rise tomorrow at 6:47. The Moon, 3 days past first quarter, will set at 2:23 tomorrow morning.

Over the past century astronomers have come to the realization that we are seeing only about 5% of the mass and energy of the universe. Galaxies in clusters seemed to move too fast to not escape, dissipating the cluster, yet after billions of years they still exist. Also, the stars in galaxies revolve about their centers much faster than expected revealing missing mass. So astronomers have come up with the idea that either there is missing matter that we can’t see, what’s called dark matter or there is something wrong with Newton’s and Einstein’s theories of gravity. Astronomers have come up with up two possible types of dark matter, which they humorously dub WIMPs and MACHOs. More about them tomorrow.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT–4 hours). Times will be different for other locations.

Addendum

Bullet Cluster showing what happened to the dark matter
This is called the Bullet Cluster. It’s two galaxy clusters that collided. The pink is hot gas visible in x-rays. The blue is added to show where dark matter resides. It is detected by studying the far distant galaxies beyond for distortion caused by the gravitational lensing of dark matter in these two clusters. Most of the mass of the galaxy clusters is dark matter, which also contain hot gas and, of course the galaxies. When galaxy clusters collide the gas of the two clusters interact and are stripped out and the dark matter and galaxies go merrily on. Image Credit: NASA, ESA, CXC, M. Bradac (University of California, Santa Barbara), and S. Allen (Stanford University)
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