Badger: Battle of brightness, spotting the Falcon 9

The brightness of stars and planets varies of such a wide range that a logarithmic scale of brightness is used: visual magnitude. A first magnitude star is one hundred times brighter than a sixth magnitude star. A difference of one magnitude is a factor of 2.53 times in brightness. It is hard to tell subtle differences visually, so amateur astronomers can visually estimate the brightness of variable stars by comparison with stars of known brightness in the same view.

It is hard though to be sure of the difference in brightness when objects are in different parts of the sky. A satellite passes through the sky getting close to many objects for comparison. Each object approached engages in a “battle of brightness” with the brighter object emerging the victor. Two bright satellites are described below, each in a different “weight class”.

There are thousands of satellites orbiting the Earth. So many that there are always some in sight. There are one hundred and sixty satellites listed as magnitude 5 or brighter tonight. That is just the ones passing before midnight. There are one hundred and sixty-three more naked-eye visible satellites coming before 6 a.m.

Even without this welter of satellites passing, there are geosynchronous satellites that hover overhead all the time. Their 24-hour orbital period matches the rotation of the Earth below, so they maintain a station in the sky. Television satellites are like that, so that your receiving dish does not have to track the satellite. Weather, communication and earth resources satellites are often placed in geosynchronous orbits to keep a certain region under view.

A geosynchronous satellite is so far away that it is generally dim—magnitude 11 to 15— thus only visible in a telescope. If you know its altitude and azimuth, you can point your telescope at it and watch it drift among the stars. In a non-motorized telescope the stars drift out of the field of view as the Earth rotates. The satellite remains in view and can be detected by its relative motion against the moving background of stars.

The brightest satellites will rival the brightest stars and planets. Tonight the brightest satellite is the Falcon 9 rocket body. It brightens as it rises higher in the sky, reaching first magnitude near its highest altitude point, around 8:54 p.m. close to Alphard, the brightest star of Hydra. Alphard is only magnitude two, so the Falcon 9 rocket body should outshine it noticeably.

The Falcon 9 rocket body will rise from the WNW at 8:48 p.m., but will start out rather dim. The sun is behind the satellite so, like a crescent Moon, it is not fully lit. It comes in over Orion’s shoulder, the star Betelgeus, and passes very close to Procyon, alpha Canis Minoris. Betelgeuse, Procyon and Sirius constitute the corners of the “Winter Triangle”. Betelgeuse is in the west, Sirius is in the WSW and Procyon is higher up in between. Procyon will no doubt outshine the Falcon 9 rocket body, even as it passes just a degree or so below.

The International Space Station, or ISS, as the advantages of size and low earth orbit to make it a potentially bright object. Nevertheless, its brightness doesvary quite a bit. Sometimes it "only” reaches magnitude 0, and at other times rivals the planet Venus. Tuesday the 23rd of May is such a time. Since it is so bright, it is easy to find. It rises in the SW at 9:15 p.m., and passes its brightest rival, Jupiter, at 9:19 p.m. Jupiter is a respectable -2.3 magnitude, but the ISS should be a dazzling -3.9 magnitude. Make a note to get out Tuesday night to see the celestial battle of brightness.

Here’s the Astronaut Memorial Planetarium schedule for the coming week:

Friday Evening, 5/19

7:00 P.M. Big - How Big is the Universe

8:15 P.M. Africa's Elephant Kingdom (IMAX movie)

9:00 P.M. Jimi Hendrix Laser Experience

Saturday Evening, 5/20

7:00 P.M. Oceans in Space

8:15 P.M. Tropical Rainforest (IMAX movie)

9:00 P.M. Beatles Laser Experience

Wednesday Matinée, 5/24

2:00 P.M. More Than Meets the Eye

3:15 P.M. Solar Max (IMAX movie)

The Eastern Florida State College’s Astronaut Memorial Planetarium and Observatory will be closed Saturday, May 27, for a private event. The EFSC observatory is regularly open to the public from 6:30 p.m. to about 10:00 p.m. most Friday and Saturday nights. Jupiter wil be visible in our telescope about 8:45 p.m., weather permitting. Bookmark the planetarium show schedule at https://www.calendarwiz.com/planetarium in your web browser.

Mr. Badger is Project Coordinator at the Eastern Florida State College Planetarium in Cocoa. Send questions, suggestions, or comments to badgerb@easternflorida.edu