November 27-28, 2025

 

What can you expect to see at the Community Observatory this weekend?

 

Our power and water have been restored. We are back in business. We are hoping for clear nights this Friday and Saturday so that we can open and you can refresh yourself from the craziness of shopping on Black Friday by immersing yourself in the cosmos. The prediction, at this point is for partially cloudy skies. There are two factors that could cause us to close, however. Those are cloud cover over 50% and humidity over 70%. High humidity causes our scopes to become useless as the lenses and mirrors are covered by dew. High humidity can also damage our electronic components. Also, remember that our weather here may not be the same as yours “down the hill.” That is why we always urge you to check communityobservatory.com or our Facebook page after 3 PM on the day you plan to visit. If we are going to be closed, we will announce it by then.

 

The Moon will be at first-quarter or about 50% illuminated. It rises close to noon and sets after midnight. That will interfere slightly with our viewing but we should still be able to see some awesome sights.

 

One exciting thing is that we should be able to see Jupiter for the first time since last Spring. Jupiter is truly the king of the planets and it makes up about two thirds of the mass of everything orbiting the Sun. A highlight is being able to see the four Galilean Moons. Those are the ones that Galileo saw on January 7^th, 1610 when he first used a telescope to view the sky. He observed them each night after that and concluded that Jupiter and its moons were a microcosm of the solar system with the Sun occupying the center rather than Earth.

 

Some of our favorite Winter deep-sky objects are also rotating into view in the evenings. These include the Pleiades Star Cluster and the Orion and Crab Nebulae.

 

The magnitude system is a bit odd. It was created to describe the brightness of stars. The brightest stars were called “first magnitude.” Slightly dimmer stars were called “second magnitude” and so on. This was a subjective system that wasn’t scientifically accurate. Rather than reinvent the wheel, science adopted the term “magnitude” and developed a system to measure brightness. They chose the star “Vega”and assigned it the value of “0” and set the increment between magnitudes at 2.51 times as bright. Like the old system, a lower number means that the object is brighter. So, for example, if a star has a magnitude of 2 it would be 2.51 times brighter than an object wit a magnitude of 3. But, since many objects are brighter than Vega, they assigned negative numbers to describe their brightness. The star Sirius is the brightest star at -1.46 magnitude.  That makes it about 3.8 times as bright as Vega. They also extended the system to include all heavenly bodies. Thus, Venus is the brightest at -5.8 magnitude. No wonder we are impressed when we see it as the “morning star.” The full moon comes in at -12.7 and the Sun at -26.7.  The dimmest objects visible with the unaided eye from a very dark location are around magnitude 6.5.

 

That discussion of magnitude is a prelude to explaining why seeing the “interstellar comet” formally known as 3I/(ATLAS) is very difficult. The 3I means that it is only the third interstellar comet that we have seen. ATLAS stands for the “Asteroid Terrestrial-impact Last Alert System.” This is a network of wide-field telescopes located in Hawaii, Chile, South Africa, and Spain to scan the entire visible sky several times each night looking for possible Earth impacting bodies. Finding comets used to be the domain of individuals but now most comets are being discovered by systems like ATLAS. I woke up Early Wednesday morning and imaged this comet from my home in Placerville. It is currently at magnitude 15.8 which is 4,200 times dimmer than the faintest naked-eye object at 6.5. The image today is that comet. Look closely, it is the fuzzy ball in the center of the image. It isn’t spectacular but conceptually, it is impressive. This object originated around another star and has been traveling perhaps billions of years to get here. It will go through our system and continue into interstellar space.