This week in What’s Up is an asteroid, one that you can actually see in a backyard telescope. Asteroid 1994 PC1, aka 7482, made its closest approach to Earth this week. It is in the Apollo class of Earth-crossing asteroids, which means it is technically “potentially hazardous”. However, its observation arc goes back decades, and its orbit is very well known so there is no risk of it impacting Earth. Asteroid 1994 PC1 has a diameter of just over a kilometer and an albedo of 0.277, meaning it reflects just over a quarter of the light that hits it. It has an orbital period of 1.57 years.

Its absolute closest approach of 0.007 Astronomical Units or just over a million kilometers was back in 1933, found in precovery data. That is old data that had the object in it before it was formally discovered. It was formally discovered in 1994 by astronomer Robert McNaught at the Siding Spring Observatory in Australia. This week’s close approach was a much further 1.5 million kilometers from Earth, according to the JPL Small Body Database.

According to JPL’s Solar System Dynamics page, this week during the close approach, it brightened from magnitude 16 to magnitude 10 on January 19, which is within the limiting magnitude of 7×50 binoculars. While you can use binoculars like this handheld, you will always get a more stable view by mounting them to a tripod. 

It is still bright enough for 7x50s for another few days, and even a three-inch telescope, such as a Short Tube 80, will be able to resolve the asteroid until early next week. I love my Short Tube 80 for low power, wide field views, but it can also handle the moderate power needed to see this asteroid well. An 8-inch telescope, such as a common beginner Dobsonian, will be able to see it for another week or so as it dims down to magnitude 15.

This evening, January 20, about an hour after sunset, asteroid 7482 is in the constellation Lacerta which is between the constellations Andromeda and Cepheus. It will be right between the unaided-eye-visible stars 5 Lac and 6 Lac, but closer to 6 Lac. Unless you have a several-meter diameter telescope, you won’t be able to resolve it as anything other than a dot, so you can use a moderate magnification, 100 to 150x, to see lots of background stars and ensure you are looking at the right dot. One of them will be moving quite quickly and should be easy to pick out from the background; that is the asteroid you are looking for.

Another interesting object in the constellation Lacerta is the open cluster NGC 7243, and in nearby Andromeda is the famous Andromeda Galaxy, aka Messier 31.

An easier, but more expensive way to find 1994 PC1, is to enter its right ascension and declination into a GoTo scope to allow the computer in the mount to point your telescope at the target. GoTo telescopes typically have an extensive database of objects, most of which the telescope optics can’t actually show you, mainly to put on the telescopes marketing (my telescope boasts “over 40,000 objects!”), but you can also add your own coordinates. You can use an interactive finding chart, such as Stellarium or an online site, to find coordinates for your location at different dates and times and enter these into your telescope. Stellarium will not have the asteroid by default so you will need to add it via the solar system editor. Links for both of these methods will be in the show notes for this episode.

Remember, go outside and look up. It’s one of the few relatively COVID-safe things you can do, until an asteroid attacks, when it will still be safe to look up but maybe not to live.

More Information

7482 (1994 PC1) (JPL Small-Body Database)

7482 1994 PC1 (Asteroid) (In-the-Sky)