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Question: I walked outside this morning about 3:30 and saw Jupiter right above me. After staring for a few seconds, I noticed three small dots to the right (west) of Jupiter. I grabbed my binoculars and looked up. Sure enough, the three small dots were actually there, all in a straight line with the planet. This was even with a bit of light pollution from a nearby city.

Are Jupiter’s moons visible with the naked eye? Or did I just see three stars that happen to line up perfectly with the planet?

I’ve never really looked at Jupiter like that before, so I wasn’t sure what I was looking at. With the air being so cold this morning, I was seeing a lot more than I expected.

Answer: Yes, indeed, Jupiter's moons can be seen with the naked eye, though if light pollution is lower in your area or if the skies are a little drier, it does help, as does a person with especially good eyesight.  The three moons you mentioned are all around magnitude 5, and the limit for human vision is generally around magnitude 6.  The lower the magnitude number, the brighter the object is.  For example, something at magnitude 1 is brighter than something else at magnitude 3.  If you watch Jupiter over the course of a few days and if the weather stays clear & dry, you may notice the moons moving in their orbits, being in different locations from day to day, but always staying close to Jupiter in the sky.  Jupiter is very bright in our skies in Fall 2011, so it is a good chance to go out and see if you can spot the moons.  For those under light-polluted skies or whose eyesight may not be quite good enough to spot them, a decent pair of binoculars is all you need to see Jupiter's four largest moons - Io, Europa, Ganymede, and Callisto.

Great observation!  Thanks for your question! Learn more on our Jupiter page.

Ask the Adler Archives

Question: Was Pluto renamed a "Plutoid" instead of a "Dwarf Planet"? Has its classification changed?

Answer: Pluto actually has several designations, among them Plutoid, Dwarf Planet and Plutino. Each designation has a different definition, so it's fine for one object to be called several things. A dwarf planet has a specific definition. A Plutino is an object locked in 2:3 resonance with Neptune, so for every 2 orbits Neptune makes, a plutino makes 3 orbits.  Pluto fits this definition perfectly, though there may be others as well. A plutoid is a dwarf planet outside the orbit of Neptune (also called a "trans-Neptunian dwarf planet").  That's Pluto, too, along with Haumea, MakeMake, and Eris. You can also call Pluto a TNO (Trans-Neptunian Object), a KBO (Kuiper Belt Object), and a "minor planet", depending on the group of objects you are studying.

Earth, to provide some contrast, can be simultaneously called a planet, an inner planet, a rocky planet and a terrestrial planet.

Learn more about Dwarf Planets in the our Investigate Space Science section.

Question: Do you have information on the current cycle of the Sun? Are we finally coming out of this horrible deep solar minimum?

Answer: Activity of the Sun's magnetic field varies, hitting highs and lows of intensity every 11 years in a fairly steady cycle. Sunspots, flares and storms will rage, get gradually get quieter, then rise again in intensity a few years later. The last solar maximum period was in 2001 and the next peak of intensity is expected to happen around 2012 or 2013.

Q: When is the next lunar or solar eclipse?

A: You can find up-to-date eclipse information on NASA's Eclipse Website:

http://eclipse.gsfc.nasa.gov/eclipse.html

Note:  Not all eclipses are visible from our area, so it is recommended that you check the visibility maps for each date if you are interested in a particular eclipse.  The next total lunar eclipse visible from Chicago is in December 2010, and the next total solar eclipse for our region is in 2017.

Q: What happened to Pluto?

A: In 2006 the International Astronomical Union officially demoted Pluto from planet status, labeling it instead a “dwarf planet.”

See the Adler’s official statement to the IAU’s decision here.

Coincidentally, when the Adler first opened in 1930, the bronze dedication plaque at its entrance featured representations of eight planets. Pluto had been discovered that year, but not in time to include it in the designing of the dedication plaque.

Q: Can I buy a star name?

A: The Adler does not “sell” star names. For more information on this issue, please refer to the International Astronomical Union’s website:

http://www.iau.org/public_press/themes/buying_star_names/

Q: What is going to happen in December 2012, and should I be concerned?

A: A number of well-written articles cover this topic:

Sky & Telescope magazine has an excellent article on this topic, written by Griffith Observatory Director E.C. Krupp, Ph.D. To download a PDF of the article, go to:

http://www.skyandtelescope.com/news/69774827.html

Astronomy Beat, an online column written by astronomy and science professionals, has an excellent article on this subject. To download a PDF of this article, go to:

http://www.astrosociety.org/2012/

Here is a link to a video produced by a NASA research scientist that may better explain what’s going on:

http://www.universetoday.com/2009/11/11/2012-nasas-scientific-reality-check/

Q: Why do stars twinkle?

A: The Earth’s atmosphere causes starlight to appear to twinkle. The more turbulent the atmosphere, the more stars seem to twinkle.

Q: Is that bright streak I saw last night a comet?

A: If it visibly moved through the sky at a detectable pace, probably not.  Comets will appear to not move much in relation to stars.  Comet sightings and other astronomical news can be found at the Sky & Telescope magazine’s website: http://www.skyandtelescope.com.

Meteor Outburst (S. Molau and P. Jenniskens, NASA Ames Research Center)

A: You can find out more about meteors, including dates of showers and a log of fireball sightings, at the American Meteor Society’s Fireball Monitoring Program (http://www.amsmeteors.org).

Q: How can I see the International Space Station? Or the Space Shuttle?

A: You can track the Space Shuttle (when it is flying) and the International Space Station through two websites:

NASA Sightings: http://spaceflight.nasa.gov/realdata/sightings/index.html

Heavens Above:   http://www.heavens-above.com

Q: Hi,  I am trying to find out if I was born on a full moon? Or how close was it?

A: This website can help you find out: http://tycho.usno.navy.mil/vphase.html. It will list the date and time of the various phases of the moon for any given year (between 1700 and 2035...).

Q: I was on the DesPlaines River yesterday in the Joliet / Wilmington area. I saw something in the sky I had never seen before — there was a circular rainbow around the sun.  Have you heard of this before or seen one?  It was amazingly spectacular, and it was not raining at all.  Thank you for any information you can provide on this.

A: What you saw was not a rainbow, per se, but another optical effect caused either by ice crystals or water droplets high in the air. True rainbows are always seen centered on the point in the sky opposite the sun, never very near it.

The first possibility is that is was a halo, caused by ice crystals, and taking the form of a circle separated from the sun by 22 degrees (roughly, the angle your thumb and pinky make when splayed out and held at arms length). The second is that it was a corona, caused by backlit water droplets, and taking the form of a colored ring with a bright white center immediately surrounding the sun.

These two phenomena, along with many other beautiful atmospheric optical sights to see in the sky, are described at this website: http://www.atoptics.co.uk/.

Rainbows in general are described at: http://www.atoptics.co.uk/bows.htm

Ice crystal halos: http://www.atoptics.co.uk/halo/circular.htm

Coronae: http://www.atoptics.co.uk/droplets/corona.htm