April is the month of the blood-red lunar eclipse where the Earth’s shadow cloaks the moon, yet star-gazers will get a special treat when this month (April 8 and 14) is also the opposition of Mars and Earth when both planets and the Sun are almost aligned in one straight line. This is when Mars and Earth are closest to each other. Mars fans may want to aim their telescope toward the red planet to not only see its white poles, but also its two moons — Phobos and Deimos. Some may ask themselves, “What other moons besides ours could be seen with my telescope?” With a clear sky with no or very little light pollution and a competent telescope, plenty. Despite their small size, faint luminosity, and distance from Earth, one can gaze further beyond the asteroid field and detect the gas giants’ moons.
The Red Planet
Starting with Mars, which will rise in the west along with Earth’s moon, it will be very close to Earth which increases the odds for star-gazers to spot its two asteroid-like moons. They are challenging to detect because Mars outshines them. Mars has a magnitude of -1.5 while Phobos and Deimos has +11.5 and +12.4, respectively. There are two ways to increase the odds of detecting them. Star-gazers could put Mars just off the field of view and use the telescope’s highest power, or they could use an occulting bar that blocks most of Mar’s light to catch a moon or two, according to Universe Today. Since Phobos orbits much closer to Mars than Deimos, the tiny moon is harder to see. However, when its orbit is at its longest elongation relative to the observer, the moon is more likely to be seen.
The Jovian Moons
Galileo Galilei, the famous Renaissance astronomer, first observed four tiny points of light around Jupiter on January 1610. Further observations convinced him that these “lights” were actually tiny worlds orbiting around the gas giant. This debunked the prevalent notion in Renaissance Europe that all celestial objects rotated around the Earth like its moon. Star-gazers can see what Galileo saw over 400 years ago with an average telescope and even binoculars, which are more powerful than Galileo’s telescope.
The four prominent moons are Io, Europa, Ganymede, and Callisto. They are so small and faint relative to Jupiter than they would look more like stars than rocky satellites. Sometimes only two or three moons could be seen because either one or two moons is behind or in front of Jupiter or one moon is eclipsed by another moon. Ganymede and Callisto are the easiest to spot because they are larger than the other two. However, Io and Europa could still be detected since they never orbit far from Jupiter.
King of the Ring
Saturn is well-known for its giant ring, however, less is known about its moons. The most famous one is Titan, which made science headlines in January 2005 when the space probe, Cassini, launched a smaller probe into the moon’s orange, nitrogen-rich atmosphere to study its composition and to photograph its surface. It is more easily seen with a telescope than the other large, close-orbiting moons, including Rhea, Dione, Tethys, and Enceladus. Like Jupiter’s moons, they would look like stars. Star-gazers should take note that in the fall of 2017, Saturn’s rings will be more visible to Earthlings because the planet will tilt on its axis.
Uranus: Can You See 3, 4, or 5?
Most people can see four of the 27 moons of Uranus with a telescope, but sometimes, a fifth one can be seen by a few. According to Space.com, astrophotographer Ed Grafton from Houston, Texas, took a portrait of Uranus with five of its moons on July 19, 2002. These moons are Titania, Miranda , Ariel, Umbriel, and Oberon. Star-gazers shouldn’t feel frustrated if they couldn’t see or capture all five moons. Even finding two or three moons could be challenging for most people.
Neptune and Pluto: Way Too Far
Even with a powerful home-use telescope, these two planets would still appear like stars, which makes it unlikely for anyone to see its moons. However, Universe Today says that it is still possible to spot Triton, Neptune’s largest moon. With some patience and skill, star-gazer could spot a very faint dot near a bigger and brighter pale blue “star.” Triton shines at a magnitude of +13.4, which is similar in brightness as Pluto, yet it s is 100 times fainter than Neptune. While Neptune and Triton may not look like much through a telescope, star-gazer should be aware that they’re seeing a gas giant that is almost four times the diameter of the Earth with a large moon over 75 percent bigger than the Earth’s.
Star-gazers can use Sky & Telescope‘s moon app to help them to differentiate the planets’ moons and stars. The app can also predict the location of the orbit and its time on any day from January 1900 to December 2100. No more guesswork for those who want to see other moons in the solar system with their telescope.
By Nick Ng