Ice giants dancing with the moon and a ring left by a dying star offer plenty to hunt for in the heavens this week.
Mercury and the Messier 35 star cluster. About 45 minutes before local sunrise on Tuesday, July 15, look for a very faint Mercury in the low northeastern sky. Make sure you find an observation point without any obstructions, since the elusive naked-eye planet will be only about 10 degrees above the horizon—the width of your fist at arm’s length.
The planet does shine brightly at magnitude 0, but if you’re having difficulty finding it, then use superbright Venus, just above it, as a guide.
As an added challenge, use binoculars to spot the fifth magnitude star cluster known as Messier 35, about 3 degrees north of Mercury. That’s roughly the distance of six full moons side by side or half the field of view in a typical pair of binoculars.
At about 3,000 light-years from Earth, this open cluster sits at the foot of the Gemini twins. It’s about 24 light-years across and contains well over 500 stars, a few dozen of them easily picked up with a low-magnification telescope or binoculars.
Moon and Neptune. Late on Tuesday, July 15, look toward the low eastern sky for the waning gibbous moon and the 8th magnitude Neptune, rising together in the constellation Aquarius.
The pair will appear closest together for telescope users from Europe through Asia, Africa, and Australia, where they will be separated by only 5 degrees, equal to the width of your three middle fingers held at arm’s length.
Moon and Uranus. By the early morning of Friday, July 18, the moon will have slid toward the east and parked next to another ice-giant planet, Uranus.
Within the faint zodiacal constellation Pisces, the two celestial objects will appear to be just a bit over one degree apart. This tight conjunction will make it easy to find the 5th magnitude planet just below the moon.
This close encounter will best be seen from North and South America.
Amazingly, this giant planet, with a diameter nearly four times that of Earth, looks like a tiny green disk even through a telescope. That’s because it’s so far away—nearly two billion miles (nearly three billion kilometers).
In fact, Uranus is so far from us that sunlight reflecting off its cloud tops takes about 243 minutes to reach us here on Earth.
Ring Nebula in Lyra. On Saturday, July 19, the moon is out of the evening sky, making this an ideal time to hunt down a small but pretty planetary nebula, a colorful bubble of gas left behind by a dying star.
Start your hunt for the Ring Nebula, also known as Messier 57, by looking high in the southeast for the star Vega and its constellation Lyra, or the Harp, which marks the brightest corner of the famous Summer Triangle pattern of stars.
Resembling a triangle hitched to a parallelogram, Lyra is one of the smallest but most easily recognized classical constellations, one that’s visible all summer long.
The Ring Nebula is located halfway along a line between the two stars forming the trapezoid wall that’s farthest from Vega.
The planetary nebula is visible only through high-magnification telescopes, and it looks like a small, pale ring. Long-exposure photographs reveal the nebula in all its glory, showing the expanding ring of hot gas in a beautiful rainbow of colors.
Though it seems of just modest size at the eyepiece, the nebula is actually a one-light-year-wide shell of gas thrown off by a dying sun-like star more than 2,300 light-years from Earth.