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Mercury Rising As The ‘Blood Moon’ Beckons: What You Can See In The Night Sky This Week

Each Monday I pick out the northern hemisphere’s celestial highlights (mid-northern latitudes) for the week ahead, but be sure to check my main feed for more in-depth articles on stargazing, astronomy, eclipses and more. 

What To Watch For In The Night Sky This Week: May 17-23, 2021

Typically a very challenging sight, little planet Mercury makes a play for “object of the week” again as it rises almost to its highest in the post-sunset sky as it does for all of 2021.

After you’ve searched for “the Swift Planet” take a look at the Moon, which passes some landmark stars and star clusters this week as its waxes past its First Quarter phase and towards a dramatic “Super Flower Blood Moon” total lunar eclipse next week. 

Monday, May 17, 2021: Mercury farthest from Sun

It’s “Mercury May,” and the closest planet to the Sun has been revealing itself each evening in the west after sunset.

It was technically highest in the night sky a few nights again, but tonight it reaches its greatest elongation east—the furthest it gets from the Sun (about 22º east), in our post-sunset evening sky—during its current apparition.

This is one of the best nights to see Mercury in its current April-June apparition, and one the best of the year, too.

Don’t hang about because it will sink quickly. 


Tuesday, May 18, 2021: Moon and the Beehive Cluster

Having glanced Mars on Sunday, the now 32%-lit Moon tonight moves in front of the mighty Beehive Cluster (see below for more details).

You can see them just under 3º apart in the post-sunset night sky. 

Wednesday, May 19, 2021: First Quarter Moon and Regulus

Tonight the Moon reaches First Quarter, when its near-side appears to us on Earth to be 53%-lit.

As that happens it will be just 5° from Regulus, the brightest star in Leo, the Lion. 

Sunday, May 23, 2021: Moon and Spica 

Tonight is a good night to look for Spica using the now 92%-lit Moon, 6.5° away, as your guide. However, there is another way to find this binary star system, in the constellation of Virgo, at this time of year.

Trace the line of the Big Dipper’s handle to to “arc to Arcturus, spike to Spica.”

Spica is one of the 20 brightest stars in the night sky and about 250 light-years distant. 

Object of the week: the Beehive Cluster

The Beehive Cluster (M44) is a one of the nearest open clusters to Earth, in the constellation of Cancer, and its 1,000 stars are a beautiful sight in binoculars. 

Constellation of the week: Coma Berenices

A simple L-shape for three stars, Coma Berenices is not an imaginative constellation. Sandwiched between Boötes, the Big Dipper and the tip of the tail of Leo, the lion, this constellation is relatively close to orange star Arcturus.

The brightest star in Coma Berenices is Beta Comae Berenices, the middle star, which is a mere 30 light years distant. However, sweep binoculars across it and you’ll come across 20 or so bright stars—and many dimmer stars—that are part of an open cluster called the Coma Star Cluster or Melotte 111.

It’s around 288 light years distant, making it one of the nearest star clusters to our Solar System. 

Times and dates given apply to mid-northern latitudes. For the most accurate location-specific information consult online planetariums like Stellarium and The Sky Live. Check planet-rise/planet-setsunrise/sunset and moonrise/moonset times for where you are. 

Disclaimed: I am the editor of

Wishing you clear skies and wide eyes. 

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