Last month we drew attention to a celestial cluster with the Moon, two bright stars, and two bright planets gracing our western evening sky.
Now another similar meeting will take place this week; an arrangement that will change night to night as we transition from spring to summer season with the summer solstice on June 21st. Here’s a look at how the stars of Gemini will shine with the Moon, Mars, and Venus as summer begins.
Related: The brightest planets in the night sky in June (guide)
Monday, June 19: Twin Gemini starring Castor and Pollux
The weekly skygazing festival begins Monday evening, June 19th, the “Juneteenth” holiday in the United States. Begin 45 to 60 minutes after sunset and look low at the west-northwest horizon. There you will find a narrow sliver of a crescent moon less than two days after the new phase. And just above you should be able to make out two stars, Pollux and Castor, marking the heads of the twin brothers, Gemini. There seems to be evidence that when they were first chosen to represent the Gemini, they did in fact look like twin stars of the same magnitude.
If that’s true, either Pollux has gotten brighter or Castor has disappeared from the night sky, because there’s a clear difference between them now. Pollux now appears a little more than twice as bright as Castor and is also one of the 57 standard navigation stars. But Castor is the true “star” of the twins. Although it appears as a single star to the naked eye, it is actually a system of six stars. In a telescope we see two, Castor A and B. Furthermore, both A and B are doubles themselves, albeit much too close together to be optically separated (so-called spectroscopic doubles). Finally, far south of the main pair is Castor C, a pair of faint red stars.
Tuesday, June 20: Crescent near Venus
Tuesday evening, June 20th: A slightly broader crescent moon will have shifted to the upper left of the twin stars and be about a dozen degrees lower right of the evening sky dazzler, the planet Venus. Her clenched fist is about 10 degrees at arm’s length, so the Moon and Venus are just a little more than a fist’s breadth apart in the sky that night.
Of course, Venus continues to easily outshine everything in the evening sky except for the Moon itself. It currently shines at a magnitude of -4.6. Compared to Pollux and Castor, Venus outshines these stars by a factor of 100.
Continue reading: The Native American Night Sky: 7 Starry Sights
Wednesday, June 21: Summer Solstice and Moon
Wednesday June 21: This is the summer solstice and the first official day of summer for the northern hemisphere, and this evening will be the most beautiful to the eye for the confluence of the moon, stars and planets. About an hour before sunset, look due west and look about halfway up the sky to find the crescent moon.
Now if you have binoculars, point them at the moon and look to the left and slightly under the crescent. Then you shouldn’t have a problem spotting Venus, which appears as a bright white patch of light against the blue of the daytime sky. And once you’ve found it with the binoculars, try to find it with just your eyes. If you have good visibility and your sky is clear and not too hazy, you should have little trouble seeing Venus in daylight.
Of course, once the sun has set and the sky is darkening, both the moon and the planet will keep everyone’s attention focused on the western sky for nearly three hours after sunset.
But Venus is not the only planet visible tonight.
About 4 degrees to the upper left, Mars appears to be glowing rather faintly. You’ll probably need binoculars to even see it in the bright twilight, even after Venus has become visible. With a brightness of +1.7, Mars is only one of the second magnitude objects and shines more than six orders of magnitude fainter or about 331 times fainter than Venus! One reason is that Mars is only about half the size of Venus and is currently 200 million miles (322 million km) from Earth, compared to just 53 million miles (85 million km) for Venus.
And about a dozen degrees up left of Mars is another bright sparkle: the bluish 1st mag star Regulus, the brightest star of Leo the Lion. Regulus was notable to ancient skygazers because it was one of the four “royal” stars long ago thought to rule the four cardinal points.
Thursday, June 22: The Moon joins Mars and Regulus
The moon, now a thick crescent almost five days into the new phase, will form a fairly broad isosceles triangle with the star Regulus and Mars.
The Moon marks the vertex angle with the “legs” measuring about 6 degrees and formed by the Regulus/Moon and Mars/Moon sides of the triangle, and Regulus and Mars, which are about 10 degrees apart, mark the base of the triangle.
No “official” meeting
It also appears that Venus will be rapidly racing east each night and will eventually reach slower-moving Mars. However, this scenario will not occur.
Venus has already reached its greatest angular distance east of the Sun on June 4th, so from our perspective it is now swinging around on its orbit and moving towards the Sun again. Although they appear to be chasing Mars in the evening sky, the two will never get together.
In fact, Mars will experience a “quasi-conjunction” with Venus from June 19 through July 10, as the brighter world draws closer but never quite catches up. A quasi-conjunction is defined as two planets approaching within 5 degrees of each other—that’s half the width of your clenched fist held out in front of you—without actually conjunct the right ascension process. They will appear closest together on July 1st, when they will be just 3.57 degrees apart.
Editor’s note: If you take a picture of the Moon and Saturn and would like to share it with Space.com readers, send your photos, comments, and your name and location to email@example.com.