(Above: Mars will dramatically increase in size during June, as shown in these simulated telescope views of the Red Planet. A developing global dust storm on Mars may spoil our views, however.)

The Solstice starts the Northern Summer

The beginning of summer in the Northern Hemisphere, known as the Summer Solstice, occurs on Thursday, June 21 at 6:07 am Eastern Daylight Time. At that moment, the northern end of the Earth’s axis of rotation will be tilted 23.5° towards the sun. As a result, the Sun will reach its highest noonday position in our sky for the year as viewed from the Northern Hemisphere. It will shine more intensely on the Northern Hemisphere, and deliver our longest amount of daylight. More hours of concentrated, direct sunlight translates to more solar energy and warmer days! It is NOT the case, as some people think, that we are warmer because we are closer to the Sun — that event, called perihelion, actually happens in early January every year! As a matter of fact, the Earth is only two weeks away from reaching its widest separation from the sun, or aphelion for this year. That occurs on Friday, July 6.

For our friends in the southern hemisphere, this solstice signals the sun’s lowest noon-time height of the year, and marks the start of their winter. The summer solstice is good news for astronomers — after Wednesday, the days will slowly start to get shorter while the nights lengthen.

The Moon and Planets

This is the week of the moon’s monthly trip around Earth when it will be sitting prettily in the evening sky as a beautiful, partially lit orb. Grab binoculars or your telescope and enjoy close-up views of the dramatic lunar terrain, especially along the terminator — the boundary between the lit and dark hemispheres. Steeply slanting sunlight creates brightly lit peaks and crater rims that cast deep black shadows between them. And new vistas appear every night as the sun slowly rises over the moon and the terminator slides west.

(Above: The young Moon will meet Regulus on Sunday evening, June 17, as shown here for 11 pm local time. A binoculars field is indicated by the orange circle. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android. )

The moon will reach its First Quarter Phase on Wednesday morning, so it will appear close to half illuminated on both Tuesday and Wednesday evening. In the meantime, look in the western sky in late evening tonight (Sunday) for the waxing crescent moon situated approximately four finger widths to the lower right (west) of Regulus, the brightest star in Leo (the Lion). Both objects will fit into the field of view of binoculars. The moon will set about 12:30 am local time. Observers in the Pacific Ocean region will see the moon pass very close to the star before the pair sets.

Starting in the southern sky after sunset on Saturday evening, the waxing gibbous moon will sit less than four finger widths to the upper left of very bright Jupiter. The two objects will cross the sky together during the night. The sky’s rotation will carry the moon higher and above Jupiter after midnight. Meanwhile, the moon’s separation from the planet will noticeably increase as the moon slides eastwards in its orbit.

(Above: On Tuesday, June 19, Venus will skim past the northern edge of the large Beehive open cluster in Cancer, as shown here for 10:20 pm local time. To see more stars, use binoculars when the sky has darkened a little. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

Venus continues to dominate the western evening sky this week while it continues to swing away from the sun. The planet will set at about 11:30 pm local time all week because it is travelling east while the entire sky is shifting west, holding it in place. Venus is gradually growing larger as it moves towards Earth. In a small telescope, it will exhibit a gibbous (74% illuminated) phase. On Tuesday evening, Venus’ orbital motion will place the planet on the northern edge of the huge open star cluster called Messier 44, also known as the Beehive. Both objects will fit together in the same binocular field of view, with the cluster situated to the lower left of Venus. From about 10:30 pm onwards, more of the cluster’s stars will be apparent in the darker sky.

(Above: The inner planets Mercury and Venus will appear in the western evening sky this week, as shown here on Wednesday at 9:50 pm local time. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

Jupiter is the bright object you will see shining brightly in the southern sky after dusk this week. Around that time, it will be at its highest elevation (about three fist diameters) above the southern horizon. Over the following hours, it will move west and descend — setting in the west-southwest about 3:15 am local time. Once it’s dark enough, look for a bright star sitting just to the lower left of Jupiter. That’s Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars or a small telescope, it splits into a closely separated pair of stars. The waxing gibbous moon will sit near Jupiter on Saturday night.

On Wednesday, June 20, and visible from 10:58 pm to 1:13 am EDT, the little, round, black shadow of Jupiter’s moon Europa will cross (or transit) Jupiter’s disk. On Friday, June 22 between 11:19 pm and 1:29 am EDT, the shadow of Jupiter’s moon Io will transit. A reasonable backyard telescope will show the black shadows, but a very good telescope is needed to see the moons themselves. More shadow transits are available in other time zones around the world.

The Great Red Spot (or GRS, for short) takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. The best times to try this week are: Wednesday, June 20 at 10 pm and Friday, June 22 at 11:39 pm (with an Io shadow transit bonus!). All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone. Try to look within an hour before or after the times I’ve given.

Yellow-tinted Saturn will be rising in the southeastern sky about 9:30 pm local time this week. It will spend the summer of 2018 just to the left of the Milky Way, and just above the Teapot-shaped stars that form Sagittarius (the Archer). Saturn moves over the southern horizon, its highest point in the sky at 2 am local time. It will remain visible until about 5 am local time, when it will sit a generous fist width above the southwestern horizon. Next week, Saturn reaches opposition — its brightest and closest for the year.

(Above: Three bright planets will reward observers who stay up until late evening, as shown here at midnight on Saturday, June 23, 2018)

The Summer of Mars is here! The Red Planet will be rising in the east just before midnight this week. Mars, already noticeably brighter than Saturn, will continue to steadily brighten and increase in apparent size as the Earth’s faster orbit brings us closer to the red planet until late July. In the meantime, look for bright reddish Mars shining over the southern horizon just before dawn.

This week, Mercury can be spotted low over the northwestern horizon for a brief period after sunset. It will become easier to spot as this week wears on — with the best time being between 9:45 and 10 pm local time, when it will be about four finger widths above the horizon. While Mercury will spend the rest of June increasing its separation from the sun, the Earth’s tilted axis will pull the evening ecliptic, and all the planets’ orbits, lower over the next couple of months, so our prime Mercury viewing time is sooner rather than later.

(Above: The orbital path in red of the major asteroid (4) Vesta, which reaches opposition and peak visibility for the year on June 19. The sky is shown for 10:30 pm local time. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

On Tuesday, the Earth’s orbit will carry us between the minor planet (4) Vesta and the sun. (It was the fourth asteroid discovered, hence the numeral in its name.) Sitting opposite the sun in the sky, Vesta will be visible all night long, and appear at its brightest (magnitude 5.33) for the year; within reach of binoculars and small telescopes. Look for the object in northern Sagittarius, approximately 8.5° (somewhat less than a fist’s diameter) to the upper right of Saturn.

Distant blue Neptune, among the modest stars of Aquarius (the Water-bearer), is observable in telescopes in the pre-dawn eastern sky after it rises around 1 am local time. This week, look for the magnitude 7.9 planet sitting one finger width to the right of the naked eye star Phi (φ) Aquarii and about five finger widths to the left of brighter Hydor (Lambda Aquarii).

Uranus is also in the eastern pre-dawn sky, located about four finger widths to the left of the modest star Torcular, which is down toward the “V” where the two cords of Pisces (the Fishes) meet.

(Above: The distant ice giants Uranus and Neptune are visible for a few hours in the eastern pre-dawn sky this week, as shown here for 4 am local time. Night Sky Chart made via Star Walk 2 iOS and Star Chart for Android.)

Astronomy Skylights for this week (from June 17th, 2018) by Chris Vaughan. Keep looking up to enjoy the sky!