In July we are able to see all five “naked eye” planets, a mere six months after the last time this happened.
Before the winter of 2016, it had been a decade since all the visible planets could be seen at one time.
We also enter the heart of summer as such classic starry patterns as the Summer Triangle and the Scorpion glisten in the July evening sky.
Venus returns to our skies in late July after a 10-week absence behind the sun. However, while Venus is the brightest dot in the sky, it will be tricky to find this summer. In late July you will only have 30 minutes from the time Venus appears at dusk, extremely low in the west, until the time it sets.
You can start looking for Venus around July 15. Around 7:30 p.m., scan the western horizon, and look for Venus a mere 5 degrees (roughly the width of two fingers at arm’s length) above the western horizon. It will be extremely bright (minus 3.9 magnitude), which will make it easier to spot; but make sure you are searching over a flat horizon or you’ll miss it. By 8 p.m., the planet will set.
Venus does a dance with the planet Mercury for the last two weeks of July. On July 15, Mercury is less than 1 degree to the right of Venus, less than the thickness of your pinkie finger at arm’s length. Mercury shines at minus 1 magnitude, similar to a bright star.
Night by night, Mercury will appear a little higher above Venus. By the end of July, Mercury will be about 8 degrees (four fingers) to the upper left of Venus, and will set by 8:15 p.m. The planet Mercury does fade in brightness from minus 1 in mid-July to zero magnitude at the end of the month; but since it does not set until 8:15 p.m. your odds of catching it do improve.
Throughout this July, look for the distinctive triangle formed by Mars, Saturn and Antares, the brightest star in the Scorpion. Mars remains the brightest member of the triangle and in early July is as bright as the brightest star in the sky. As Earth pulls away from the Red Planet, Mars fades in brightness by 40 percent by month’s end.
Throughout the month, the three dots make a triangle. At the start of July look for the trio high in the south as it gets dark at 8 p.m., with Mars leading the way; the Red Planet is the point of a narrow triangle, with dimmer Saturn and Antares each about the width of two palms to the left of Mars. In early July, the triangle hits the western horizon in the early hours of the morning, with Mars plunging below the horizon at 2:30 a.m., followed by Saturn and Antares an hour later.
By the end of July, we have a more compact triangle than we saw early in the month, with each dot separated from the others by the distance of a single palm. By the end of July, the triangle is due south at dusk. In late July, Mars sets a few minutes before 1 a.m., and the other two dots follow it down less than an hour later.
At the start of July, look for Jupiter halfway up in the west at dusk, setting at 11 p.m. The planet shines at minus 1.8. At the start of July, Mars and Jupiter will still seem rivals in brightness; by the end of July there will be no contest, as Jupiter shines nearly three times brighter than fading Mars. By month’s end, Jupiter is only about 20 degrees above the west at dusk, and sets around 9:30 p.m. On July 8, look for the slender crescent moon just below Jupiter.
In late January we were able to see all five naked eye planets in the morning sky at one time. This phenomenon returns in late July, now in the evening sky. You need to go out between 7:30 and 8 p.m. with good weather conditions and a flat horizon. Venus and Mercury huddle just above the western horizon. Then look for Saturn and Mars high in the south and Jupiter above Venus and Mars.
Other sky events in July:
Lahaina Noon returns
In the tropics the sun passes overhead twice during the year. On these two days, at local noon, the sun will be exactly overhead and an upright object such as a flag pole will have no shadow. The northern reaches of the Hawaiian Islands, such as Midway Island, are north of the tropics and do not experience the overhead sun.
The dates of your “overhead sun” in Hawaii vary by location: Lihue on July 11 at 12:42 p.m.; Honolulu, July 15, 12:37 p.m.; Kaunakakai, July 16, 12:34 p.m.; Lanai City, July 18, 12:34 p.m.; Lahaina, July 18, 12:33 p.m.; Kahului, July 18, 12:32 p.m.; Hana, July 18, 12:30 p.m.; Hilo, July 24, 12:27 p.m.; Kailua-Kona, July 24, 12:30 p.m.; South Point, July 28, 12:28 p.m.
Southern Cross
Generally, the first days of July are the last chance we have in the islands each year to see the Southern Cross.
At dusk in late June and the first few days of July, look due south; you will see two brilliant stars just above the south horizon. The one on the left is Alpha Centauri; the one on the right, Beta Centauri. These are also called “The Southern Pointers.” Draw a line to the right from these stars that is about three times the distance between the two stars themselves. This will point you to Gacrux, the top star in the Cross. Look down to the horizon to catch the lowest star in the Cross, Acrux; then try to find the two stars that make the crossbeam. Make sure you have a flat horizon, such as the ocean.
After July 4, Crux gets lost behind the sun and returns to the morning sky in December.