An evening sky without bright planets and the Summer Triangle in the eastern sky: June brings new views for star lovers. Towards the end of the month, the crescent moon and bright Venus make for a spectacular sight.
When darkness falls late in the evening of June, bright star Arcturus in the far south constellation of Bootes will be the first to shine. Arcturus means something like Bear Guardian because he constantly follows the Great Bear as he orbits the north celestial pole. Bootes is the cattle herder walking after the seven stars of the Big Dipper. The seven chariot stars, which revolve around the North Star and are easy to recognize, were called Septemtriones – the seven threshing oxen – by the ancient Romans.
Arcturus was already known as the bear keeper in ancient times. The Polynesians called Arcturus the Star of Joy because they used it as a navigational star. In the South Seas, Arcturus reaches its highest point high in the firmament and is almost at the zenith. It is a red giant star 37 light years away. Its luminosity is 215 times that of our sun. Its diameter is 25 times larger than that of our sun.
The Summer Triangle occupies the eastern sky in June. It is composed of the main stars of three constellations: Vega in the lyre, Deneb in the swan and Atair in the eagle. Along with Arcturus, Vega is one of the two brightest stars in the northern sky. While Arcturus appears in an orange-red light, Vega glows bluish. At a distance of 25 light years, Vega is one of our sun’s neighboring stars. Vega rotates very rapidly and is therefore strongly flattened. A Vega rotation takes only twelve hours, while our sun rotates once in 25 days. Vega is an ellipsoid of revolution and not a sphere like our sun. Their pole diameter is one-twentieth shorter than the equatorial diameter.
The lion can still be seen far to the west, a relict of the starry spring sky. In the southwest, the Jungfrau prepares for her sinking. It is also one of the spring constellations. Deep in the south, Scorpio wanders along the horizon. Its red supergiant star Antares, which means Mars-like star, is striking. Ares is the Greek god of war, who was called Mars by the Romans.
Since Antares not only shines reddish like Mars, but is also close to the sun’s orbit in the zodiac, it can occasionally be confused with Mars. While the evening sky is currently without bright planets, the bright planets are bustling about in the second half of the night. Venus rules the morning sky. Shortly after the middle of the month, she changes from the constellation Aries to Taurus, as she assumes more and more northerly positions. The morning star rises just before 4 a.m. at the beginning of the month, and 20 minutes earlier at the end of June.
Mars in the Pisces and Whales region is noticeably brightening. It rises earlier and earlier, at the end of the month it appears a quarter of an hour before 2 a.m. Jupiter becomes the planet of the second half of the night. The giant planet rises just before three o’clock in the morning on June 1st, at the end of June already five minutes after one o’clock. Saturn in the constellation of Capricorn shifts its sunrise time to around midnight. At the beginning of June, the ringed planet rises above the eastern horizon line at 20 minutes to two in the morning, and at the end of the month it is already a quarter of an hour to midnight.
At 1:52 p.m. on June 14, the full moon position is reached, with the moon in the zodiacal constellation of the Ophiuchus. A good twelve hours later, the moon comes close to earth at 357,430 kilometers. The near coincidence of near-Earth and full moon results in spring tides. On June 2nd the Moon will be 406,190 kilometers away from Earth. The waning crescent moon can be seen early in the morning of June 23 in Mars. A day earlier, the moon is in the morning sky between Jupiter and Mars. The extremely thin crescent of the waning Moon meets bright Venus on the 26th, a spectacular sight around 5am. Finally, on the 29th at 4:52 a.m., the new moon is reached, with the moon being 406,580 kilometers away from Earth again on the same day.
It is delightful to observe the moon with binoculars or a telescope. The lunar formations appear particularly three-dimensional at the light boundary between the light and dark part of the lunar sphere, for example at half moon. Craters, ring walls and lunar mountains cast long, deep black shadows. They are sharply defined because the moon has no atmosphere to scatter sunlight. The dark lowlands filled with solidified lava were seen as seas by early telescopic observers. But in the space vacuum there are no free water surfaces. The astronomer Franz von Paula Gruithuisen even said in 1824 that he saw a castle near the Schröter crater that had been built by the Selenites, the moon dwellers. But: there are no moon dwellers.
At 11:14 a.m. on June 21, the sun reaches the peak of its annual path, the summer solstice begins. After that, the sun no longer rises any higher, but sinks back down to the celestial equator, which it reaches on September 23 at the beginning of autumn. The summer point of the sun’s path is in the constellation Taurus on the border with Gemini. On the same day, one hour before midnight, the sun moves out of Taurus into the constellation Gemini. 2000 years ago the summer point was still in the constellation Cancer. That is why we still speak of the Tropic of Cancer.
A number of large sunspots are currently visible. The sun is heading for a new spot maximum. Every eleven years, the sun shows a particularly large number of spots, as the pharmacist Samuel Heinrich Schwabe from Dessau recognized as early as 1843. Sunspots are, so to speak, the weather patterns on our day star. They are huge storm areas where the temperature drops by around 1000 degrees. Their size often reaches several earth surfaces. The sunspots are accompanied by massive outbursts of radiation and matter. The plasma clouds ejected in the process occasionally reach the earth and produce polar lights. They interfere with radio communications as well as electronic devices.
The sun is our primary source of energy. Without their light and warmth, Earth would tumble through space as an ice-armored chunk of minus 200 degrees and below. While fossil fuels such as oil, natural gas and coal will be used up in a relatively short time, the sun’s nuclear reactor will continue to shine for billions of years.
However, the luminosity of the sun is steadily increasing. When it formed almost five billion years ago from an interstellar cloud of gas and dust, it provided only 60 percent of its current amount of energy. In about a billion years, the surface temperature of the earth will reach 100 degrees, the oceans will evaporate, in short: it will be uncomfortable. In about five billion years, the sun will expand into a red giant star and bring a fiery end to Earth.
