When enjoying the cool in summer, enjoy the beauty of these stars.

While enjoying the coolness in summer, enjoy the beauty of these starry sky.

The sky already knows.

On June 1 1, Venus and Uranus met.

Venus is the brightest star in the night sky. At present, its brightness is close to -4, and it appears in the eastern low altitude before dawn. At this time, we call it the morning star. On the other hand, Uranus is far from the sun and its brightness is very low, only 5.8. Under ideal conditions, we can barely reach the limit of being visible to the naked eye. But under general conditions, it is still difficult to find its trace without certain observation experience and equipment.

The conjunction of Venus and Uranus provides a good opportunity to find Uranus. We can try to find Uranus nearby with the help of bright Venus. Of course, observation must use telescopes, even small binoculars. Venus and Uranus meet on June 1 Sunday 2 1. At this point, they are still below the horizon and we can't observe them. They will only rise from the eastern horizon in the early hours of 12. At this time, Uranus is at the upper left of Venus, and the angular distance between them is about 1.5 degrees, which is almost equivalent to the apparent diameter of three full moons. However, due to the dawn soon, the observable time is less than 1 hour.

June 14 "Super Moon"

On June 14, we are about to usher in the second full moon this year, which is also a "super moon". Why is the full moon big and small? This is because the moon orbits the earth in an elliptical orbit, with a running period of about 27.3 days, sometimes closer to the earth and sometimes farther away. The closest point on the lunar orbit to the earth is called perigee, and the farthest point is called apogee. The moon is closest to us at perigee and looks the largest, while it looks the smallest at apogee. If the moon happens to be near perigee during the full moon, it will appear "big and round", which is the so-called "super moon". In fact, "super moon" is not an astronomical term. From an astronomical point of view, it is more accurate to call it a perigee full moon. In the same way, if the moon is near apogee during the full moon, it will look "small and round" and should be called apogee full moon.

What's the difference between perigee full moon and apogee full moon? The moon is about 360 thousand kilometers away from the earth at perigee, and the farthest distance from the earth at apogee can reach more than 400 thousand kilometers. It can be calculated that the apparent diameter of the moon at perigee is about 14% larger than that at apogee, and the area is about 30% larger than that at apogee, and the difference is quite obvious.

However, it is almost impossible for the full moon to appear exactly at the moment when the moon passes through perigee. Generally, it appears about one day before and after perigee, so it can be called "super moon". The time of this full moon is around 20 o'clock in the evening of June 14, and the time of the perigee of the moon is around 7 o'clock in the morning of June 15, with a difference of about 1 1 hour.

June 16 Mercury westward distance

Mercury is in the orbit of the earth. From the earth's point of view, it always swings back and forth in a certain range near the sun. When the angle between the west of the sun and the sun reaches the maximum, it is the west distance. Mercury appears at low altitude in the east before sunrise in the morning, far from the west. Because mercury is the closest planet to the sun, it orbits the sun once in 88 days, so it can have a distance to the west 3-4 times a year.

This is the second time this year that Mercury is far away from the West. The observation conditions this time are average. At sunrise, the height of mercury's horizon is only about 12 degrees, and the time interval between mercury's rising above the horizon and sunrise is only over an hour. When mercury rises to a few degrees above the ground, the sky has already begun to brighten. At this time, the brightness of mercury is about 0.5, so it is still difficult to see. When the weather is clear, with the help of binoculars in the morning light, there is still a chance to find rare mercury on the horizon north of the east.

However, it is not necessary to observe mercury on the day when the western sky is far away. In fact, the height of Mercury's horizon remained basically unchanged at sunrise for more than ten days after the Western Heaven. Even a few days after 16, the height of the horizon was slightly higher and the brightness of Mercury gradually became brighter. When looking for mercury, we can use its bright Venus in the upper right corner. Although the distance between them is about 10 degree, there is at least one reference object.

Extended reading

Why can't you see the telephone pole at noon in summer?

Summer solstice, like winter solstice, vernal equinox and autumnal equinox, is not only an important node in astronomy, but also one of the traditional 24 solar terms in China. The earth goes around the sun once a year. Seen from the earth, the sun seems to move slowly in the sky. In astronomy, the trajectory of the sun in the sky is called the ecliptic. Divide the great circle of the ecliptic into 24 segments, each segment is 15 degrees, and every time the sun passes 15 degrees from west to east, it passes through a solar term. The position of the sun on the ecliptic is different, and the height of the horizon of the sun on the ground at noon is also different. The summer solstice usually occurs one or two days before and after June 2 1 of the Gregorian calendar every year. The specific time of the summer solstice this year is June 2 1, 17, 14. At this time, the sun runs to 90 degrees of the yellow meridian and is located in Taurus.

On the solstice of summer, the sun shines directly on the tropic of cancer on the earth. At this time, the position where the sun shines directly on the ground reaches the northernmost point, with the longest sunshine time and the shortest shadow at noon in the northern hemisphere. There can be a phenomenon of "no shadow between Japan and China" on the Tropic of Cancer. Because the height of the sun horizon in these places is 90 degrees at noon from the summer solstice, objects on the ground will not be reflected when the sun shines directly overhead. This phenomenon of "no shadow between Japan and China" will only appear in the area between the Tropic of Cancer.

The solstice in summer means that the hot weather officially begins, and then it will get hotter and hotter. There is a folk proverb in our country that the solstice in summer is not too hot. After the summer solstice, the direct point of the sun began to move southward gradually, and the days in most parts of the northern hemisphere became shorter day by day. However, since the heat radiated from the sun to the ground is still more than that radiated from the ground to the air, the temperature will continue to rise. (The writer is a senior engineer at the Beijing Planetarium)