At some point in the year, before the sun rises, or after the sun sets, a very bright star appears in the eastern or western sky. So, what are these two stars? Why do they always rise or set with the sun every time they appear?
In ancient China, the bright star that rose from the east in the morning was called the day star, and the bright star that appeared in the west in the evening was called the Chang Gung star. The two stars are very bright, looking brighter than any other star in the night sky. So, in modern astronomy, what stars are they?
<h1>Same star</h1>
In fact, Daystar and Chang Gung Star are not two stars, but the same star that appears in different celestial regions, it is Venus. This is our close neighbor, which is the closest (average distance) planet to Earth. Like Earth, Venus revolves around the Sun.
Since it is a planet, Venus itself does not emit light, and its bright light also relies on reflecting sunlight like the moon. Because Venus is very close to Earth and its acidic atmosphere is so reflective, it looks very bright, it is the brightest star in the night sky (excluding the Moon), and its brightness is much brighter than those extrasolar stars that are far away from Earth, although those stars are actually brighter than the Sun.
<h1>Venus appears only in the early morning and at dusk</h1>
In the middle of the night, we can see the three planets of Mars, Jupiter and Saturn. However, venus appears every time it is in the early morning and at dusk, and it is impossible for us to see venus at midnight. So why is Venus different from other planets?
The reason is that Venus is closer to the sun than Earth, and it is an inner planet. When Venus, Earth, and the Sun move to nearly the same straight line, Venus is difficult to see. In this case, Venus's position in the sky is very close to the Sun's, with a small angular distance. Although Venus is very bright, it is still submerged in the dazzling sun's rays and becomes invisible.
Only when the angular distance between Venus and the Sun is large, and their position in the sky appears to be far apart, venus will not be flooded by sunlight, which is easy to see with the naked eye. When Venus is near the Great Western Distance, it appears in the eastern sky before the Sun has risen. When Venus is near the Great East, it appears in the western sky after the sun has set.
Currently, Venus is moving toward the east, which means that in the near future, we will see bright Venus in the western sky. However, Venus cannot be seen yet because it rises only a few degrees above the horizon at dusk. Venus will reach its highest point in the night sky on March 23, 2020, and appear at the East Grand Distance the following day. At that point, Venus will shine in the western sky.
In addition to Venus, Mercury is also an earthly planet. Since Mercury is closer to the Sun, its angular distance from the Sun is so small that it is often difficult for us to see it. Mercury will appear at the eastern distance on the 20th of this month, and at dusk around that time, Mercury can be seen with the naked eye in places with good observation conditions.
<h1>Venus profit and loss</h1>
Observing Venus at different times will also see profit and loss phenomena like the moon. Although it is invisible to the naked eye, it is easy to identify the phase of Venus with the help of astronomical telescopes. Before the last great distance to the west of Venus, I had photographed Venus in the early morning with a Newtonian reflective telescope with a diameter of 150 mm:
It can be seen that after more than half a month, the phase of Venus has changed significantly. When Venus is at a large distance, we can see that the illuminated part of Venus can reach halfway, but at this time Venus is far away from Earth and appears smaller.