Planetary dance

The picture on the left was taken of the south-eastern sky at 6.54am on 29 March 2022, while the one on the right was snapped at 6.36am on 30 March 2022. The difference in the lightening dawn sky is remarkable. Timewise, there was only an 18 minutes difference when I took the two photographs.

But what I want to draw attention to is the position of the very bright Venus, the so-called "morning star" which we know is not a star at all but a planet, in the sky over a matter of one day. Within 24 hours, it had travelled some distance in a diagonal line towards the horizon. I dare say by June or July, it would be very difficult to notice this planet as its position moves closer to the rising sun. 

Mars is also moving slowly towards Saturn and on the fourth and fifth of April, both planets will be very close together when best viewed in the hour before sunrise. Weather permitting, I shall be out of my house on those two pre-dawn mornings! Of course, these planets aren't close together. Their proximities are all seen from the Earth's perspective because in actuality, they are separated by millions of kilometers. Venus is about 110 million kilometers from us while Mars is about 270 million kilometers away and Saturn is around 1,560 million kilometers.

As observed from the earth, Venus is a "morning star” for 263 days. It then disappears below the horizon for 50 days. Venue then reappears as an "evening star" for another 263 days. Thereafter, it disappears again but for only eight days this time. The ancient Greeks were so confused by this movement that they thought it as two different "stars". 

At the start of the 263-day morning star phase, Venus appears over the horizon just as the day breaks. Each day, the planet rises a little earlier and climbs a little higher. The pattern then reverses and Venus rises a little later each day until finally it fails to rise. For the next 50 days, Venus disappears behind the sun and cannot be seen at all.

Then, Venus reappears in the evening sky where it remains for another 263-day phase before dipping below the horizon for eight days as it transits in front of the sun. At the end of these eight days, Venus reappears as a morning star again, and the cycle repeats.

The entire cycle — 263 as a morning star, 50 days in superior conjunction, 263 days as an evening star, and finally, eight days in inferior conjunction — takes 584 days, an interval also known as the synodic period of Venus.

The above description of Venus' apparent movement in the sky also applies to Mercury. But this planet is even more difficult to observe in the sky either in the morning or evening because its orbit is so close to the sun. Only once have I managed to see Mercury as a small, faint dot of light in the morning sky and that was only because the condition was perfect enough to see it.