The 2 inner planets will be best viewed on the same day
As the planets perform in their stately dance circles around the Sun, they move in position in the sky. On March 24 of 2020, Mercury will be at its greatest western elongation, and on the same day, Venus will be at its greatest eastern elongation. This means you will have the best view of Mercury in the sky in the morning and Venus in the sky in the evening on the same day.
Venus will be visible at sunset in the west (Image courtesy of Jon Bunting @ Flicker)
The inner planets, Venus and Mercury, orbit the Sun closer than we do on Earth. As a result, they are often in the sky when the Sun is out. When they are at their elongation points, it means that both Earth and the planet are positioned so that they are at the greatest angle away from the Sun from our point of view, so are visible in the sky.
Easter and Western elongation shown in a diagram by Wmheric @ Wikimedia
Uniquely, both will be positioned at opposite elongations on March 24, so that you will have the best view of these two planets on the same day. For Mercury, early risers will see it not far above the horizon and get the best view just before dawn. In the evening, Venus will be visible high in the western sky just after sunset. Though both planets will be visible for weeks before that time. Venus especially is one of the easiest objects to spot, often being the brightest object in the sky other than the moon. Mercury is the planet that is best described as mercurial, with fewer chances to get a view of it, so on March 24, it should be at its easiest to spot.
Venus and the moon (image courtesy of Tony Armstrong-Sly @ Flickr)
The best times to look for Mercury and Venus is when the sun is either about to rise or has just set so that the sky is a little light. At these times it will be easy to spot Mercury and Venus as they will be either the only star visible in the sky or one of few visible.
In Brisbane on the morning of the 24th, Mercury will rise at 3:48 am and will be best viewed at 5:29 am when it is 22 degrees above the horizon, with the sun rising at 5:53 am. You can spot it at 91 degrees in the East. Venus will be best viewed at 6:05 pm, not long after the sunset at 5:54 pm. At its height, it will be 22 degrees above the horizon in the north-west at 209 degrees.
Mercury will be best viewed at 6:35 am in Sydney , about 25 minutes before sunrise. Look to the east at 89 degrees. Venus will be best viewed at 7:13 pm, just 12 minutes after sunset. It will be at a height of 18 degrees above the horizon in the north-west at 311 degrees.
The people of Melbourne don't need to be such an early riser, with Mercury best viewed on March 24 at 7 am, 27 minutes before sunrise. It will appear in the east at 87 degrees and be 21 degrees above the horizon. In the evening Venus is best viewed at 7:36 pm, only 11 minutes after sunset. It will be at an altitude of 15 degrees and in the north-west at 312 degrees.
Mercury will rise in Adelaide at 5:09 am, with the best view at 6:56 am. This will be 26 minutes before sunrise, and at 21 degrees above the horizon in the east at 88 degrees. In the evening Venus will be best viewed at 7:32 pm, 11 minutes after sunset. Look to the north-west at 312 degrees and 17 degrees above the horizon.
Over in Perth, Mercury will rise at 4:13 am and will be best viewed at 5:58 am, 25 minutes before sunrise. At this time the planet will be 21 degrees above the horizon in the east at 89 degrees. Venus will be best viewed at 6:33 pm, at an altitude of 19 degrees and in the north-west at 311 degrees. This is 11 minutes after sunset.
For fans of Astronomy, the opportunity to get the best view both of the inner planets easily on the same day shouldn't be missed. For families, this is a great opportunity to show your kids how the planets move across the sky and in their orbits.