What’s up? Night sky for April 2011

Amateur astronomers using a telescope at dusk

Autumn nights are ideal for stargazer. Autumn mornings too, with some planets making a welcome return to our pre-dawn skies.

LIKE LAST MONTH, Venus is the star of the show in April, high in the eastern sky before sunrise. You can’t miss it—it is big and bold and brilliant.

Mercury makes a reappearance in the eastern morning sky from mid-month. As the April progresses, you’ll notice it rising higher and higher in the sky.

Ditto for Mars, which has been lost from view in the glare of the Sun for a while, but is making a reappearance in the morning sky this month, very low down in the east.

The largest planet in the Solar System, Jupiter, will also be low down on the eastern horizon before sunrise during April.

So that’s four planets all quite near to one another in roughly the same part of the sky! Definitely worth getting up early for.

Shifting to the evening sky, and the ringed planet Saturn will be bright and bold in the eastern sky after sunset.

Except where indicated, all of the phenomena described here can be seen with just the unaided eye. And unless otherwise specified, dates and times shown here are for the Australian Eastern Standard Time zone, and sky directions are from the point of view of an observer in the Southern Hemisphere.

April 1

Have a look out to the east before sunrise and you’ll see the Moon just below the planet Venus. You can’t miss Venus—apart from the Moon and the Sun, it’s the brightest thing in the sky!

April 2

Today the Moon will be at the farthest point in its orbit, called apogee, at a distance from Earth of 406,657 kilometres.

Also, you’ll notice that compared to yesterday the Moon has moved downwards in the sky and away from Venus. Now, it will be closer to the planet Mars, which is fainter than Venus and a ruddy colour.

April 3

New Moon occurs today at 11:32pm Sydney time (April 3, 14:32 Universal Time).

April 4

The planet Saturn reaches opposition today. This is a fancy way of saying that, from an Earth-bound observer’s point of view, it is in the opposite side of the sky to the Sun. In other words, if you could look down on the Solar System from above, the Sun, Earth and Saturn would be in a line, with Earth in the middle. Opposition generally is a good time to view a planet.

Stargazers with telescopes

Take the opportunity to get out and do some stargazing before the weather becomes too cold

April 7

The planet Jupiter reaches conjunction with the Sun today, which is a fancy way of saying that it is on the other side of the Sun as seen from Earth…although, being on the other side of the Sun, we can’t actually see it. You can think of conjunction as being the opposite of opposition (see April 4 above), so to speak. If you could look down on the Solar System from above, you’d see Jupiter, the Sun and the Earth in a line, with the Sun in the middle.

April 10

Today, the innermost planet, Mercury, reaches ‘inferior conjunction’. This is another kind of conjunction, again signifying that certain celestial bodies are in a line. In this case it is the Sun, Mercury and the Earth in a line, with Mercury in the middle. This makes it impossible to see the tiny planet, as it is lost in the glare of the Sun.

On certain special occasions, the tilt of Mercury’s orbit means that it can be seen crossing the face of the Sun when it is at inferior conjunction, in an event known as a transit. That’s not the case here—the next one will be in 2016.

April 11

It is First Quarter Moon today at 9:05pm Sydney time (April 11, 12:05 Universal Time). First Quarter is a good time to look at the Moon through a telescope, as the sunlight angle means the craters and mountains are throwing nice shadows, making it easier to get that 3D effect.

April 14

The almost-full Moon will appear close to the star Regulus in this evening’s sky. Regulus is a large, blue star, and is the brightest star in the constellation Leo.

April 17

Today the Moon will be at the closest point in its orbit, called perigee, which is the opposite of apogee (see April 2). The distance between the two bodies today will be 358,090 kilometres.

Still on the Moon…take a look slightly below and to the left, and you’ll see a bright whitish-yellowish star. Well, that’s not a star, it’s the planet Saturn. If you have a telescope, or have a friend who has one, zero in on it and you’ll get a lovely view of its magnificent rings.

April 18

Full Moon occurs today at 11:44am Sydney time (April 18, 02:44 Universal Time). You won’t actually be able to see the Moon at that time, as it will be below the horizon. But take a look at sunset, and you’ll see that as the Sun sets in the west, the big, bright Moon will rise in the east.

April 20

Two planets get to say hello to each other this morning. In the eastern sky before sunrise, Mars and Mercury will appear close to each other. Be warned, though, that they will be very low down toward the horizon, so you’ll need a clear view if you’re to see them.

Over the next few weeks, four planets will be seen together in the morning sky. Here’s a short video from Tanya Hill, astronomer at the Melbourne Planetarium, explaining what we can expect to see:

April 21

Today will be an interesting to demonstrate to yourself how the Moon moves through the sky. If you get up in the morning while it’s still dark, take a look slightly above the Moon and you’ll see a ruddy-coloured star. That’s Antares, the brightest star in the constellation Scorpius. Remember that view. Now, go back outside later today in the mid-evening and find the Moon again, and you’ll see that the separation between the two has increased. This shows you how the Moon has trundled along a bit in its orbit throughout the day.

April 25

It is Last Quarter Moon today at 11:47pm Sydney time (14:47 Universal Time).

April 30

Today the Moon will again reach the farthest point in its orbit, apogee, at a distance from Earth of 406,038 kilometres. Take a look out to the east this morning and you’ll see the crescent Moon with Venus, Mercury, Mars and Jupiter (refer to the video above).

If you have any questions or comments on the night sky, we’d be happy to answer them. Please use the Feedback Form below. Happy stargazing!

Images courtesy IAU.

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