Close encounters with Mars

As April begins, Jupiter hangs low in the west-northwest as darkness falls. It glows at magnitude –2.1 among the background stars of Aries the Ram, well below and a bit to the left of the more prominent constellation Orion the Hunter. By the end of the month, the giant planet sets only 45 minutes after the Sun and is difficult to spot against the bright twilight.

Jupiter and Earth now lie far from each other, which makes the distant world appear small through a telescope, just 34" across its equator. But the main problem with getting a clear view comes from the poor seeing that typically occurs at such low altitudes. This is the time to grab your last evening look at the planet and its four bright moons.

Although Mercury begins April a decent 15° east of the Sun, it sets just 30 minutes after sundown and can’t be seen in the twilight. Blame the shallow angle of the ecliptic — the apparent path of the Sun and planets across our sky — to the western horizon at sunset during autumn.

The innermost planet reaches inferior conjunction April 11 and then climbs rapidly into view before dawn because the ecliptic makes a steep angle to the eastern horizon before sunrise. On the

30th, the planet stands 10° high in the east an hour before sunup. Mercury shines at magnitude 1.1 and a telescope shows a 10"-diameter disk that appears about one-quarter lit.

As we welcome Mercury back to the morning sky, we also must bid farewell to

Venus. Although the inner world remains conspicuous in early April, shining at magnitude –3.9 low in the east before sunrise, it disappears after midmonth. A telescope reveals a fully lit disk that spans 10".

Saturn fares far better. The ringed planet rises three hours before the Sun in mid-April and stands 20° high in the east as twilight starts to paint the sky. It shines at magnitude 1.0 against the much fainter stars of Aquarius the Water-bearer.

If you’re an early riser, take some time to observe Saturn through a telescope. Those who haven’t seen Saturn up close recently might be surprised to find the rings nearly edge-on. At midmonth, they tilt only 4° to our line of sight. With less distraction from the rings, the planet’s 10th-magnitude moons — Tethys, Dione, and Rhea — become easier to spot. Of course, 8th-magnitude Titan is always an easy target.

The morning sky’s other naked-eye planet is Mars. The Red Planet’s relatively fast orbital motion allows it to catch up with distant Saturn this month. On April 11, the two pass only 0.5° apart. Because they appear almost equally bright, use their color contrast to tell them apart.

Mars also has its sights set on a more distant target. On

April 29, the ruddy planet has an even closer conjunction with 8th-magnitude Neptune. Mars slides just 2.2' south of its bluegreen sibling.

A total solar eclipse occurs April 8, but only a short part of its path lies in the Southern Hemisphere — and it’s an uninhabited part of the Pacific Ocean. The best views of totality come along a narrow track that cuts through Mexico, the United States, and Canada. See Astronomy’s April issue for complete coverage.

The starry sky

During my early stargazing days, I delighted in scanning the sky with my first reflecting telescope: an 11.4-centimeter model that was popular back then. It certainly revealed more of the heavens than my smaller refractor did.

One night after looking at the Carina Nebula (NGC 3372) — which was easier to observe from the suburbs than it is today — I scanned to the northwest and came across the delightful star cluster NGC 3293. I didn’t know how I had missed seeing this stunning object before, but the beautiful, tight open cluster quickly became one of my favorites.

This region of northeastern Carina the Keel climbs high in the south on April evenings. NGC 3293 shines at 5th magnitude and shows up to the naked eye under good conditions (averted vision helps). Henry Chamberlain Russell, who was

Government Astronomer for New South Wales from 1870 to 1905, christened it the

Gem Cluster.

I think NGC 3293 rivals the more famous Jewel Box Cluster (NGC 4755) in the constellation Crux the Cross. Like the Jewel Box, the Gem contains a conspicuous red star, which in NGC 3293’s case lies near the cluster’s southwestern edge. Designated V361 Carinae, this object is a pulsating supergiant that varies between magnitudes 7.1 and 7.6. Several other prominent stars call this cluster home, the brightest of which glows at magnitude 6.5.

NGC 3293’s stars are only about 10 million years old. A 2017 study published in the journal Astronomy & Astrophysics attempted to confirm or refute previous reports that claimed the cluster contained fewer low-mass stars than would be typical for such a group. The new paper, authored by astronomer Thomas Preibisch of the Universitäts-Sternwarte in Munich and colleagues, used the Chandra X-ray Observatory to confirm the presence of hundreds of low-mass young stars in the cluster, verifying that NGC 3293 fits in well with other open clusters in the

Milky Way.

I am sure that you will enjoy this cluster as much as I do. Target NGC 3293 some clear April evening and don’t be afraid to use high power — it stands magnification well.

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