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Invasive species are reshaping the desert

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About the cover


Leo Minor, the Little Lion

Plus citizen science and the planets for April.


Leo Minor is almost overhead on April evenings. This tiny constellation (64th in area out of the 88 constellations) lies between Ursa Major to the north and Leo to the south. To the ancients, this area was not a part of any constellation figure, but in 1687, Polish astronomer Johannes Hevelius released his star atlas Firmamentum Sobiescianum, which plotted this constellation for the first time. Hevelius felt that a young lion would fit in well with the Great Bear (Ursa Major) and the Lion (Leo). Since this is a modern constellation, there is no mythology associated with it.

Click the image for a bigger map

Looking north on April evenings, you can find Leo Minor three-quarters of the way up in our sky, nestled between Ursa Major and Leo. This small constellation contains a number of interesting galaxies. Everything in this view appears upside-down, since we are used to seeing the sky with south being down instead of north being down in this view. So both Ursa Major and Leo appear to be standing on their heads—a somewhat uncomfortable position, but nonetheless correct in this view.


This constellation has a number of galaxies that are visible in medium and small telescopes. One of the most visually interesting is NGC 3432, known as the Knitting Needle Galaxy. It is a spiral galaxy oriented in space so that we see it edge-on. This gives it a long and skinny appearance, like a knitting needle. This galaxy is 6.8 minutes-of-arc along the plane and 1.4 minutes-of-arc in width. It shines at magnitude 11.7 and is 42 million light-years away. You can locate this gem just three degrees south of the star 38 Leonis Minoris.

Leo Minor is also home to a citizen-science success story. With the ever-increasing number of telescopes (both ground and space) and the even more rapid increase in the data collection ability of the instruments connected to those telescopes, astronomers have been deluged with raw data. They do not have the time to dig through all these images and classify all the objects that are visible. For example, the Sloan Digital Sky Survey at Apache Point, in the Sacramento Mountains here in New Mexico, creates about 200 gigabytes of data every clear night, and has been in operation almost every clear night since 2000.

Computer programs were written to attempt to classify galaxies from these images, but the programs were unable to correctly classify each galaxy. The human mind is much better at pattern interpretation than a computer, so each image needed to be examined by person, but the astronomers were already too busy to do the job — ideal or what is called a citizen science project.

Early citizen science projects included SETI-At-Home, which used spare processing power in participants' home computers to look for unusual radio signals from space. This required no active participation, beyond leaving the computer powered on.

When the Stardust spacecraft returned to Earth on Jan. 15, 2006, it carried blocks of aerogel that had been exposed to space, collecting cosmic dust particles. These blocks had to be inspected at high magnifications, resulting in over 700,000 fields to be examined. NASA was able to perform automatic scans of the aerogel, and put them on the Internet for volunteers to search for cosmic dust particles. This was the Stardust@home citizen science project.

Kevin Schawinski, an astrophysicist at Oxford University, thought that something similar could be done for astronomical images and created the Galaxy Zoo project. Volunteers were asked to look at images previously unseen by humans, originally taken and processed by robotic telescopes. The volunteer would classify each galaxy as elliptical or spiral and, if a spiral, rotating clockwise or counter-clockwise. This would provide a more complete census of the galaxy types in our universe.

Almost 83,000 people volunteered and managed to classify over 10 million galaxies. In 2007, Dutch schoolteacher Hanny van Arkel was analyzing galaxies near IC 2497 in Leo Minor and she found a strange greenish object nearby. Dubbed Hanny's Voorwerp (Dutch for "Hanny's Object"), it's near (in space, not just in the sky) IC 2497, about 650 million light-years away. It is 100,000 light-years across, with an immense central hole of over 16,000 light-years.

Research is still continuing on this object, but it is thought that a small galaxy passed IC 2497, pulling out a long streamer of dust and gas, referred to as a "tidal tail." This also disrupted the gas and dust near IC 2497's central black hole. The dust and gas started falling into the black hole, creating an immense amount of energy — called a "quasar event" — roughly 100,000 years ago. The energy was beamed out in a cone that happened to illuminate the section of the tidal tail that we see. The quasar event is long over, but we can still see its effects in Hanny's Voorwerp.



The Planets for April


Both Mars and Venus remain too close to the Sun to be seen this month, but Venus will appear in our evening sky next month.

Now getting out of prime observing season, Jupiter is 35 degrees up in the west as it gets dark and sets by 11:30 p.m. Moving eastward in northeastern Taurus, the King of the Planets shines at magnitude -2.1 and its disc is 34.5 seconds-of-arc across at midmonth.

Watch the Skies
(times MDT)

April 2, 10:37 p.m. — Last Quarter Moon
April 10, 3:53 a.m. — New Moon
April 18, 6:31 a.m. — First Quarter Moon
April 22, 5 a.m. — Lyrid Meteor Shower peaks
April 25, 1:57 p.m. — Full Moon, partial Lunar Eclipse
April 28, 2 a.m. — Saturn at opposition

Saturn reaches opposition at the end of April, so it is visible all night. It starts out on the eastern horizon as it gets dark and ends up low in the west as it get light. The Ringed Planet is moving slowly westward in far western Libra. Shining at magnitude +0.2, Saturn's disc is 18.7 seconds-of-arc across at midmonth. The Rings are 42.5 seconds-of-arc across and tilted down 18.4 degrees with the northern face showing.

Mercury continues its appearance in the morning sky. It starts the month eight degrees above the east-southeastern horizon as it gets dark. Mercury will move northward along the eastern horizon, getting lower each day. By the last week of April it will be very hard to find, disappearing completely by month's end. Each day Mercury will get fuller as it goes around on the far side of the Sun. At midmonth, the Messenger of the Gods' disc is 5.3 seconds-of-arc across and magnitude -0.9. Mercury starts the month moving eastward in Aquarius but soon moves into Pisces. It nicks the corner of Cetus, then moves back into eastern Pisces to end the month.

There will be a partial lunar eclipse on April 25, but it will be visible only in eastern Europe, western Asia and all of Africa. We will not see any of it, but we can still "keep watching the sky"!  


An amateur astronomer for more than 40 years, Bert Stevens is co-director
of Desert Moon Observatory in Las Cruces.



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