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The Lion in Spring
The Lion in Spring

Are you looking for it, too? It's that frustrating time of year again. As the Northern Hemisphere rolls away from winter we eagerly await signs of spring. For many, spring comes with returning robins bobbing along the ground in a spirited hunt for lunch. For others it's spring flowers putting in a first appearance. But the most reliable sign of spring is not of the Earth, but of the sky. It is the stars of Leo.

Leo the lion is a prominent spring constellation. When I see Leo riding high in the southern sky before midnight (figure 1), I know that Earth has not stalled in its yearly orbit and we are not stuck in perpetual winter.


Figure 1. The constellation of Leo is a rich hunting ground for sky gazers with telescopes. This part of the sky is relatively poor in stars but rich in galaxies.


At night, we face away from the Sun. Our nighttime view changes through the year. As Earth orbits around the Sun our view sweeps through the yearly cycle of seasonal constellations. The solar system is tilted compared to the plane of the galaxy (figure 2), and this also affects what we see as we look out into the stars. During spring nights we face away from the rich star fields of our galaxy. The Milky Way hugs the western horizon and our view is up and out of the galaxy (figure 3). This gives us a clear view into the deeps of intergalactic space.

In spring, the rest of the universe is on display. There is little interference from the Milky Way's intervening clouds of gas, dust and stars. Millions of external galaxies glow faintly in the blackness of space, beckoning telescopes to reveal their splendor. Astronomers answer the call of the galaxies each spring with eager enthusiasm. Leo and its neighboring constellations are rich territory for observers wanting to soak up photons from hundreds of millions of light years away. Such intergalactic communion is an experience like none other.


Figure 2. Earth orbits in the plane of the solar system, which is tiled with respect to the plane of the Milky Way. This is why our view of the Milky Way changes dramatically throughout the year. The Milky Way is seen here as a glowing cloud in the background, stretching diagonally from the upper left toward the lower right of the image. The purple line marks the central plane of our galaxy.



Figure 3. From high above Earth we can see North America in the shadow of night while Europe and Africa, on the right limb of the planet, are in daylight. North Americans looking into the night sky are looking away from the plane of the galaxy. The galaxy appears as a glowing cloud running vertically through the image below Earth. The purple line represents the central plane of the Milky Way. The curving green line at top, on which the Sun is located, marks the ecliptic — the plane of the solar system.


We all have our favorite signs of spring. This year spring arrived officially on March 21 at seven minutes after midnight Universal Time. For sky gazers, spring is synonymous with the arrival of Leo and a sky blooming with galaxies. The celestial lion is the surest signal that terrestrial blossoms will soon follow.

April 2007

Date Taken: 06/02/2011
Author: Mary Lou Whitehorne
Category: Archives

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