Find Lyra the Harp's variable star
11 comments Print Me Email to FriendTonight is Sunday, Dec 28 2008
At dusk and early evening in December and January, the three brilliant stars of the Summer Triangle asterism – Vega, Deneb and Altair – light up the northwest sky. An asterism is a pattern of stars that is not a constellation.
This evening, we zoom in on Vega and its small but distinctive constellation, Lyra the Harp. A dark sky brings out the four rather faint stars to the left of Vega. These stars form a parallelogram – a four-sided figure with its opposite sides equally long and parallel to one another. Three fingers at an arm length are enough to cover over this small parallelogram of stars.
The two stars shining on the left-hand side of the parallelogram are Sulafat and Sheliak. Sheliak is a binary star – two stars that revolve around one another. Moreover, this star is an eclipsing binary – one star blocks out the light of its companion star in regular periods. Although this binary looks single to the eye, its brightness dims every 6.5 days.
Normally, Sheliak and Sulafat are equal in brightness. But when one of Sheliak’s stars eclipses the other, Sheliak is the fainter star. Find brilliant Vega first tonight, then Sheliak and Sulafat.
How do you know where north is from using the North Star?
Does the Big Dipper side point to it? Always?
Thank you
Terry
Terry,
Yes, the Big Dipper always points to Polaris, the North Star. If you travel directly toward Polaris, you are going north. If you went all the way to the northermost point on the globe, the North Star would appear straight over your head and you’d be at the north pole. If you travel about-face of Polaris, you are going south. The farther south you go, the lower the North Star is in the northern sky. South of the equator, the North Star sinks below the horizon and can no longer be seen. For more on the subject read Spot the Big and Little Dippers before dawn.
Bruce
I’d like to see a daily listing (maybe under “Moon Phase”) that gives the Morning and Evening Stars for the date.
Thank You Bruce for your explanation of the Dec. 28, 2008 sky.
Also, Thank You Terry for your question about the North star because this is something I have always wanted to know about since the early travelers and today’s travelers use this star to guide them.
What is the evening star on the ssw horizon tonight? It’s just past sunset…the star is bright and beautiful.
Thanks
Marge
Marge, Peggy & Bob,
Marge, that brilliant object in the SW sky at dusk and early evening is the planet Venus, the brightest point of light in the heavens.
Peggy, it’s my pleasure to talk about the North Star and other wonders of the sky.
Bob, good idea about listing the evening and morning stars! Perhaps we can accommodate your request sometime in the future. In the meantime, you can find out the rising and setting times for the planets at the links on our almanac page.
Bruce
why does it look sometimes like the clouds are behind the stars?
i thought the bright planet in the SW was jupiter…i was just looking at it through my telescope
Do you know where I can find information that is orientated to the southern hemisphere? I am in New Zealand, so the stars are different down here!
Melony, Anthony, Stephanie,
Melony, I don’t know why it sometimes looks like the clouds are behind the stars.
Anthony, Jupiter and Venus are both in the SW quadrant of the sky at dusk. Venus is the higher and the brighter of these two planets. See the December 29 EarthSky Tonight Observer’s challenge: Moon, Jupiter, Mercury.
Stephanie,
For the New Zealand perspective on stars, check out the Royal Astronomical Society of New Zealand.
Bruce
this site rulz!!