Two Reasons to Wake Up Early Wednesday Morning
April 20, 2009 2 Comments
Reason #1 …
On the morning of April 22, the Moon will occult (or pass in front) of Venus for observers in most of North America. This event happens in daylight for most people. Only observers roughly west of the Rockies will see it in a dark sky. The below map from the International Occultation Timing Association (IOTA) shows where the occultation will be visible. Times for the beginning and end of the occultation can be found at IOTA’s site. A map showing time of disappearance and reappearance can be found at Science@NASA.
Venus and the Moon will rise around ~4 am local time in the east. It will help if you have a clear eastern horizon since all of the action will occur close to the horizon. [Added Apr 21: This morning I was up at ~5 am similar to the time when the occultation will start this morning. In Tucson at 5 am, twilight has already started. Still the sky is dark enough that the Moon and Venus are obvious. I didn’t appreciate how low Venus is though. It was just barely visible between the trees. You may have to find a clear view of the eastern horizon to see the show.]
The following diagram gives a good representation of what the occultation will look like right before the Moon passes in front of Venus on the morning of April 22. Note that Mars will be located nearby as well. For those with binoculars or a telescope, Venus will appear as a thin crescent similar to, but much smaller than, the Moon.
Even if you can’t see the occultation, the close proximity of the Moon and Venus will appear awe inspiring. For those who want a nice challenge, try spotting Venus in broad daylight near the Moon. Venus is more than bright enough to be seen in a clear daylight sky assuming you know exactly where to look. Luckily the nearby Moon can help guide you.
Reason #2 …
The first few months of the year usually bring few meteors. After the excitement of early January’s Quadrantids there are no major showers for the next 3 months. This month the drought ends as the Lyrids, and in 2 weeks the Eta Aquarids, bring some much welcomed meteor “rain”.
The Lyrids are usually classified as a major shower though they are just barely so. They can be considered the weakest of the major showers or the strongest of the minor ones. They are produced by Comet Thatcher, a comet on a ~400 years orbit that has only been observed in 1861. The Lyrids, on the other hand, can be seen every year.
Comet Thatcher was discovered by American Professor A. E. Thatcher on April 5, 1861, only a week before start of hostilities in the US Civil War. Thatcher discovered the comet from New York City. Back in those days, light pollution was not a problem and the sky was dark even in the middle of major cities. One wonders if NYC will ever be the host any more comet discoveries. A short piece in the New York Times published on Feb. 28, 1870 contains a private letter sent from Sir John Herschel to Professor A. E. Thatcher. The letter was published nearly a decade after the discovery but shows the excitement in having a local scientist being personally congratulated by one of the world’s eminent astronomers of the time.
Thatcher first detected the comet as a 7thmagnitude object with no tail in the constellation of Draco. The comet brightened to magnitude 2 or 3 a month later as it passed closest to Earth at 0.34 AU on May 5. At the time the comet was an easy naked eye object with a 1 degree long tail. Perihelion occurred on June 3rd at a distance of 0.92 AU from the Sun. The parent of the Lyrids was last seen on Sept. 7, 1861. [Ref: Cometography, Volume II and Comets – A Descriptive Catalog, both by Gary Kronk]
The Lyrid meteors have been known for thousands of years. The earliest definite observation of the Lyrids goes back to 687 BC China. Many additional metoer displays in 11th and 12th centuries have been linked to the Lyrids. One of the best displays occured in 1803 when an observer noted 167 Lyrids in only 15 minutes. The last great Lyrid outburst happened in 1982 when 3-5 Lyrids per minute were seen. The next Lyrid outbursts are predicted for 2040 and 2041. Regardless, our understanding of meteor stream dynamics is still poor and a major outburst could happen in any year making yearly observations important.
This year the Lyrids are predicted to peak at 11 hour UT on the morning of April 22. The timing is great for the Americas which should see rates of ~15-25 meteors per hour. (These rates are only valid for observers under dark rural skies and when the radiant is nearly overhead.) Rates should be above ~10 per hour for a 24 hour period centered on the peak. A live plot of visual Lyrid rates from the International Meteor Organization can be found here.
Like most meteor showers, the Lyrids are best observed early in the morning a few hours before dawn. If you don’t want to get up that early, meteors can be seen, in diminished numbers, anytime after ~11 pm. The radiant is located between the constellations of Lyra and Hercules just to the west of the bright star Vega.
When you see a Lyrid, what are you actually seeing? You regular run-of-the-mill Lyrid is a small piece of dust that was ejected from the nucleus of Comet Thatcher many hundreds to thousands of years ago. The reason why the meteor “burns” up in the atmosphere is due to the friction caused by its rapid velocity. The Lyrids strike the Earth’s atmosphere at 49 km/s or 30 miles/second.