Nova

Novae

新星

Nova means "new star", but they are actually "newly visible" stars caused by brightening of an existing star by 5 to 15 magnitudes. This can be brightening by hundreds of millions of times. The brightening may occur within a few days or weeks, but usually fades again within months. There are some recurring novae, but most are one-time events. One model of novae suggests that they occur in binary systems where one is a white dwarf and the other is on its way to becoming a red giant . The red giant can lose mass which would trigger hydrogen fusion as it falls on the white dwarf. This would blow the gas off and the process could repeat itself. A notable nova example is Nova Cygni 1975. It was the second brightest observed nova in the 20th century, after CC Puppis in 1942. CC Puppis reached a magnitude of 0.35 on November 11, 1942 and is considered to be one of the four brightest novae in the past three hundred years.

'新星'的意思是'新星'，但它们实际上是由于恒星亮度增加5到15个星等而变得'重新可见'的星体。这种亮度增加可能达到数亿倍。亮度增加可能在几天或几周内发生，但通常在几个月内再次减弱。有一些重复的新星，但大多数是单次事件。一种新星的模型认为，它们发生在双星系统中，其中一个是白矮星，另一个正在向红巨星转变。红巨星可以失去质量，当它落到白矮星上时，会触发氢的融合。这会将气体吹走，从而使过程重复。一个显著的新星例子是1975年天琴座新星。它是20世纪第二亮的观测到的新星，仅次于1942年11月11日达到0.35星等的CC天琴座。CC天琴座被认为是过去三百年内最亮的新星之一。

The spectra of light emitted by a nova are Doppler shifted toward the blue, implying that the luminous gas is exploding off the star and traveling toward us at a high speed.

新星发出的光的光谱向蓝端偏移，这表明发光气体正从恒星上爆炸并以高速向我们运动。

Nova Cygni 1975

天琴座新星1975

The brightest Nova in recent years was Nova Cygni 1975 which became visible in Cygnus in August. It reached a magnitude of 1.8 after a rise in magnitude of about 15 in two days time. This is a million-fold increase in luminosity!

(Image accessed Astrophysique gamma nucleaire, Toulouse 19-21 avril 2004. Novae- M. Hernanz)

（图片源自Astrophysique gamma nucleaire，Toulouse 19-21 avril 2004. Novae- M. Hernanz）

近年来最明亮的新星是1975年天琴座的新星，它在8月出现在天琴座。它在两天时间内亮度上升了约15等，达到1.8等。这是光度增加了一百万倍！

Nova Cygni 1975 was close to the bright star Deneb, a member of the "summer triangle", and reached a brightness comparable to Deneb. The photo is a 30sec time exposure taken on August 30, 1975. (Accessed at Astronomeer.com)

1975年天琴座的新星接近明亮的星体天琴座β星（夏季三角星团成员），其亮度与天琴座β星相当。这张照片是1975年8月30日拍摄的30秒曝光照片。（访问地址：Astronomeer.com）

The images below show the difference in brightness in two days. They were taken by Ben Mayer who was taking photographs in a search for meteors. They were 25 minute exposures on Tri-X film. The were reproduced by Jay Pasachoff, see reference. The bright star at right is Deneb.

下面的图像显示了两天之间的亮度差异。这些照片由Ben Mayer拍摄，他正在寻找流星进行摄影。曝光时间为25分钟，使用的是Tri-X胶片。这些图像由Jay Pasachoff重新制作，详见参考文献。右上方的明亮星体是Deneb。